Can enamel microstructure be used to establish the presence of different species of Plio-Pleistocene hominids from Omo, Ethiopia?

Microstructural characteristics of enamel are minimally influenced by extrinsic / non-genomic factors and are thus potentially important in any attempt to establish the taxonomic attribution of Plio-Pleistocene hominids. The aim of this work is to assess the potential use of enamel microstructural characteristics in attributing teeth from the Omo to different Plio-Pleistocene hominid species. First, the results from this study are compared to data for extant hominoids in order to observe whether Omo teeth show similar or larger variation. This might suggest that more than one species is represented in the Omo sample. Alternatively, a similar or smaller variation would suggest that no more than one species could be reliably recognized in the sample using enamel microstructural characteristics. Secondly, since all previous studies suggest that more than one species is present in the large sample of teeth from the Omo, enamel microstructure characteristics with the largest variability are used to group teeth into morphs. These morphs are compared with previous taxonomic attributions of Omo teeth in order to determine if the morphs grouped teeth in a similar way to previous studies. The results of this study demonstrate that enamel microanatomy characteristics in Plio-Pleistocene hominid teeth from the Omo do not present a larger variation than that observed in extant hominoid species. This suggests that no more than one species can be recognized by using these characteristics. These results also indicate a large overlap in enamel microstructure characteristics between Plio-Pleistocene hominid species from Omo and place serious doubt on the theoretical potential for using enamel microstructural characteristics as a taxonomic tool. The morphs defined in this study do not correspond with any previous taxonomic attributions based on macrostructural analysis of the same teeth and cannot be referred to different species. However, macrostructural characteristics have never been assessed in the same way in extant hominoids and it remains to be seen to what extent these characters reflect interspecific, intraspecific or even intra-individual variation. For now therefore, the taxonomy of Plio-Pleistocene hominids from the Omo still remains unresolved.