Prodinoceras efremovi ( Flerov, 1957 )

Missiaen, Pieter & Smith, Thierry, 2008, The Gashatan (late Paleocene) mammal fauna from Subeng, Inner Mongolia, China, Acta Palaeontologica Polonica 53 (3), pp. 357-378 : 372

Prodinoceras efremovi ( Flerov, 1957)

Fig. 14 .

Referred material: IMM−2001−SB−060, right calcaneum; possibly IMM−2004−SB−055, incisor.

Discussion.—Dinoceratans are important biogeographic markers for the early Paleogene of Asia ( Ting 1998), and they have been reported from the Subeng locality ( Russell and Zhai 1987).

A moderately well preserved calcaneum ( Fig. 14 ) is the only specimen in our Subeng collection that can be confidently assigned to Dinocerata . The calcaneum from Subeng very closely matches the calcaneum of “ Mongolotherium ” efremovi in size and morphology, as described and illustrated by Flerov (1957). These similarities include the anterodorsally facing ectal and sustentacular facets and the relatively long tuber with a constricted anterior portion, an expanded posterior part, and a large posteroventrally facing posterior end. In later reviews, the genus “ Mongolotherium ” was considered a subgenus of Prodinoceras ( Tong 1978; Dashzeveg 1982; Schoch and Lucas 1985). In non−taxonomic literature, “ M.” efremovi has even been synonymised with P. martyr ( Russell and Zhai 1987; Ting 1998; Bowen et al. 2002), but without justification by a species level review of Prodinoceras . Based on available information, we identify the dinoceratan calcaneum from Subeng as pertaining to P. efremovi .

Based on the presence of Prodinoceras efremovi at Subeng, and the similarity of a large incisor with the tip of the crown broken off, IMM−2004−SB−055, to one of the isolated incisors of the type specimen of P. martyr, AMNH 21714, ( Matthew et al. 1929), we here tentatively assign IMM−2004−SB−055 also to P. efremovi .

There seems to be considerable size and morphological variation in species attributed to Prodinoceratidae , and sexual dimorphism has been suggested for many prodinoceratids ( Schoch and Lucas 1985; Thewissen and Gingerich 1987). The possibility that many, or even all Prodinoceras specimens from Naran Bulak and Gashato ( Mongolia) and from Subeng and Bayan Ulan (Inner Mongolia, China), represent one species cannot be ruled out. A revision of Asian prodinoceratids is definitely needed both at both generic and specific levels, and may have biogeographic implications.

Stratigraphic and geographic range.— Prodinoceras efremovi is known from the Gashatan (late Paleocene) in the Naran Member of the Naran Bulak Formation at Ulan Bulak ( Mongolia) and in the Nomogen Formation at Subeng.

Figures

Fig. 14. The dinoceratan Prodinoceras efremovi (Flerov, 1957), from the Gashatan (Paleocene) of Subeng, China. IMM−2001−SB−060, right calcaneum in proximal (A), distal (B), dorsal (C), lateral (D), ventral (E), and medial (F) views.