RHINOCEROTIDAE, Gray, 1821

Geraads, Denis & Miller, Ellen, 2013, Brachypotherium minor n. sp., and other Rhinocerotidae from the Early Miocene of Buluk, Northern Kenya, Geodiversitas 35 (2), pp. 359-375 : 372-373

RHINOCEROTIDAE gen. et sp. indet.

KNM WS-12855 is a DP2 that is significantly larger (32 × 30) than the one assigned to Brachypotherium ; it further differs in that the central buccal rib is stronger, the buccal cingulum is complete around the hypocone, and the crochet and crista unite to form a medifossette.

KNM WS-13 is a P 4 in early-medium wear ( Fig. 4A ). It differs from those of Brachypotherium in its larger size, presence of a complex crochet that would have contacted a long crista in later wear, closing the medifossette (these spurs are much weaker in Brachypotherium ), and in the parallelism of its mesial and distal borders in buccal view, indicating that is was probably somewhat more hypsodont.

KNM WS-12843 ( Fig. 4B ) is an incomplete upper molar that can be compared with the Brachypotherium molar WS-12844, which is at the same wear stage. The most obvious difference is that WS- 12843 bears a thick coat of cement; it is the only tooth from Buluk where cement is preserved. It is also distinctly more hypsodont than WS-12844, as it was certainly higher than long when unworn, whereas these dimensions were roughly identical in WS-12844. Furthermore, the antecrochet is weaker, and the parastyle is curved buccally, being almost as prominent as the moderate paracone fold.

KNM WS-144 is a mandible fragment with p3, dp4 not shed yet, m1 and m2 ( Fig. 4C ). On the molars, the paralophid is longer lingually, the protolophid is more transverse, and the hypolophid more L-shaped, and the ectoflexid is deeper; m2 is shorter relative to its width. Identification of two other lower cheek teeth, WS-12842 and WS- 12846, is less secure, but they are probably also not of Brachypotherium .

Comparison of these teeth with most of the other Early and Middle Miocene rhinoceroses in the KNM reveals no satisfactory match. In the lack of lingual connection of the lophs or strong antecrochet, they differ from those of the elasmotherines s.l. (including Chilotheridium ), in the lack of lingual expansion of the lophs, they differ from Rusingaceros .

KNM WS-1 and WS-7 are weathered astragali much higher than those of Brachypotherium ; they lack the characteristic lateral shift of the trochlea of Chilotheridium astragali, but have no remarkable feature. We prefer to leave all these specimens as indeterminate, but they definitely point to the occurrence of another species.

Figures

FIG. 4. — Rhinocerotidae gen. et sp. indet. from Buluk: A1, P4 WS-13, buccal; A2, same, occlusal views; B1, M2 WS-12843, buccal; B2, same, occlusal views; C, right lower dp4-m2, WS- 144, occlusal view. Scale bar: 10 cm.