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Late Miocene fossil hominid teeth recovered from Ethiopia's Middle Awash are assigned to Ardipithecus kadabba. Their primitive morphology and wear pattern demonstrate that A. kadabba is distinct from Ardipithecus ramidus. These fossils suggest that the last common ancestor of apes and humans had a functionally honing canine-third premolar complex. Comparison with teeth of Sahelanthropus and Orrorin, the two other named late Miocene hominid genera, implies that these putative taxa are very similar to A. kadabba. It is therefore premature to posit extensive late Miocene hominid diversity on the basis of currently available samples.
The phylogenetic status of the earliest hominid genera Sahelanthropus, Orrorin, and Ardipithecus (1-6) and the definition of the family Hominidae (7-10) are in debate. By what derived characters should the hominid (1, 11) clade be recognized? Bipedality might be an arbiter of hominid status, but "bipedality" involves a large and complex set of anatomical traits and is not a dichotomous character. Femora attributed to Orrorin tugenensis at ~5.8 million years ago (Ma) constitute the earliest postcranial evidence for early hominid bipedality (2, 12). However, the O. tugenensis femora are different from those of later hominids such as Australopithecus afarensis (13). Indeed, some question whether Au. afarensis was habitually bipedal (14-17), despite evidence indicating that some form of bipedality appears to have arisen before 5 Ma (1, 2).
Early hominids have also been identified through dental characters. For example, a functional canine-third premolar (C/P3) honing complex is present in fossil and modern apes but absent in all hominids. Among late Miocene hominids, derived features of the lower canines of Sahelanthropus tchadensis and A. ramidus kadabba have contributed to the recognition of these two taxa as early hominids. However, only one partial upper canine of S. tchadensis and a complete crown of O. tugenensis are known. Here, we describe teeth from the late Miocene of the Middle Awash, Ethiopia.
In 2001, hominid fossils from the Middle Awash that were dated 5.2 to 5.8 Ma (18) were assigned to A. r. kadabba (1). Continued work in November 2002 produced additional remains. An upper canine and a lower third premolar are among six new teeth (19) recovered from Asa Koma Locality 3 (ASK-VP-3), with an estimated age of 5.6 to 5.8 Ma (18). The new...