Rhinocerotidae

Abstract

The remains of fossil rhinoceroses from Laetoli represent at least three taxa: Ceratotherium efficax, Ceratotherium cf. simum, and Diceros sp. The great majority of the material from the Pliocene Laetolil Beds belongs to C. efficax, for which we provide a revised diagnosis. This taxon has been frequently misidentified and inaccurately referred to as C. praecox, C. germanoafricanum, or C. mauritanicum. A cranium from the Upper Ndolanya Beds shows more derived dental features, but a precise assignment to C. germanoafricanum or C. simum is presently not possible. The occurrence of true Diceros in the Laetolil Beds is demonstrated by a partial cranium with incomplete dentition, but very few other specimens can be potentially attributed to this genus. Analysis of occlusal wear patterns suggests that C. efficax was a grazer or possibly a graze-dominated mixed feeder; in either case it probably included a variable component of browse in its diet. The transition from a Diceros-like ectolophodont dentition to the full-fledged plagiolophodonty seen in extant Cera­totherium simum included a substantial period of stasis, spanning at least the interval represented by the Laetolil Beds. A shift in the dietary regime towards increased grazing had occurred by the Upper Ndolanya time, and this trend continued from the early Pleistocene to the Recent. Based on the available fossil record, the split of the two lineages leading to the extant species must have taken place in Africa during the Miocene.