Dmanisi and Hominin Taxonomy

Given the nature/extent of morphological diversity documented at Dmanisi, it is to be anticipated that hominin assemblages containing both robust and also lightly constructed individuals, differing in supraorbital prominence and vault dimensions as well as facial proportions, may be encountered in the ancient record. Here, it is important to sound a note of caution. Particularly where samples are limited and/or composed of fragmentary specimens, the sorting process will not be straightforward. There is a real risk of assigning individuals to separate populations, when in fact the level and pattern of variation are consistent with what may be expected within a single species. An obvious example is afforded by the finds from Olduvai and Koobi Fora that have been referred to Homo habilis and Homo rudolfensis. Here, only a few fossils are relatively complete, and there is a long history of disagreement as to how they should be identified. The evidence has been read to support different species definitions based on varying hypodigms, but a fair assessment is that the information available is insufficient for this purpose. For the moment, it is difficult to offer any final resolution of the taxonomy for early Homo.

The Dmanisi skulls display some traits that are shared with early Homo sp., along with others that are more clearly diagnostic for Homo erectus. Given the morphology of the cranial base and face, it is appropriate to refer the Dmanisi assemblage to Homo erectus (contra de Lumley et al., 2006). However, it should be recognized that this decision has the effect of expanding the species hypodigm, by adding adult crania (D2282, D3444) that have low capacities, and a subadult (D2700) that resembles KNM-ER 1813. Such a change will alter the definition of Homo erectus and erode the distinction between erectus and other early taxa. Thus, as new discoveries are made, there will be a question as to whether small skulls should be identified as Homo habilis, or placed instead within the range of variation accepted for Homo erectus. Precisely this issue has come up, in respect to a diminutive cranium from Ileret. Recently, Spoor et al. (2007) have elected to group KNM-ER 42700 with Homo erectus, although Baab (2008b) has suggested otherwise.

0 0

Post a comment