Premolar microwear and tooth use in Australopithecus afarensis

The mandibular third premolar (P3) of Australopithecus afarensis is notable for extensive morphological variability (e.g., metaconid presence/absence, closure of the anterior fovea, root number) and temporal trends in crown length and shape change over its 700 Ka time range. Hominins preceding A. afarensis have unicuspid, mesiodistally elongated P3s with smaller talonids, and subsequent australopiths have bicuspid, more symmetrically-shaped P3 crowns with expanded talonids. For these features, A. afarensis is intermediate and, thus, evinces the incipient stages of P3 molarization. Here, we examine A. afarensis P3 Phase II microwear and compare it with that of Australopithecus africanus and Cercocebus atys, an extant hard-object specialist, to assess whether the role of the P3 in food processing changed over time in A. afarensis. Premolar Phase II microwear textures are also compared with those of the molars to look for evidence of functional differentiation along the tooth row (i.e., that foods with different mechanical properties were processed by separate regions of the postcanine battery). Microwear textures were also examined along the mesial protoconid crest, the site of occlusion with the maxillary canine, of the A. afarensis P3 and compared with the same region in Pan troglodytes to determine whether microwear can be useful for identifying changes in the occlusal relationship between the P3 and maxillary canine in early Australopithecus. Finally, temporal trends in P3 Phase II and mesial microwear are considered. Results indicate that 1) both the P3 and molar Phase II facets of A. afarensis have less complex microwear textures than in A. africanus or C. atys; 2) A. afarensis P3 and molar Phase II textures differ, though not to the extent seen in taxa that eat hard and tough items; 3) microwear along the A. afarensis mesial protoconid crest is clearly distinct from that of the P. troglodytes, indicating that there is no honing equivalent in A. afarensis; and 4) there is little evidence of change over time in A. afarensis P3 microwear on either the mesial or Phase II facet. In sum, these results provide no evidence that A. afarensis routinely loaded either its premolars or molars to process hard objects or that A. afarensis P3 function changed over time.