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 : 7

Okapia johnstoni Lankester, 1901

Specimens. AMNH 51196, AMNH 51107, AMNH 51218

Description. The medial and lateral epicondyles are symmetrical in size ( Figure 7 ). The proximal articular surface extends onto the palmar lateral epicondyle. There is a rounded circular protrusion on the medial aspect of the proximal medial epicondyle and a slight protrusion of the lateral aspect of the lateral epicondyle. There is also a flattened, fainter second circular protrusion on the central aspect of the medial epicondyle. There is a slight depression on the palmar surface of the medial epicondyle. The medial epicondyle is squared shaped and the lateral is triangular ( Figure 5.6 ). There is shallow groove that separates the medial and lateral epicondyles. There is an elongated, rod-like bony protrusion on the medial aspect of the shaft that extends slightly distal to the medial epicondyle to midway down the shaft. It is fused to the medial shaft distally, and is sometimes fused proximally and throughout the length. The central trough is intermediate in depth, and it flattens distally ( Figure 6.3 ). There is a distinct pyramidal rise. The medial and lateral ridges are rounded and full. The medial edge of the shaft flares towards the distal condyle. The keels of the distal condyle extend onto the palmar distal shaft. The distal condyle is distinctly separated from the distal shaft.

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 6. Representative cross sections of right metacarpals. 1, Helladotherium duvernoyi, late Miocene, Pikermi, MNHNP 1527; 2, Birgerbohlinia schaubi, late Miocene, Samos, AMNH 20610 (reversed); 3, Okapia johnstoni, AMNH 15218 (reversed); 4, Samotherium major, late Miocene, Samos, AMNH 22790; 5, Bohlinia attica, late Miocene, Pikermi, PA 1474-1991; 6, Giraffa camelopardalis, AMNH 70016. Scale bar equals 80 mm.

FIGURE 7. Three additional metacarpal characteristics. This simplified table can be used to facilitate specimen identifications and differentiate between different giraffid taxa.