Mid-Pliocene hominin diversity revisited

Geometric morphometric analyses are used to examine the maxillary shape of the Kenyanthropus platyops Leakey, Spoor, Brown, Gathogo, Kiarie, Leakey & McDougall, 2001 holotype KNM-WT 40000 and the Australopithecus deyiremeda Haile-Selassie, Gilbert, Melillo, Ryan, Alene, Deino, Levin, Scott & Saylor, 2015 holotype BRT-VP-3/1, expanding on the work of Spoor et al. (2010, 2016) by using more accurate data and a larger comparative sample. The main objective is to assess whether these two specimens differ from the contemporary taxon Australopithecus afarensis Johanson, White & Coppens, 1978 and more broadly from species of Australopithecus Dart, 1925 and ­Paranthropus Broom, 1938, as well as from each other. Five two-dimensional landmarks recorded on virtual models obtained from computed tomography scans quantify key features of the maxilla used in the differential diagnoses of K. platyops and A. deyiremeda. Principal component analyses were performed to describe shape differences, and the magnitudes of these differences and their statistical significance were assessed using Procrustes and Mahalanobis distances, respectively. The maxillary shapes of both KNM-WT 40000 and BRT-VP-3/1 are significantly different from A. afarensis, the former more so than the latter, and they differ from A. afarensis in dissimilar ways. Where KNM-WT 40000 has a more anterosuperiorly positioned zygomatic process with a longer, more orthognathic, and transversely flat subnasal clivus than A. afarensis, the shape difference of BRT-VP-3/1 is best described as a posterior shift (retraction) of the entire dental arcade. The findings of this study quantitatively support the species status of K. platyops and A. deyiremeda, and corroborate the notion that hominin diversity extended well into the mid-Pliocene of eastern Africa.