A Unitary Association-based conodont biozonation of the Smithian–Spathian boundary (Early Triassic) and associated biotic crisis from South China

Abstract

The Smithian–Spathian boundary (SSB) crisis played a prominent role in resetting the evolution and diversity of the nekton (ammonoids and conodonts) during the Early Triassic recovery. The late Smithian nektonic crisis culminated at the SSB, ca. 2.7 Myr after the Permian–Triassic boundary mass extinction. An accurate and high-resolution biochronological frame is needed for establishing patterns of extinction and re-diversification of this crisis. Here, we propose a new biochronological frame for conodonts that is based on the Unitary Associations Method (UAM). In this new time frame, the SSB can thus be placed between the climax of the extinction and the onset of the re-diversification. Based on the study of new and rich conodont collections obtained from five sections (of which four are newly described here) in the Nanpanjiang Basin, South China, we have performed a thorough taxonomical revision and described one new genus and 21 new species. Additionally, we have critically reassessed the published conodont data from 16 other sections from South China, and we have used this new, standardized dataset to construct the most accurate, highly resolved, and laterally reproducible biozonation of the Smithian to early Spathian interval for South China. The resulting 11 Unitary Association Zones (UAZ) are intercalibrated with lithological and chemostratigraphical (δ¹³C_carb) markers, as well as with ammonoid zones, thus providing a firm basis for an evolutionary meaningful and laterally consistent definition of the SSB. Our UAZ_8, which is characterized by the occurrence of Icriospathodus ex gr. crassatus, Triassospathodus symmetricus and Novispathodus brevissimus, is marked by a new evolutionary radiation of both conodonts and ammonoids and is within a positive peak in the carbon isotope record. Consequently, we propose to place the SSB within the separation interval intercalated between UAZ₇ and UAZ₈ thus leaving some flexibility for future refinement and updating.

Introduction

Ca. 2.7 Myr after the Permian–Triassic boundary mass extinction (PTBME), at the Smithian–Spathian boundary (SSB), nektopelagic organisms such as ammonoids and conodonts suffered their severest loss of diversity within the Triassic (Brayard & Bucher, 2015; Orchard, 2007; Stanley, 2009; Zhang et al., 2019). The SSB crisis has long been overlooked and considered as part of a protracted Early Triassic environmental stress that would have prohibited complete recovery of the biosphere until the Middle Triassic (e.g. Alroy, 2008). It has now become clear that episodic abiotic environmental stresses were still of high amplitude during the Early Triassic and that this time interval witnessed at least three biotic crises: at the Griesbachian–Dienerian boundary (GDB), at the Dienerian–Smithian boundary (or Induan–Olenekian boundary, IOB) and at the SSB (e.g. Wei et al., 2015). Furthermore, the recovery dynamics of benthonic organisms (Friesenbichler et al., 2019; Hautmann et al., 2015; Hofmann et al., 2014) contrast with those of nektonic ones (Brayard & Bucher, 2015; Brayard et al., 2009a, 2009b; Brühwiler et al., 2010; Ware et al., 2015), the latter being clearly affected only by the SSB crisis. This crisis is associated with major, global environmental changes, whose role is still debated: the palynological record suggests a transition from a humid (spore-dominated) climate during the middle Smithian to a drier (conifer-dominated) climate during the late Smithian and the Spathian (Hochuli et al., 2016; Schneebeli-Hermann et al., 2012); the stable oxygen isotopic composition of conodont elements (Romano et al., 2013; Sun et al., 2012) and the geographical repartition of segminiplanate forms of conodonts (Leu et al., 2019) reveal a major (7 to 8 °C) cooling of Tethyan waters that initiated during the late Smithian Glyptophiceras–Xenoceltites ammonoid zone (Goudemand et al., 2019). Moreover, the late Smithian is marked by a global and conspicuous positive excursion of the stable carbon isotope record (Galfetti et al., 2007; Payne et al., 2004; Wei et al., 2015).

Because of their high evolutionary rates, ammonoids and conodonts are ideal clades for biochronology, especially during the Early Triassic. During the Smithian and Spathian both clades experienced unusually high evolutionary rates and were abundant and widespread (Brayard & Bucher, 2015; Orchard, 2007). Thanks to their tiny size and their phosphatic composition, conodont elements have a good preservation potential and abundant collections can be recovered from nearly any marine sedimentary rock of that age, allowing for worldwide correlations and unsurpassed spatial and temporal resolution.

Although SSB conodonts are known from many localities around the globe, including British Columbia (Orchard & Zonneveld, 2009), the Canadian Arctic (Orchard, 2008), Spitzbergen (Nakrem et al., 2008), Siberia (Dagis, 1984), Western USA (Maekawa & Jenks, 2021; Solien, 1979) Europe (Chen et al., 2016; Kolar-Jurkovšek et al., 2017, 2021), Japan (Maekawa et al., 2018), Oman (Chen et al., 2019), and the Northern Indian Margin (NIM, including southern Tibet) (Brühwiler et al., 2009; Goel, 1977; Lyu et al., 2021; Matsuda, 1981, 1982, 1983, 1984; Romano et al., 2013; Sun et al., 2021; Sweet, 1970; Tian et al., 1983), the South China Block is certainly the most studied and one of the best documented areas for that interval (e.g. Zhang et al., 2019). Most sections are found in the Nanpanjiang Basin in the south western part of the block, and in northern part of the block (Yangtse Platform), as well. During the Early Triassic, the South China Block occupied an equatorial position in the eastern Tethys (Fig. 1).

Fig. 1

A Locations of the studied sections in the Nanpanjiang Basin (Luolou platform) (modified from Bagherpour et al., 2017). a—flood alluvial facies, b—shallow water siliclastic deposit, c—carbonate platform, d—slope, e—basin. Sections: 1—Qiakong, 2—Laren, 3—Shanggang, 4—Lilong, 5—Youping cascade. B Simplified palaeogeographical map of the Early Triassic (modified after the PANALESIS plate tectonic model of Vérard, 2019) South China indicated with a star

Classic sections from the Yangtze platform include Meishan (e.g. Jiang et al., 2007), North Pingdingshan (Zhao et al., 2007) and West Pingdingshan (Liang et al., 2011). Other conodont-rich sections from the northern part of the South China Block include Huangzhishan (Chen et al., 2008), Chaotian (Ji et al., 2011), Shangsi (Jiang et al., 2011), Daxiakou (Zhao et al., 2013) Jianshi (Lyu et al., 2019), Ganxi (Lyu et al., 2019), South Majiashan (Zhao et al., 2007), Qingshan (Liu et al., 2019; Qiu et al., 2019), Longtan (Liu et al., 2019) and Yiwagou (Li et al., 2019).

The Nanpanjiang basin, presently situated at the southern margin of the South China Block, includes several isolated platforms and extends as far south as the “An Chau” basin in northern Vietnam (Enos, 2006; Feng et al., 2015; Galfetti et al., 2008; Komatsu et al., 2016), where intercalated volcanic rocks become abundant. In the Nanpanjiang basin, Early Triassic marine record includes abundant benthos, ammonoids and conodonts (e.g. Brayard & Bucher, 2008; Foster et al., 2019; Hautmann et al., 2011; Wu et al., 2019b). Detailed Early Triassic conodont biostratigraphical analyses have been performed in a number of sections including Guandao (Lehrmann et al., 2015), Gaimao (Yang et al., 2012), Dawen (Chen et al., 2009), Dajiang (Jiang et al., 2014), Mingtang (Liang et al., 2016), Jiarong (Chen et al., 2015), Sidazhai (Liang, 2017), Bianyang (Yan et al., 2013) and Qingyan (Ji et al., 2011) in southern Guizhou, and Zuodeng (Tong et al., 2007, revised after Yang et al., 1984), Motianling (Wu et al., 2019a), and Wuzhuan (Brosse et al., 2015) in northwestern Guangxi.

However, to date, most biochronological studies used continuous interval zones. These are prone to diachronism, largely because the time of the first occurrences (FO) of index species may vary across different sections. Moreover, the fossil record is intrinsically discrete and incomplete, which leads to frequent contradictions in the observed relative sequences of FOs. These contradictions may originate from local ecological controls, sampling effort, selective preservation, disjunctive reworking, condensation, and taxonomic inconsistencies. In our view, the best method to detect and consistently solve these contradictions are discrete maximal association zones such as those constructed by means of the Unitary Association (UA) method (e.g. Brosse et al., 2016; Guex, 1991; Monnet & Bucher, 2002). For the SSB, only a few recent studies have been based on this method: Wu et al. (2019b) constructed a biozonation for South China that includes 26 sections; Chen et al. (2019) constructed a Tethyan biozonation using four SSB sections, two from Oman, one from Slovenia and the well-documented Jiarong section from South China. Yet, these two studies led to strikingly different sets of characteristic species and they diverged in their respective positioning of the SSB.

Based on the study of new and rich conodont collections from five sections (of which four are newly described here) from the Nanpanjiang basin, South China, we perform here a thorough taxonomical revision and describe a series of new taxa. By critically reassessing the published conodont data from 16 other sections from South China, and by applying the UA method to our taxonomically updated dataset, we constructed a new conodont-based biozonation of the Smithian to Early Spathian interval for South China with no internal contradictions and which is consistent with the global carbon isotope signal and the ammonoid zonation. This new UA-based zonation is, in our view, more accurate than the previously available schemes.

Geological setting

During the Late Permian to Early Triassic, the Nanpanjiang basin evolved as a pull-apart basin in a back-arc context (Bagherpour et al., 2017; Duan et al., 2020). The basin is presently exposed across Guangxi, southern Guizhou and eastern Yunnan, as well as northern Vietnam. This basin (also called Guizhou–Guangxi–Hunan Basin, see Feng et al., 2015) was an epicontinental sea situated in the equatorial realm between the eastern Tethys (Yangtze Platform) and the western Panthalassa Ocean (Enos, 2006). The five newly described sections are located in the present-day Guangxi and Guizhou provinces (see Fig. 1).

The Lilong (24° 54′ 41.40ʺ N 106° 32′ 11.00ʺ E), Shanggang (24° 48′ 44.40ʺ N 106° 32′ 31.90ʺ E), Laren (24° 36′ 25.30ʺ N 106° 52′ 40.70ʺ E), Banhaipo (24° 37′ 58.80ʺ N 106° 51′ 43.40ʺ E) and Youping cascade sections (24° 55′ 26.12ʺ N, 106° 31′ 42.63ʺ E) are located in the northern part of Guangxi province. These sections all belong to the Luolou Formation, an Early Triassic outer platform setting (Galfetti et al., 2008) whose paleogeographic distribution defines the largest know platform in the north-central part of the Nanpanjiang Basin (Bagherpour et al., 2017). The Luolou Formation is an ammonoid- and conodont-rich sedimentary succession (see Fig. 2), whose subdivision into units (equivalent to members) has been established by Galfetti et al. (2008). The Smithian and Spathian units comprise, in ascending order: (1) a light-grey, bioturbated, thin-bedded, ammonoid-rich “Flemingites”-limestone (unit III, Early Smithian); (2) mixed thin-bedded, dark, finely laminated limestone alternating with dark silty shales (unit IVa, middle Smithian); (3) black shales intercalated with thin, dark limestone beds (unit IVb, mostly late Smithian); (4) a prominent, cliff-forming, light-grey, medium to thick-bedded, nodular limestone (unit V, Spathian).

Fig. 2

Pictures from four of the five studied sections in the Nanpanjiang basin. A Qiakong, B Shanggang, C Laren (Kuang Guodun for scale), D Lilong (Hugo Bucher for scale)

The Qiakong section (25° 51′ 26.38ʺ N 107° 18′ 32.09ʺ E) is situated in the southern part of the Guizhou province, within the Pingtang syncline (Bagherpour et al., 2020), which belongs to the north-eastern edge of the Nanpanjiang basin. Within this syncline, the Griesbachian to middle Smithian succession belongs to the Daye Formation consisting essentially of basinal deposits (black shales of Griesbachian age) grading upwards into thick slope deposits (thin-bedded limestone with traction patterns) of Smithian age. Here the Daye Formation is overlain by an expanded version of the Luolou Formation, but whose age ranges only from the late Smithian to the late Spathian (see Fig. 2).

Material and methods

We collected 180 conodont samples, 3 to 8 kg each. Furthermore, fist-sized samples were also taken for C-isotope analysis from the same beds as the conodont samples. In order to build a taxonomically consistent data set before the analysis by means of Unitary Associations, we also reassessed published conodont data from 16 additional SSB sections that were included.

Conodont sampling and preparation

The samples were collected from the limestone beds across Smithian and Spathian strata of the Luolou Formation. The spacing between samples varies from 10 cm to 2 m. Highest resolution sampling was achieved near the Smithian–Spathian transition. We collected 49 conodont samples from Qiakong, 57 from Laren, 38 from Shanggang, 21 from Lilong, and 15 from Youping cascade, respectively. The samples were dissolved with a ~ 10% buffered acetic acid solution following the procedure after Jeppsson et al. (1999). The residues were concentrated via heavy liquid separation using sodium polytungstate (Jeppsson & Anehus, 1999) and sieved with a 0.075-mm mesh. The heavy fraction was handpicked under a binocular microscope and selected conodont elements were illustrated using a scattered electron microscope (SEM) (JEOL JSM-6010).

Carbon isotopes

In Early Triassic studies, it has become a frequent and useful approach to analyse carbon isotopes along with biochronology. The combination of these two methods provides a further test for the consistency of the results, and we follow this usage here. With the exception of the carbon isotope carbon record from Youping Cascade which is here newly documented, all other carbon isotope records illustrated here were already made available by Widmann et al. (2020). Therefore, carbon isotope records are here only shown graphically for the purpose of intercalibration and coherence with the new biochronological frame. For the carbonate carbon isotope measurements, heterogeneous samples were carefully cleaned and cut into slabs in order to recover unaltered micrite. The most homogenous part was drilled on a sawed surface with a diamond-tipped drill to produce a fine powder. The isotopic composition of the carbonates was measured with a GasBench II connected to a Finnigan MST DeltaPlus XL mass spectrometer, using a HE-carrier gas system, after the method from Spötl and Vennemann (2003). Reproducibility of replicate analysis was better than ± 0.1% for standards and ± 0.15% for sedimentary samples. All reported isotopic results are in standard δ notation (VPDB).

Biochronology

For the construction of the biochronological scheme, specimens left in open nomenclature were excluded from the dataset. In addition to the new data presented here, we have included the published data from 16 well-sampled and well-documented sections, in particular those for which key taxa had been illustrated. These sections include Jiarong (Chen et al., 2015, 2019), Motianling (Wu et al., 2019a), Mingtang (Liang et al., 2016), Guandao (Lehrmann et al., 2015), Bianyang (Yan et al., 2013), Qingyan (Ji et al., 2011), Sidazhai (Liang, 2017), Ganheqiao (Liang, 2017) for the Nanpanjiang basin, and Daxiakou (Zhao et al., 2013), Ganxi (Lyu et al., 2019), Yiwagou (Li et al., 2019) Jurong, Qingshan and Longtan (Liu et al., 2019), West Pingdingshan (Liang et al., 2011; Zhao, 2005; Zhao et al., 2007, 2008), North Pingdingshan (Zhao et al., 2007, 2008) for the Yangtze Platform (see Additional file 1). The raw data of 12 of these SSB sections were obtained from the synthesis papers of Wu et al. (2019b) and Chen et al. (2019). We have used the original descriptions and illustrations to assess whether and where our newly defined taxa may have occurred in these sections and for taxonomic consistency in general. Their occurrence tables were completed and revised accordingly (see Figs. 3, 4, 5, 6, 7, “Systematic palaeontology” section and Additional files 2 and 3). For the published sections that span more than the Smithian and Spathian, we have taken into consideration the interval bound by the first occurrence (FO) of Neospathodus dieneri to the last occurrence (LO) of Chiosella timorensis.

Fig. 3

Qiakong. Detailed stratigraphic log of the studied interval of the Qiakong section showing the distribution of conodont taxa and the δ¹³C_carb record throughout the middle Smithian part of the Daye Formation and the late Smithian to Spathian Luolou Formation. The LMHs and UAZs are indicated

Fig. 4

Laren. Detailed stratigraphic log of the studied interval of the Laren section showing the distribution of conodont taxa and the δ¹³C_carb record throughout the Smithian and Spathian part of the Luolou Formation. The LMHs and UAZs are indicated

Fig. 5

Shanggang. Detailed stratigraphic log of the studied interval of the Shanggang section showing the distribution of conodont taxa and the δ¹³C_carb record throughout the Smithian and Spathian part of the Luolou Formation. The LMHs and UAZ are indicated. Note the gap because of low angle faulting in the upper part of the black shales

Fig. 6

Lilong. Detailed stratigraphic log of the studied interval of the Lilong section showing the distribution of conodont taxa and the δ¹³C_carb record throughout the late Smithian and Early Spathian part of the Luolou Formation. The LMHs and UAZs are indicated

Fig. 7

Youping Cascade. Detailed stratigraphic log of the studied interval of the Youping Cascade section showing the distribution of conodont taxa and the δ¹³C_carb record throughout the late Smithian and Early Spathian part of the Luolou Formation. The LMHs and UAZs are indicated

We have used the Unitary Association method (Brosse et al., 2016; Guex, 1991; Monnet & Bucher, 2002) as implemented within the software PAST (Hammer et al., 2001) in its 2013 version (Version 2.17c, year 2013), which unlike the most recent versions enables to detect and analyse Z₄-type contradictions. The taxa found only in one section were temporarily removed from the analysis via the “null endemic taxa” option.

The first run with the full initial data set (see Additional file 2) led to the detection of 453 contradictions, of which 31 cycles between cliques and a large number of Z4 cycles (313), suggesting a rather low internal consistency of the initial data.

If we exclude the Sidazhai and Ganheqiao sections the number of contradictions drops to 164, the number of Z₄ cycles to 100 and cycles between cliques to 0: hence about two-thirds of all contradictions are generated by these two noisy sections. A critical view of the source data (Liang, 2017) reveals that these faunas include a mixture of Smithian taxa with Spathian ones. This mixing likely originates from the occurrence of limestone breccias (in Sidazhai) and possibly from poorly resolved taxonomy. Therefore, we excluded these two sections from the subsequent analyses.

One of the main advantages of the UA method is that not only it detects automatically biostratigraphic contradictions, but it allows establishing the respective contributions of the different taxa involved. These contradictions may result from misidentifications, condensation, reworking, insufficient sampling effort, or from sparse and too poorly constrained biostratigraphic relations (i.e. low-quality record). We have iteratively modified the data, e.g. by reassessing some identifications and revising the corresponding occurrences, by expanding the local range of some taxa when their co-occurrence with other taxa has been documented elsewhere, or in the worst case by excluding some taxa if they were involved in too many contradictions. The latter case usually involves rare and/or long ranging taxa, thereby implying under-constrained biostratigraphic relationships. This selective process is applied iteratively until a minimum amount of contradictions is reached (Guex, 1991). The details of this procedure can be found in Additional file 3.

In the present case, all contradictions and cycles between cliques could be eliminated and only 5 minor contradictions (Z₄ cycles) did remain, in which Neospathodus spitiensis and Pachycladina peculiaris are the most frequently involved taxa. Because the stratigraphic range of these two species does not overlap with the SSB, we have not tried to solve these minor contradictions.

This last run produced a total of 24 preliminary Unitary Associations (UAs). Because only UAs that are laterally reproducible, that is, UAs that occur in several sections, are actually useful for correlation purposes, we followed the propositions of PAST (see the reproducibility matrix in Fig. 8) and merged the following UAs: UA_2–3, UA_4–5, UA_6–7 UA_9–10, UA_11–14, UA_15–17 and UA_18–22. This merging step results in fewer UAs but the resulting Unitary Association Zones (UAZ) have a higher lateral reproducibility (in other words their spatial scope is enhanced) and hence, are more robust and more useful than the preliminary UAs.

Fig. 8

Sequences of Unitary Association (UAs), Unitary Associations Zones (UAZs), lateral reproducibility and dissimilarity index (D) resulting from the biochronological analyses of the 19 sections in South China from the final run. Note the grey shades in the upper figure with rather poor lateral reproducibility and/or poor dissimilarity index of the UA₂, UA₃, UA₄, UA₅, UA₆, UA₇, UA₉, UA₁₀, UA₁₁, UA₁₂, UA₁₃, UA₁₄, UA₁₅, UA₁₆, UA₁₇, UA₁₈, UA₁₉, UA₂₀, UA₂₁ and UA₂₂. This 20 UAs were merged into a final total of 11 UAZs (lower figure)

Results

Carbon isotope record

The stable carbon isotope data from all the studied sections, including the new data from Youping Cascade (see Figs. 7, 9 and Additional file 4), display consistent trends: a negative excursion of the δ¹³C_carb in the Flemingites beds, a negative plateau around − 2‰ in the Owenites beds, a prominent positive excursion in the late Smithian interval peaking at the top of unit IVb within the black shales, and a negative excursion at or closely following the abrupt lithological change from black shales to nodular limestones (from unit IVb to unit Va). The greatest variability (up to 3–4‰) of the δ¹³C_carb values occurred during the middle and late Smithian, where the deeper water section (Qiakong) shows the most negative values (Fig. 12). This variability noticeably decreases to ca. 2‰ in the Spathian. Meyer et al. (2011) interpreted such difference as a vertical depth gradient, thus suggesting a weakening of this gradient across the SSB.

Fig. 9

Position of the UAZs in the studied sections Qiakong, Laren, Shanggang, Lilong and Youping Cascade. The lithological units are simplified and represented from unit III to unit Vc. Note the ammonoid zones recorded from Laren, Shanggang, Lilong and Youping Cascade

Conodonts

The CAI (Conodont Alteration Index) in Qiakong is ~ 3 (brownish colour). In all other studied sections, the CAI was around 5 (black colour). All sampled sections yielded abundant conodont material. Only 5 out of 172 samples were barren, namely samples SHA 324C (Shanggang), QIA 156 C, QIA 139 C (both Qiakong), LAR 211 and LAR 201 (both Laren). Abundance of conodont elements is the highest in units III and IVb. In all sections, the segminate elements were recovered in much higher abundance than segminiplanate elements. Segminiplanate forms are completely absent from the Flemingites beds (early Smithian) and the Owenites beds (middle Smithian).

In total, we have recovered elements belonging to 46 conodont species assigned to 16 genera. 40 of these species are illustrated and discussed in the “Systematic palaeontology” section. In particular, we describe 21 new species: Neospathodus bevelledi n. sp., Novispathodus gryphus n. sp., Novispathodus n. sp. Z, Novispathodus praebrevissimus n. sp., Discretella pseudodieneri n. sp., Urdyella unicorna n. gen. n. sp., Urdyella tridenta n. gen. n. sp., Gladigondolella laii (morphotype A and B), Novispathodus n. sp. A, Discretella? n. sp. B, Discretella? n. sp. C, Discretella? n. sp. D, Spathicuspus n. sp. A, Spathicuspus? n. sp. B, Spathicuspus? n. sp. C, Urdyella n. sp. A, Neostrachanognathus n. sp. A, Triassospathodus aff. symmetricus, Icriospathodus aff. crassatus and Discretella aff. discreta. The new forms for which only a small number of specimens (< 10) were recovered and/or the preservation was considered inadequate, were left in open nomenclature. Finally, we revised the diagnosis of two species: Icriospathodus zaksi and Hadrodontina aequabilis.

Description of the biozonation

The final biozonation is based on 58 conodont taxa from 19 sections and it comprises 11 Unitary Association Zones (UAZ) (Fig. 8). We propose (see below) to place the SSB within the separation interval intercalated between UAZ₇ and UAZ₈. Five sections record both the late Smithian UAZ₇ and the earliest Spathian UAZ₈: Qiakong, Laren, Youping Cascade, West Pingdingshan and Longtan (Jurong) (see Figs. 3, 4, 5, 6, 7, 8, 9).

UAZ₁

Content: Sw. kummeli, Ns. dieneri, Ns. chaohuensis and Ns. ex. gr. cristagalli.

Age: Dienerian.

Geographical distribution: Daxiakou, Motianling, West- and North Pingdingshan.

Characteristic species: Sw. kummeli.

This UAZ occurs in the Ns. dieneri interval zone of Motianling, and Daxiakou and in the Ns. kummeli interval zone of North- and West Pingdingshan.

UAZ₂

Content: Ns. dieneri, Ns. chaohuensis, Ns. ex. gr. cristagalli, Ns. chii, Ns. tongi, Ns. peculiaris, Ns. posterolongatus, Nv. ex gr. waageni and Eu. costatus.

Age: early Smithian.

Geographical distribution: Jiarong, Ganxi, Jianshi, Daxiakou, Motianling, Guandao, West- and North Pingdingshan.

Characteristic species: Ns. chii and Ns. peculiaris.

Characteristic pairs of species: Ns. chaohuensis with either Ns. tongi, Eu. costatus, Ns. posterolongatus or Nv. ex. gr. waageni.

UAZ₂ overlaps with the Flemingites beds in Daxiakou, West- and North Pingdingshan (Zhao et al., 2007, 2013).

UAZ₃

Content: Ns. dieneri, Ns. ex. gr. cristagalli, Ns. tongi, Ns. posterolongatus, Nv. ex gr. waageni, Eu. costatus, Eu. hamadai, Di. discreta and Pg. peculiaris.

Age: early Smithian.

Geographical distribution: Shanggang, Jiarong, Daxiakou, Motianling, Yiwagou, West- and North Pingdingshan.

Characteristic species: Eu. hamadai.

Characteristic pairs of species: Ns. tongi or Eu. costatus with either Di. discreta or Pg. peculiaris.

In Shanggang, UAZ₃ overlaps with the beginning of the negative carbon isotope excursion (CIE). In deeper water sections such as North- and West Pingdingshan, UAZ₃ falls within the ill-defined “Flemingites–Euflemingites Zone”, which is confusingly reported to include middle Smithian genera (Tong & Zakharov, 2004).

UAZ₄

Content: Ns. dieneri, Ns. ex. gr. cristagalli, Nv. ex gr. waageni, Di. discreta, Pg. peculiaris, Sc. lachrymiformis, Ns. spitiensis, Ns. bevelledi, Pc. obliqua, Sc. mosheri, Sc. milleri, Di. n. sp. C.

Age: Early to middle Smithian.

Geographical distribution: Laren, Mingtang, Motianling, Yiwagou and West Pingdingshan.

Characteristic species: Sc. lachrymiformis. So far, this species has been documented only from the northern marginal basin of the Yangtze platform (e.g. in Yiwagou) and is apparently missing in the Nanpanjiang basin. However, UAZ₄ is identified in the Nanpanjiang basin by means of its characteristic pairs of species.

Characteristic pairs of species: Ns. dieneri or Ns. ex. gr. cristagalli with either Ns. spitiensis, Ns. bevelledi, Pc. obliqua, Sc. mosheri, Sc. milleri, or Di. n. sp. C.

In Laren, UAZ₄ overlaps is within the negative carbon isotope shift that culminates higher up during the middle Smithian. UAZ₄ is still within unit III which corresponds to the early Smithian Flemingites Beds. Similarly, UAZ₄ overlaps with the end of the negative CIE (beds 13–15) in Mingtang.

UAZ₅

Content: Nv. ex gr. waageni, Di. discreta, Pg. peculiaris, Ns. spitiensis, Ns. bevelledi, Pc. obliqua, Sc. mosheri, Sc. milleri, Di. n. sp. C, Ns. pseudodieneri, Ur. unicorna, Di. aff. discreta, Gu. bransoni, Di. n. sp. D and Di. n. sp. B.

Age: middle Smithian.

Geographical distribution: Shanggang, Qiakong, Laren, Youping Cascade, Jiarong, Bianyang, Guandao and West Pingdingshan.

Characteristic species: Ns. pseudodieneri, Ur. unicorna, Di. aff. discreta, Gu. bransoni, Di. n. sp. D and Di. n. sp. B.

UAZ₅ has an excellent lateral reproducibility in the newly documented sections. UAZ₅ largely overlaps with the Owenites beds in Laren. In Qiakong, UAZ₅ occurs within the Daye Fm., which represents slope deposits typically yielding a meagre conodont record. In Laren, Shanggang and Youping Cascade, this zone is within unit IVa, where it coincides with the negative plateau of the stable carbon isotope curve. In Jiarong, UAZ₅ corresponds to sample JRC-39 (Chen et al., 2015). UAZ₅ partly overlaps with the Nv. waageni interval zone in West Pingdingshan, and with the Di. discreta interval zone of Jiarong and Bianyang.

UAZ₆

Content: Nv. ex gr. waageni, Di. discreta, Pg. peculiaris, Pc. obliqua, Sc. mosheri, Sc. milleri, Ha. aequabilis, Nv. expansus, Bo. buurensis, Nv. aff. clinatus and Nv. ex gr. pingdingshanensis.

Age: late Smithian.

Geographical distribution: Shanggang, Lilong, Qiakong, Laren, Youping Cascade, Jiarong, Bianyang, and Jurong (Longtan).

Characteristic species: Hadrodontina aequabilis.

Characteristic pairs of species: either Di. discreta, Pg. peculiaris, Pc. obliqua, Sc. mosheri, or Sc. milleri with either Nv. expansus, Bo. buurensis, Nv. aff. clinatus, or Nv. ex gr. pingdingshanensis.

UAZ₆ has an excellent lateral reproducibility and occurs in all five newly described sections. UAZ₆ concurs with the late Smithian ammonoid Anasibirites beds as documented in Laren, Shanggang and Youping Cascade. UAZ₆ occurs in the lower part (Shanggang, Qiakong, Youping Cascade) and in the middle part (Laren) of Unit IVb. In Jiarong and Bianyang, UAZ₆ corresponds to the Parachirognathus–Pachycladina assemblage zone. In Longtan (Jurong), UAZ₆ partly overlaps with the lower part of the Nv. pingdingshanensis interval zone (Bed 57). Apart from Nv. ex gr. pingdingshanensis, all the taxa found in this zone are traditionally considered to be typical Smithian taxa. Similarly, the Anasibirites beds classically define the early late Smithian.

UAZ₇

Content: Nv. ex gr. waageni, Nv. expansus, Bo. buurensis, Nv. aff. clinatus and Nv. ex gr. pingdingshanensis, Nv. ex gr. abruptus, Ic. zaksi, Nv. gryphus n. sp. and Nv. praebrevissimus n. sp.

Age: late Smithian.

Geographical distribution: Shanggang, Qiakong, Laren, Youping Cascade, Jiarong, West Pingdingshan and Jurong (Longtan).

Characteristic pairs of species: either Nv. ex gr. waageni, Nv. expansus, Bo. buurensis, or Nv. aff. clinatus with either Nv. abruptus, Ic. zaksi, Nv. gryphus n. sp. or Nv. praebrevissimus n. sp.

UAZ₇ occurs in Qiakong, Laren, Shanggang and Youping Cascade. UAZ₇ occurs within unit IVb and within the late Smithian positive CIE in all studied sections. In Jiarong and West Pingdingshan, UAZ₇ partly overlaps with the Nv pingdingshanensis interval zone and is within the positive CIE (and beds JB-11 and JC-5 in Jiarong). The ammonoid Glyptophiceras–Xenoceltites beds are also included within UAZ₇ in Laren and Youping Cascade. This ammonoid zone has been usually regarded as late Smithian in age. In terms of conodonts, this zone is composed by the association of ‘typical Smithian’ forms such as Nv. ex gr. waageni and Bo. buurensis with ‘typical Spathian’ forms such as Nv. abruptus and Ic. zaksi. Here, we assign a late Smithian age to this zone because of the clear ammonoid intercalibration.

UAZ₈

Content: Nv. ex gr. pingdingshanensis, Nv. ex. gr. abruptus, Ic. zaksi, Nv. gryphus n. sp., Nv. praebrevissimus n. sp., Nv. n. sp. Z, Tr. aff. symmetricus, Nv. brevissimus, Tr. symmetricus, Ic. ex gr. crassatus and Sp. n. sp. A.

Age: early Spathian.

Geographical distribution: Lilong, Qiakong, Laren, Youping Cascade, West Pingdingshan and Jurong (Longtan and Qingshan).

Characteristic species: Nv. n. sp. Z.

Characteristic pairs of species: either Nv. ex. gr. pingdingshanensis, Nv. gryphus n. sp., or Nv. praebrevissimus n. sp. with either Tr. aff. symmetricus, Nv. brevissimus, Tr. symmetricus, Ic. ex gr. crassatus, or Sp. n. sp. A.

UAZ₈ consistently occurs in the upper part of unit IVb in all our newly described sections, except Shanggang where the top of Unit IVb has been obscured by a low angle fault.

All the conodont taxa found in this zone are traditionally considered to be typical Spathian taxa. As a consequence, this zone is considered as the oldest one known from the Spathian, and the SSB must be placed within the interval of separation that intercalates between UAZ₇ and UAZ₈.

In Qiakong, Laren and Youping Cascade, the SSB can be unambiguously placed in the interval of separation between UAZ₇ and UAZ₈. In Lilong, the SSB is located within the thin interval bracketed by Xenoceltites–Glyptophiceras beds below and UAZ₈ above, hence ca. 50 cm below the sharp lithological boundary between units IVb and Va. In all these sections, UAZ₈ overlaps with the positive peak of the CIE except in Laren where the peak is located within the uncertainty interval between UAZ₇ and UAZ₈. In Longtan, UAZ₈ is recognized in bed 70, which separates the Nv. pingdingshanensis and the Tr. aff. homeri interval zones, whereas in Qingshan, UAZ₈ overlaps only with the Nv. pingdingshanensis interval zone (bed 70). In West Pingdingshan this zone is recognized within bed 54 and it overlaps with the positive peak of the CIE, as well.

UAZ₉

Content: Nv. ex. gr. abruptus, Ic. zaksi, Tr. aff. symmetricus, Nv. brevissimus, Tr. symmetricus, Ic. ex gr. crassatus, Sp. n. sp. A, Gl. laii (morph. B), Sp. n. sp. B, Gl. laii (morph. A), Ic. collinsoni, Nv. brochus, Sp. spathi, Tr. homeri, Cr. kochi, Ad. unicosta, Sp. n. sp. C, Nv. triangularis, Nv. clinatus, Nv. curtatus.

Age: early-to-middle Spathian.

Geographical distribution: Shanggang, Lilong, Qiakong, Laren, Youping Cascade, Jiarong, Mingtang, Qingyan, Bianyang, Motianling, Guandao, West Pingdingshan and Jurong (Longtan and Qingshan).

Characteristic species: Gl. laii (morph. B), Sp. n. sp. B, Gl. laii (morph. A), Ic. collinsoni, Cr. kochi, Ad. unicosta, Sp. n. sp. C, Nv. triangularis, Nv. clinatus, and Nv. curtatus.

Characteristic pairs of species: either Ic. zaksi, Tr. aff. symmetricus, Nv. brevissimus, or Ic. ex gr. crassatus with either Nv. brochus, Sp. spathi, or Tr. homeri.

This UA zone is recognized in all newly studied sections. In Qiakong and Youping Cascade, the base of UAZ₉ corresponds to the lower limit of Unit Va. In Qiakong and Laren, UAZ₉ ranges up into unit Vc and in Laren, UAZ₉ includes the Tirolitid n. gen A beds, the Tirolites/Columbites beds and the middle Spathian Procolumbites beds. UAZ₉ is the laterally most reproducible zone and occurs in all investigated sections. AZ₉ also includes the Ic. collinsoni, Tr. homeri and Nv. triangularis interval zones (e.g. Jiarong, Bianyang, Mingtang, Jurong, Motianling and West Pingdingshan).

UAZ₁₀

Content: Nv. ex. gr. abruptus, Tr. symmetricus, Sp. n. sp. A, Nv. brochus, Sp. spathi, Tr. homeri, Ch. gondolelloides, Ch. timorensis.

Age: late Spathian.

Geographical distribution: Guandao.

Characteristic pairs of species: Nv. brochus with either Ch. gondolelloides, or Ch. timorensis.

UAZ₁₁

Content: Nv. ex. gr. abruptus, Tr. symmetricus, Sp. n. sp. A, Sp. spathi, Tr. homeri, Ch. gondolelloides, Ch. timorensis, Ni. germanicus, Ni. kockeli.

Age: Anisian.

Geographical distribution: Mingtang and Guandao.

Characteristic species: Ni. germanicus and Ni. kockeli.

Discussion

Comparison with other SSB UA-based conodont biozonations in South China

Wu et al. (2019b) have recently presented a UA-based biozonation using 72 conodont species from 28 sections in South China. The time interval they studied spans from the latest Permian to the earliest Middle Triassic and led to a succession of 26 UAZ (note that our UAZ numbering is distinct from theirs). However, their study did not address several critical issues pertaining to the quality of raw data, most importantly the Sidazhai and Ganheqiao sections as mentioned above. For instance, their UAZ₁₉ of supposed Spathian age, includes Ns. dieneri, a taxon that is usually restricted to the Dienerian and earliest Smithian. This unusual occurrence roots into the work of Liang et al. (2016), who illustrated a specimen of ‘Ns. dieneri’ from a Spathian horizon (their fig. 4.5 from bed 18 in Mingtang section). Although Wu et al. (2019b) noticed that this was an incorrect identification (their Table 2), they did not update the data set accordingly. Apart from Liang et al. (2016), there is no other known report of Ns. dieneri from the Spathian. Lehrmann et al. (2015) reported the occurrence of the typically Smithian Guangxidella bransoni in a Spathian sample on the basis of a single broken element whose diagnostic cusp is missing (their fig. 5.18, sample WG-82), thus making this identification problematic. Zhao et al. (2013) reported Nv. pingdingshanensis from early Smithian strata at Daxiakou (their bed 91) on the basis of a single broken specimen whose diagnostic lower margin is missing (their fig. 11.I; note that the captions of their figs. 10 and 11 have been mistakenly swapped). This single specimen can probably be assigned to Nv. waageni, thus leading to a virtual co-occurrence with Eurygnathodus hamadai. Finally, the upward extension of Nv. waageni so that it intersects with Tr. homeri as done by Wu et al., (2019b, Additional files 2 and 3) is an unwarranted assumption that could never be confirmed by real samples. In our view, the above-mentioned occurrences and associations are questionable, either from a taxonomic and/or a stratigraphic point of view. In this work, we have revised these conflicting data before the analysis, thus explaining the differences with the earlier zonation of Wu et al. (2019b).

Chen et al. (2019) published a UA-based SSB conodont biozonation with an extremely heterogenous paleobiogeographic scope. Their data set comprises two sections from Oman, one from Slovenia and one (Jiarong) from South China. They obtained 7 UAZs and proposed to place the SSB between their UAZ₄ and UAZ₅ (no correspondence with our own UAZ numbering). Their biozonation suggests that Nv. pingdingshanensis is a characteristic species of their latest Smithian UAZ₄, which is at odd with most reports documenting the association of this species with ‘typical’ Spathian taxa such as Nv. brevissimus, Tr. symmetricus, or Ic. ex gr. crassatus. Furthermore, most of the characteristic species of their latest Smithian and earliest Spathian zones (Neospathodus planus and Neospathodus robustus on one hand, and Platyvillosus corniger and Platyvillosus regularis on the other) are not know from South China, thus making the identification of their SSB in South China difficult. Their UAZ₂ partly correlates with our UAZ₅, their UAZ₃ with our UAZ₆, their UAZ₄ with our UAZ₇, and their UAZ₇ with our UAZ₉.

The conodont dataset produced by Widmann et al. (2020) was exclusively based on Qiakong, Shanggang, Laren and Lilong, without taking other published sections into account. The addition of 17 other sections as done here did not lead to substantial changes in the initial zonation proposed by Widmann et al. (2020). This underlines the overall quality and completeness of the conodont record in these four initial sections. The minor modifications introduced here are mostly due to the larger temporal and spatial scope of the present study. Note that the latest Smithian UAZ₇ (equivalent to UAZ₅ in Widmann et al., 2020) can now be recognized in Laren but no longer in Lilong, since Nv. n. sp. A is excluded from the present analysis.

Comparison with carbon-isotope chemostratigraphy

The evolution of the stable carbon isotopic ratio can be an important additional proxy for Early Triassic correlations because it appears as global signal overriding local fluctuations (e.g. Payne et al., 2004). Chen et al. (2019) and Wu et al. (2019b) could not establish a clear intercalibration between their UAZs and their δ¹³C_carb records, whereas our new biozonation is fully consistent with the δ¹³C_carb fluctuations within the South China Block. Zhang et al. (2019) proposed a convenient numbering of the distinct phases of the δ¹³C_carb signal that we adopt here. The middle Smithian negative plateau (referred as N3, Zhang et al., 2019) always includes our UAZ₅ in West Pingdingshan, Guandao, Bianyang, Jiarong, Shanggang, Qiakong, Laren and Youping Cascade (Chen et al., 2013, 2015; Lehrmann et al., 2015; Song et al., 2013; Tong et al., 2007; Wang et al., 2005; Widmann et al., 2020; Zhao et al., 2007; Zuo et al., 2003, 2004; Fig. 9).

The positive CIE that marks the transition from N3 to P3 in Qiakong, Laren, Shanggang, Lilong, Youping cascade, Jiarong and West Pingdingshan consistently includes UAZ₆ and UAZ₇. With the exception of Shanggang where P3 is removed by a low angle fault, UAZ₈ coincides with P3 in our other sections. The same correlation can be observed in West Pingdingshan. Zhang et al. (2019) proposed to define the SSB at the midpoint of the N3-to-P3 positive shift. Because the end of the late Smithian is frequently affected by unconformities (see Hammer et al. (2019) for Spitsbergen; Widmann et al. (2020) for the Luolou Fm.) such a definition cannot be recommended. In the Luolou Fm. the abrupt end of this positive shift is an additional sign pointing to the presence of unconformities within the end of the late Smithian black shales.

Definition of the SSB

Tozer (1967) first defined the Smithian and the Spathian stages on the basis of ammonoids. His definitions were later refined by Silberling and Tozer (1968) who placed the SSB between the Anasibirites beds (which correlate with our conodont UAZ₆) and the Tirolites/Columbites beds (which correlate with our conodont UAZ₉) in North America. In the northern Indian margin (NIM) and the Western US, an intermediate Glyptophiceras sinuatum Zone (Brühwiler et al., 2010; Jenks & Brayard, 2018; Jenks et al., 2015) of Smithian affinity is found above the Anasibirites multiformis Zone and below the typical Spathian Tirolites/Columbites beds. Since UAZ₇ coincides with the Glyptophiceras sinuatum beds in South China, it seems most appropriate to place the SSB above UAZ₇ and UAZ₈. The latter is characterized by the overlap of Nv. pingdingshanensis with either Nv. brevissimus, Tr. symmetricus or Ic. ex gr. crassatus, the last three species being exclusively known from the Spathian.

Zhao et al. (2007) proposed the FO of Nv. pingdingshanensis as the main proxy for a definition of the base of the Spathian and this definition has been subsequently endorsed by many conodont workers (e.g. Lyu et al., 2021; Sun et al., 2012; Wu et al., 2019a, 2019b). Yet, we confirm that Nv. pingdingshanensis also occurs in the late Smithian (i.e. UAZ₆ and UAZ₇). Late Smithian occurrences of Nv. pingdingshanensis were also reported by Orchard and Zonneveld (2009), Komatsu et al. (2016), Leu et al. (2019) and Maekawa and Jenks (2021). As a consequence, the FO of Nv. pingdingshanensis is not a suitable proxy for the base of the Spathian because it ranges from the late Smithian into the early Spathian. Our results also indicate that Nv. pingdingshanensis is the only known ‘segminate’ conodont that ranges across the SSB (from UAZ₆ to UAZ₈), thus supporting the hypothesis that this species may be the rootstock of most Spathian segminate conodonts, i.e. representatives of Novispathodus, Triassospathodus and Icriospathodus (Orchard, 2007).

Extinction and recovery patterns across the SSB

As illustrated in Figs. 10 and 11, conodont taxonomic richness and turnover rate experienced two peaks during the middle Smithian and the middle Spathian, respectively. The relatively low diversity observed in the Dienerian (UAZ₁) may be underestimated because the most relevant sections for that time interval are not included here. The early-to-middle Smithian rapid increase in conodont diversity reflects a global pattern that was first noticed by Orchard (2005, 2007). This diversity increase is also mirrored in terms of multi-element apparatuses (Orchard, 2005, 2007). This radiation initiated during the cool early Smithian (UAZ_2–4) and culminated during the middle Smithian (UAZ₅) thermal maximum (Goudemand et al., 2019; Romano et al., 2013).

Fig. 10

Temporal evolution of species- genera- and subfamily-diversity (succession of UAZs) for all the characteristic (part of UAZ) conodonts from South China during the Smithian and Spathian interval. Calculated from the optimal solution given in Fig. 8. Note the Early Smithian and Early Spathian radiation and the late Smithian and middle/late Spathian extinction. Absolute ages from Widmann (2019) and Widmann et al., (2020)

Fig. 11

Faunal turnover rate for all the relying conodont UAZs from South China during the Smithian and Spathian interval. Calculated from the optimal solution given in Fig. 8. Note the early Smithian and early Spathian radiation and the late Smithian and middle/late Spathian extinction

The subsequent loss of more than a third of the conodont species between UAZ₅ and UAZ₇ corresponds to the largest conodont turnover of the studied interval (Figs. 8, 10 and 11). Previous interpretations (Orchard, 2007) and our preliminary observations from other basins suggest that this pattern may be of global significance. However, our refined biozonation indicates that changes in conodont diversity are not immediate and simple responses to changing trends in temperature (see Fig. 10). On the one hand, the conodont extinction already started during the end of the warm interval and continued during the late Smithian cooling. On the other hand, the early Spathian re-diversification started during the end of the cooling phase and extended further during the following warming phase. Therefore, changes in conodont diversity cannot be uniquely related to reversals in temperature trends. Moreover, segminate and segminiplanate conodonts have also been documented to have experienced opposite size trends during the late Smithian cooling (Chen et al., 2013; Leu et al., 2019). Hence, no simple causal relation can be inferred between temperature change and conodont diversity or size during the Smithian–Spathian transition. As suggested by Ginot and Goudemand (2020), other abiotic (sea level, salinity, oxygen content, etc.) and biotic factors must have come into the play.

The Spathian radiation of conodonts that spanned the time interval UAZ₇ to UAZ₉ (see Figs. 10 and 11) appears to be of greater magnitude than the early Smithian diversification (Fig. 11). We also note that middle Smithian and middle Spathian warm intervals (Goudemand et al., 2013, 2019) both corresponds to peak values in conodont species richness. However, the taxonomic structure of the two diversification events differed in that the Smithian one produced a higher diversity at the subfamily level than the Spathian one (see Fig. 10).

Based on U–Pb ages provided by Widmann et al. (2020), the respective duration of our UAZs can be assessed. The Bayesian age depth model constructed by Widmann et al. (2020) suggests that the absolute ages of individual UAZs decreased from the middle Smithian to the earliest Spathian (UAZ_6–8, Fig. 12). Absolute durations of UAZ₅ to UAZ₉ can be derived from this age–depth model [Fig. 12 and Additional file 5, Widmann et al. (2020)]. The resulting figures are UAZ₅: 366 ± 193 ka; UAZ₆: 147 ± 146 ka; UAZ₇: 91 ± 112 ka; UAZ₈: 7 ± 86 ka and UAZ₉: 290 ± 89 ka. Although error margins are substantial, the duration of the zones are lowest either side of the SBB, in UAZ₇ and UAZ₈. This result indicates that the assumption of equal duration time bins should be used with caution when computing rates of extinction, rate of origination and turnover rate.

Fig. 12

Calibration between U-Pb ages and fossiliferous beds, UAZs, δ¹³C_carb record, climatic proxies and conodont diversity. A U–Pb ages (after Widmann et al., 2020). B Geological timescales with Early Triassic substages C ammonoid biochronozones modified from Brayard and Bucher (2008), D Conodont beds from South China (this work), E Newly established conodont UAZs from South China. See Figs. 3, 4, 5, 6, 7, 8, 9. F Evolution of the composite δ¹³C_carb record during the Smithian and early Spathian from Qiakong, Laren, Shanggang, Lilong (see also Figs. 3, 4, 5, 6). G Temporal evolution of species- genera- and subfamily-diversity (after Fig. 10), H δ¹⁸C_phos from conodont apatite from Pakistan (after Goudemand et al., 2019). I: Palynological events (after Hermann et al. 2011)

Conclusion

We reported five new SSB sections from the Nanpanjiang basin (Qiakong, Shanggang, Laren, Lilong and Youping Cascade) with high-resolution conodont and stable carbon isotope sampling. Using the abundant conodont material, we described one new conodont genus and 21 new conodont species from these sections. After having standardized the conodont taxonomy on the basis of 19 SSB sections from the South China Block, we processed the updated dataset by means of the Unitary Associations Method. The resulting, new, robust, high-resolution biozonation comprises 11 UAZs whose good lateral reproducibility ensures accuracy for correlating all the sections included in the data set. The new biozonation is also intercalibrated with ammonoid biochronozones, C-isotope chemostratigraphy and lithological markers.

We propose placing the SSB between UAZ₇, a zone characterized by the association of, for instance, Novispathodus ex. gr. waageni with either Icriospathodus zaksi or Novispathodus praebrevissimus n. sp., and UAZ₈, a zone characterized by the association of, for instance, Novispathodus ex gr. pingdingshanensis with either Icriospathodus. ex gr. crassatus or Triassospathodus symmetricus. We further confirm that Novispathodus pingdingshanensis straddles the SSB, thus making its first occurrence a poor marker for the base of the Spathian.

Systematic palaeontology (Leu and Goudemand)

Synonymies are limited to key citations and illustrations. All illustrated specimens are shown at the same scale. Many species descriptions are based on the P₁ element only. All figured specimens are located and stored in the Paleontological Institute and Museum of the University of Zurich (PIMUZ), Karl-Schmid-Strasse 4, 8006 Zürich, Switzerland. Suprageneric classification is following mostly Donoghue et al. (2008) and Orchard (2005). The terminology for the orientation of the element is the traditional one based on the orientation and curvature of the cusp. It only refers to the element itself and not its natural orientation within the animal (Purnell et al., 2000). ‘Lower’ refers to the side of the element from which the basal cavity opens. ‘Upper’ refers to the opposite side. The term ‘cusp’ refers only to the cusp sensu stricto (Klapper & Philip, 1972). For the figures, the orientation is standardized with the anterior side to the top, and the denticles tips to the left in ‘lateral’ views. For each element, the order of views from left to right is ‘lateral’, ‘oral’ and ‘aboral’ views, unless otherwise specified.

Class CONODONTA Eichenberg, 1930

Division PRIONIODONTIDA Dzik, 1976

Order OZARKODINIDA Dzik, 1976

Superfamily GONDOLELLOIDAE (Lindström, 1970)

Family GONDOLELLIDEA Lindström, 1970

Subfamily GLADIGONDOLELLINAE Hirsch, 1994

Genus GLADIGONDOLELLA Müller, 1962

1968 Dichodella Mosher, p. 923

Type species. Polygnathus tethydis Huckriede, 1958, p. 157–158, pl. 2, fig. 38a–b.

Type stratum and locality. Trachyceras austriacum bed (Julian), Feuerkogel near Röthelstein, Austria.

Remarks. This genus was first introduced by Müller (1962) for a Middle Triassic carminiplanate P₁ element with a relatively short posterior process and corresponding keel posteriorly of the pit, a narrow platform and a low carina. As the type species may have been significantly different from some Spathian forms, the phylogenetic relationships of Gladigondolella are uncertain but the rootstock might lie within the evolution from Borinella (Orchard, 2007).

Gladigondolella laii Chen et al. morphotype A

Fig. 13B, C, G?

Fig. 13

Gladigondolellinae, Neogondolellinae and Cornudininae from Qiakong, Laren, Shanggang and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A Borinella buurensis (Dagis), LAR212, PIMUZ 39103. B, C, G Gladigondolella laii (morphotype A); B LAR231C, PIMUZ 39132; C BAN2, PIMUZ 39133; G LAR227C, PIMUZ 39134. D, sp. indet. (P₂ element?), SHA319, PIMUZ 39293. E, F, H, I Gladigondolella laii (morphotype B); E LIL510, PIMUZ 39135; F LIL512, PIMUZ 39136; H QIA140, PIMUZ 39137; I LIL510, PIMUZ 39138. J–L, O, Spathicuspus spathi (Sweet); J QIA141, PIMUZ 39300; K QIA144, PIMUZ 39301; L BAN1, PIMUZ 39302; O SHA322, PIMUZ 39303. M, P Spathicuspus n. sp. A; M QIA144, PIMUZ 39297; P, QIA143, PIMUZ 39298. N, R Spathicuspus spathi (juvenile) (Sweet); N, LIL515D, PIMUZ 39304; R QIA143, PIMUZ 39305. Q Spathicuspus n. sp. B; LAR226C, PIMUZ 39299

2013 Neogondolella sp.; Yan et al., fig. 6, nr. X.

2015 Neogondolella? n. sp. A; Chen et al., figs. 9.5–9.8.

2019 Neogondolella? n. sp. A; Chen et al., figs. 6.8, 6.9.

2021 Gladigondolella laii sp. nov.; Chen et al., figs. 4.20, 4.21 (only).

Material. ca. 15 specimens.

Diagnosis. Segminiplanate P₁ element. Platform is arched, thickened and the platform margins are oriented orally. Denticles slightly fused at mid-length, larger and more discrete towards the anterior end.

Description. The element is arched in lateral view. In oral view, the margins of the thickened platform are subparallel at mid-length, and taper anteriorly. The platform is V-shaped, and the margin is directed orally. The cusp may be conspicuous in well preserved specimens. A posterior process may be present, which bears additional posterior denticles, otherwise the posterior margin is rounded. The carina denticles are partly fused at mid-length, taller and more discrete towards the anterior end.

Remarks. Gladigondolella laii differs from Borinella by having a more fused carina and an arched and thick platform whose margin are oriented orally. In comparison with the type species of Gladigondolella, a Middle Triassic species, the posterior process is much less developed and less arcuated in the carinal axis. Chen et al. (2015) rejected the assignment of their Ng. n. sp. A to Gladigondolella on the basis that posterior denticles are never present behind the cusp. In our material (e.g. Fig. 13C) small denticles are present occasionally. With the exception of these additional posterior denticles, our specimens resemble those of Chen et al. (2015) very closely, hence they are synonymized here. Implicitly we assume there is variation within the species, a small posterior process being present or not. This taxon is thought to be intermediary between Borinella and Gladigondolella, but through the shared derived characteristic of the posterior cusp we determine it as the former genus. Chen et al., (2019; figs. 6.8, 6.9) illustrated similar and coeval (associated with Ic. collinsoni) elements from Oman, which they assigned to Neogondolella n. sp. A. Their illustrated specimens more closely resemble Gladigondolella tethydis (Huckriede) and were later assigned to a new species of Gladigondolella: Gladigondolella laii (Chen et al., 2021). To date Gladigondolella is mostly known from the Middle Triassic (e.g. Goudemand et al., 2012a; Orchard et al., 2007a, 2007b). If, as it seems, the here illustrated specimens and/or those from Chen et al., (2019, 2021) do indeed belong to Gladigondolella, then they represent their oldest known representatives of this genus so far. A few unpublished specimens from middle Smithian rocks of Oman may also belong to this genus (Leu et al., submitted; L. Dudit, pers. comm.), which further question the origin and age of Gladigondolella. Its preference for deeper, colder habitats (Trotter et al., 2015) may then explain its spotty occurrences within the Early Triassic, preferably during relatively colder intervals and/or in deeper, colder refuge areas like Oman.

Occurrence. South China; Ic. collinsoni and Tr. homeri zone, Jiarong (Chen et al., 2015). Bed 54, Luolou formation, Ic. collinsoni and Tr. homeri zone, Bianyang section, Guizhou (Yan et al., 2013).

Gladigondolella laii Chen morphotype B

Fig. 13E, F, H, I

2015 Neogondolella? n. sp. B; Chen et al., figs. 9.9–9.10.

2019 Neogondolella? n. sp. A Chen; Liu et al., p. 14, pl. 4, fig. 19 (only).

2019 Neogondolella? n. sp. B Chen; Liu et al., p. 14, pl. 4, fig. 9.

2021 Gladigondolella laii sp. nov.; Chen et al., figs. 4.5, 4.22, 4.25, 4.26 (only).

Material. ca. 20 specimens.

Diagnosis. Segminiplanate P₁ element, narrow platform tapers towards the anterior, denticles moderately discrete. Very large, distinct, terminal, strongly reclined cusp.

Description. The platform is narrow, subparallel, slightly upturned and tapers towards the anterior end. The posterior margin is rounded in a narrow platform brim around the large terminal cusp. The cusp is massive and inclined posteriorly. The carina is moderately high with pointed denticles which are almost uniform in height.

Remarks. The large terminal cusp differs from Borinella whose denticles are also higher and more discrete, but resembles that of Scythogondolella. Yet, Gl. laii morphotype B lacks a prominent rounded basal loop surrounding a small pit, a distinctive feature of Scythogondolella. Chen et al. (2015) suggests that their Ng. n. sp. B could be a juvenile stage of Ng. n. sp. A (reassigned here and in Chen et al. (2021) to Gladigondolella laii see above) based on size considerations and the fact that they are both found in the same interval. Yet, they were not found in the same samples and the small forms (Gl. laii morphotype B) lack a posterior process, although the juvenile forms of ‘true’ gladigondolellids usually bear a posterior process. Hence, we tentatively keep them as separate morphotypes. Nevertheless, in Chen et al. (2021), both forms are found in the same sample (e.g. figs. 4.23 and 4.24) and can therefore be considered as different growth stages.

Occurrence. Ic. collinsoni and Tr. homeri zone, Luolou formation, Jiarong, Guizhou, South China (Chen et al., 2015).

Subfamily NEOGONDOLELLINAE Hirsch, 1994

Genus BORINELLA Budurov & Sudar 1994

1988 Pseudogondolella Kozur, p. 244.

1993 Kozurella Budurov & Sudar, p. 24.

*1994 (June) Borinella Budurov & Sudar, p. 30.

1994 (September) Chengyuania Kozur, pp. 529–530.

Type species. Neogondolella buurensis Dagis, 1984.

Type stratum and locality. Buur River Basin, Northern middle Siberia, Early Triassic Hedenstroemia Zone, Russia.

Remarks. The multi-element apparatus of this genus appears to be essentially the same as that of Neogondolella (Orchard, 2008). The P₁ elements of the species of this genus all have in common discrete blade-carinal denticles that lengthen towards the anterior.

Borinella buurensis (Dagis, 1984)

Fig. 13A

1978 Neogondolella jubata Sweet; Weitschat & Lehmann, p. 98, pl. 13, figs. 1–6.

*1984 Neogondolella buurensis n. sp.; Dagis, p. 12, pl. 2, figs. 6–15, pl. 3, fig. 1–2, pl. 11, figs. 1–4, pl. 12, figs. 1, 2, pl. 16, figs. 1–4.

1984 Neogondolella elongata Sweet; Hatleberg & Clark, Pl. 1, fig. 14 (only).

2005 Neogondolella aff. sweeti Kozur & Mostler; Zhao, p. 131, pl. 13, fig. 1.

2007 Borinella buurensis (Dagis); Orchard, p. 113, pl. 1, nr. 7, 15, 27.

2008 Borinella buurensis (Dagis); Nakrem et al., p. 528, fig. 4.19.

2008 Borinella aff. buurensis (Dagis); Nakrem et al., p. 528, fig. 4.17–4.18.

2008 Borinella buurensis (Dagis); Orchard, p. 400, figs. 5.9–5.13.

2012a Borinella aff. buurensis (Dagis); Goudemand & Orchard in Goudemand et al., p. 1032, figs. 2AA.

2015 Borinella aff. buurensis (Dagis); Chen et al., fig. 9.11.

2018 Borinella aff. buurensis (Dagis); Maekawa in Maekawa et al., p. 45, fig. 29.27.

2019 Neogondolella ex. gr. jakutensis Dagis; Chen et al., figs. 4.3, 4.5 (only).

2019 Borinella aff. buurensis (Dagis); Liu et al., p. 13, pl. 3, fig. 10 (only).

2021 Borinella aff. buurensis (Dagys); Chen et al., fig. 5.9 (only).

Number of specimens. 5

Description. Subsymmetrical segminiplanate P₁ element whose platform extends as a brim around the posterior edge, but not to the anteriormost quarter of the unit. In the posterior half, the platform margins are subparallel in oral view. The cusp varies in height and may be conspicuous. A smaller posterior denticle may be present in some specimens, in which case, it tends to be offset from the main axis. As in any Borinella species, the denticles become gradually more discrete and taller towards the anterior end. As illustrated by the figured specimen, whose denticles at mid-length are almost as high as the anteriormost ones, this denticulation gradient may be variable.

Remarks. Orchard (2007) suggested that the cusp of the P₁ of B. buurensis is typically weak, contrary to that of B. sweeti. Our collections suggest instead it is variable, as illustrated here. In our view it is difficult to differentiate B. sweeti and B. buurensis.

Occurrence. South China; Nv. pingdingshanensis Zone, Tsoteng section (Goudemand et al., 2012b), Jiarong section, Guizhou (Chen et al., 2015): Southwest Japan (Maekawa et al., 2018): Boreal region; Hedenstroemia zone, Siberia (Dagis, 1984), Tardus zone, Canadian Arctic (Orchard, 2008), Spitsbergen (Nakrem et al., 2008; Weitschat & Lehmann, 1978).

Genus NEOSPATHODUS Mosher, 1968

Type species and holotype. Spathognathodus cristagalli Huckriede, 1958, pp. 161–162, pl. 10, fig. 15.

Type stratum and locality. Lower Ceratite Limestone (LCL), Mittiwali near Chhidru, Salt Range, Pakistan.

Neospathodus dieneri Sweet, 1970

Fig. 14H

Fig. 14

Neogondolellinae, Novispathodinae and uncertain from Shanggang. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A, Eurygnathodus costatus (Staesche); SHA325, PIMUZ 39130. B Eurygnathodus hamadai (Koike); SHA326, PIMUZ 39131. C, D, F, G Novispathodus ex gr. waageni (Sweet); C SHA328, PIMUZ 39238; D SHA328, PIMUZ 39239; F SHA325, PIMUZ 39240; G SHA326, PIMUZ 39241. E Neospathodus ex gr. cristagalli (Huckriede); SHA330, PIMUZ 39182. H Neospathodus dieneri (Sweet); SHA338, PIMUZ 39181

*1970 Neospathodus dieneri n. sp.; Sweet, pp. 249–251, pl. 1, figs. 1, 4.

1982 Neospathodus dieneri Sweet; Matsuda 1982, p. 90, pl. 2, figs. 1–11.

1982 Neospathodus dieneri Sweet; Koike, p. 37, pl. 6, figs. 15–21.

1984 Neospathodus dieneri Sweet; Dagis, p. 27, pl. 6, figs. 4–7.

1991 Neospathodus dieneri Sweet; Beyers & Orchard, pl. 5, fig. 4.

2007 Neospathodus dieneri Sweet; Orchard & Krystyn, p. 33, figs. 3, 6, 7.

2007 Neospathodus dieneri Sweet; Zhao & Orchard in Zhao et al., p. 35, pl. 1, figs. 9A–C, 12A–B.

2009 Neospathodus dieneri Sweet; Igo in Shigeta et al., p. 186, figs. 151.6–151.16, 152.8 (only).

2009 Neospathodus dieneri Sweet; Orchard & Zonneveld., pp. 782–784, fig. 14, parts 1–4.

2016 Neospathodus dieneri Sweet; Maekawa et al., p. 199, figs. 4.8–4.10.

2018 Neospathodus dieneri Sweet; Maekawa in Maekawa et al., pp. 25–28, figs. 15.8–15.9, 15.12–15.14, 15.18–15.19, 15.21–15.28 (only).

Material. ca. 40 specimens.

Diagnosis. See Sweet (1970), pp. 249–251. The basal cavity is symmetrically rounded with a circular outline. The posterior margin is upturned. The denticles are round (subcircular in cross-section) with a pointy end, discrete and slightly recurved posteriorly. Basal groove runs from the basal pit to the anterior end.

Remarks. Zhao et al. (2007) distinguished three morphotypes of Neospathodus dieneri on the basis of the length of the terminal cusp relative to the other denticles. Their illustrated morphotype 3 (Zhao et al., 2007, Fig. 11A–C) however does not, in our opinion, belongs to N. ex gr. dieneri but is more closely related to N. cristagalli on the basis of its laterally flattened denticles and S-shaped posterior margin. Maekawa and Igo (2014, in Shigeta et al., 2014) assigned specimens to N. dieneri which is laterally flattened, blade-shaped denticles look very different from the holotype. They may instead belong to another species or even to another genus (possibly to Discretella?).

Occurrence. This species has been reported worldwide from the Dienerian and early Smithian. This includes South China (Zhao et al., 2007 and this study), Malaysia (Koike, 1982), the Northern Indian margin (Matsuda, 1982; Sweet, 1970), South Primorye in Russia (Shigeta et al., 2009), Canada (Beyers & Orchard, 1991) and Japan (Maekawa et al., 2018).

Neospathodus ex gr. cristagalli Huckriede, 1958

Fig. 14E

1970 Neospathodus cristagalli Huckriede; Sweet, p. 346, pl. 1, figs. 14, 15.

1982 Neospathodus cristagalli Huckriede; Matsuda p. 92, pl. 3, figs. 1–12.

2005 Neospathodus cf. cristagalli Sweet; Orchard, p. 89, text-fig. 14.

2014 Neospathodus cristagalli Huckriede; Maekawa & Igo in Shigeta et al., p. 223, figs. 161.10–161.12.

2015 Neospathodus cristagalli Huckriede; Maekawa in Maekawa et al., p. 315, figs. 5.4–5.6.

Material. ca. 30 specimens.

Remarks. In comparison with the holotype of N. cristagalli (Huckriede, 1958, Pl. 10, fig. 15), this element is much shorter, the basal cavity is oval, posteriorly rounded and only partly inverted, and the posterior triangular cusp is not conspicuously separated from the other denticles. Sweet still included such forms within N. cristagalli, but excluded similar forms with a rounded basal cavity and rounded, pointy denticles and assigned them to the then new species N. dieneri. In our opinion, such short elements where the cusp is not separated from the other denticles would deserve to be differentiated as a new species.

Occurrence. N. cristagalli is known worldwide in the Dienerian and earliest Smithian. It is not clear yet whether the present form is younger than N. cristagalli sensu stricto and occurs only close to the Dienerian–Smithian (Induan–Olenekian) boundary: Toad Formation, British Columbia (Orchard, 2005). Salt Range, Pakistan (Sweet, 1970). Guryul Ravine, Kashmir (Matsuda, 1982). Nanpanjiang basin; north-eastern Vietnam Flemingites beds within the Novispathodus ex. gr. waageni Zone (Maekawa et al., 2015; Shigeta et al., 2014). Luolou Formation, Flemingites limestone (this study).

Neospathodus bevelledi n. sp.

Figs. 15A, D, 16P–R.

Fig. 15

Neogondolellinae and Mullerinae from Qiakong, Laren and Shanggang. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A, D Neospathodus bevelledi n. sp.; A SHA333, PIMUZ 39176; D, SHA332, PIMUZ 39177. B, J Discretella aff. discreta (Müller); B SHA304, PIMUZ 39104; J SHA334, PIMUZ 39105. C, L Discretella discreta (Müller); C SHA334, PIMUZ 39107; L SHA332, PIMUZ 39108. E Guangxidella bransoni (Müller); SHA304, PIMUZ 39139. F, H, K, M, P Discretella pseudodieneri n. sp.; F QIA124, PIMUZ 39120; H QIA124, PIMUZ SQL54990; K QIA121, PIMUZ 39121; M QIA120, PIMUZ 39122; P LAR232, PIMUZ 39123. G Discretella cf. discreta (Müller); QIA120, PIMUZ 39109. I sp. indet.; QIA120, PIMUZ 39294. N Discretella? n. sp. B; LAR232, PIMUZ 39112. O Discretella? n. sp. C; SHA342, PIMUZ 39114

Fig. 16

Neogondolellinae, Novispathodinae and Mullerinae from Shanggang and Youping cascade. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A, F, M Discretella? n. sp. C; A YC16, PIMUZ 39115; F YC16, PIMUZ 39116; M SHA342C, PIMUZ 39117. B Discretella? n. sp. B; YC16, PIMUZ 39113. C Discretella aff. discreta (Müller); YC22, PIMUZ 39106. D, S Discretella discreta (Müller); D YC16, PIMUZ 39110; S SHA304C, PIMUZ 39111. E Novispathodus ex gr. abruptus (Orchard); YC41, PIMUZ 39225. G–I, K, L, N, O Discretella pseudodieneri n. sp.; G YC16, PIMUZ 39124; H YC25, PIMUZ 39125; I SHA304C, PIMUZ 39126; K YC22, PIMUZ 39127, L YC25, PIMUZ 39128; N SHA304C, PIMUZ 39129; O SHA343C, PIMUZ SQL54979. J Guangxidella bransoni (Müller); YC16, PIMUZ 39140. P–R Neospathodus bevelledi n. sp.; P SHA 304C, PIMUZ 39178; Q SHA333C, PIMUZ 39179; R YC12, PIMUZ 39180

1990 Neospathodus pamirensis n. sp.; Dagis, p. 79–80, pl. 4, fig. 8, pl. 6, fig. 9 (only).

2007 Neospathodus n. sp. V Orchard; Orchard, p. 96, fig. 2.

2013 Neospathodus cristagalli Huckriede; Yan et al., p. 516, fig. 6, I–L.

2014 Neospathodus spitiensis Goel; Maekawa & Igo in Shigeta et al., p. 233–236, figs. 167.17–167.30, 168.7–168.9, 168.16–168.27, 168.34–168.36, 169.4–169.9, 169.21–169.32, 170.1–3.

2014 Neospathodus sp. indet A Maekawa & Igo; Shigeta et al., p. 179, fig. 170.10–170.33.

2014 Novispathodus ex gr. waageni Sweet; Maekawa & Igo in Shigeta et al., p. 244, figs. 179.4–179.6, 179.13–179.15.

2015 Neospathodus cristagalli Huckriede; Chen et al., p. 112, fig. 8.12–13, 8.15.

2016 Neospathodus sp. indet A; Maekawa et al. p. 200, figs. 5.2–5.7.

2018 Neospathodus cristagalli Huckriede; Maekawa in Maekawa et al., p.22, fig. 14.24 (only).

?2019a Novispathodus pingdingshanensis Zhao & Orchard; Wu et al. figs. 32–34.

2021 Novispathodus waageni (Sweet); Sun et al., fig. 5.22 (only).

Etymology: named after the Latin (and British English) word ‘bevelled’, which refers to the wedge-like cessation of the denticles of the P₁ element.

Holotype: specimen illustrated in Fig. 15A

Paratype: specimen illustrated in Fig. 15D

Type locality: Shanggang road cut, Luolou formation, Guangxi Province, China.

Type level: Luolou Formation, within the early-to-middle Smithian limestones (Owenites beds), 2–3 m above Flemingites limestone.

Material. > 10 specimens.

Diagnosis. A species with a segminate-to-carminate P₁ element with distinctively wedge-shaped, bevelled denticle tips. Cusp is either terminal or in front of one or two posterior denticles. The shallow basal cavity is posteriorly elongated and tapered. In lateral view the lower margin is straight or upturned anteriorly, conspicuously upturned at mid-length, in front of the cusp, and straight or upturned posteriorly. The denticle directly in front of the cusp and above the kick in the lower margin may get broader towards its wedge-shaped tip and is usually conspicuously broader than the other denticles.

Description. The P₁ element is segminate to carminate (the posterior process bearing one or two denticles) and has a rigid cockscomb-like form. In lateral view, the lower margin is conspicuously bent or upturned at mid-length, the anterior and posterior parts of the lower margin making an angle of 15° to 40° and being often offset. The anterior lower margin is straight or slightly upturned, the posterior lower margin is usually more upturned. The upper margin is arcuate, with a peak in height slightly behind mid-length. The length-to-height ratio of the element is about 1–1.2:1. The moderately fused and laterally flattened denticles seem to radiate from a point that is located below the element, slightly anterior of the lower margin kick. The denticles are usually slightly recurved posteriorly. The cusp is located directly behind the lower margin kick and is as high as, or smaller than the up to 2 posterior denticles. The denticle directly in front of the cusp is usually conspicuously larger and broader than the other denticles. It may get broader towards its characteristically wedge-shaped tip. In lower/aboral view, the shallow basal cavity is subtriangular, being elongated and tapered posteriorly. The posterior end of the basal cavity can be either pointy or sub-rounded (as in the holotype). A groove runs from the basal cavity pit to the anterior end.

Remarks. Orchard (2007) was the first to differentiate such forms on the basis of their wedge-shaped denticle tips (his Neospathodus n. sp. V). The holotype of Neospathodus pamirensis Dagis (1990) appears to fall within the scope of Ns. bevelledi n. sp. but Dagis differentiated Ns. pamirensis on the basis of a “sharply angular lower margin” of the P₁ element and “cut-off ends” of the denticles (our rough translation from Russian), which based on his illustrations seem to correspond to sharply broken denticles, not to the wedge-shaped natural end that we use as a diagnostic feature of Ns. bevelledi n. sp., a feature that cannot be observed in his holotype of Ns. pamirensis. Moreover, the “sharply angular lower margin” does not differentiate his elements from those of Ns. spitiensis. Ns. bevelledi n. sp. compares most to Ns. cristagalli and Ns. spitiensis but none of the latter display the mid-length located, broad, large and bevelled denticle that is characteristic of Ns. bevelledi n. sp. Furthermore, Ns. spitiensis, as defined and illustrated by Goel (1977) has a similarly extended basal cavity and hence a similar lower margin but a much larger length-to-height ratio of about 1.8:1, its denticles being essentially smaller and more reclined posteriorly than in Ns. bevelledi n. sp. Maekawa and Igo (in Shigeta et al., 2014) assigned similar elements from Vietnam either to Ns. spitiensis or to their ‘Ns. sp. indet. A’. They differentiated ‘Ns. sp. indet. A’ on the basis that the P₁ elements are higher and display fewer denticles. In our view, most of the elements they assigned to Ns. spitiensis are already too high to belong to Ns. spitiensis and most of them display the characteristic bevelled denticles that none of the original Ns. spitiensis possessed. Hence, they probably belong to Ns. bevelledi n. sp. instead. Their material, however, shows a possible somewhat continuous transition between Ns. spitiensis Goel and Ns. bevelledi n. sp., suggesting a close relationship between both taxa. In comparison with Ns. cristagalli, the P₁ elements of Ns. bevelledi n. sp. are shorter and higher and although some elements display a posteriormost denticle that is triangular, it is neither smaller nor separated from the other denticles as is characteristic of Ns. cristagalli.

Occurrence. China: Bianyang and Jiarong sections, Nanpanjiang basin, Guizhou province (Chen et al., 2015; Yan et al., 2013); Japan: Taho Formation (Maekawa et al., 2018); Vietnam: Bac Thuy Formation, Smithian Flemingites to Owenites beds (Shigeta et al., 2014); Oman: Smithian age (Orchard, 2007).

Subfamily NOVISPATHODINAE Orchard, 2005

Genus NOVISPATHODUS Orchard, 2005

Type species and holotype. Neospathodus abruptus Orchard, 1995, pp. 118–119, figs. 3.23–24.

Type stratum and locality. Jabral Safra, Oman.

Remarks. The genus Novispathodus was introduced as a new genus with a 15-element apparatus by Orchard (2005) and revised by Goudemand et al. (2012b) based on the swapping of the S₁ and S₂ positions. Additional to the type species (Nv. abruptus) and other species whose multi-element apparatus has been reconstructed (e.g. Nv. pingdingshanensis (Goudemand et al., 2012b), Nv. waageni (unpublished)), we tentatively assign also the following species to Novispathodus on the basis that they co-occur with S and M elements that are reminiscent of Novispathodus.

Novispathodus pingdingshanensis (Zhao & Orchard, 2007)

Fig. 17D–F; M–P, R, S, U, X, AA, AB, AD, AF

Fig. 17

Novispathodinae from Qiakong, Laren, Shanggang, and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A–C, J, T, AA Novispathodus ex gr. pingdingshanensis (Zhao & Orchard); A, QIA138, PIMUZ 39226; B QIA138, PIMUZ 39227; C LAR202, PIMUZ 39228; J QIA136, PIMUZ 39229; T LIL504, PIMUZ 39230; AA LIL508, PIMUZ 39231. D–F, M–P, R, S, U, X, AB, AD Novispathodus pingdingshanensis (Zhao & Orchard); D QIA135, PIMUZ 39259; E LIL508, PIMUZ 39260; F LIL506, PIMUZ 39261; M LIL506, PIMUZ 39262; N LIL506, PIMUZ 39263; O LIL507, PIMUZ 39264; P LIL506, PIMUZ 39265; R LIL508, PIMUZ 39266; S LAR204, PIMUZ 39267; U LIL507, PIMUZ 39268; X LIL508, PIMUZ 39269; AB LIL508, PIMUZ 39270; AD LIL508, PIMUZ 39271. G, I, Q Novispathodus cf. ?gryphus n. sp.; G QIA136, PIMUZ 39204; I QIA136, PIMUZ 39205; Q QIA135, PIMUZ 39206. H, K, L Novispathodus gryphus n. sp.; H QIA135, PIMUZ 39243; K LIL506, PIMUZ 39244; L LIL506, PIMUZ 39245. V Novispathodus praebrevissimus n. sp.; LIL507, PIMUZ 39273. W, Y, Z, AE Novispathodus ex gr. abruptus (Orchard); W LIL505, PIMUZ 39208; Y SHA346, PIMUZ 39209; Z LIL506, PIMUZ 39210; AE SHA346, PIMUZ 39211. AC sp. indet.; LIL504, PIMUZ 39295. AF Novispathodus pingdingshanensis (P₁ cluster) (Zhao & Orchard); QIA136, PIMUZ 39272

*2007 Neospathodus pingdingshanensis n. sp.; Zhao & Orchard, Zhao et al., p.36, pl. 1, fig. 4A–C.

2012a Novispathodus pingdingshanensis (Zhao & Orchard); Goudemand & Orchard in Goudemand et al., p. 1030–1031, figs. 2B, F, G, I–J, M, P, Q, AD, 3T-U, 6.

2013 Neospathodus pingdingshanensis Zhao & Orchard; Chen et al., p 825, fig. 3.10, 3.12.

2013 Neospathodus waageni subsp. nov. A; Metcalfe et al., p. 1144, figs. 9.1–9.5, 9.7, 9.8, 9.10.

2014 Novispathodus pingdingshanensis (Zhao & Orchard); Maekawa & Igo in Shigeta, p. 239–240, figs. 171.13–171.31.

2015 Novispathodus pingdingshanensis (Zhao & Orchard); Chen et al., p. 111, 112, figs. 7.1–7.4, 8.5, 8.6.

2016 Novispathodus ex. gr. pingdingshanensis (Zhao & Orchard); Komatsu et al., p. 69, figs. 5.4a–5.5c.

2016 Neospathodus robustus Koike; Chen & Kolar-Jurkovšek in Chen et al., p. 93, fig. 9.5 (only).

2018 Novispathodus pingdingshanensis (Zhao & Orchard); Maekawa in Maekawa et al., p. 36–37, figs. 20.2–20.18, 21.1–21.13.

2019 Novispathodus pingdingshanensis (Zhao & Orchard); Chen et al., fig. 3, nr. 8.

2019 Novispathodus pingdingshanensis (Zhao & Orchard); Liu et al., p. 13, pl. 3 fig. 5 (only).

Material. > 100 specimens.

Diagnosis (Zhao and Orchard, in Zhao et al., 2007; emended by Goudemand, in Goudemand et al., 2012b). Small segminate P₁ elements characterized by a length/height ratio in the range of 1.32–2.34, and about 4–9 robust, wide, mostly fused, and distinctively posteriorly recurved denticles. In lateral view, the basal margin is usually straight. A large, broadly expanded oval to sub-rounded basal cavity is upturned on the inner margin and flat to downturned on the outer margin.

Remarks. Goudemand (in Goudemand et al., 2012b) revised the original diagnosis by noticing that the basal margin is not necessarily straight and therefore, the most strikingly difference to Nv. waageni is the denticulation: the denticles axes are distinctively recurved posteriorly whereas in Nv. waageni and Nv. abruptus, the denticles are straight, inclined or radiating. The two or three denticles anterior of the cusp are often clearly asymmetrical and the posterior edge of the element is much shorter than the anterior one. In most sections worldwide, Nv. pingdingshanensis first occurs within the positive δ¹³C_carb excursion of the latest Smithian and may extend to the earliest Spathian (Goudemand et al., 2019; Leu et al., 2019; Zhang et al., 2019). Some elements within our rich material resemble Ns. Pingdingshanensis, but appear to have a relatively small basal cavity, more posteriorly recurved denticles or more numerous denticles that what was previously described for this species. These elements (Figs. 17C, J, K, T; 18E, I–K; 19O, Q; 20H, N–O, S; here assigned to N. ex gr. pingdingshanensis) may deserve differentiation in the future. Two elements illustrated by Metcalfe et al., (2013, figs. 9.6, 9.9, p. 1144) as ‘Neospathodus waageni subsp. nov. A’ display a higher anterior end and more recurved denticles than the other elements they included in ‘Neospathodus waageni subsp. nov. A’, which we synonymized with Ns. pingdingshanensis: elements like these two elements do not seem to fit in Ns. pingdingshanensis and may deserve assignment to a new species. Some further elements resembling Ns. pingdingshanensis but distinctively shorter than Ns. pingdingshanensis are herein assigned to a new species (Nv. gryphus n. sp. see below).

Fig. 18

Novispathodinae from Laren and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A, B, D, F, L–N, Q, S, T Novispathodus praebrevissimus n. sp.; A LIL506, PIMUZ 39274; B LAR207, PIMUZ 39275; D LIL508, PIMUZ 39276; F LIL507, PIMUZ 39277; L LIL507, PIMUZ 39278; M LIL509, PIMUZ 39279; N LIL507, PIMUZ 39280; Q LIL507, PIMUZ 39281; S LIL507, PIMUZ 39282; T LIL507, PIMUZ 39283. C, O, R Novispathodus ?praebrevissimus n. sp.; C LAR204, PIMUZ 39284; O LIL507, PIMUZ 39285; R LIL507, PIMUZ 39286. E, I Novispathodus ex gr. pingdingshanensis (Zhao & Orchard); E LIL507, PIMUZ 39232, I LIL507, PIMUZ 39233. G Triassospathodus aff. symmetricus (Orchard); LIL507, PIMUZ 39309. H Novispathodus ex gr. abruptus (Orchard); LIL507, PIMUZ 39212. J, K Novispathodus praebrevissimus (juvenile) n. sp.; J LIL507, PIMUZ 39287; K LIL507, PIMUZ 39288. P Novispathodus robustispinus (Zhao & Orchard); LIL507, PIMUZ 39290

Fig. 19

Novispathodinae from Qiakong, Laren and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A Novispathodus cf. brevissimus (Orchard); LIL515C, PIMUZ 39199. B, F Novispathodus brevissimus (Orchard); B LIL515B, PIMUZ 39200; F BAN1, PIMUZ 39201. C Triassospathodus homeri (Bender); LIL515D, PIMUZ 39317. D, H Novispathodus ?brevissimus (Orchard); D LIL515D, PIMUZ 39202; H LIL514A, PIMUZ 39203. E Triassospathodus cf. homeri (Bender); LIL515C, PIMUZ 39318. G, K, O–Q Novispathodus n. sp. A; G LIL504, PIMUZ 39251; K LIL504, PIMUZ 39252; O LIL505, PIMUZ 39253; P LIL505, PIMUZ 39254; Q LIL505, PIMUZ 39255. I, L, M, Triassospathodus symmetricus (Orchard); I QIA141, PIMUZ 39336; L LIL512, PIMUZ 39337; M LIL514A, PIMUZ 39338. J Novispathodus ex gr. pingdingshanensis (Zhao & Orchard); QIA138, PIMUZ 39237. N Triassospathodus cf. symmetricus; LIL514B, PIMUZ 39339. R Novispathodus praebrevissimus n.sp; LIL505, PIMUZ 39289

Fig. 20

Novispathodinae from Qiakong, Laren and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A–G, K–M, Q, X Novispathodus ex gr. abruptus (Orchard); A LAR212, PIMUZ 39213; B LAR207, PIMUZ 39214; C LAR205, PIMUZ 39215; D LAR202, PIMUZ 39216; E LAR202, PIMUZ 39217; F LIL506, PIMUZ 39218; G LAR210, PIMUZ 39219; K LIL505, PIMUZ 39220; L LIL506, PIMUZ 39221; M LIL505, PIMUZ 39222; Q LAR203, PIMUZ 39223; X QIA136, PIMUZ 39224. H, V Novispathodus sp. indet.; H QIA136, PIMUZ 39291; V, QIA134, PIMUZ 39292. I, J, P, AA Novispathodus n. sp. Z; I QIA138, PIMUZ 39247; J QIA138, PIMUZ 39248; P LIL506, PIMUZ 39249; AA QIA136, PIMUZ 39250. N, O, S Novispathodus ex gr. pingdingshanensis (Zhao & Orchard); N LIL506, PIMUZ 39234; O LIL505, PIMUZ 39235; S QIA136, PIMUZ 39236. R sp. indet.; LIL511, PIMUZ 39296. T, Y, Z Novispathodus n. sp. A; T QIA134, PIMUZ 39256, Y QIA135, PIMUZ 39257; Z QIA134, PIMUZ 39258. U Novispathodus expansus (Zhao & Orchard); QIA134, PIMUZ 39242. W Novispathodus gryphus n. sp.; QIA135, PIMUZ 39246

Occurrence. Worldwide occurrence. China: Jinya/Waili area, Guangxi (Goudemand et al., 2012b) Jiarong, southern Guizhou (Chen et al., 2013, 2015). Anshun Fm., Qingyan section, Guizhou (Ji et al., 2011). Chaohu (Zhao et al., 2007, 2008). Daxiakou, Hubei (Zhao et al., 2013). Vietnam: Bac Thuy Fm., Xenoceltites variocostatus and Tirolites beds, (Komatsu et al., 2016; Shigeta et al., 2014). Canada: Scythogondolella mosheri zone, Wapiti Lake (Orchard & Zonneveld, 2009). Australia: Hovea Member of Kockatea Shale, upper part of Neospathodus waageni Zone, Smithian substage (Metcalfe et al., 2013).

Novispathodus gryphus n. sp.

Fig. 17G–I, K?, L

Etymology: from the Greek root ‘gryph’ referring to the hooked shape of the P₁ element.

Holotype: specimen illustrated in Fig. 17H.

Paratype: specimen illustrated in Fig. 17L.

Type locality: Qiakong, Luolou formation, Guizhou Province, China.

Type level: Luolou Formation, within latest Smithian black shales.

Number of specimens. ca. 10 specimens.

Diagnosis. A species with a short segminate-to-segminiscaphate P₁ element with 3 to 5 highly recurved denticles and a relatively large, sub-rounded basal cavity.

Description. The P₁ element is segminate to segminiscaphate, the sub-rounded basal cavity extending to most of the length of the element with a tapering at the anterior end. The denticles are mostly fused and highly recurved posteriorly: although the denticles get larger from the anterior to the posterior, except for the posteriormost one, the height of the carina looks sub-uniform because of the way the denticles are recurved. The length-to-height ratio is about 1:1.

Remarks. These elements resemble strongly the homologous ones of Nv. pingdingshanensis, except that they are much shorter and bear less denticles, which are usually more recurved. Still, some may be confused with broken elements of Nv. pingdingshanensis whose anteriormost end is missing (Fig. 17G). Hence the anterior end must be inspected for traces of breakage. Although the specimens we have seen do not show obvious, surfacial traces of breakage, it is not excluded that some of these elements were broken and were subsequently repaired, thus covering such traces at the surface of the crown. Goudemand and Orchard (in Goudemand et al., 2012b) differentiated similar but longer elements as Nv. aff. pingdingshanensis (Goudemand et al., 2012b, figs. 2K, 2L) because they are lower and their denticles more recurved than in elements of Nv. pingdingshanensis: their denticles are so recurved that their upper profile appears straight; as such they are reminiscent of the present species, with whom they may be closely related. In comparison with Nv. soleiformis (Zhao & Orchard, 2008) Nv. gryphus n. sp. has a higher carina with less numerous but more posteriorly recurved denticles. Furthermore, the basal cavity of Nv. gryphus n. sp. does not extend as a wide deep groove anteriorly like in Nv. soleiformis.

Occurrence. Luolou Formation, within the latest Smithian black shales, Guangxi and Guizhou, South China (this study).

Novispathodus ex gr. abruptus (Orchard, 1995)

Figs. 16E; 17W, Y, Z, AE; 18H; 20A–G, K, L, M, Q, X

1981 Neospathodus homeri Bender; Koike, pl. 1, fig. 5.

1984 Neospathodus sp. A; Hatleberg & Clark, pl. 3, fig. 8, 21.

*1995 Neospathodus abruptus n. sp.; Orchard, p. 118, 119, figs. 3.16–3.19, 3.23–3.26.

2005 Novispathodus abruptus (Orchard); Orchard, p. 90, text-fig. 16.

2009 Novispathodus abruptus (Orchard); Orchard & Zonneveld, p. 784, fig. 15 parts 34–37.

2012a Novispathodus sp. nov. A; Goudemand & Orchard in Goudemand et al., p. 1031, figs. 2A, R?, Z?.

2012a Novispathodus sp. nov. B; Goudemand & Orchard in Goudemand et al., p. 1031, fig. 3V.

2018 Novispathodus abruptus (Orchard); Maekawa in Maekawa et al., p. 33, figs., 18.1–18.3, 18.20, 18.23, 18.24, 18.26, 18.27 (only).

Material. > 50 specimens.

Diagnosis. As in Orchard, 1995.

Remarks. Here we consider Nv. abruptus in a broad sense, including elements that correspond to Nv. abruptus sensu stricto together with forms that have been suggested to deserve assignment to separate species, such as Nv. sp. nov. A and Nv. sp. nov. B Goudemand and Orchard (in Goudemand et al., 2012b). We consider the most diagnostic feature of Nv. ex gr. abruptus is the terminal 1–3 progressively smaller denticles at the posterior end.

The P₁ element of this species is less robust, more rectangular with more fused denticles than that of Ic. crassatus. Its morphology also recalls that of the homologous element in Nv. pingdingshanensis, but its basal cavity is relatively smaller and its denticles are not as posteriorly recurved nor usually as broad as in the latter. The P₁ element of Tr. symmetricus has more posteriorly reclined denticles, it may have a small terminal denticle but not several of increasingly smaller size. Yet, the distinction between Tr. symmetricus and Nv. abruptus may be confusing. The P₁ element of Tr. homeri has a more elongated basal cavity and a more developed, posteriorly reclined and laterally deflected process than in both Tr. symmetricus and Nv. abruptus. Goudemand and Orchard (in Goudemand et al., 2012b) implicitly suggested that elements like those of their Nv. sp. nov. B, where the small terminal denticles are not increasingly smaller but of equal (small) height instead, may be transitional between Nv. abruptus and Tr. homeri (compare the elements illustrated in figs. 2.9 and 3.17 of Orchard 1995, assigned to Tr. homeri and Nv. Abruptus, respectively). Note further that, based on the material from Tsoteng, it is likely that such P₁ elements were still associated with a Novispathodus apparatus. This suggests that P₁ elements like that of Tr. homeri may have evolved before the more substantial modifications of the rest of the apparatus implied by the difference between Novispathodus and Triassospathodus.

Occurrence. Worldwide occurrence in latest Smithian and early Spathian rocks. Xenoceltites and Tirolites beds within Nv. pingdingshanensis and Nv. brevissimus zones, Japan (Koike, 1981; Maekawa et al., 2018). Oman (Orchard, 1995). British Columbia (Orchard & Zonneveld, 2009), South China; Goudemand et al., 2012b; this study).

Novispathodus n. sp. Z Orchard, 2007

Fig. 20, I, J, P, AA

*2007 Ns. n. sp. Z; Orchard, p. 96, fig. 2.

2016 Novispathodus ex gr. abruptus (Orchard); Komatsu et al., p. 77, figs. 5.6a–c.

2018 Novispathodus abruptus (Orchard); Maekawa et al., p. 33, fig. 18.8.

2019 Novispathodus pingdingshanensis (Zhao & Orchard); Liu et al., p. 13, pl. 3, figs. 3, 6 (only).

2019 Triassospathodus symmetricus? (Orchard); Chen et al., fig. 4.15.

Material. ca. 15 specimens.

Remarks. One small terminal denticle behind the cusp is present. The denticles are mostly fused, with subtriangular tips and increasingly reclined towards the posterior end. A moderately deep, conical, subcircular shaped basal cavity is present. The overall shape of the segminate P₁ element is reminiscent of that of the sub-coeval Nv. pingdingshanensis or Nv. abruptus except that, contrary to Nv. pingdingshanensis, the denticles are reclined not recurved, and contrary to Nv. abruptus, there is only one small denticle behind the cusp, the latter being also conspicuously broader than adjacent denticles. Our specimens from China resemble the specimens from Panthalassa California (Darwin material), suggesting that this species may be important for worldwide correlations. Orchard (2007) mentioned, that Neospathodus kedahensis (Koike 1973) might be an available name for his Ns. n. sp. Z (Orchard 2007). However, Neospathodus kedahensis (Koike 1973) a Middle-to-Late Triassic species, lacks a conspicuous cusp and its posterior part is composed of slightly inclined and subequal denticles.

Occurrence. Taho Formation, Japan (Maekawa et al., 2018). North America (Orchard 2007, Goudemand et al., in prep.). Oman: Radio Tower section, UAZ₅ (Chen et al., 2019), South China; Nanpanjiang basin: Bac Thuy Formation, Nv. pingdingshanensis zone (Komatsu et al., 2016); Qinglong Formation, Nv. pingdingshanensis Zone, Jiangsu Province (Liu et al., 2019) Luolou Formation, Qiakong section, Southern Gouizhou, China (this study).

Novispathodus brevissimus (Orchard, 1995)

Figs. 19A, B, D, F; 21A–J, L, M; 22B, C, E, F?

Fig. 21

Novispathodinae from Qiakong, Laren, Shanggang and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A–J, L, M, Novispathodus brevissimus (Orchard); A LIL515A, PIMUZ 39184; B LIL513A, PIMUZ 39185; C BAN2, PIMUZ 39186; D SHA312, PIMUZ 39187; E SHA313, PIMUZ 39188; F LIL515A, PIMUZ 39189; G LIL509, PIMUZ 39190; H LIL509, PIMUZ 39191; I LIL514B, PIMUZ 39192; J LIL509, PIMUZ 39193; L QIA141, PIMUZ 39195; M QIA144, PIMUZ 39197. K, Novispathodus clinatus (Orchard and Sweet in Orchard); BAN5, PIMUZ 39207

Fig. 22

Novispathodinae from Laren and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A, D Icriospathodus cf. crassatus? (Orchard); A BAN1, PIMUZ 39168; D LIL513A, PIMUZ 39169. B, E Novispathodus brevissimus (Orchard); B LIL513B, PIMUZ 39194; E LIL514A, PIMUZ SQL55056. C, F Novispathodus cf, brevissimus (Orchard); C LIL513A, PIMUZ 39196; F, LIL514A, PIMUZ 39198

1981 Neospathodus triangularis Bender; Koike, pl. 1, fig. 6.

*1995 Neospathodus brevissimus n. sp., Orchard, pp. 117, pl. 3, figs. 14–15, 20–22.

2011 Neospathodus brevissimus Orchard; Ji et al., p. 219, fig. 3, nr. 7.

2014 Novispathodus triangularis (Bender); Maekawa and Igo in Shigeta et al., p. 241–243, figs. 172.1–9, 172.13–27, 173.1–3, 173.6–12, 173.16–21, 173.28–44, 174.1–174.24.

2015 Triassospathodus brevissimus (Orchard); Yan et al., p. 240, fig. 3.4.

2016 Novispathodus triangularis (Bender); Komatsu et al., p. 69, fig. 5.8.

2018 Novispathodus brevissimus (Orchard); Maekawa in Maekawa et al., p. 34, figs. 19.4, 19.5, 19.7.

2019 Neospathodus curtatus Orchard; Chen et al., fig. 6 nr. 13, 14.

2019 Neospathodus brevissimus Orchard; Chen et al., fig. 6 nr. 15.

2019a Triassospathodus brevissimimus [sic.] (Orchard); Wu et al., fig. 4, nr. 36.

2019 Novispathodus brevissimus (Orchard); Liu et al., p. 14, pl. 4, figs. 15, 18

Number of specimens. > 50.

Original diagnosis. “Species characterized by small, short, and high segminate elements with a length:height ratio of 1:1, about 8–12 largely fused, generally upright denticles atop a deep blade, and a large basal cavity with a subcircular basal outline that occupies most of the lower side” (Orchard, 1995).

Remarks. Characteristic of this species is the posterior lateral margin which is slightly to strongly curved. Subcircular to subtriangular outline of the large basal cavity in the lower view. The denticles are fused and compressed with an erect to radial outline (bouquet-like). The carina is relatively high. In lateral view, the upper edge is usually straight to slightly arched. Cusp is usually undistinguishable from other denticles.

The here illustrated adult specimens are a bit larger with more denticles than the holotype (Orchard, 1995; pp. 117, Pl. 3, fig. 22), but the denticulation and the convex posterior edge of the process is very distinct in this species. Therefore, the holotype (Orchard 1995) might represent a younger, juvenile morphotype of this taxon. Novispathodus eotriangularis (Zhao & Orchard in Zhao et al., 2007) has a more triangle-shaped basal cavity and the anterior half of the carina is gradually declining in height, whereas Novispathodus brevissimus shows a more abrupt decline at the posterior end. Compared to Novispathodus clinatus (Orchard 1995), this species shows more numerous, short and upright denticles. Novispathodus brevissimus shares most similarities with Novispathodus curtatus (Orchard, 1995), but the latter has a relatively smaller basal cavity, is longer and bears larger and more reclined denticles. Some specimens (e.g. Fig. 19F) bear the postero-lateral pinching that is usually considered diagnostic of Nv. triangularis (Bender), as revised by Orchard (1995). Chen et al. (2015) illustrated very similar specimens from a higher horizon (their figs. 7.9, 7.10). Contrary to ‘true’ Nv. triangularis, our specimens have more rounded denticles tips and the pinching is less conspicuous, suggesting they can still be retained within Nv. brevissimus sensu lato.

Occurrence. Oman, Jabal Safra, lower Spathian (Orchard, 1995); Japan, Taho Limestone, occurs with Nv. pingdingshanensis, Tahogawa Member (Koike, 1981; Maekawa et al., 2018); Nanpanjiang basin, South China and North Vietnam, together with Tirolites sp. nov. and Icriospathodus collinsoni (Komatsu et al., 2016; Liu et al., 2019; Shigeta et al., 2014; Yan et al., 2015).

Novispathodus expansus (Zhao & Orchard 2008)

Fig. 20U

2008 *Neospathodus expansus n. sp.; Zhao & Orchard in Zhao et al., p. 211, pl. 1, figs, 2a, 2b, 2c.

Submitted Novispathodus expansus (Zhao & Orchard); Leu et al., fig. 12Q.

Number of specimens. 5.

Remarks. Short robust denticles, a large basal cavity and a midlateral thickening are diagnostic for Nv. expansus. Some specimens of Nv. praebrevissimus n. sp. (Fig. 18O, P, T) feature a lateral, knob-like bulging on the flanks of the basal pit, but not a flange-like thickening along the mid-part of the carina as in Nv. expansus. Furthermore, in the latter the carina is lower than in Nv. praebrevissimus n. sp.

Occurrence. Columbites–Tirolites Zone, Nanlinghu Formation, Lower Triassic, Chaohu, Anhui Province, China (Zhao et al., 2008) Luolou Fm. Qiakong (this study); sample, JA15C, Jebel Aweri, Batain, early Spathian age, Oman (Leu et al., submitted).

Novispathodus clinatus (Orchard 1995)

Fig. 21K

*1995 Neospathodus clinatus n. sp. Orchard & Sweet in Orchard, p. 119, figs. 3.5–3.7

Number of specimens. 8

Remarks. This segminate element is relatively short and small. The basal cavity is subtriangular in outline. The posterior and anterior margins are abrupt and show both a bowed outline. The seven denticles are uniformly reclined. Other specimens assigned to Novispathodus clinatus sensu lato (e.g. Nv. aff. clinatus in Chen et al., 2015, fig. 5 or Nv. aff. clinatus in Maekawa et al., 2018, figs. 19.9–19.13) usually show a more elliptical basal cavity and a blade with a higher length: height ratio with more gradually declining denticles in the anterior part. This species resembles Nv. brevissimus with a subtriangular shaped basal cavity but the denticles in the latter species are less uniformly reclined and more numerous.

Occurrence. Top of Narmia Member of the Mianwali Formation at Narmia Pakistan (Orchard 1995); Laren section, Luolou Fm., Spathian, Guangxi, South China (this study).

Novispathodus praebrevissimus n. sp.

Figs. 17V; 18A–D, F, J–N, O?, P?, Q, S, T; 19R

1984 Neospathodus sp. aff. triangularis Bender; Hatleberg & Clark, pl. 3, fig. 16

2014 Icriospathodus? zaksi (Buryi); Maekawa & Igo in Shigeta et al., fig. 192, nr. 10–13 (only).

2015 Novispathodus brevissimus (Orchard); Chen et al., p. 111, fig. 7.8.

2019 Novispathodus pingdingshanensis (Zhao & Orchard); Chen et al., fig. 3 nr. 5, 9 (only) fig. 5, nr. 6 (only).

2019 Novispathodus pingdingshanensis (Zhao & Orchard); Liu et al., p. 13, pl. 3, fig. 7 (only).

Etymology: According to its presumed relationship as a predecessor of Nv. brevissimus.

Holotype: specimen illustrated in fig. 24R

Paratype: specimen illustrated in fig. 24Q

Type locality: Lilong cliff, Luolou formation, Guangxi Province, China.

Type level: Luolou Formation, within latest Smithian black shales. Present in UAZ₅ which corresponds to the peak of the positive δ¹³C_carb excursion and the Xenoceltites/Glyptophiceras beds.

Number of specimens. > 40.

Diagnosis. Short robust segminate P₁ element. Large rounded-to-sub-rounded basal cavity. Posterior margin often slightly concave. Small, largely fused denticles. Groove from basal pit to anterior end.

Description. The segminate P₁ element shows a very large rounded to sub-rounded basal cavity in the posterior half of the element. A very deep basal groove is present from the basal pit to the anterior end of the lower margin. The carina is relatively high with numerous small, fused denticles. The cusp is undistinguishable. The posterior lateral margin (posteriormost edge between basal cavity and last denticle) is slightly to strongly curved. Sometimes, the height of the posteriormost denticles is gradually but rapidly decreasing. In lateral view, the denticles tend to be radiating or recurved.

Remarks. This species is thought to be intermediate between Nv. pingdingshanensis and Nv. brevissimus. The P₁ element of this species is very similar to that of Nv. pingdingshanensis, but the basal cavity is much larger and rounded. In comparison to Nv. brevissimus, this species is usually smaller and has a relatively bigger and more rounded basal cavity. Furthermore, the carina is lower, with less numerous denticles. The new species is distinguished from the similar Novispathodus shirokawai (Maekawa et al., 2018) by reclined and less pointy denticles, a larger, rounded basal cavity and a less triangular shape in lateral view. Compared to Ic. zaksi, the P₁ element of this species is less robust and has a relatively higher carina. Ns. expansus (Zhao & Orchard) has a very similar morphology to Nv. praebrevissimus n. sp., but it has a distinct conspicuous thickening in the middle part of its unit. Some specimens of Nv. praebrevissimus n. sp. (Fig. 18L, O and P) show a bulbous thickening in the posterior part of the carina but never as pronounced as in Ns. expansus.

Occurrence. Spitsbergen, Botneheia Formation (Hatleberg & Clark, 1984). South China, Nanpanjiang basin: Jiarong, southern Guizhou (Chen et al., 2015). Luolou Formation, within latest Smithian black shales. Present in UAZ₅ which corresponds to the peak of the positive δ¹³C_carb excursion and the Xenoceltites/Glyptophiceras beds, Guangxi, South China (this study). Oman (Leu et al., submitted).

Novispathodus ex gr. waageni (Sweet, 1970)

Fig. 14C, D, F, G

*1970 Neospathodus waageni n. sp.; Sweet, pp. 260–261, pl. 1, figs. 11, 12.

1977 Neospathodus waageni Sweet; Goel, p. 1094, pl. 2, figs. 1–4.

1978 Neospathodus waageni Sweet; Weitschat & Lehmann, pl. 14, figs. 11–12.

1979 Neospathodus waageni Sweet; Solien, p. 292, pl. 3, fig. 9.

1980 Neospathodus waageni Sweet; Chhabra & Sahni, pl. 1, figs. 9–10, 14?, 16, 20?.

1982 Neospathodus waageni Sweet; Koike, p. 39, pl. 6, figs. 24–27.

1983 Neospathodus waageni Sweet; Matsuda, p. 88–91, pl. 1, figs. 6–10.

1984 Neospathodus waageni Sweet; Berry et al., p. 133, pl. 1, figs. 1–4.

1984 Neospathodus waageni Sweet; Dagis, p. 24, pl. 7, figs. 2–5, 7–10, pl. 8. fig. 7 (only).

2004 Neospathodus waageni Sweet; Zhao et al., figs. 1, 3.

2007 Neospathodus waageni Sweet; Zhao & Orchard in Zhao et al., pp. 36–37, pl. 1, figs. 5A, B, 10A, B.

2007 Neospathodus ex gr. waageni Sweet; Orchard & Krystyn, plate, figs. 8–18.

2008 Neospathodus waageni Sweet; Nakrem et al., figs. 5.7, 5.8, 5.11, 5.14.

2008 Neospathodus waageni Sweet; Orchard, p. 406, pl. 8, figs. 8.1, 8.2, 8.8, 8.9.

2009 Novispathodus waageni (Sweet); Orchard & Zonneveld, p. 785, figs. 13.1–13.10, 14, 15.

2009 Neospathodus ex gr. waageni Sweet; Igo in Shigeta et al., p. 194, figs. 152.1, 152.3, 152.14–15?, 152.1618, 152.19?, 153.8–9, 156.9, 156.14–19.

2010 Novispathodus waageni (Sweet); Beranek et al., figs. 6.22–23.

2012a Novispathodus waageni (Sweet); Goudemand & Orchard in Goudemand et al., p. 1031, figs. 3C?, D, E, H, N, S.

2013 Novispathodus waageni (Sweet); Zhao et al., figs. 9CC, 10A-H, 11F?, 11P-R?.

2014 Novispathodus waageni n. subsp. A; Goudemand, figs. 1A–1D

2014 Novispathodus ex gr. waageni (Sweet); Maekawa & Igo in Shigeta et al., p. 244, figs. 174.31–174.57, 175–178, 179.1–179.3, 179.7–179.12, 179.16–179.30, 180, 181.1–181.27.

2015 Novispathodus waageni (Sweet); Chen et al., figs. 6.23, 7.11, 8.3, 8.8, 8.9, 8.11, 8.14.

2016 Novispathodus waageni (Sweet); Liang et al., fig. 4.8.

2018 Novispathodus ex gr. waageni (Sweet); Maekawa in Maekawa et al., figs. 22.3, 22.10–11, 22.13?, 23.14–15, 23.18?.

2018 Novispathodus waageni (Sweet); Lyu et al., figs. 5, 6.

2019 Novispathodus waageni (Sweet); Lyu et al., figs. 7.8–10.

2019 Novispathodus waageni (Sweet); Souquet & Goudemand, figs. 3, 4a, 4g-4t.

2019 Novispathodus aff. waageni (Sweet); Souquet & Goudemand, figs. 4b–4f.

Number of specimens. > 50.

Diagnosis. See Sweet (1970).

Remarks. Despite the exclusion of several former morphotypes which have been formally described as separate species, this common species still encompasses a lot of variation in the P₁ element and may deserve further differentiation in the future. Up to six morphotypes have been recognized by distinct authors, e.g. Zhao et al. (2004) or Orchard and Krystyn (2007), and several others later by Goudemand (unpublished Ph.D. thesis, 2011). It is not yet clear whether these various morphotypes may be of any utility and hence whether some of those may deserve assignment to separate species (see for instance Lyu et al., 2018 for a discussion on the value of N. waageni eowaageni).

Occurrence. N. waageni is a very common species in Smithian rocks worldwide. Its FAD has been proposed as a proxy for defining the base of the Olenekian (see discussions in e.g. Goudemand 2014; Lyu et al., 2018; Orchard, 2007, 2010; Orchard & Krystyn, 2007; Zhao et al., 2007; Shigeta, 2009).

Novispathodus n. sp. A

Figs. 19G, K, O, P, Q; 20T, Y, Z

2015 Novispathodus aff. Clinatus Orchard & Sweet; Chen et al., p. 111, fig. 7, nr. 6 (only).

Number of specimens. > 10.

Description. Segminate P₁ element. 6–10 denticles present. The cusp is terminal and distinctly conical and often more reclined than anterior denticles. Anteriorly, the denticles are almost as high as the cusp and decline gradually towards the anterior end. The denticles are mostly fused and the cusp is conical or sometimes swollen at mid-height. The lower margin is straight to slightly upturned in the posterior half. Basal cavity rounded at posterior margin and tapers towards the anterior end. Basal groove runs from the basal pit to the anterior end.

Remarks. Similar to Nv. ex gr. pingdingshanensis in size and in its overall morphological outline, but differs by having a conical and terminal cusp. The denticles are straight, upright to slightly reclined, not recurved as in Nv. pingdingshanensis. In Nv. abruptus, the posteriormost denticles show a gradual decline that is not observed here. One of the elements illustrated by Chen et al. (2015) as Nv. aff. clinatus seems to fall within the variation of this species although it has more inclined posterior denticles.

Occurrence. In the late Smithian UAZ₇ in Qiakong, Lilong, Guangxi, South China (this study).

Genus TRIASSOSPATHODUS Kozur et al., 1998

Type species and holotype. Spathognathodus homeri Bender, 1970, pp. 528–529, pl. 5, fig. 16a–c.

Type stratum and locality. Marmarotrapeza Formation, Marathovuno, Chios, Greece.

F23;F24

Triassospathodus symmetricus (Orchard, 1995)

Figs. 19H, I–M; 23A, B, D, E, H, I; 24C, I–Q

Fig. 23

Novispathodinae from Qiakong, Laren, Shanggang and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A, B, D, E, H, I, Triassospathodus symmetricus (Orchard); A, LIL509, PIMUZ 39320; B, LIL509, PIMUZ 39321; D, QIA202, PIMUZ 39322; E, LIL509, PIMUZ 39323; H, LIL509, PIMUZ 39324; I, BAN2, PIMUZ 39325. C, F, G, Triassospathodus homeri (Bender); C, LAR231C, PIMUZ 39310; F, QIA155, PIMUZ 39311; G, SHA318, PIMUZ 39312

Fig. 24

Novispathodinae and uncertain from Qiakong, Laren, Shanggang, and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A, D, G, H Triassospathodus homeri (Bender); A LIL515C, PIMUZ 39313; D QIA155, PIMUZ 39314; G LIL513B, PIMUZ 39315; H LIL515B, PIMUZ 39316. B, E, F Triassospathodus aff. symmetricus (Orchard); B QIA138, PIMUZ 39306; E LIL505, PIMUZ 39307; F QIA136, PIMUZ 39308. C, I–Q Triassospathodus symmetricus (Orchard); C QIA140, PIMUZ 39326; I SHA313, PIMUZ 39327; J QIA143, PIMUZ 39328; K QIA144, PIMUZ 39329; L QIA141, PIMUZ 39330; M LIL515D, PIMUZ 39331; N LIL509, PIMUZ 39332; O LIL513B, PIMUZ 39333; P LIL513B, PIMUZ 39334; Q LIL513A, PIMUZ 39335. R–T Aduncodina unicosta (Ding); R BAN5, PIMUZ 39100; S SHA320, PIMUZ 39101; T SHA318, PIMUZ 39102

1970 Neospathodus homeri Bender; p.245, pl. 1, figs. 2, 3, 9, 10.

1970 Neospathodus triangularis Bender; Sweet, pp. 253–254, pl. 1, figs. 7, 8.

1973 Neospathodus homeri Bender; Mosher, p. 171, pl. 20, fig. 14.

1977 Neospathodus homeri Bender; Goel, p. 1097, pl. 2, figs. 10, 11.

1986 Neospathodus homeri Bender; Durkoop et al., pl. 20, figs. 9–10.

*1995 Neospathodus symmetricus n. sp.; Orchard, p. 120, 121, figs. 2.6, 2.10–2.13, 2.18.

2004 Neospathodus symmetricus Orchard; Koike, p. 137, figs. 35–38.

2007b Triassospathodus ex. gr. homeri (Bender); Orchard et al., p. 345, fig. 5.5, 5.6.

2009 Triassospathodus ex. gr. homeri (Bender); Orchard & Zonneveld, p. 788, fig. 15, parts 38–40.

2011 Neospathodus symmetricus Orchard; Ji et al., p. 219, figs. 3.5a, b, c.

2014 Triassospathodus symmetricus (Orchard); Maekawa & Igo in Shigeta et al., p. 254, figs. 182–185, 186.1–186.3

2015 Triassospathodus symmetricus (Orchard); Chen et al., figs. 7.16–7.17, 8.19, 9.15.

2015 Novispathodus abruptus (Orchard); Chen et al., figs. 8.2, 9.13.

2018 Novispathodus abruptus (Orchard); Maekawa in Maekawa et al., p. 33, figs. 17.22, 17.24, 17.25, 18.4–18.12, 18.14–18.22, 18.25, 18.28 (only).

2019 Triassospathodus symmetricus (Orchard); Chen et al., fig. 4, nr. 8, 1–13, fig. 5, nr. 4 (only)

Number of specimens. >50

Description. Segminate P₁ element with length/height ratio of 2.0–2.5:1 and usually 10–13 subequal, variably fused denticles that become increasingly reclined posteriorly. Straight or arcuate upper margin, subtriangular denticles edges. The cusp is indistinct, it has as high or slightly higher than the other denticles. The basal margin is straight anteriorly and may be downcurved posteriorly. The margin of variably shaped basal cavity is expanded laterally and downturned posteriorly. A basal groove extends from the basal pit to the anterior end. Some specimens develop a midlateral rib.

Remarks. The elements are similar to Tr. homeri but usually shorter and they lack a ‘true’ denticulate posterior process: in Tr. symmetricus, the basal cavity is more or less rounded posteriorly, whereas in Tr. homeri it tapers posteriorly below the inturned posterior edge of the carina (Orchard, 1995). Some elements (Fig. 23B, E, H) may deserve differentiation in the future as they bear strongly reclined and gradually smaller, posteriormost denticles, as opposed to typical elements of this species.

Occurrence. Almost worldwide distribution. Nanpanjiang basin: North-eastern Vietnam, Bac Thuy Formation, Tirolites cf. cassianus beds (Shigeta et al., 2014). South China, Luolou Formation (several sections in this paper), Qingyan section, (Neospathodus homeri Zone, Ji et al., 2011); Northern Indian margin: Salt Range, Pakistan (Zone 9, Sweet, 1970). Spiti India (Goel, 1977), Oman, Jabal Safra (Orchard, 1995). Japan: Taho limestone (Koike, 2004). British Columbia: Canada (Keyserlingites subrobustus Zone, Mosher, 1973).

Triassospathodus aff. symmetricus (Orchard, 1995)

Figs. 18G; 24B, E, F

2004 Neospathodus sp. aff. N. symmetricus Orchard; Koike, p. 133, figs. 2.4–2.5.

2015 Triassospathodus symmetricus (Orchard); Chen et al., fig. 8.1.

Number of specimens. > 20.

Remarks. The biostratigraphical range of these specimens is usually slightly older than that of Tr. symmetricus. The P₁ element of Tr. aff. symmetricus resembles that of Tr. symmetricus, but is shorter with fewer denticles and a more circular and larger outline of the basal cavity. The denticles are less inclined posteriorly compared to Tr. symmetricus and often have one additional small posteriormost denticle. Its denticles are not posteriorly arched as in Nv. pingdingshanensis. It differs from the very similar Nv. abruptus by having a downturned posterior part and posteriorly reclined denticles. This species might represent a transitional form between Novispathodus abruptus and Triassospathodus symmetricus but a multi-element apparatus reconstruction is currently lacking.

Occurrence. Taho Formation, Southwest Japan, Spathian age (Koike, 2004); South China, Luolou Formation, at the top of the black shales and the base of the nodular limestone in the earliest Spathian (this study).

Triassospathodus homeri (Bender, 1970)

Figs. 19C; 23C, F, G; 24A, D, G, H

*1970 Spathognathodus homeri n. sp.; Bender, p. 528, pl. 5, figs. 16a–c.

1970 Neospathodus homeri (Bender); Sweet, p.245, pl. 1, figs. 2, 3, 9, 10.

1980 Neospathodus homeri (Bender); Chhabra & Sahni, pl. 1, figs. 28 (only).

1983 Neospathodus homeri (Bender); Matsuda, p. 94–95, pl. 4, figs. 3, 4, 5.

1986 Neospathodus homeri (Bender); Durkoop et al., pl. 20, figs. 8a–d.

1995 Neospathodus homeri (Bender); Orchard, p. 115, figs. 2.1–2.3, 2.7–2.9, 2.14–2.17, 2.20, 2.21.

2005 Triassospathodus homeri (Bender); Orchard, p. 93, figs. 19.

2007 Triassospathodus ex. gr. homeri (Bender); Lucas & Orchard, p. 123, figs. 7.8, 7.9.

2007b Triassospathodus ex. gr. homeri (Bender); Orchard et al., p. 353, figs. 6, nr. 10–12.

2011 Neospathodus homeri (Bender); Ji et al., p. 220, figs. 3.9a, b, c.

2014 Triassospathodus homeri (Bender); Maekawa & Igo in Shigeta et al., p. 253, figs. 181.43–181.48.

2015 Triassospathodus homeri (Bender); Chen et al., figs. 7.13, 8.18, 9.14, 9.19.

2015 Novispathodus abruptus (Orchard); Chen et al., figs. 7.16–7.17, 9.16.

2019 Triassospathodus homeri (Bender); Chen et al., fig. 7, nr. 1.

2019 Triassospathodus symmetrucis [sic.] (Orchard); Liu et al., p. 12, pl. 2, fig. 11.

2021 Novispathodus abruptus (Orchard); Chen et al., fig. 4.3.

2021 Triassospathodus homeri (Bender); Chen et al., fig. 4.15, 4.16 (only).

Number of specimens: >30

Diagnosis. “Species with segminate elements that have a length:height ratio of 2.5–3:1, and commonly 15–18 subequal, moderately fused denticles that are increasingly reclined toward the posterior end where 3–5 small, low denticles occur on a short, variably inturned process. The posterior edge of the blade is moderately reclined. In basal outline, the basal cavity is elliptical, tapers in both anterior and posterior directions, and is strongly asymmetrical in specimens with an inturned posterior process.” (Orchard, 1995).

Remarks. This species may be slightly younger than the closely related Tr. symmetricus.

Occurrence. Worldwide distribution. Nanpanjiang basin: North-eastern Vietnam, Bac Thuy Formation, Tirolites beds (Shigeta et al., 2014). South China, (Orchard et al., 2007b, this study). Northern Indian margin: Kashmir (Matsuda, 1983). Jabal Safra, Oman (Orchard, 1995). Salt Range, Pakistan (Sweet, 1970). Western USA: Lower Spathian interval of Thaynes Group (Tirolites beds, Lucas & Orchard, 2007).

Genus ICRIOSPATHODUS Krahl et al., 1983

Type species and holotype. Neospathodus collinsoni Solien, 1979.

Type stratum and locality. Unit D, Thaynes Formation, near Salt Lake City, Utah, USA.

Remarks. Originally, the basis for establishing this genus was the characteristic ridge-like denticulation of the P₁ element of Ic. collinsoni. Orchard (2005) reconstructed the multi-element apparatus of Ic. collinsoni, showing a smaller degree of denticulation of the P₂, M and S elements in comparison to Novispathodus. Because their S elements (especially the S₁) are significantly different from those of the subfamily Novispathodinae, he regarded their subfamily assignment as uncertain. Pending future multi-element reconstructions of the herein included taxa, we tentatively retain Icriospathodus within the Novispathodinae. The affinity of Ic. collinsoni, Ic. crassatus and Ic. zaksi was recognized in several studies (Koike, 1992; Orchard, 2007; Maekawa & Igo in Shigeta et al., 2014; Maekawa in Maekawa et al., 2018), and we follow these authors.

Icriospathodus collinsoni (Solien, 1979)

Fig. 25M, O, P

Fig. 25

Novispathodinae from Laren, Shanggang and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A–F, Icriospathodus zaksi (Buryi); A LAR205, PIMUZ 39170; B LIL508, PIMUZ 39171; C LIL508, PIMUZ 39172; D LAR204, PIMUZ 39173; E LIL510, PIMUZ 39174; F LAR203, PIMUZ 39175. G–L Icriospathodus aff. crassatus (Orchard); G LIL510, PIMUZ 39159; H LIL508, PIMUZ 39160; I LAR203, PIMUZ 39161; J LIL509, PIMUZ 39162; K LAR202, PIMUZ 39163; L LAR210, PIMUZ 39164. M, O, P Icriospathodus collinsoni (Solien); M SHA313, PIMUZ 39165; O SHA320, PIMUZ 39166; P LIL515A, PIMUZ 39167. N Triassospathodus symmetricus (Orchard); SHA320, PIMUZ 39319

1964 Icriodus; Clark et al., p. 376, pl. 60, fig. 1.

1970 Neospathodus n. sp. G; Haselmüller, p. 45–47, pl. 2, fig. 12a–b.

1971 Neospathodus n. sp. G; Sweet et al., p. 453, pl. 1, figs. 12, 13

*1979 Neospathodus collinsoni n. sp.; Solien, p.302, pl. 3, figs. 10, 12–20

1981 Neospathodus? collinsoni (Solien); Koike, pl. 1, figs. 42–44.

1987 Neospathodus collinsoni (Solien); Zakharov & Rybalka, p. 43–44, pl. 5, figs. 4, 5.

1990 Neospathodus collinsoni (Solien); Metcalfe, p. 136, pl. 1, figs. 6, 7, 17.

1992 Spathoicriodus collinsoni (Solien); Koike, p. 357–361, figs. 11, 12.13–12.42, 12.44, 12.47–12.50, 13.8–13.37.

1995 Icriospathodus collinsoni (Solien); Orchard, p. 113, fig. 2.22–2.24.

2005 Icriospathodus collinsoni (Solien); Orchard, p.96, fig. 22A

2007 Icriospathodus collinsoni (Solien); Orchard p.96, fig. 2

2007 Icriospathodus collinsoni (Solien); Lucas & Orchard, p. 123, figs. 7.4–7.7, 7.13–7.15.

2011 Icriospathodus collinsoni (Solien); Ji et al., p. 221, figs. 5a–5c.

2014 Icriospathodus collinsoni (Solien); Maekawa & Igo in Shigeta et al., p. 260, figs. 186.10–186.22, 187–191, 192.1–192.6.

2015 Icriospathodus collinsoni (Solien); Chen et al., p.113, figs. 9.1–9.4.

2015 Icriospathodus collinsoni (Solien); Yan et al., p. 240, figs. 3.5, 3.6.

2016 Icriospathodus collinsoni (Solien); Komatsu et al., p. 69, fig. 5.9.

2018 Icriospathodus collinsoni (Solien); Maekawa in Maekawa et al., p. 49–51, figs. 28.5–28.10, 29.1–29.7.

2019 Icriospathodus collinsoni (Solien); Chen et al., fig. 6, nr. 10–12.

2019 Icriospathodus collinsoni (Solien); Liu et al., p. 14, pl. 4, figs. 6–8.

2021 Icriospathodus collinsoni (Solien); Chen et al., figs. 4.9–11.

Number of specimens: >40

Description. A robust segminate P₁ element. The upper edge bears biserial or/and ridge-like denticles. The width of the denticles is usually longest in the middle part to the posterior third. The basal cavity shows a lot of variation, but is mostly asymmetrical.

Remarks. Koike (1992) showed a wide range of intraspecific variation within this species (see below). The two rows of nodes on the upper margin and the pairs of nodes connected by a ridge are diagnostic features that are easy to determine and miss-identification of even broken elements is unlikely. P₁ elements of Eurygnathodus are superficially similar but they are scaphate, not segminate.

Occurrence. I. collinsoni indicates the early Spathian worldwide and generally co-occurs with the Tirolites and Columbites beds. USA: Idaho, (Zone 11, Sweet et al., 1971), Utah (Thaynes formation, Solien, 1979), Nevada (Lucas & Orchard, 2007), South China (Chen et al., 2015; Ji et al., 2011), Vietnam (Bac Thuy formation, Komatsu et al., 2016; Shigeta et al., 2014), Oman (Orchard, 1995), Primorye (Zakharov & Rybalka, 1987), Japan (Maekawa et al., 2018), Malay Peninsula (Metcalfe, 1990).

Icriospathodus aff. crassatus (Orchard, 1995)

Figs. 22A?, D?; 25G–L, N

2019 Icriospathodus crassatus (Orchard); Liu et al., pl. 4, figs. 10, 14.

Number of specimens: >30

Diagnosis. In lateral view, the segminate P₁ element is subrectangular. Moderately fused carina. Denticles increasingly lower at both anterior and posterior ends. Posteriormost denticles often bent inwards. Basal cavity generally symmetrical and subquadrate to subtriangular in shape. Lateral margins and basal cup often relatively thick and sometimes accessory nodes on the latter.

Description. In oral view, the rather symmetrical large basal cavity looks bulbous. Laterally, the thick node-like, irregular denticles are lower and more bent inwards towards the posterior end. The basal cavity is symmetrical. The subterminal cusp is situated near the posterior end, up to two more reclined denticles being sometimes present behind it. The lower margin is downturned posteriorly.

Remarks. Orchard (1995) created Ic. crassatus for Ic. collinsoni-like elements that lack the ridge-like or paired platform nodes. Our specimens share the attributes of Ic. crassatus but their basal cavities are subsymmetrical, which is uncommon for Ic. crassatus. The elements of N. symmetricus have a similar outline in lateral view but have relatively higher and more uniform denticles with a pointy tip, and a relatively larger basal cavity. In our material, Ic. zaksi and Ic. aff. crassatus are morphologically similar, but Ic. aff. crassatus is longer, bears more denticles, has a relatively smaller basal cavity and is usually found in younger strata. Ic. zaksi may be a forerunner of Ic. aff. crassatus. In the material studied from South China, no “true” Ic. crassatus was found. In addition, all illustrated specimens from South China determined as Ic. crassatus from the literature can neither be determined as Ic. crassatus sensu stricto in the authors view. The specimen illustrated in Lehrmann et al. (2015) (fig. 5.16, 5.17), resembles more Tr. homeri (see Additional files). The studies from West and North Pingdingshan do either not provide any illustrations (Liang et al., 2011; Zhao et al., 2007, 2008) or the specimens cannot be determined as Ic. crassatus with certitude because the specimens are broken and resembles more Ic. cf. zaksi (Pl. 6 fig. 2) or Ic. cf. aff. crassatus (Pl. 12 fig. 11) in Zhao (2005). In Ji et al. (2011) the illustrated specimen from Qingyan consists of a large subsymmetrical basal cavity and resembles more Ic. aff. crassatus. The specimen determined as Ic. crassatus in Liu et al. (2019) is in the synonymy list of Ic. aff. crassatus (see above). Furthermore, the specimen illustrated in Yan et al. (fig. 6GG, 2013) resembles more Tr. homeri with an inturned posterior end. Therefore, it has to questioned if Ic. aff. crassatus is provincialistic of South China and is worth of defining a new species formally in the future.

Occurrence. South China, Nanpanjiang basin, Luolou Fm., Laren, Lilong, Shanggang top of black shales to nodular limestone, SSB and early Spathian, (this study).

Icriospathodus zaksi (Buryi, 1979)

Fig. 25A–F

*1979 Neospathodus zaksi Buryi, p. 60 pl. 18 figs. 3a, b.

2007 Icriospathodus? zaksi (Buryi); Orchard, fig. 2.

2013 Neospathodus novaelhollandiae McTavish; Yan et al., p. 516, fig. 6BB–DD.

2014 Icriospathodus? zaksi (Buryi); Maekawa & Igo in Shigeta et al., fig. 192, nr. 14–29.

2015 Novispathodus pingdingshanensis (Zhao & Orchard); Chen et al., p.111, figs. 7.1–7.2.

2016 Neospathodus planus sp. nov. Chen & Kolar-Jurkovšek; Chen et al., p.92, fig. 7.9a–c, 8.10.

2016 Neospathodus robustus Koike; Chen & Kolar-Jurkovšek in Chen et al., p.92, figs. 8.7–8.9.

2016 Icriospathodus? zaksi (Buryi); Komatsu et al., p. 69, fig. 5, nr. 2–3.

2018 Icriospathodus zaksi (Buryi); Henderson et al., p.18 pl. 1, figs. 18–19.

2018 Icriospathodus zaksi (Buryi); Maekawa in Maekawa et al., p. 51, figs. 29.20–29.26.

2018 Icriospathodus? sp. 1; Maekawa in Maekawa et al., p. 54, figs. 30.1–30.2.

2019 Triassospathodus symmetricus (Orchard); Chen et al., fig. 5, nr. 8 (only).

2019 Neospathodus ex. gr. planus Chen & Kolar-Jurkovšek; Chen et al., fig. 6, nr. 2.

2019 Icriospathodus zaksi (Buryi); Chen et al., fig. 6, nr. 4, fig. 7, nr. 9, 10.

2019 Novispathodus pingdingshanensis (Zhao & Orchard); Liu et al., p. 13, pl. 3, fig. 4 (only).

Number of specimens: >30

Revised diagnosis. Low, robust segminate P₁ elements usually with 8–9 wide denticles. 2–3 small denticles may be located behind the variably conspicuous cusp. Denticles are node-like in form. The lower margin is straight. Deep, wide basal cavity. One or two variably shaped, lateral processes are occasionally present.

Description. Robust segminate P₁ element with 7–12 short, robust, erect to uniformly recurved, mostly fused, triangular-shaped denticles. Rectangular to subrectangular outline of the element. In most elements, the cusp is distinct. Unit lowest at the posteriormost end. Big sub-rounded, bulbous, slightly concave basal cavity. The basal cavity occupies the entire posterior half of the element. The posterior margin coincides with the edge of the cavity.

Remarks. The holotype (Buryi, 1979) has postero-lateral processes, which, in the original diagnosis were considered “complex in form” and characteristic of this species. Because the holotype is broken and the original diagnosis was based only on that specimen, we revise here the diagnosis on the basis of more than 30 specimens that show broader morphological variation in the platform: as illustrated by others (e.g. Chen et al., 2019), a lateral process may or may not be present. Koike (1992) reported a similar morphological variation within Ic. crassatus and Ic. collinsoni, suggesting it is a generic property of Icriospathodus. The P₁ element of Ic. zaksi resembles that of Ic. crassatus but it is smaller, has a shorter carina and a much larger basal cavity relatively to its length.

Occurrence. Worldwide occurrence. India: Unit H3, Khunamuh formation, Guryul Ravine; North-eastern Vietnam: Novispathodus pingdingshanensis Zone, Xenoceltites variocostatus beds, Bac Thuy Formation (Maekawa & Igo in Shigeta et al., 2014); Russia: upper part of Anasibirites nevolini Zone to lower part of Tirolites cassianus Zone, South Primorye (Buryi, 1979); South China: Bed 51, Luolou Formation, Bianyang Section, Guizhou province (Yan et al., 2013); Canada: British Columbia, Montney Formation; late Smithian–early Spathian (Henderson et al., 2018). Oman; Wadi Bani Khalid section, UAZ₄, Nv. pingdingshanensis range Zone (Chen et al., 2019); Japan: Taho Formation, Novispathodus brevissimus Zone (Maekawa et al., 2018).

Subfamily MULLERINAE Orchard 2005

Genus DISCRETELLA Orchard 2005.

Type species. Ctenognathodus discreta Müller 1956, p. 821–822, pl. 95, fig. 28.

Type stratum and locality. Smithian ammonoid bed, Crittenden Springs, Elko County, Nevada.

Discretella discreta (Müller, 1956)

Figs. 15C, G, L; 16D, S.

*1956 Ctenognathodus discreta n. sp.; Müller, pp. 821–822, pl. 95, fig. 28.

1989 Neospathodus discreta (Müller); Thang, p. 402, pl. 30, fig. 7.

2005 Discretella sp. A; Orchard, p. 83, fig. 8.

2008 Discretella discreta (Müller); Orchard 2008, p. 402, figs. 8.18, 8.19.

2010 Discretella discreta (Müller); Beranek et al., p. 65, figs. 6.18, 6.19.

2014 Discretella discreta (Müller); Maekawa & Igo in Shigeta et al., pp. 196–202, figs. 141.13–141.33, 142–145, 146.1–146.30.

2018 Discretella discreta (Müller); Maekawa in Maekawa et al., p. 23, fig. 14.4.

Number of specimens: >20

Diagnosis. See Müller, 1956.

Description. The carminate-to-segminate P₁ element has an upturned and inverted basal margin in the posterior one-third to one-half of the element. The cusp is usually larger than the other discrete and upright denticles but not conspicuously.

Remarks. Maekawa & Igo (in Shigeta et al., 2014) described two different morphotypes, A and B, for Discretella discreta. Their morphotype A would correspond to the holotype (Müller, 1956) and their morphotype B has an upturned posterior margin and a relatively broader and triangular cusp. Although Maekawa & Igo (in Shigeta et al., 2014) have recently illustrated numerous specimens, the intraspecific variation of this species remains unclear due to its general scarcity. Based on their illustrations and unpublished material, there seems to be scope for further differentiation. Both morphotypes A and B have a posterior process and hence a tapered posterior margin of the basal cavity. However, some of our specimens do not develop a posterior process and have a rounded posterior margin at the basal cavity. Those are here assigned to a different species, which for now is kept in open nomenclature (Discretella aff. discreta).

Occurrence. Wide global occurrence in the Smithian. Meekoceras beds, Nevada (Müller, 1956). Euflemingites romunderi Zone, Canadian Arctic (Orchard, 2008). Jabal Safra, Oman (Orchard, 2005). North Vietnam (Thang, 1989). Nv. ex. gr. waageni Zone, Taho Formation, Japan (Maekawa et al., 2018).

Discretella aff. discreta (Müller, 1956)

Figs. 15B, J; 16C?.

1989 Neospathodus bransoni (Müller); Thang, p. 417, pl. 29, fig. 10.

2009 Guangxidella? sp. A; Orchard & Zonneveld, p. 780, fig. 14, parts 33, 34.

2013 Discretella discreta (Müller); Yan et al., p. 516, fig. 6W.

Number of specimens: >15

Diagnosis. Segminate P₁ element with rounded, upturned basal cavity at the posteriormost part. Large conspicuous cusp above basal cavity. Discrete, smaller upright denticles in the anterior part.

Description. These P₁ elements have markedly discrete denticles and a large cusp. The lower margin is straight in the anterior and upturned at the posterior part. The basal cavity is drop-shaped, being rounded at the posterior edge and tapered at the anterior end. The cusp is relatively large and reclined. A small, accessory, posterior denticle is occasionally present.

Remarks. In comparison to Discretella discreta, this species has a rounded posterior margin of the basal cavity, more discrete denticles and the cusp is relatively larger and often recurved. In lateral view, the lower margin is upturned as in morphotype B of Discretella discreta (Maekawa & Igo, in Shigeta et al., 2014).

Occurrence. Luolou formation, Owenites beds Smithian age, Shanggang road cut, Guangxi, South China.

Discretella pseudodieneri n. sp.

Figs. 15F, H, K, M, P; 16G–I, K, L, N, O

2013 Neospathodus dieneri Sweet; Yan et al., p. 516, fig. 6S (only).

2014 Neospathodus dieneri Sweet; Maekawa & Igo in Shigeta et al., p. 224, fig. 162, nr. 40–42, 46–54 (only).

2014 Discretella sp. indet. A; Maekawa & Igo in Shigeta et al., p. 202–207, fig. 151.13–151.15 (only).

2015 Discretella sp.; Chen et al., p. 112, fig. 8.12.

2018 Neospathodus dieneri Sweet; Maekawa in Maekawa et al., p. 26, fig. 15.32–15.34 (only).

2021 Neospathodus cf. dieneri discreta; Sun et al., fig. 5.10.

2021 Discretella sp. A; Sun et al., fig. 6.15.

Etymology: Named after its superficial resemblance to Ns. dieneri.

Holotype: specimen illustrated in Fig. 16O.

Paratype: specimen illustrated in Fig. 16H.

Type locality: Shanggang road cut, Luolou formation, Guangxi Province, China.

Type level: Luolou Formation, within the early-to-middle Smithian limestones (Owenites beds).

Number of specimens: >30

Diagnosis. Segminate P₁ element, laterally flattened. Few, discrete, large denticles. Terminal cusp. Flat to slightly posteriorly upturned basal margin. Asymmetrical basal cavity.

Description. These P₁ elements have markedly discrete denticles and a relatively large cusp, sometimes slightly larger than the other denticles that is situated terminally. In early ontogenetic stages (for adult forms, see Leu et al., submitted), the elements bear 3 erect to slightly and gradually reclined denticles. The basal margin is straight to slightly upturned posteriorly. In aboral view, the basal cavity is sub-rounded to lanceolate and asymmetrical.

Remarks. The P₁ element of this species shows some superficial similarities with that of Neospathodus dieneri, but differs in being laterally flattened and having much less denticles (usually 3, vs. 5 to 10 in Ns. dieneri). Moreover, N. dieneri ranges up to the early Smithian only, whereas D. pseudodieneri occurs in the middle Smithian Owenites beds. Included here are also specimens where the cusp is less discrete, more robust and broader at the base (Figs. 15M, 16L).

Occurrence. Tahogawa Member, Olenekian Nv. ex gr. waageni Zone, Japan (Maekawa et al., 2018). Jiarong, Discretella discreta Zone, Smithian age Nanpanjiang basin, southern Guizhou, South China (Chen et al., 2015).

Discretella? n. sp. B

Figs. 15N; 16B

Number of specimens: >10

Diagnosis. Segminate P₁ element with subsymmetrical, posteriorly rounded and anteriorly tapered basal cavity. Large terminal, subtriangular, recurved cusp. Anterior process bearing a few denticles only.

Description. The element shows a large cusp at the posterior end. In lateral view, the large, recurved, subtriangular cusp is about as high as the whole unit is long. An anterior process with two or three small upright to reclined denticles is present. The lower margin is straight to concave. In aboral view, the subsymmetrical basal cavity is sub-rounded at the posterior margin and tapers towards the anterior end.

Remarks. These P₁ elements most closely resemble Discretella aff. discreta, but differ in having a much shorter anterior process and recurved denticles. They also bear some superficial resemblance with the P₁ elements of the Spathian–Anisian genus Cornudina, but differ in their conformation of the basal cavity. Urdyella unicorna n. gen. n. sp. usually has a much thinner and larger, sickle-shaped cusp and a rounded basal cavity.

Because of the absence of a posterior process, some elements, especially arched ones, resemble homologous elements of Guangxidella and could possibly be assigned to that genus, but their basal cavity do not match those of Guangxidella and resemble instead that of Discretella aff. discreta, hence we tentatively retain them within Discretella.

Occurrence. South China: Luolou, Smithian age, Laren, Guangxi.

Discretella? n. sp. C

Figs. 15O; 16A, F, M.

1989 Cratognathodus sp. A; Thang, p. 405, pl. 32, fig. 8.

2013 Neospathodus? peculiaris Sweet; Yan et al., p. 516, fig. 6M.

2014 Discretella sp. indet. A; Maekawa & Igo in Shigeta et al., p. 202–207, fig. 151.1–151.12, 151.16–151.18 (only).

2014 Genus gen. indet. D; Maekawa & Igo in Shigeta et al., p. 269, figs. 193.10–193.12.

Number of specimens: >10

Diagnosis and description. Same as Discretella? n. sp. B except that a very small posterior process without denticle is always present and the laterally twisted basal cavity tapers at both ends. The anterior process may bear up to 5 denticles.

Remarks. The P₁ elements of this species are very similar to those of the coeval Discretella? n. sp. B and both species may be conspecific although the presence of the incipient posterior process and the geometry of the basal cavity suggest they correspond at least to two different morphotypes, possibly due to sexual dimorphism. They also share strong similarities with the P₁ of Discretella? n. sp. D, which may be a descendant of Discretella? n. sp. B via reduction/loss of the anterior process, forms like, Fig. 16M (and figs. 193.10–193.12 of Maekawa and Igo in Shigeta et al., 2014) that bear only one or two anterior denticles being intermediary. The relationship with Discretella sp. indet. A Maekawa & Igo is unclear but the P₁ of the latter is almost identical, except that the incipient posterior process bears a small triangular denticle. Maekawa & Igo noted also that the anterior process of the P₁ element of Discretella sp. indet. A (Maekawa & Igo) may also have been reduced over time. Conversely, Discretella robustus (Wang & Wang, 1976), which share a similar recurved cusp and a sigmoidal profile in lower view, has more developed anterior and posterior processes and may be their forerunner.

Occurrence. South China: Luolou, Smithian age, Laren, Guangxi.

Discretella? n. sp. D

Fig. 26AB, AC.

Fig. 26

Cornudininae from Qiakong, Laren and Shanggang. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A–W Urdyella unicorna n. gen. n. sp.; A LAR225, PIMUZ 39345; B LAR225, PIMUZ 39346; C LAR229, PIMUZ 39347; D LAR227, PIMUZ 39348; E LAR229, PIMUZ 39349; F LAR229, PIMUZ 39350; G LAR225, PIMUZ 39351; H LAR229, PIMUZ 39352; I QIA123, PIMUZ 39353; J LAR227, PIMUZ 39354; K QIA123, PIMUZ 39355; L QIA123, PIMUZ 39356; M LAR227, PIMUZ 39357; N LAR225, PIMUZ 39358; O QIA120, PIMUZ 39359; P LAR225, PIMUZ 39360; Q QIA121, PIMUZ 39361; R LAR232, PIMUZ 39362; S LAR232, PIMUZ 39363; T QIA124, PIMUZ 39364; U LAR232, PIMUZ 39365; V QIA123, PIMUZ 39366; W SHA341, PIMUZ 39367. X-AA Urdyella tridenta n. gen. n. sp.; X LAR227, PIMUZ 39341; Y LAR227, PIMUZ 39342; Z LAR227, PIMUZ 39343; AA LAR227, PIMUZ 39344. AB, AC Discretella? n. sp. D; AB QIA124, PIMUZ 39118; AC QIA123, PIMUZ 39119. AD Neostrachanognathus n. sp. A; LAR232, PIMUZ 39183. AE Urdyella n. sp. A; LAR232, PIMUZ 39340

2014 Genus gen. indet. D; Maekawa & Igo in Shigeta et al., p. 269, figs. 193.8–9.

Holotype. Specimen illustrated in Fig. 26AB.

Number of specimens: >20

Diagnosis. Same P₁ element as in Discretella? n. sp. C except it bears no anterior process.

Remarks. As for Discretella? n. sp. B and C (see above) the generic assignment of these forms is uncertain and may deserve a new genus name, especially given that the present taxa bear neither posterior nor anterior denticles.

Occurrence. Laren road cut, Luolou Formation, Smithian age, Nanpanjiang basin, South China (this paper); North-eastern Vietnam, Novispathodus ex gr. waageni Zone between Flemingites rursiradiatus beds and Urdyceras tulongensis beds and within the Owenites koeneni beds, Bac Thuy Formation (Shigeta et al., 2014).

Genus GUANGXIDELLA Zhang & Yang, 1991

Type species. Neoprioniodus bransoni Müller 1956, p. 829, pl. 95, figs. 19–21.

Type stratum and locality. Smithian ammonoid bed, Crittenden Springs, Elko County, Nevada.

Guangxidella bransoni (Müller, 1956)

Figs. 15E; 16E.

*1956 Neoprioniodus bransoni n. sp.; Müller, p. 829, pl. 95, figs. 19–21.

1956 Neoprioniodus bicuspidatus n. sp.; Müller, p. 828, pl. 95, figs. 16, 17.

1979 Neospathodus bicuspidatus (Müller); Solien, p. 302, pl. 3, figs. 2, 3.

1989 Ozarkodina gigantea n. sp.; Thang, p. 409, pl. 31, figs. 10, 14.

1991 Guangxidella typica n. sp.; Zhang & Yang, p. 33, pl. 1, figs. 1a, b, 2a, b.

2009 Guangxidella bransoni (Müller); Orchard & Zonneveld, p. 780, fig. 15, parts 26–28.

2014 Guangxidella bransoni (Müller); Maekawa & Igo in Shigeta et al., p. 211, figs. 152.16–152.18, 153–159, 160.1–160.4

2018 Guangxidella bransoni (Müller); Maekawa in Maekawa et al., p. 24, figs. 14.7–14.10.

Number of specimens: >30

Description. The segminate P1 element has variably discrete, laterally compressed denticles whose height decreases to the anterior and a very large, variably reclined, terminal cusp. The basal margin is up-arched and the basal cavity is flat, cordiform and asymmetrical.

Remarks. Gu. bicuspidatus was differentiated from Gu. bransoni on the basis of its closer spaced denticles, the one in front of the cusp being almost as high as the latter (Müller, 1956). Yet, given the broad range of intraspecific variation present in large collections such as those illustrated by Shigeta et al. (2014), it is in our opinion no longer tenable to keep both species separated. Although both taxa are defined in the same paper by Müller (1956) and the definition of Gu. bicuspidatus appears before that of Gu. bransoni, we have decided to name them bransoni because the etymology of bicuspidatus refers to a 2-cusp element, which is not typical of the revised species. Furthermore, Müller’s holotype of Gu. bicuspidatus is broken, whereas his holotype of Gu. bransoni is better preserved (not broken), better illustrated (also in aboral view) and corresponds better to the revised type.

Occurrence. USA: Dinner Springs Canyon, Lower Triassic Meekoceras beds, Crittenden Ranch, Elko County, Nevada (Müller, 1956); Thaynes Formation (Parachirognathus Zone, Utah, (Solien 1979). British Columbia, Canada (Orchard & Zonneveld, 2009). Taho Formation, Novispathodus ex. gr. waageni Zone) Southwest Japan (Maekawa et al., 2018). Nanpanjiang basin: Bac Thuy Formation, Owenites beds within the Novispathodus ex. gr. waageni Zone, North-eastern Vietnam (Shigeta et al., 2014). Luolou Formation, Neospathodus waageni Zone, Guangxi, China (Zhang & Yang, 1991).

Subfamily CORNUDININAE Orchard 2005

Genus SPATHICUSPUS Orchard 2005

Type species. Neospathodus spathi Sweet, 1970, pp. 257–258, pl. 1, fig. 5.

Type stratum and locality. Mittiwali Member, Mianwali Formation, Narmia, Pakistan.

Remarks. Based on his reconstruction of the multi-element apparatus of ‘Neospathodus’ spathi Orchard (2005) considered these taxa deserved assignment not only to a new genus, but also to a new subfamily.

Spathicuspus n. sp. A

Fig. 13M, P

2005 Neospathodus spathi Sweet; Gaetani et al., p. 288, pl. 1, fig. 2

2015 Spathicuspus spathi (Sweet); Chen et al., p. 112, fig. 8.16–8.17.

2015 Spathicuspus spathi (Sweet); Lehrmann et al., p. 123, fig. 5.28.

2016 Spathicuspus spathi (Sweet); Liang et al., p. 385, fig. 4.10.

Number of specimens: >10

Description. Short segminate P1 element with large, terminal, reclined or recurved cusp. Only two anterior denticles. Basal cavity is drop-shaped.

Remarks. Very similar to Spathicuspus? n. sp. B (see below), but much shorter and with a larger basal cavity. Similar elements have been illustrated from other Chinese sections by Chen et al. (2015) and Liang et al. (2016) and hence this species may be useful as an index fossil for intrabasinal correlations.

Occurrence. South China: Luolou Formation, Spathian, Nanpanjiang basin, Mingtang section, (Liang et al., 2016) Upper Guandao section, (Lehrmann et al., 2015), Triassospathodus homeri zone, Jiarong (Chen et al., 2015).

Spathicuspus? n. sp. B

Fig. 13J–L, O (N, R juvenile forms?)

2005 Spathicuspus sp. A; Orchard, p.77, fig. 2, Nr. A.

2016 Spathicuspus spathi (Sweet); Liang et al., p. 385, fig. 4.9.

2019 Spathicuspus spathi (Sweet); Chen et al., fig. 7, nr. 6–8.

2021 Spathicuspus spathi (Sweet); Chen et al., fig. 7.8 (only).

Number of specimens: >30

Description. Slender segminate P₁ element with a terminal, reclined or recurved cusp that is usually broader than adjacent denticles, a shallow, posteriorly rounded basal cavity and three to seven anterior denticles.

Remarks. Despite their overall resemblance with Spathicuspus spathi these elements are either too long and bear too many denticles or their cusp is not broad and blunt enough to be assigned to that species. Some of them may not belong to Spathicuspus at all. Similar and apparently coeval elements were illustrated by Liang et al. (2016) and Chen et al. (2019) from other sections in China and Oman. The element illustrated by Orchard (2005) has similar aspect ratio and denticulation as for instance the specimen we illustrated in Fig. 13O, but it is also much younger and may be only superficially similar.

Occurrence. South China: Luolou Formation, Spathian, Mingtang section, Nanpanjiang basin (Liang et al., 2016), Upper Guandao section (Orchard, 2005). Oman: Wadi Bani Khalid section, Spathian UAZ₇ (Chen et al., 2019).

F13

Spathicuspus? n. sp. C

Fig. 13Q

2016 Spathicuspus spathi (Sweet); Liang et al., p. 385, fig. 4.11.

2021 Spathicuspus spathi (Sweet); Chen et al., fig. 7.5 (only).

Number of specimens: >5

Description. Small P1 element with a rounded basal cavity, a large, reclined and broad cusp, a small posterior denticle and a couple of declining denticles to the anterior.

Remarks. Although the relationship of this species to Spathicuspus spathi and Spathicuspus n. sp. A is unclear, its shape is intermediate. It differs in the presence of a posterior denticle.

Occurrence. South China: Luolou Formation, Spathian, Mingtang section, Nanpanjiang basin (Liang et al., 2016).

Genus URDYELLA gen. nov.

Type species. Urdyella unicorna n. sp.

Type stratum and locality. Luolou Formation, Laren road cut, Guangxi Province, China.

Etymology: Named after Severine Urdy.

Diagnosis. Short coniform-to-segminiscaphate P₁ element with a long cusp, usually at least twice the length of the adjacent denticle, a very short anterior process, and a broadly excavated basal cavity.

Remarks. The relationship of this genus to Cornudina is uncertain (Orchard, 2005, 2007). P₁ elements similar to the P₁ element of Urdyella n. gen. are often considered as belonging to Cornudina. Yet, as explained by Orchard (2005), the holotype of Cornudina (O. breviramulus) appears to be a P₂ element. Both Kozur and Mostler (1971, p. 11) and Sweet (in Clark et al., 1981, p. W155) placed Cornudina with Chirodella as a multi-element Chirodella. The holotype of Chirodella (Metalonchodina triquetra) is an S₂ element. The holotypes of both Cornudina and Chirodella are from Muschelkalk (Middle Triassic) collections made by Tatge (1956), who described no elements like those described by Orchard (2005) as P₁. ‘Chirodella’ sensu formo does not occur in Orchard’s nor in Koike’s Spathian collections of Cornudina. For this reason, Koike (1996) and Orchard (2005) regarded the two genera as unrelated: Koike reconstructed Cornudina as an apparatus consisting of P₁ and P₂ elements only (Cornudina breviramulis) or of P₁ elements only (Cornudina igoi), whereas Orchard reconstructed Cornudina? as having an octomembrate apparatus whose P₂ element vaguely resembles the holotype of Cornudina, but he questioned the very validity of that name for Spathian forms that might be unrelated to the ‘true’ Middle Triassic Cornudina.

‘Chirodella’ sensu formo does not occur in our Smithian collections of Urdyella n. gen. and neither does ‘Cornudina’ sensu formo. Hence we suggest that Cornudina-like P₁ elements found in the Smithian, and possibly those found in the Spathian, belong to Urdyella n. gen. not to Cornudina.

Based on multi-element considerations, Orchard grouped both ‘Cornudina’ and Spathicuspus within the same subfamily Cornudininae. Because Spathicuspus seemed to occur first, he hypothesized that ‘Cornudina’ evolved from Spathicuspus near the Lower/Middle Triassic boundary through overall shortening of the P₁ element. Since Urdyella occurs already in the Smithian, we suggest that Spathicuspus may have evolved from Urdyella and the Spathian forms of ‘Cornudina’ either belong to Urdyella, derived directly from Urdyella, or as assumed by Orchard, evolved from Spathicuspus, although the latter hypothesis seems less likely. Urdyella itself may have evolved from Discretella via forms like Discretella? n. sp. B. Discretella has a much shorter cusp and a larger anterior process. Furthermore, the basal cavity in Urdyella is flatter and not as broadly excavated as in Cornudina.

Urdyella unicorna n. sp.

Fig. 26A–W, AE?

1970 Neospathodus peculiaris Sweet?; Hasenmüller, p. 62, pl. 2, fig. 10

2005 Aduncodina unicosta Ding; Zhao, pl. 6, nr. 9–10.

Etymology: Named after the unicorn, a mythical creature with a single horn on its forehead, for the huge cusp of the P₁ element of this species.

Holotype: specimen illustrated in Fig. 26A.

Paratypes: specimens illustrated in Fig. 26K, Q, W.

Type locality: Laren road cut, Luolou formation, Guangxi Province, China.

Type level: Luolou Formation, upper Owenites to lower Anasibirites beds, middle Smithian to early late Smithian, Olenekian, Early Triassic_.

Number of specimens. > 40.

Diagnosis. P₁: Short coniform-to-segminiscaphate element with a very long, needle-like, recurved cusp, sometimes one (or two in large specimens) tiny, anterior denticle, and a broadly excavated basal cavity.

Description. P₁: The cusp is about 3–4 times longer than the basal cavity is broad, is usually slightly recurved, sometimes only reclined, and it makes an angle of about 40°–60° with the baseline of the lower margin in lateral view. Many specimens are coniform and may bear a tiny anterior process, some (usually larger) specimens have a very short anterior process bearing up to two anterior denticles and may be better described as segminiscaphate. The deep basal cavity is oval to drop-shaped in aboral view. In lateral view, the base of the cusp occupies the anterior half of the basal cup.

Remarks. Specimens of this species were found by Zhao et al., (2007, without illustrations; but two specimens are illustrated in Zhao’s Ph.D thesis, 2005) in coeval strata of the Chaohu section, Anhui Province but reported as Aduncodina unicosta, a possibly related form that in all our collections from China is otherwise restricted strictly to the Spathian interval.

Occurrence. India: Mud, Mikin Formation, maximal horizon 1 (Goudemand, 2011); Western USA, Parachirognathus-Furnishius zone, Thaynes Formations, Utah (Hasenmüller, 1970). South China: Chaohu section, Anhui Province (Zhao, 2005; Zhao et al., 2007); Pingtang Syncline, uppermost Daye Formation and Luolou Formation, Smithian (this paper). Upper Smithian, Khunamuh Formation, Guryul Ravine, Northern Indian Margin (Leu et al. in prep.), Oman (Leu et al. submitted).

Urdyella tridenta n. sp.

Fig. 26X-AA

Etymology: The species is named after the trident, Poseidon’s weapon in the Greek mythology.

Holotype. Specimen illustrated in Fig. 26AA.

Paratype. Specimens illustrated in Fig. 26Z.

Number of specimens. 5

Diagnosis. Coniform P₁ element with three subequally long and slightly recurved denticles all attached to the basal cup. Deep, teardrop shaped basal cavity. No clear anterior process.

Remarks. The P₁ element of this species is very similar to the one of Urdyella unicorna n. sp. except for the lack of an anterior process and the fact that the single large cusp of Urdyella unicorna n. sp. is replaced by three subequally long denticles in Urdyella tridenta n. sp.

Occurrence. Laren road cut, Luolou Formation, Smithian age, Nanpanjiang basin, South China (this paper).

Urdyella n. sp. A

Fig. 26AE

Number of specimens. 1

Remarks. This one specimen does look like it may belong to Urdyella and it was found within the Smithian range of Urdyella, but it differs in its posterior configuration and in having a smaller cusp.

Occurrence. Laren road cut, Luolou Formation, Smithian age, Nanpanjiang basin, South China (this paper).

Genus NEOSTRACHANOGNATHUS Koike 1998

Type species. Neostrachanognathus tahoensis Koike 1998,

Type stratum and locality. The Taho Limestone, Ehime, Japan.

Neostrachanognathus n. sp. A

Fig. 26AD?

Number of specimens. 1

Remarks. That one specimen looks like it could be a P element of Neostrachanognathus as reconstructed by Agematsu et al. (2008). Since it possesses a posterior denticle, it does not belong to Neostrachanognathus tahoensis and may instead belong to Neostrachanognathus sp. A (Agematsu et al., 2008) or to a different species. This element was found in middle Smithian strata together with representatives of Urdyella spp. If it does indeed belong to Neostrachanognathus it is its oldest representative.

Occurrence. Laren road cut, Luolou Formation, Smithian age, Nanpanjiang basin, South China.

Genus ADUNCODINA Ding, 1983

Type species. Aduncodina unicosta Ding, 1983.

Type stratum and locality. Biandanshan formation, Mountain Majiashan of Chaoxian, Anhui province, China.

Aduncodina unicosta Ding, 1983

Fig. 24R–T

*1983 Aduncodina unicosta n. sp.; Ding, p.41, pl. 6, figs. 10–14, 20(?)-21.

1983 Cornudina cf. oezdemirae Gedik; Ding, p. 42, pl. 7, figs. 25–26

1998 Aduncodina unicosta Ding; Koike, p. 126, fig. 8.4–8.26.

2007 Aduncodina unicosta Ding; Orchard, p. 96, fig. 2

2019 Aduncodina unicosta Ding; Chen et al., figs. 5.7, 5.9, 6.6.

Number of specimens. > 30.

Description. Aduncodina unicosta has been reconstructed by Koike (1998) as a quadrimembrate skeletal apparatus encompassing only S_a–c (S_1–3) and M nongeniculate coniform elements. The adenticulated, subsymmetrical element is regarded by Koike as the M element, whereas the denticulated elements are interpreted as pertaining to the S series, the subsymmetrical one that bears one denticle being the S_a (S₀), the asymmetric one that bears up to three antero-lateral, hook-like denticles (in Zhao’s collections, those elements may bear up to five denticles, see his Ph.D thesis, 2005) and whose basal cavity is triangular in cross-section being the S_b (S₁) and the asymmetric one with a lenticular basal cavity being the S_c (S₂). All elements share common characteristics such as a thin wall, a relatively large and long and laterally flattened basal cavity. The slender cusp is suberect and subcircular in cross-section. Basal margin weakly to strongly convex anteriorly.

Remarks. We agree with Orchard (2007) that the reconstruction by Koike (1998) might be incomplete. Neostrachanognathus was also reconstructed by Koike (ibid) as including only coniform elements but later revised by Agematsu et al. (2008) with convincing evidence from natural assemblages as including also complex multidenticulate (bipennate) elements in the S positions. It is to be expected that Aduncodina too may possess complex multidenticulate elements in those positions. The morphology of the illustrated elements of Aduncodina unicosta resembles that of Ordovician forms such as Strachanognathus. In common with Neostrachanognathus, Aduncodina has a suite of denticulate elements, identified as S_b and S_c by Koike (1998), with an antero-lateral denticle or process that is directed posteriorward at its base, which is a feature of the Cornudininae (Orchard, 2007).

Occurrence. Japan: Taho Formation, co-occurrence with Ic. collinsoni in the Spathian substage (Koike, 1998); China: Biandanshan formation, co-occurrence with Ic. collinsoni and Tr. homeri, Mountain Majiashan of Chaoxian, Anhui province (Ding, 1983). Oman: Wadi Bani Khalid section, Spathian between UA₁₀ and UA₁₁ (Chen et al., 2019).

Subfamily UNCERTAIN

Genus EURYGNATHODUS Staesche 1964.

Type species. Eurygnathodus costatus Staesche, 1964

Type stratum and locality. Campiller member, Skyth, South Tirol, Italy.

Description. Scaphate P₁ element bearing a variably broad, oval-shaped platform with or without transverse ribs. So far, the multi-element apparatus of Eurygnathodus is unknown.

Remarks. Recent discussions for the definition of the Global Stratotype Section and Point (GSSP) for the Induan–Olenekian Boundary (IOB) emphasize that this easily identifiable and cosmopolitan genus may be a useful index for the base of the Olenekian. Yet, its phylogenetic origin is still unclear, leaving opened the question of whether its seemingly sudden appearance in equatorial and tropical localities close to the IOB may reflect an ecological signal.

Eurygnathodus costatus Staesche, 1964

Fig. 14A

*1964 Eurygnathodus costatus n. sp.; Staesche, p. 269, pl. 28, figs. 1–6.

1977 Platyvillosus costatus (Staesche); Goel, p. 1098, pl. 2, figs. 15–21.

1981 Platyvillosus costatus (Staesche); Wang & Cao, p. 371, pl. 2, figs. 1–4, 28–30, 33.

1981 Platyvillosus paracostatus n. sp.; Wang & Cao, p. 371, pl. 2, figs. 9,10.

1984 Platyvillosus costatus (Staesche); Matsuda, p. 128, pl. 6, figs. 6–10.

1988 Platyvillosus costatus (Staesche); Koike, p. 65, pl. 1, figs. 1–57, pl. 2, figs. 1–37.

1991 Platyvillosus costatus (Staesche); Beyers & Orchard, pl. 5, fig. 10.

2009 Eurygnathodus costatus Staesche; Igo in Shigeta et al., p. 183, figs. 152.23–152.24.

2010 Eurygnathodus costatus Staesche; Orchard, p. 145, fig. 5.9–5.10.

2013 Platyvillosus hamadai Koike; Zhao et al., p.535, figs. 10K, L.

2013 Platyvillosus costatus (Staesche); Zhao et al., p.535, figs. 10M, 10N, 10O.

2014 Eurygnathodus costatus Staesche; Maekawa & Igo in Shigeta et al., p. 220, figs. 161.4–161.6

2015 Eurygnathodus hamadai Staesche; Maekawa in Maekawa et al., p. 316, fig. 5.1.

2016 Eurygnathodus costatus Staesche; Chen et al., fig. 11.3, 11.6–11.7.

2018 Eurygnathodus costatus Staesche; Maekawa in Maekawa et al., pp. 45–50, figs. 25–27.

2019 Eurygnathodus costatus Staesche; Li et al., p. 6, fig. 4.22–4.36.

2019 Eurygnathodus costatus Staesche; Lyu et al., fig. 7.12.

2019a Eurygnathodus costatus Staesche; Wu et al., fig. 4.20.

Material. > 30 specimens.

Remarks. Goel (1977), Matsuda (1984), Koike (1988) and Maekawa et al. (2018) documented a large intraspecific variation of the platform morphology and its oral ornamentation. It follows that Platyvillosus paracostatus Wang and Cao (1981) likely corresponds to a variant of Eu. costatus (Form A in Koike 1988). Maekawa et al., (2018, figs. 25.1d) documented also specimens covered with microgranules.

Occurrence. This species has been reported worldwide from the early Smithian Flemingites zone. Japan: Tahogawa member within the Novispathodus ex gr. waageni Zone (Koike, 1988; Maekawa et al., 2018), Europe: South Tyrol, Slovenia, Croatia and Bosnia and Herzegovina (Aljinović et al., 2006; Chen et al., 2016; Kolar-Jurkovšek et al., 2021; Staesche, 1964), India: Spiti and Kashmir (Goel, 1977; Matsuda, 1984; Orchard, 2010; Orchard & Krystyn, 2007), Russia; South Primorye (Shigeta, 2009), Canada: British Columbia (Beyer & Orchard, 1991), South China and North-eastern Vietnam (Chen et al., 2015; Shigeta et al., 2014).

Eurygnathodus hamadai (Koike, 1982)

Fig. 14B

1981 Platyvillosus costatus (Staesche); Wang and Cao, p. 371, pl. 2, figs. 31–32.

*1982 Platyvillosus hamadai n. sp.; Koike, p.45, pl. 5, figs. 10–36.

1988 Platyvillosus hamadai Koike; Koike, p. 71, pl. 2, figs. 38–45.

2010 Eurygnathodus hamadai (Koike); Orchard, p. 145, fig. 5.11.

2015 Eurygnathodus hamadai (Koike); Maekawa in Maekawa et al., p. 317, fig. 5.2.

2018 Eurygnathodus hamadai (Koike); Maekawa in Maekawa et al., p. 50, figs. 28.1–28.4.

2019 Eurygnathodus hamadai (Koike); Li et al., p. 6, figs. 4.37–4.45.

2019a Eurygnathodus hamadai (Koike); Wu et al., fig. 4.22.

Material. > 30 specimens.

Remarks. Eurygnathodus hamadai is easily distinguished from Eurygnathodus costatus by its smooth, flat upper surface lacking ornamentation. Koike (1988) reported transitional forms between E. costatus and E. hamadai (Morphotype δ), raising the question whether both forms may be conspecific, E. hamadai representing an extreme variant of E. costatus. In our material and in that of other authors, Eu. costatus and Eu hamadai co-occur in several samples. Their relative abundance, however, does change. Eu. costatus is more common in older strata, whereas Eu. hamadai is more abundant than Eu. costatus in younger strata. Although the FO of Eu. costatus appears to predate that of Eu. hamadai in several sections around the world, it is thus still unclear whether they share the same temporal range or not.

Occurrence. early Smithian in China (Wang & Cao, 1981, this study), Malaysia (Koike, 1982), Japan (Koike, 1988; Maekawa et al., 2018, and India, Spiti (Orchard, 2010).

Suborder PRIONIODININA Donoghue et al., 2008

Family ELLISONIDAE Clark, 1972

Subfamily HADRODONTINAE Koike, 2016

Genus HADRODONTINA Staesche, 1964

Type species. Hadrodontina anceps Staesche, 1964.

Type stratum and locality. Campiller member, Skyth, South Tirol, Italy.

Remarks. There is still an ongoing debate about the phylogenetic relationships of Pachycladina, Parapachycladina and Hadrodontina. Sweet (1988) in his prioniodinid phylogeny considered Pachycladina and Hadrodontina as sister taxa. Some species of Pachycladina were assigned to a new genus Parapachycladina by Shunxin et al. (1997), but this view is not widely accepted. Orchard (2007) observed that Hadrodontina anceps, Ellisonia aff. triassica and Pachycladina peculiaris appear to constitute a natural group, although they are currently assigned to different genera. Based on their cladistics analysis, Donoghue et al. (2008) concluded that Pachycladina is either a sister taxon to Ellisonia or stays unresolved in a polytomy with Ellisonia, Hadrodontina and Furnishius. Based on his multi-element apparatus reconstructions, Koike (2016) included Hadrodontina and Pachycladina within the subfamily Hadrodontinae (Koike, 2016), supporting the original view of Sweet (1988). We follow here this suprageneric classification and include Hadrodontina and Pachycladina within the subfamily Hadrodontinae. More recently, Sun et al. (2020) published 3 natural assemblages of Hadrodontina aequabilis and confirmed the suprageneric classification of Koike (2016).

In P₁ elements, what most distinguishes Pachycladina from Hadrodontina is the basal configuration: the inverted basal ‘attachment’ surface of Pachycladina occupies the entire lower side plus one lateral side of the carina, whereas in Hadrodontina, a basal cavity with a deep basal groove is usually formed on the lower side and the attachment surface rarely extends over the mid-part of the keel, if at all. The denticles of Pachycladina are also less numerous but much larger in relative size than those of Hadrodontina. Based on multi-element reconstructions however, Koike (2016) showed that Pachycladina peculiaris, as well as Ellisonia aff. triassica (Koike et al., 2004), should be synonymized with Hadrodontina aequabilis.

Hadrodontina aequabilis Staesche, 1964

P₁ elements: Figs. 27F–M; 28A, C, E

Fig. 27

Hadrodontinae from Qiakong, Laren, Shanggang and Lilong. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A, Hadrodontina aequabilis (S₂ element) (Staesche); SHA344, PIMUZ 39141. B–E, Hadrodontina aequabilis (P₂ element) (Staesche); B LAR214, PIMUZ 39142; C QIA13, PIMUZ 39143; D LIL500, PIMUZ 39144, E SHA344, PIMUZ 39145. F–M Hadrodontina aequabilis (Staesche); F LIL502, PIMUZ 39146; G LIL503, PIMUZ 39147; H QIA134, PIMUZ 39148; I QIA134, PIMUZ 39149; J QIA 133, PIMUZ 39150; K LIL502, PIMUZ 39151; L LIL501, PIMUZ 39152; M LIL501, PIMUZ 39153

Fig. 28

Hadrodontinae from Shanggang. Magnification is × 80. The scale bar is 400 μm. All elements are considered to be P₁ elements if not specifically identified otherwise. A, C, E Hadrodontina aequabilis (Staesche); A SHA 345C, PIMUZ 39154; C SHA345C, PIMUZ 39155; E SHA344C, PIMUZ 39156. B, D Hadrodontina aequabilis (P₂ element) (Staesche); B SHA345C, PIMUZ 39157; D SHA345C, PIMUZ 39158

P₂ elements: Figs. 27B–E; 28B, D

S₂ elements: Fig. 27A

P₁ element:

*1964 Hadrodontina aequabilis n. sp.; Staesche, p. 275, figs. 43, 44.

1984 Sweetocristatus unicus n. sp.; Dagis, pp. 37–38, pl. X, figs. 6–9.

1990 Pachycladina peculiaris n. sp.; Shunxin (Zhang), pl. 2, fig. 4

1991 Pachycladina peculiaris n. sp.; Zhang in Zhang & Yang, p. 40, pl. 3, figs. 1, 2.

1997 Parapachycladina peculiaris Zhang; Shunxin et al., pp. 65–69, pl. 1, figs. 1–2, pl. 2, figs. 1–2, pl. 3 figs. 1–2.

2004 Ellisonia sp. aff. E. triassica Müller, 1956; Koike et al., figs. 8.7, 8.8.

2009 Ellisonia? cf. peculiaris Sweet; Igo in Shigeta et al., p. 182, fig. 152.22.

2013 Parachirognathus geiseri Clark; Yan et al., p. 516, fig. 6 FF.

2015 Parachirognathus peculiaris Zhang & Guo; Chen et al., figs. 8.20–21, 24.

2015 Sweetocristatus unicus Dagis; Chen et al., fig. 8.23.

2016 Hadrodontina aequabilis Staesche; Koike, pp. 164–167, fig. 2, nr. 1–3.

2018 Hadrodontina aequabilis Staesche; Maekawa in Maekawa et al., p. 18, figs. 13.3?–13.4 (only).

2020 Hadrodontina aequabilis Staesche; Sun et al., figs. 1–7 (natural assemblage of the Hadrodontina apparatus).

P₂ element:

*1964 Hadrodontina aequabilis n. sp.; Staesche, p. 275, fig. 44.

2004 Ellisonia sp. aff. E. triassica Müller; Koike et al., p. 247, fig. 8.6

2016 Hadrodontina aequabilis Staesche; Koike, p. 165, figs. 2.4 (P2 element).

2020 Hadrodontina aequabilis Staesche; Sun et al., figs. 1–7 (natural assemblage of the Hadrodontina apparatus).

S₂ element.

2004 Ellisonia sp. aff. E. triassica Müller; Koike et al., p. 247, fig. 8.4

2016 Hadrodontina aequabilis Staesche; Koike, p. 165, figs. 2.9–11.

2020 Hadrodontina aequabilis Staesche; Sun et al., figs. 1–7 (natural assemblage of the Hadrodontina apparatus).

Material. P₁, more than 40; P₂, more than 40; S₂ more than 10.

Revised diagnosis. Robust to slender angulate P₁ element. The 6–8 (usually 7) denticles are rather short, radiating, conical, with subtriangular free ends and they are increasingly reclined towards the posterior. The concave lower side is occupied by a large and wide groove.

Remarks. The observed variation in the denticulation of the P₁ and P₂ elements suggests there may be scope for further specific differentiation: in some elements the height of the denticles changes smoothly along the unit (Fig. 28B), whereas in others the denticles are alternatively high and low (Fig. 28D). Dagis (1984) assigned some specimens (here considered as junior synonyms of Ha. aequabilis) to Sweetocristatus unicus. Yet, the genus Sweetocristatus Szaniawski (in Szaniawski & Malkowski, 1979) was established for Upper Artinskian to Lower Guadalupian (Permian) P₁ elements that, although superficially similar to homologous elements of Hadrodontina and Pachycladina, bear a more developed, higher cusp, a higher carina and have a more elongated process. The cusp in Ellisonia P₁ elements is more conspicuous than in those of Hadrodontina or Pachycladina. Chen et al. (2015) illustrated coeval specimens from Jiarong they assigned to either Sweetocristatus unicus or Parachirognathus peculiaris (see their figs. 8.20 and 8.23) but we fail to distinguish them from Hadrodontina aequabilis. With three natural assemblages of Hadrodontina aequabilis from the late Smithian Helongshan Formation, South China, Sun et al. (2020) observations fits with our findings; the angulate shape and no distinct cusp in the P₁ element and the distally twisting shape of the P₂ element.

Occurrence. Russia; Smithian Hedenstroemia and tardus zone, Siberia (Dagis 1984), Zhitkov Formation, Smithian age, Abrek Bay area, South Primorye (Shigeta, 2009). China; Beisi Formation, Taiping, Pingguo Western Guangxi Province (Shunxin et al., 1997), Luolou Formation, Smithian age, Jiarong and Bianyang, Nanpanjiang Basin, southern Guizhou Province (Chen et al., 2015; Yan et al., 2013), Late Smithian Helongshan Formation, Chaohu, Anhui Province (Sun et al., 2020). Japan: Taho Formation, Shirokawa-cho, Higashiuwa-gun, Ehime Prefecture (below Smithian–Spathian boundary) (Koike 2016; Koike et al., 2004). Europe: Campiller member, Werfen Formation, Skyth, South Tirol, Italy (Staesche, 1964), Slovenia (Kolar-Jurkovšek & Jurkovšek, 2019).