A possible ancestor of the living waterbuck and lechwes: Kobus basilcookei sp. nov. (Reduncini, Bovidae, Artiodactyla) from the Early Pliocene of the Middle Awash, Ethiopia

Abstract

The new species is a small to medium-sized reduncine antelope from 4.4-Ma-old strata in the Aramis Member (Sagantole Formation, Central Awash Complex). In terms of anatomy and chronology it is a suitable common ancestor of Kobus sp. A from Hadar, Ethiopia, and oricornus from the Turkana Basin, Ethiopia and Kenya. Material from a later assemblage in the Sagantole Formation, 4.2–4.1 Ma old, represents an evolved descendant of K. basilcookei and shows changes in the direction of Kobus sp. A and K. oricornus, suggesting rapid evolution in the 4.4–4.2 Ma interval. I argue that these three species belong in the same subclade of Kobus as the living waterbuck, K. ellipsiprymnus, and the semi-amphibious lechwes, leche and megaceros, and that paedomorphosis (in which the descendant adults resemble ancestral juvenile stages) has played a major part in the evolution of this clade.