Pliocene Giraffidae (Mammalia) from the Hadar Formation of Hadar and Ledi-Geraru, Lower Awash, Ethiopia

ABSTRACT

The Hadar giraffids belong to the genera Giraffa and Sivatherium. We recognize two species in the former genus; distinguishing between them on dental elements is straightforward, but it is more difficult on other remains. Giraffa jumae is about the size of the modern G. camelopardalis, but has a less pneumatized skull with more conical ossicones, more slender and often longer limb bones, and also differs in some dental features, making it an unlikely ancestor of the modern giraffe. Giraffa stillei has teeth that are always smaller than those of the modern form, less molarized premolars, ossicones smaller but otherwise similar to those of the larger Hadar species, and slender limb bones that are probably relatively long, thus not much shorter than those of the modern form. It might be the ancestor of the later G. gracilis from the Turkana Basin, and of G. camelopardalis. We assign no specimen to Giraffa pygmaea. Sivatherium maurusium, a well-known form of the African Pliocene and Pleistocene, is a rare form at Hadar. In contrast to most bovids, giraffids are more common in the Sidi Hakoma than in the overlying Denen Dora Member, perhaps as a result of grassland expansion at Hadar at that time.

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ACKNOWLEDGMENTS

We are grateful to Y. Desta (Authority for Research and Conservation of Cultural Heritage), G. Senishaw (NME), M. Ahamadin, Afar Regional State Representative, and the regional states for allowing us to work in the field and at the Museum. The Hadar fossil catalogue and stratigraphic data are mostly due to C. Campisano. This paper benefited from the insightful comments of the reviewers, J. M. Harris, and C. Robinson. Thanks also to A. Currant (NHMUK), W. D. Heinrich and O. Hampe (HUB), E. Mbua and F. Kyalo Manthi (KNM), and C. Argot, J. Cuisin, and J. Lesur-Gebremariam (MNHN) for giving access to collections in their care.

Handling editor: Blaire Van Valkenburgh