Kenyapotamus, PICKFORD, 1983

Boisserie, Jean-Renaud, Lihoreau, Fabrice, Orliac, Maeva, Fisher, Rebecca E., Weston, Eleanor M. & Ducrocq, Stéphane, 2010, Morphology and phylogenetic relationships of the earliest known hippopotamids (Cetartiodactyla, Hippopotamidae, Kenyapotaminae), Zoological Journal of the Linnean Society 158 (2), pp. 325-366 : 346

CF. KENYAPOTAMUS PICKFORD, 1983

Two specimens are considered here as possibly belonging to Kenyapotamus , but without certainty. KNM-SH 41516 was identified as a distal fragment of M 2 ( Tsujikawa, 2005: 31). This specimen differs from other lower molars of Kenyapotamus by: shallower, almost lacking fossae; labial and lingual walls that strongly taper just above the cervix in distal view, whereas in kenyapotamine lower molars these walls usually exhibit less pronounced tapering that is concentrated in the apical area; a particularly large distostylid. Two of these features could be interpreted as linked to enamel hypoplasia, a defect generally caused by environmental stress during tooth growth. The heavily pitted enamel band found just above the cervix on this tooth is symptomatic of this defect. The large distostylid is however difficult to explain in this context, and we attribute KNM-SH 41516 to Kenyapotamus with some caution.

Using an illustration of hippopotamid stratigraphical distribution Pickford (1983: fig. 18) indicated a late middle Miocene age (12 Mya) for ‘BN’ material attributed to Kenyapotamus . This filled the large temporal gap between K. coryndonae and K. ternani . Later ( Pickford et al., 2006), material from the late middle Miocene of the Ngorora Formation (members A to D, dated between 13 and 12 Mya) was attributed to K. ternani ( Pickford et al., 2006: tab 1), reinforcing the number of taxa shared by these levels and Fort Ternan and supporting a biochronological correlation. In the absence of further details in these works ( Pickford, 1983; Pickford et al., 2006) and to our knowledge, the sole specimen attributed to Kenyapotamus from the Ngorora Formation and not found in the late Miocene deposits of Ngeringerowa is KNM-BN 1618 ( Fig. 5E ), identified as a fragmentary lower molar ( Pickford, 1983: 196). This specimen, preserving about one-third of the molar, could be better interpreted as a partial labial portion of a left upper molar ( Fig. 5E ). In the absence of additional remains from the lower members of the Ngorora Formation that would allow further comparisons, this specimen appears to be too fragmentary to provide a more precise attribution than cf. Kenyapotamus .

Figures

Figure 5. Maxilla and upper molars of Kenyapotaminae. A, Kenyapotamus coryndonae, KNM-BN 1321, right M3, holotype with KNM-BN 2075 (left, labial view; middle, mesial view; right, occlusal view). B, K. aff. coryndonae, KNM-NA 251, right M3 (left, labial view; middle, mesial view; right, occlusal view). C, K. coryndonae, KNM-BN 1494, fragmentary palate with left M1 and right M2 (occlusal view). D, K. coryndonae, KNM-NA 188, right M1 (left, labial view; middle, mesial view; right, occlusal view). E, cf. Kenyapotamus, KNM-BN 1618, upper molar fragment (top, labial view; bottom, occlusal view). F, Kenyapotamus ternani, KNM-FT 3934, right M1 - holotype (left, labial view; middle, mesial view; right, occlusal view). G, K. cf. coryndonae, KNM-BN 1601, molar fragment (labial view). Localities: BN, Ngeringerowa, except KNM-BN 1618: lower members of the Ngorora Formation; FT, Fort Ternan; NA, Nakali. Scale bars = 1 cm.