Stephanocemas, SP.

Wang, Xiaoming, Xie, Guangpu & Dong, Wei, 2009, A new species of crown-antlered deer Stephanocemas (Artiodactyla, Cervidae) from the middle Miocene of Qaidam Basin, northern Tibetan Plateau, China, and a preliminary evaluation of its phylogeny, Zoological Journal of the Linnean Society 156 (3), pp. 680-695 : 688-690

STEPHANOCEMAS SP. ( FIGS 7 , 8 )

Referred materials: IVPP V15725 ( Fig. 7 ), a partial antler from IVPP CD9818 (N37° 14′ 12.6″ E96° 44′ 49.8″), in the north limb of the Keluke anticline of the eastern Qaidam Basin, collected by Feng Wenqing on 8 July 1998 ; IVPP V15726 ( Fig. 8 ), an antler fragment from IVPP CD0406 (N36° 58′ 54.5″ E97° 23′ 29.3″), in the Bayin Mountain section of the eastern Qaidam Basin, collected by Ni Xijun on 3 September 2004 .

Geological age: IVPP locality CD9818 is in the upper range of the Olongbuluk Fauna ( Wang et al., 2007) and has been palaeomagnetically estimated to be between 12–13 Mya ( Fang et al., 2007). This locality also produced an antler fragment of Lagomeryx , another early cervid frequently associated with Stephanocemas . The Bayin Mountain exposures, to the east of the fossiliferous Naoge area, have yielded few vertebrates, and IVPP CD0406 is one of a handful that produced identifiable materials. CD0406 has been correlated with the Olongbuluk Fauna as well, based on section measurements and biostratigraphical comparisons ( Wang et al., 2007). Lithologically, CD0406 and CD9818 are both in the predominantly greenish sandstones. Vertebrate fossils in the Olongbuluk Fauna in both sections (Huaitoutala and Bayin Mountain) are relatively rare, and a precise correlation of the two localities, separated by a distance of 65 km, is not possible at this moment. It is likely, however, that both CD0406 and CD9818 are stratigraphically lower than beds that produced S. palmatus in Barun Yawula, and that all Stephanocemas -producing localities in the Qaidam Basin are middle Miocene in age (see further discussion in ‘Geology and age’ under S. palmatus ).

Description and comparison: Both IVPP V15725 and V15726 are of similarly small sizes, but lack of additional materials from their respective localities makes it difficult to judge if they belong to juvenile individuals. Although their tips are mostly missing, V15725 has at least six tines, and those for V15726 are not clear because only the posterior half the palm is preserved. The presumed posterior tine on V15725 is short, broad-tipped, and vaguely suggestive of a branched tip. If the latter is not an artefact of weathering, it recalls the condition in S. palmatus . The pedicel is partially preserved in V15725 , suggesting that this antler was not shed during life. In contrast, V15726 has a distinct burr, as seen in most materials of Stephanocemas . Both specimens display a relatively flat palm portion of the antler, and even a relatively mediolaterally expanded palm. They also possess a distinct dorsal ridge connecting the anterior and posterior tines.

The latter two features are perhaps the most revealing about phylogenetic relationships. Whereas a flat and laterally expanded palm may indicate affinity with S. palmatus , the dorsal ridge, however, seems to imply a more primitive status as seen in species of Paradicrocerus and possibly in S. actauensis [the illustration in Tleuberdina et al. (1993: pl. XI, fig. 2a, b) is not clear enough to be sure of this feature]. Future discoveries may prove that IVPP V15725 and V15726 belong to a distinct species of their own if such a unique combination of primitive and derived characters is confirmed, but because of the poor state of preservations we refrain from naming a new species.

Figures

Figure 7. IVPP V15725, Stephanocemas sp. from IVPP locality CD9818. A, stereophoto of dorsal view, B, lateral view, and C, ventral view of partial antler.

Figure 8. IVPP V15726, Stephanocemas sp. from IVPP locality CD0406. A, dorsal, and B, ventral views of antler fragment. Scale is for both views.