Family Tainoceratidae Hyatt, 1883

Fig. 30

Diagnosis

Family of the superfamily Tainoceratoidea with a discoidal to pachyconic, subinvolute or subevolute conch. Whorl profile always with midventral longitudinal groove; in early species subquadrate with a distinct ventrolateral shoulder and a distinct umbilical margin, in derived species polygonal with divergent or convergent flanks. Dorsal whorl zone always very small. Sculpture with rows of ventrolateral nodes, in some species with rows of nodes on the flank. Septa simply domed; suture line depending on the whorl profile, usually with shallow lobes and low saddles.

Included genera

Tainoceras Hyatt, 1883 (Kasimovian to Changhsingian; 41 species).

Tainionautilus Mojsisovics, 1902 (Wuchiapingian to Early Triassic; 6 species).

Tirolonautilus Mojsisovics, 1902 (Changhsingian; 8 species).

Tylonautilus Pringle & Jackson, 1928 (Serpukhovian to Bashkirian; 6 species).

Aulametacoceras Miller & Unklesbay, 1942 (Roadian; 2 species).

Hexagonites Hayasaka, 1947 (Permian; 1 species)?

Hunanoceras Chao, 1954 (Roadian; 1 species).

Hefengnautilus Xu, 1977 (Roadian; 1 species).

Clavinautilus Zhao, Liang & Zheng, 1978 (Changhsingian; 1 species).

Eulomacoceras Zhao, Liang & Zheng, 1978 (Wuchiapingian; 3 species).

Lirometacoceras Zhao, Liang & Zheng, 1978 (Changhsingian; 1 species).

Neotainoceras Zhao, Liang & Zheng, 1978 (Changhsingian; 5 species).

Paratainonautilus Zhao, Liang & Zheng, 1978 (Changhsingian; 1 species).

Seironautilus Zhao, Liang & Zheng, 1978 (Wuchiapingian; 1 species).

Neoclavinautilus Liang, 1984 (Changhsingian; 1 species).

Nodonautilus Liang, 1984 (Wuchiapingian; 1 species).

? Aulagonoceras Zheng, 1984 (Changhsingian; 4 species).

Nodopleuroceras Zheng, 1984 (Changhsingian; 2 species).

Meixianlingites Qin, 1986 (Wuchiapingian; 1 species).

Paratainoceras Qin, 1986 (Wuchiapingian; 1 species).

Siamnautilus Ishibashi et al., 1994 (Changhsingian; 1 species).

Gujiaonautilus Miao et al., 2019 (Changhsingian; 1 species).

New genus F to be described by Korn & Ghaderi (in press) (Wuchiapingian; 1 species).

New genus D to be described by Korn & Hairapetian (in press) (Wuchiapingian; 2 species).

Remarks

The Tainoceratidae are a fairly well-defined family characterised by the presence of a prominent midventral groove; most of the species possess at least two rows of ventral or ventrolateral nodes. Additional rows of nodes may be developed on the flanks and ventrolateral shoulder. However, there is a reduction in the number of nodes in some derived Late Permian genera.

Ruzhencev & Shimansky (1954) stated that Tainoceras appears to be derived from Metacoceras. An argument in favour of this hypothesis could be the stratigraphic co-occurrence of the oldest species of the two genera in Late Carboniferous cephalopod assemblages. However, this hypothesis implies a significant leap in morphological evolution towards Tainoceras. It should be noted that Metacoceras and related genera usually have inverted trapezoidal or rectangular whorl profiles, in contrast to the polygonal whorl profiles of Tainoceras. Metacoceras and its close relatives also lack a midventral groove. Finally, Metacoceras does not have a sculpture with rows of nodes on the venter; the sculpture elements are restricted to the flanks.

The family Tainoceratidae became diverse in the latest Carboniferous Gzhelian stage, when the single genus Tainoceras was geographically widespread with a number of species (e.g., Sturgeon et al. 1982, 1997). The family persisted with this single genus throughout most of the Permian (e.g., Miller et al. 1933; Miller & Unklesbay 1942; Miller & Youngquist 1949). It continued into the Late Permian, when a large number of new species had evolved, particularly in the Late Permian shelf seas of southern China. To date, more than twelve tainoceratid genera have been described from this single region (Chao 1954; Xu 1977; Zhao et al. 1978; Liang 1984; Zheng 1984; Qin 1986; Miao et al. 2021). This is far more than in any other region where tainoceratids occur at the same time, such as Europe with the Dolomites (Prinoth & Posenato 2007), the Bűkk Mountains (Schréter 1974) and Serbia (Simić 1933). Transcaucasia (Korn & Ghaderi in press) and central Iran (Korn & Hairapetian in press) are also relatively poor in tainoceratids compared to southern China.

There is a very asymmetric distribution of species composing the genera of the family Tainoceratidae. Of the 22 genera, 14 are monospecific and four have two or three previously known species. The most species-rich genera Tainoceras (41 species), Tirolonautilus (8 species) and Tainionautilus (6 species) are, interestingly or significantly, the first described genera of the family (Hyatt 1883 –1884; Mojsisovics 1902).