For the systematic descriptions, the works of Kummel (1953, 1964), Mundlos et al. (1984), Dzik (1984) and Perez-Valera et al. (2017) have been used.
Class Cephalopoda Cuvier, 1797
Subclass Nautiloidea Agassiz, 1847
Suborder Tainoceratina Shimansky, 1957.
Family Tainoceratidae Hyatt, 1883
Genus Enoploceras Hyatt in Zittel, 1900.
Type species. Nautilus wulfeni Mojsisovics, 1873
Systematic position: Enoploceras was previously considered as subgenus of Pleuronautilus Mojsisovics, 1882 by Kummel (1953), later as a genus by Kummel (1964). Dzik discussed the phylogeny of Pleuronautilus and the possibility that it is a polyphyletic taxon composed of several evolutionary lineages that branched independently. In his phylogenetic reconstruction (Dzik, 1984, p. 162, Fig. 62), the type species Enoploceras wulfeni (no. 77) evolved from Metacoceras Hyatt, 1883, without direct relationship with Pleuronautilus, while in his proposed systematics (Dzik, 1984, p. 173), he considers Enoploceras a junior synonym of Metacoceras.
Enoploceras rieberi sp. nov. ZooBank LSID: urn:lsid:zoobank.org:act:AFEF292E-55CF-4E36-8BB1-05AF39386182, Fig. 2 a–g.
Derivatio nominis Honoring the paleontologist Hans Rieber (PIMUZ), who has contributed so much to the knowledge of fossils from Monte San Giorgio.
Holotype Specimen PIMUZ 37902, preserved as internal mold (Steinkern), partially covered by shell (right side) and partially included in the matrix.
Locus typicus Point 902/ Mirigioli, Meride, Ticino, Switzerland.
Stratum typicum Middle Besano Formation, Illyrian, Secedensis Zone (laminated dolostone, bed 73).
Diagnosis Enoploceras with evolute to advolute conch with a very low whorl overlap and subquadrate whorl section; umbilicus wide and shallow; umbilical walls subvertical; flanks flat, irregularly sculptured. Umbilical nodes fused with the consecutive massive ribs. Number of marginal nodes twice as many as the umbilical nodes. Venter arched, with shallow central furrow at mature stage. Suture simple, with broadly arched lateral lobe, almost straight on the venter.
Measurements dm = 88.5 mm (dm2 = 57.9 mm), wh = 31.5 mm, uw = 34.5 mm, ww = 37 mm.
Description Evolute to advolute conch, with the last whorl only slightly embracing the former volution and a whorl expansion rate of about 2.3. The preserved conch comprises slightly more than the last whorl. The umbilicus is moderately wide (uw/dm = 0.39) and shallow. The whorl section, wider than high, is subquadrate to subrectangular, with the maximum width at the umbilical shoulders. The ventral area is convex, arched, with rounded but distinct ventrolateral shoulders. On the body chamber, from the diameter of 77 mm, the ventral area bears a longitudinal shallow depression. This depression corresponds to a rounded and shallow hyponomic sinus at the aperture. The flanks are slightly convex, subparallel. The umbilical shoulders are angular and rounded. The umbilical wall is subvertical. The ribs on the flanks are simple, straight, massive and scarcely elevated. These ribs start from the umbilical shoulder with a small swelling, fading before reaching the ventrolateral margin, where they meet a row of rounded nodes. In the last half-whorl, there are 6 irregularly spaced ribs, whereas the marginal nodes are 13. The nodes increase in size through ontogeny, but only the last marginal node and the last two ribs are well marked and bear true umbilical nodes. The growth lines as well as the siphuncle are not preserved. The suture line shows a shallow rounded lobe on the flank, while it is almost straight on the venter. The body chamber corresponds to 100° of volution. The recrystallized shell has a coarse surface.
Discussion The new species, based on a single specimen, shows similarities with some other species documented in the literature, which belong to the Triassic genus Enoploceras. According to Kummel (1953), the whorl cross section of Enoploceras is slightly wider than high, subquadratic, with ventral and umbilical shoulders sharply rounded, with flattened venter, flanks and umbilical walls at maturity. The present specimen is probably closely related to the type species of Enoploceras, Nautilus wulfeni Mojsisovics, 1873, from the Carnian of Hallstatt (Austria). The type species, however, is slightly more involute (uw/dm = 0.27) with a more steeply inclined umbilical wall and with a lower number of marginal nodes connected to the umbilical nodes by feeble radial ribs.
Enoploceras rieberi sp. nov. resembles Pleuronautilus semseyi Frech, 1911 (Carnian, Hungary), assigned by Kummel (1953) to Enoploceras, which has a similar umbilical width (uw/dm = 0.38) and bears massive irregular ribs. However, this species has a higher number of ribs per whorl, without marginal nodes separated from the ribs, a wider whorl section and less rounded lateral lobe. This species was previously described by Diener (1901) as “Pleuronautilus cf. tommasii” (Parona, 1889). The specimen described by Diener (1901: pl. 1, Fig. 2a, b) shows sigmoidal ribs and the venter joins the convex flank at a longitudinal keel. In the original specimen described by Parona (1889: pl. 1, Fig. 2; Carnian, Lombardy, Italy) as “Nautilus (Trematodiscus) Tommasii”, the umbilical nodes are connected by ribs to the corresponding marginal nodes. The specimen figured by Diener (1901) is probably related to forms such as Nautilus rectangularis Hauer, 1855 (= Trematodiscus rectangularis in Mojsisovics, 1882 = Thuringionautilus rectangularis in Mojsisovics, 1902 = Aulametacoceras rectangulare in Kummel, 1953).
Other species, similar to the present one, assigned to Enoploceras by Kummel (1953) are considered here. Nautilus planilateratus Hauer, 1860, Nautilus fischeri Mojsisovics, 1873, Pleuronautilus gaudryi Mojsisovics, 1902 (see also Jurkovšek et al., 2002, Carnian, Slovenia), Pleuronautilus lepsiusi Mojsisovics, 1902, P. (Enoploceras) ausseanus Diener, 1919, and P. (Enoploceras) lepsiusiformis Diener, 1919 have been described from the Carnian of Hallstatt. These species are characterized by more involute conchs, three or four rows of nodes, and, keels on the venter in some species. Pleuronautilus tibeticus Mojsisovics, 1896 from the Carnian of the Himalayas, is more involute, with an octagonal whorl section and a venter area defined by two low keels. Pleuronautilus kossmati Diener, 1901 from the Carnian of Hungary, has a higher number of ribs, four rows of nodes on the ribs and a marginal keel. From the Upper Triassic of Timor, some species were described by Kieslinger (1924): Pleuronautilus (Enoploceras) molengraaffi Kieslinger, 1924; P. (Enoploceras) lepsiusi Mojsisovics, 1902; P. (Enoploceras) malayicus Welter, 1914; P. (Enoploceras) wulfeniformis Kieslinger, 1924; P. (Enoploceras) pseudoplanilateratus Kieslinger, 1924; P. nov. sp. ex aff. wulfeni (Mojsisovics) Kieslinger, 1924; P. (Enoploceras) pseudowulfeni Kieslinger, 1924. These species differ notably from the present one in their peculiar sculpture on the flanks, which consists of sigmoid ribs or three rows of strong nodes, while some other species are quite smooth.
Pleuronautilus (Enoploceras) newelli Kummel, 1953 from the Lower Triassic (Olenekian) of Idaho, U.S.A., has a much wider whorl section, is more rapidly expanding and has no ribs. It represents the only Lower Triassic species belonging to Enoploceras, while the other documented species come from the Upper Triassic.
There are three additional species sharing some character states quite with the new species, which are, however, not considered to belong to Enoploceras by the authors. Pleuronautilus rollieri Arthaber, 1896 from the Anisian of Tiefengraben (Austria) has a higher number of ribs, which are always connected to the small marginal nodes, and has a deeper lateral lobe. Anoploceras qinghaiense He, 1986 from the Anisian (Aegean) of China (Mt. Burhan Budai, Central Qinghai) has a trapezoidal whorl section, a higher number of ribs, and an almost smooth mature conch. The specimen figured by Gliwa et al., 2020 (fig. 17b, Lower Julfa Formation, Upper Permian, Iran) classified as Pleuronautilus sp. (specimen MB.C.29347) shows a quite similar overall shape. However, not all characters are visible on that incomplete specimen.
Enoploceras rieberi sp. nov. is characterized by its unusual lateral sculpture: there are twice as many marginal nodes as umbilical nodes; these umbilical nodes are fused with the consecutive massive ribs, which fade before they reach the marginal nodes. This particular feature is not present in other species of Enoploceras documented in the literature and discussed here. The present new species appears to be the only Middle Triassic representative of the genus Enoploceras.
Genus Germanonautilus Mojsisovics, 1902 (rev. Mundlos et al., 1984).
Type species. Nautilus bidorsatus Schlotheim, 1832.
Systematic position: following Dzik (1984), this genus might have evolved from Domatoceras Hyatt, 1891 (family Grypoceratidae Hyatt in Zittel, 1900) rather than Metacoceras Hyatt, 1883 (family Tainoceratidae), such as traditionally assumed in literature. However, Mundlos et al. (1984) and Perez-Valera et al., (2017: p. 176) include Germanonautilus again in the family Tainoceratidae and define its characters. Following these last authors, Germanonautilus differs from Metacoceras and from Mojsvaroceras in the reduced sculpture pattern, which is either absent or limited to shallow growth lines and ventrolateral nodes, and also in the subtrapezoidal whorl section with tabular or slightly concave and wide venter, as well as a greater rate of whorl overlap.
Germanonautilus aff. ellipticus Parnes, 1986 Fig. 3 a–f.
Material Specimen PIMUZ 29942, a poorly preserved natural mold of the living chamber, filled by carbonate sediment; with slightly deformed coiling, partially included in the matrix. The original shell is dissolved, with its morphology preserved on the ventral area.
Measurements At maximum dm (deformed) of 95 mm other dimensions are: wh = 40 mm, uw = 33 mm, ww = 75 mm; at dm of 70 mm other dimensions are: wh = 34 mm, uw = 24 mm, ww = 69 mm.
Locality and age Valle Stelle (Meride, Canton Ticino). Middle Besano Formation, Illyrian, Secedensis Zone (recovered from a laminated bituminous dolostone in a gallery of the former mine; correlating to bed 73). In association with an imprint of an ammonoid (Fig. 4) classified here as Stoppaniceras cf. artinii (Airaghi, 1912a, 1912b).
Description Evolute shell (uw/dm = 0.34), consisting of about the last whorl. The umbilicus is broad, without any preserved structure. Siphuncle and suture line are not visible. The whorl section, wider than high, is subelliptical, with the maximum width at the umbilical shoulders. The ventral area is convex, widely arched, with more or less rounded distinct ventrolateral shoulders. The flanks are rounded and convex. The umbilical shoulder passes to the inclined umbilical wall forming a continuous curve. The growth lines are observable only on the ventral area and form a wide and deep hyponomic sinus.
Discussion The genus Germanonautilus is usually characterized by a narrow umbilicus and trapezoidal whorl sections, with more or less flattened or depressed venter. The specimen described here shows similarities in particular with Germanonautilus ellipticus Parnes, 1986. This species was described by Parnes (1986) from the Middle Triassic of Israel (Negev, Saharonim Formation, Lower Ladinian). It has a relatively wide umbilicus, a well-rounded elliptical whorl section, which is wider than high, and a regularly arched convex venter. The present specimen is more evolute (uw/dm = 0.34 at dm = 70 mm) than Germanonautilus ellipticus (uw/dm = 0.24 at dm = 80 mm, Parnes 1986 showing a wider umbilicus and a last whorl only slightly embracing the former volution. Up to now, forms similar to G. ellipticus were not documented in Southern Alps. Germanonautilus brooksi Smith, 1927 from Alaska (Carnian) described by Kummel (1953), shows a well-rounded elliptical whorl section and a wide umbilicus. Following Kummel (1953, p. 29). the specimens described originally by Smith are small conchs probably corresponding to immature growth stages, with deeply embracing whorls and more distinct umbilical shoulders.
Family Syringonautilidae Mojsisovics, 1902
Genus Syringonautilus Mojsisovics, 1902
Type species. Nautilus lilianus Mojsisovics, 1882
Syringonautilus sp. Figure 5 a–c.
Material Specimen PIMUZ 37903, partially preserved as internal mold (about the last half-whorl, fractured and slightly deformed), partially as external mold from which a silicon cast was produced.
Measurements At maximum dm (deformed) of 44.5 mm other dimensions are: wh = 23.5 mm, uw = 10 mm, ww = 25 mm.
Locality and age Point 902/ Mirigioli (Meride, Canton Ticino). Middle Besano Formation, Illyrian, Secedensis Zone (bed 104, light grey dolomite).
Description The specimen consists of about the last whorl, lacking its inner whorls. It shows a rapidly expanding smooth conch, with whorls deeply embracing. The whorl section is more or less elliptical. The anterior whorl section is higher than wide, well rounded and with the maximum width at the umbilical shoulders. The umbilical shoulder passes to the inclined umbilical wall forming a continuous curve. The flanks are convex, but slightly flattened, converging externally. In the last half-whorl, the ventrolateral shoulder becomes angularly rounded and corresponds to the maximum width of whorl. The venter is convex and rounded, slightly flattened. The other characters are not observable.
Discussion This poorly preserved specimen shows similarities with species of Syringonautilus (e.g., Mojsisovics, 1882; Pieroni, 2020) from the Middle Triassic of the Alps. Following Kummel (1953, p. 60), Syringonautilus can be distinguished from Syringoceras only by the position of its siphuncle: while in Syringonautilus it is subcentral, in Syringoceras it is nearly marginal. However, this character is still unknown in many species, and it is not visible in the present specimen. The whorl section of Syringoceras is usually slightly compressed (Kummel, 1953, p. 61) and more expanded in Syringonautilus as in the present specimen. Among the species belonging to Syringonautilus documented in literature, Syringonautilus bosnensis (Hauer, 1892, p. 6 [254], pl. 1, Fig. 3a–c; Trinodosus Zone of Han Bulog, Bosnia) shares the shape of whorl section and the umbilical width with the specimen here described. The whorls of Syringonautilus lilianus (Mojsisovics, 1882) are less rapidly expanding and the conch has a wider umbilicus and circular to subquadrate whorl sections. Syringonautilus cf. lilianus (Mojsisovics, 1882) from Rasa di Varese (Varese, Lombardy, Rasa Dolomite, San Salvatore Dolomite, Reitzi Zone sup.) was described by Pieroni (2011, p. 57, pl. 2 cefalopodi, Fig. 3). It shows a more subquadrate whorl section and is more evolute.
Nautilida gen. et sp. indet. Figure 6 a–d.
Material Specimen PIMUZ 38668, internal and external mold of a poorly preserved phragmocone (about half a whorl, fractured and deformed), with some recrystallized shell remains.
Measurements Deformed preserved portion with maximum dm of 105 mm, estimate dm (at this position) = 125, estimate wh = 29 mm aperturally, estimate wh = 23 mm apically, ww = 58 mm aperturally, ww = 51 mm apically.
Locality and age Point 902/ Mirigioli (Meride, Canton Ticino). Middle Besano Formation, Illyrian, Secedensis Zone (bed 98, laminated bituminous dolostone).
Description The specimen consists of about half-whorl, lacking inner whorls and umbilical wall not visible (included in the matrix?). It has rather rapidly expanding whorls, with strongly depressed whorl sections (estimate ww/wh = 2). Some blunt ribs are visible on the flank. The suture line shows a shallow rounded lobe on the flank, while it forms a shallow arched ventral saddle.
Discussion This specimen represents an additional taxon, although it is too poorly preserved for identification even on family level. Among the Middle Triassic Nautilida from the Tethys, strongly depressed whorl section with blunt lateral ribs and rapidly expanding whorls occur in some species of Mojsvaroceras Hyatt, 1883 (see M. gianii Pieroni & Prinoth, 2021). The ventral saddle is a character known from the family Syringonautilidae. Their conchs are usually without ribs (in this family, only Weitschatinautilus Engeser, 1995 bears ribs in the mature stage), and in the genus Holconautilus Mojsisovics, 1902 (Tainoceratidae), the whorls are usually expanding more slowly.
