Okapia johnstoni Lankester, 1901

Rios, M, Danowitz, M & Solounias, N, 2016, First comprehensive morphological analysis on the metapodials of Giraffidae, Palaeontologia Electronica 410 (10453), pp. 1-39 : 17

Okapia johnstoni Lankester, 1901

Specimens. AMNH 51196, AMNH 51107, AMNH 51218

Description. The proximal articular surface exhibits three distinct facets. The lateral facet for the os naviculocuboideum is kidney-shaped. The medial facet for the os cuneiforme intermediolaterale is more oval and is not contacting the os cuneiforme mediale facet. On the lateral facet, there is a distinct constriction where the lateral ridge meets the lateral epicondyle. The medial epicondyle is significantly fuller and protrudes more than the lateral side ( Figure 5.6 ). This is due to a large, circular bony protrusion on the plantar surface of the medial epicondyle. A wide, shallow groove separates the medial epicondyle into a dorsal and a plantar head, both of which are oriented longitudinally. There is a confined groove on the lateral aspect of the lateral epicondyle, separating it into a plantar and a dorsal head. The plantar head is oriented longitudinally with the shaft, and the dorsal head slightly flares outward. There is a very shallow and wide groove between the medial and lateral epicondyle. The pygmaios is a notably reduced, flat, rounded protrusion between the medial and lateral epicondyles that does not protrude proximally ( Figure 16 ). Medial to the medial epicondyle, there is a confined, oval bony extension running longitudinally ( Figure 17). This extends just distal to the proximal articular surface. The central trough is intermediate in depth, and it flattens distally. The medial and lateral ridges are sharp and thin. There is a distinct pyramidal rise on the distal shaft. The keels of the distal condyle extend onto the distal shaft, outside the synovial cavity.

Figures

FIGURE 5. Palmar views of the right metacarpals (left) and plantar views of metatarsals (right) of certain Giraffidae. 1, Helladotherium duvernoyi, late Miocene, Pikermi, NHM 11382 (metacarpal), MNHNP 1554 (metatarsal) (both reversed); 2, Bramatherium megacephalum, late Miocene-Pliocene, Siwaliks, AMNH 29820, (metacarpal), AMNH 19668 (metatarsal); 3, Sivatherium giganteum, Pleistocene, Siwaliks, NHM 39553 (metacarpal), NHM 39752 (metatarsal); 4, Decennatherium pachecoi, late Miocene, Los Valles de la Fuentidueña, MNCN 42769 (metacarpal), MNCN 42764 (metatarsal) (both reversed); 5, Birgerbohlinia schaubi, late Miocene, Piera, IPS 5060 (metacarpal), Crusafont, 1952, fig. 15-5 (metatarsal), (both reversed); 6, Okapia johnstoni, Zaire, AMNH 51196 (metacarpal), AMNH 51196 (metatarsal). Scale bar equals 200 mm.

FIGURE 16. Three selected metatarsal characteristics. This simplified table can be used to facilitate specimen identifications and differentiate between different giraffid taxa.