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Abstract
Recently, the number of hominin genera has increased dramatically. Prior to the announcement of Ardipithecus, only two genera were used by paleoanthropologists: Australopithecus and Homo. Presently, up to eight hominin genera are used: Sahelanthropus, Orrorin, Ardipithecus, Australopithecus, Praeanthropus, Kenyanthropus, Paranthropus and Homo. Unlike species concepts, the genus category has not received wide critical examination. To investigate the use of the genus category in paleoanthropology, a comparative framework drawing on morphometric data from a large number of catarrhines is developed. Cranial variables include 36 standard linear measurements from representatives of catarrhine genera across the major tribes/families. This study seeks to assess whether too few or too many hominin genera have been recognized compared with extant catarrhines. Moreover, two published hypotheses about the use of Homo are examined: 1) Wood & Collard's (1999) proposal to transfer Homo habilis/rudolfensis to Australopithecus; and 2) Goodman et al's (1998) classification of both humans and chimpanzees in Homo. To analyze these cranial variables and a number of shape indices calculated from them, as well as to assess competing hypotheses, univariate, bivariate and multivariate statistical approaches are used.
The results allow the identification of a set of variables and shape indices which distinguish genera across the catarrhines. Importantly, body size seems to be the major separator of catarrhine genera, reinforcing the idea that they occupy discrete adaptive zones. Moreover, differences between these genera mostly represent contrasts in the size of the neuroversus the viscerocranium. When applied to hominins, a picture emerges which distinguishes them from extant catarrhines: cranial shape rather than size is the major component distinguishing them; this suggests that extinct hominins occupied similar habitats and adaptive zones; variability in size and shape within hominin genera is much lower than extant catarrhines; and the major differences seen in shape among hominins are the result of encephalization in Homo. It is concluded here that both Wood & Collard's (1999) and Goodman et al.'s (1998) proposals appear to be premature. Moreover, while the earliest hominins may be too finely split at the genus level, the evidence for distinction of Australopithecus and Paranthropus is solid.