Serometacoceras, Korn & Ghaderi, 2025

Korn, Dieter & Ghaderi, Abbas, 2025, Late Permian nautiloids from Julfa (NW Iran), European Journal of Taxonomy 1018, pp. 1-113 : 34-35

Genus Serometacoceras gen. nov.

urn:lsid:zoobank.org:act:

New genus C – Korn 2025: 50.

Type species

Pleuronautilus Verae von Arthaber, 1900 .

Diagnosis

Genus of the family Metacoceratidae with a subinvolute or subevolute conch; whorl profile equidimensional or more or less strongly depressed, usually trapezoidal with weakly divergent flanks. Venter usually weakly convex or flattened; ventrolateral shoulder narrowly or broadly rounded. Umbilical margin pronounced and subangular in the intermediate growth stage, rounded in the adult stage. Sculpture with conical nodes on the ventrolateral shoulder or on the umbilical margin or both, sometimes connected by low ribs on the flank. Suture line with shallow external lobe or very low external saddle and broadly rounded lateral lobe; without annular process. Siphuncle small with subcentral position ventrad of septum centre.

Etymology

From the Latin ‘ serus ’(adj., net.)=‘late’; because of the high stratigraphic position and the similarity to Metacoceras .

Included species

Transcaucasia and NW Iran ( Abich 1878; von Arthaber 1900; Shimansky 1965b; Kotlyar et al. 1989; this paper): Nautilus dorso armatus Abich, 1878 , Wuchiapingian, Azerbaijan; Nautilus tubercularis Abich, 1878 , Wuchiapingian, Azerbaijan; Nautilus incertus Abich, 1878 , Wuchiapingian, Azerbaijan; Nautilus Verae von Arthaber, 1900 , Wuchiapingian, Azerbaijan; Metacoceras dorashamense Shimansky, 1965 , Wuchiapingian, Azerbaijan; Pleuronautilus dzhulfensis Shimansky, 1965 , Wuchiapingian, Azerbaijan [synonym of Serometacoceras verae gen. et comb. nov.]; Pleuronautilus costalis Shimansky, 1965 , Wuchiapingian, Armenia; Pleuronautilus dzhagadzurensis Zakharov in Kotlyar et al., 1989, Capitanian, Azerbaijan; Serometacoceras cingulum gen. et sp. nov., Wuchiapingian, NW Iran; Serometacoceras inflatum gen. et sp. nov., Wuchiapingian, NW Iran; Serometacoceras parvituberculatum gen. et sp. nov., Wuchiapingian, NW Iran; Serometacoceras arasense gen. et sp. nov., Changhsingian, NW Iran.

Central Iran ( Korn & Hairapetian in press): new species I to be described by Korn & Hairapetian (in press), Wuchiapingian.

Pakistan ( Waagen 1879; Reed 1931, 1944): Nautilus latissimus Waagen, 1879 , Wuchiapingian, Salt Range; Gyroceras Medlicottianum Waagen, 1879 , Wuchiapingian, Salt Range; Metacoceras warchense Reed, 1931 , Wuchiapingian, Salt Range; Metacoceras chittidilense Reed, 1944 , Wuchiapingian, Salt Range; Parametacoceras venustum Reed, 1944 , Wuchiapingian, Salt Range.

South China ( Xu 1977; Zheng 1984; Ma 1997): Metacoceras hunanense Xu, 1977 , Changhsingian, Hunan; Pleuronautilus changxingensis Zhao, Liang & Zheng, 1978 , Changhsingian, Zhejiang; Pleuronautilus zhongyingensis Zheng, 1984 , Changhsingian, Guizhou; Pleuronautilus magnus Zheng, 1984 , Changhsingian, Guizhou; Pleuronautilus anfuensis Ma, 1997 , Wuchiapingian, Jiangxi; Pleuronautilus curvatus Ma, 1997 , Wuchiapingian, Jiangxi; Pleuronautilus robustus Ma, 1997 , Wuchiapingian, Jiangxi.

Remarks

The Transcaucasian material appears to represent a morphocline ranging from forms with a relatively simple sculpture consisting only of ventrolateral nodes to forms with ribs and a few rows of nodes on the flank. All of these forms have previously been assigned to the genera Metacoceras and Pleuronautilus Mojsisovics, 1882 ( Kummel 1953; Shimansky 1965b; Teichert & Kummel 1973). However, Shimansky (1965b: 158) already noted some uncertainties regarding the exact delimitation of the two genera on the basis of the specimens from Dzhulfa.

A division of the morphocline represented in the material from Julfa into the two genera Metacoceras and Pleuronautilus would have consequences for the phylogenetic reconstruction of the suborder Tainoceratina . Species previously assigned to Pleuronautilus are already known from Early Permian strata, such as the Leonard Formation of Texas. These were placed in the genus Foordiceras Hyatt, 1893 by Miller & Youngquist (1949) and in Pseudofoordiceras by Ruzhencev & Shimansky (1954). Kummel (1953: 12) discussed at length the phylogenetic relationships within the family Tainoceratidae (as he understood it) and concluded that these species belong to Pleuronautilus , a view that was supported by Shimansky (1967). However, this would mean that the origin of the genus Pleuronautilus was in the Early Permian or even earlier. Assigning parts of the Transcaucasian morphocline to Pleuronautilus would mean that this genus is polyphyletic or that very similar morphologies occur in the genera Metacoceras and Pleuronautilus .

Dzik (1984: 161) already assumed that the genus Pleuronautilus , as previously used by many authors, is a polyphyletic taxon containing several evolutionary lineages. In contrast to previous authors ( Kummel 1953; Ruzhencev & Shimansky 1954), who proposed a relatively simple evolutionary scenario starting with the main genus Metacoceras , from which most of the other of the tainoceratid genera branched off, Dzik (1984, p. 162, fig. 62) proposed a much more complex picture with a number of independent evolutionary lineages. In this phylogenetic reconstruction, Metacoceras does not play a central role and is not considered to be ancestral to genera such as Tainoceras Hyatt, 1883 and Pleuronautilus . Also, the Late Permian species known from Transcaucasia, which Shimansky (1965b) and Teichert & Kummel (1973) referred to as Metacoceras and Pleuronautilus , were thought to have evolved independently of Metacoceras .

In the following, we place the morphocline with “ Nautilus dorso armatus ” and “ Pleuronautilus verae ” completely in the new genus Serometacoceras gen. nov. Some representatives of these Late Permian forms that have previously been placed in Pleuronautilus actually have a sculpture very reminiscent of Pleuronautilus , but they lack an annular process. Such forms are described by Korn & Hairapetian (in press) as belonging to the new genus C to be described by Korn & Hairapetian (in press).

Serometacoceras gen. nov. differs from Metacoceras in the shape of the whorl profile, which in Serometacoceras is depressed and usually trapezoidal with weakly divergent flanks, while Metacoceras normally has converging flanks. A further difference lies in the formation of the sculpture, which is composed of coarser ribs in Serometacoceras .