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Table 4 Proposed high-level classification of nautiloid cephalopods to be used in the revision of the Treatise Part K

From: High-level classification of the nautiloid cephalopods: a proposal for the revision of the Treatise Part K

Subclass Plectronoceratia nom. correct. Wade, 1988a
 Order Plectronoceratida Flower, 1964a
 Order Yanheceratida Chen and Qi in Chen, Tsou, Chen and Qi, 1979
 Order Protactinoceratida Chen and Qi in Chen, Tsou, Chen and Qi, 1979
Subclass Multiceratia nom. correct. Mutvei, 2013b
 Order Ellesmeroceratida Flower in Flower and Kummel, 1950
 Order Cyrtocerinida Flower, 1964a
 Order Bisonoceratida Evans and King, 2012m
 Order Oncoceratida Flower in Flower and Kummel, 1950
 Order Discosorida Flower in Flower and Kummel, 1950
Subclass Tarphyceratia nov.c
 Order Tarphyceratida Flower in Flower and Kummel, 1950d
 Order Ascoceratida Kuhn, 1949e
Subclass Nautilia nom. correct. Wade, 1988
 Order Nautilida Agassiz, 1847f
Subclass Orthoceratia nom. correct. Teichert, 1967g
 Order Rioceratida nov.h
 Order Dissidoceratida Zhuravleva, 1964i
  Suborder Dissidoceratina Zhuravleva, 1964
  Suborder Troedssonellina Kobayashi, 1935
 Order Orthoceratida Kuhn, 1940
 Order Pseudorthoceratida Flower and Caster, 1935j
 Order Actinoceratida Teichert, 1933
 Order Astroviida Zhuravleva and Doguzhaeva, 2004k
  Suborder Lituitina Starobogatov, 1983l
  Suborder Pallioceratina Marek, 1998k
 Order Endoceratida Teichert, 1933m
  1. aThe Subclass Plectronoceratia contains the earliest cephalopods (Late Cambrian age) which exhibit oncomyarian muscle scars (Flower 1964a). Usually small, narrow to rapidly expanding cyrtocones or slender longicones; always narrowly camerate, often with siphonal diaphragms. We follow Chen and Teichert (1983) and subsequent workers in recognising the orders Plectronoceratida, Yanheceratida and Protactinoceratida, but note that many of the constituent genera are based on longitudinal sections of shell portions only; further research will likely result in taxa being synonymised. We regard present evidence of any relationship between the Yanheceratida and Endoceratida to be unconvincing—the ‘endoconic deposits’ associated with apical diaphragms in the Yanheceratida may be diagenetic in origin
  2. bOriginally defined as a superorder by Mutvei (2013), the Multiceratoidea is considered here to merit subclass status (Subclass Multiceratia) and is emended to contain the oncomyarian orders Ellesmeroceratida, Cyrtocerinida, Bisonoceratida, Oncoceratida and Discosorida. Constituent orders are typically distinguished by the form of modified siphonal structures or siphonal deposits (e.g., thick connecting rings in the Ellesmeroceratida, extraordinarily thickened connecting rings in the Cyrtocerinida, complex endocones in the Bisonoceratida, endosiphuncular linings and bullettes in the Discosorida, actinosiphonate deposits in some Oncoceratida) or the presence of modified, often constricted, apertures (present in both the exogastric Oncoceratida and predominantly endogastric Discosorida). Many early genera in all orders possess siphonal diaphragms. The Multiceratia is derived from the Plectronoceratia via the Ellesmeroceratida during the late Cambrian and range into the early Carboniferous (e.g., Poterioceratidae)
  3. cThe Subclass Tarphyceratia nov. is proposed here for exogastrically coiled, ventromyarian taxa, becoming weakly pleuromyarian in some younger forms. Lower and Middle Ordovician tarphyceratid faunas are relatively well known and are widely regarded as a ‘natural group’ (Schröder 1882; Ulrich et al. 1942; Flower and Kummel 1950; Flower 1976; Dzik 1984; Kröger and Landing 2008, 2009; King 2014). There is no convincing evidence to suggest that tarphyconic coiling (with ventromyarian muscle scars) arose independently in more than one lineage—other coiled shell morphologies (including gyrocones, torticones, cyrtocones and ascoceroid) occur in derived forms. We, therefore, regard the ventromyarian condition as an autapomorphy for the Subclass Tarphyceratia nov. and its descendants, akin to the development of the dorsomyarian condition that defines the Subclass Orthoceratia. The Subclass Tarphyceratia nov. is considered here to contain the orders Tarphyceratida (Furnish and Glenister 1964b; King 2014) and Ascoceratida (Holland 1999; Aubrechtová and Meidla 2016). See also d and e below
  4. dThe Tarphyceratida are the earliest representatives of the Subclass Tarphyceratia nov. and contain the first ‘coiled’ nautiloids. Derivation of the tarphyceratids from the Family Bassleroceratidae, Order Ellesmeroceratida, is undisputed (Flower 1976; Dzik 1984; Kröger and Landing 2008). We follow Flower (1984) in regarding the former Order Barrandeoceratida as polyphyletic; taxa previously placed in this order are now mainly (but not entirely) re-assigned within an expanded Order Tarphyceratida. The youngest tarphyceratids occur in the Middle Devonian
  5. eThe Ascoceratida are ventromyarian (e.g., Flower 1941, 1952; Sweet 1959; Evans 1988). Kröger (2013) has presented a case for their origin from the Uranoceratidae (formerly assigned by Kröger to the Order Barrandeoceratida). The deciduous nature of the ascoceratid conch is not a feature unique to this order; similar ontogenetic truncation of the shell is recorded in other unrelated nautiloids such as the Sphooceratidae (Turek and Manda 2012) and the oncoceratid family Trimeroceratidae (Stridsberg 1985). The deciduous nature of the conch in the Brachycycloceratidae (Furnish et al. 1962) is less certain (e.g., Niko 2010, Niko and Mapes 2011) and this family may be better assigned to the Nautilida
  6. fThe Subclass Nautilia ranges from the Early Devonian (possibly late Silurian) to the present day where it is represented by the extant genera Nautilus and Allonautilus. The subordinal and superfamilial classification within the mainly pleuromyarian Order Nautilida has a very complex history and requires further analysis. Significantly different systematic schemes and approaches were adopted in the Russian and American treatises (Ruzhentsev et al. 1962; Teichert et al. 1964). Retention of a Suborder Nautilina is considered likely in the future revision of Treatise Part K, although the status of other previously recognised suborders such as the Rutoceratina is less clear. Some Devonian genera formerly assigned to the Rutoceratidae (and other nautilid families) may be better placed elsewhere, including the Order Oncoceratida
  7. gThe Subclass Orthoceratia represents one of the largest and most important nautiloid subclasses which gave rise independently to the ammonoids, bactritoids and coleoids. The subclass is regarded here to include all dorsomyarian nautiloids, the majority of which are orthoconic or weakly cyrtoconic longicones and—apart from the Rioceratida nov. and Endoceratida—mostly possess various combinations of siphonal deposits (including annuli, parietal linings, siphonal rods) and cameral deposits. The Endoceratida possess simple endocones but lack cameral deposits. The Orthoceratia ranges from Early Ordovician (Tremadocian) to Late Triassic (possibly Early Cretaceous, Doguzhaeva 1995)
  8. hThe Rioceratida nov. is proposed here to accommodate dorsomyarian orthoceratoids that lack cameral deposits and possess a ventral siphuncle which is vacuosiphonate. The new order contains two families: the Rioceratidae (Kröger and Evans 2011) and the Bactroceratidae nov. Further details are provided in the definition of new systematic names section of this paper
  9. iWe follow Zhuravleva (1994) regarding the overall classification and composition of the Dissidoceratida, with modifications and additions as published by Evans (2005). The order contains the dissidoceratids (with intrasiphonal deposits concentrated ventrally) and troedssonellids (with intrasiphonal deposits forming long, thin endocones or ‘parietal linings’ extending throughout the whole circumference of the siphonal wall); we propose these differences merit recognition at subordinal rank. The poorly known intejoceratids and bajkaloceratids (Balashov 1960, 1962b; Zhuravleva 1978) are likely dissidoceratids or possibly actinoceratids; possession of extensive cameral deposits and siphonal lamellae precludes any possible relationship between the intejoceratids and endoceratids (Flower 1976)
  10. jThe relationship of the pseudorthoceratids to other orthoceratids and actinoceratids remains uncertain in places. Several Ordovician taxa previously regarded as pseudorthoceratids in the original Treatise Part K are now considered to be better assigned to the Order Orthoceratida, possibly related to the Geisonoceratidae. Kröger and Mapes (2007) provide an important review and cladistical analysis of selected taxa and we follow them in distinguishing the Pseudorthoceratida as a separate order from the Orthoceratida and Actinoceratida
  11. kZhuravleva and Doguzhaeva (2004) defined the Superorder Astrovioidea (containing the orders Lituitida Starobogatov 1983 and Pallioceratida Marek 1998) as orthoconic or lituiticonic orthoceratoids in which the connecting ring is ruptured or destroyed during life and cameral deposits (in places apparently continuous with siphonal linings) are formed. The evidence for this and the validity of the Pallioceratida has been questioned (e.g., Turek and Manda 2012). Pending further research, we provisionally recognise these highly specialised forms as a single order Astroviida comprising the suborders Lituitina and Pallioceratina. However, should future evidence demonstrate that the astroviids or pallioceratids are polyphyletic and an invalid group, then we would propose recognising a distinct Order Lituitida (which is widely regarded to represent a natural group of related nautiloids) with taxa formerly assigned to the Suborder Pallioceratina being re-assigned elsewhere
  12. lStarobogatov (1983) proposed a fundamental restructuring of cephalopod classification based on shell position, form of the mantle, structure of arms and specialisation of the apical portion of the inner sac (summarised by Shevyrev 2006). Within his Subclass ‘Actinocerationes’, Starobogatov recognised an ‘Order Lituitiformes’ but omitted the ancestral family Sinoceratidae; he also retained a relationship between lituitids and tarphyceratids (within his Superorder ‘Tarphyceratiformii’). Although Starobogatov’s classification has not been adopted by any other workers, his brief definition of the ‘Lituitiformes’ is clear and unambiguous. Therefore, Starobogatov’s authorship of the Suborder Lituitina (or Order Lituitida—see above) has priority over the Suborder Lituitina proposed by Dzik (1984), although Dzik’s work is much closer to current views regarding definition of the lituitid nautiloids and their orthoceratid origins
  13. mWe follow Evans and King (2012) in recognising that as traditionally described, the endoceratids were polyphyletic. This necessitated a significant revision which proposed the splitting of the former ‘Order Endocerida’ (as described in the original Treatise Part K) into two orders: the Bisonoceratida (oncomyarian forms, often rapidly expanding cyrtocones or brevicones—or secondarily orthocones—which possess complex endocones with infula, multiple endosiphotubes, conchiolin crests and complex ‘endosiphoblade’ patterns); and the Endoceratida (restricted to dorsomyarian orthoconic or weakly cyrtoconic longicones with simple endocones which lack infula or conchiolin crests)