New finds shed light on diet and locomotion in Australopithecus deyiremeda

The naming of Australopithecus deyiremeda¹ from Woranso-Mille (less than 3.59 to more than 3.33 million years) indicated the presence of a species contemporaneous with Australopithecus afarensis in the Ethiopian Afar Rift. A partial foot (BRT-VP-2/73)² and several isolated teeth from two Burtele (BRT) localities, however, were not identified to the species level. Recently recovered dentognathic specimens clarify not only the taxonomic affinity of the BRT hominin specimens but also shed light on the diet and locomotion of A. deyiremeda. Here we present a comparative description of these specimens and show that they are attributable to A. deyiremeda. We also find it parsimonious to attribute the BRT foot to this species based on the absence of other hominin species at BRT. The new material demonstrates that overall, A. deyiremeda was dentally and postcranially more primitive than A. afarensis, particularly in aspects of canine and premolar morphology, and in its retention of pedal grasping traits. Furthermore, the low and less variable distributions of its dental enamel δ¹³C values are similar to those from Ardipithecus ramidus and Australopithecus anamensis, indicating a reliance on C₃ foods. This suggests that A. deyiremeda had a dietary strategy similar to the earlier A. ramidus and A. anamensis. The BRT foot and its assignment to A. deyiremeda provides conclusive evidence that arboreality was a significant component of the positional behaviour of this australopith, further corroborating that some degree of arboreality persisted among Pliocene hominins^1,3-7.