On the autapomorphic traits of Homo erectus

Abstract

Abstract An investigation was carried out on 12 character states often said to be autapomorphic of the neurocranium of H. erectus . The African pongids were used as the outgroup. The majority of these traits were qualitative (i.e., present or absent) and could thus be treated using the classic Hennigian method. Of these, none was autapomorphic in H. erectus . However, the occipital torus was apomorphic for H. erectus and anatomically modern H. sapiens ; the neandertals and the “ante-neandertals” appear to demonstrate an autapomorphic pattern in their occipital torus. The remainder of the traits were quantitative; a Student's t with a level of significance of 0·05 was used as the point of discrimination between primitive and derived character states, although problems with this technique were noted. Of these metric character states, none was autapomorphic in H. erectus . However, one included metric trait, increased cranial vault thickness, was found to show significant statistical discrimination of H. erectus from the outgroups, the australopithecines and anatomically modern Homo sapiens . However, thickened cranial vault bone was also found in the neandertals and in most other non-modern hominids although it was generally less in these groups relative to H. erectus . The presence of thickened vault bone in these groups prevents the trait from being a H. erectus autapomorph. It was hypothesized here that cranial thickness in hominoids occurs in two ways. Increased superior vault thickness is derived for H. erectus and most other non-modern hominids. Thickness of the inferior cranium, on the other hand, reflects retained pneumatodiploic bone and is symplesiomorphic, being shared by the outgroups, the australopithecines and H. erectus . Inferior vault expansion has decreased (relative to H. erectus , the australopithecines and the outgroups) in the neandertals and most other non-modern hominids. Several hypotheses concerning the relationship of H. erectus to other hominids were tested. Among the conclusions are that on the basis of the included traits H. erectus , as presently defined and using the methodology of phylogenetic systematics, cannot be considered a valid species. It was argued, however, that the challenge to the taxon H. erectus rests less with the biological reality of such a group than with the present taxonomic configuration of middle and early upper Pleistocene hominids. It was also suggested that the neandertals, who appear to have a number of autapomorphs, should not be included within the modern species, Homo sapiens .