Eurygnathohippus woldegabrieli, sp. nov. (Perissodactyla, Mammalia), from the Middle Pliocene of Aramis, Ethiopia

Abstract

Eurygnathohippus is a genus of hipparionine horse that evolved in and was confined to the African continent from the late Miocene to Pleistocene interval. Eurygnathohippus woldegabrieli is a new species from Aramis, Ethiopia, dated between 4.4 and 4.2 Ma. The hypodigm is currently restricted to 157 specimens from 14 Aramis localities and one nearby Gona locality. We nominate a mandible as the type and a maxillary dentition and two complete metacarpal IIIs as paratypes. Our analysis reveals that Eurygnathohippus woldegabrieli is derived compared with late Miocene Eurygnathohippus feibeli in its overall size, cheek tooth crown height, mandibular symphysis length, and robusticity of distal limb elements. It is primitive in mandibular symphysis length and robusticity of distal limb elements compared with the more advanced medial Pliocene species Eurygnathohippus hasumense. A study of Eurygnathohippus woldegabrieli's paleodiet as measured by two mesowear methods, corroborated by carbon isotope studies, reveals that it was a dedicated grazer with a coarse C4 diet akin to that of modern zebras, wildebeests, and white rhinoceroses.