Fossil Giraffidae (Mammalia, Artiodactyla) from Lee Adoyta, Ledi-Geraru, and Late Pliocene Dietary Evolution in Giraffids from the Lower Awash Valley, Ethiopia

摘要

The giraffid fossils recovered from similar to 2.8-2.6 million year old (Ma) sediments from Lee Adoyta, Ledi-Geraru, Ethiopia, are described here. Sivatherium maurusium and Giraffa cf. G. gracilis are the two identified taxa, with the former being more abundant than the latter. We interpret this skew of relative abundance to be of paleoenvironmental significance, as Sivatherium is rare and Giraffa is common in the adjacent, but older sediments of the Hadar Formation at Hadar (similar to 3.4 to 2.95 Ma), which was characterized by wooded and well-watered habitats through most of its sequence. Stable carbon isotope analyses show that Giraffa remained an obligate browser throughout the lower Awash Valley (LAV) sequence while Sivatherium underwent a dietary transition from a browser in the Hadar Formation to a grazer at Lee Adoyta. This dietary shift in Sivatherium reflects local environmental change through time in the LAV as open habitats spread during the late Pliocene. A compilation of isotopic data from other sites in eastern Africa shows that the LAV dietary shift in Sivatherium occurred roughly one million years earlier than in the Turkana Basin, Kenya, reflecting a spatiotemporally staggered expansion of C-4 vegetation across eastern Africa.