The Pleistocene site has yielded an impressive assemblage of hominin fossils, opening fresh perspectives for understanding the nature of the first Eurasian human settlers, and providing important data for reassessing the origin and evolution of the genus – however, the authors of a new study published in PLOS ONE have put forward a different interpretation.
Two separate species?
Based on one of the lower jaws recovered previously (D2600), and which is considerably larger than the other ones found at the site, and which also morphologically fits with the newly described skull (D4500), the researchers point out the remarkable shape differences that do not depend on body size or sex. They state that the larger fossil exhibits a mosaic of primitive and derived features absent from the smaller specimens D211 and D2735, flagging the presence of a separate species. The small jaws come from a population closely related to early African Homo populations, with the larger jaw belongs to a poorly understood species – Homo georgicus.
Dmanisi excavation director David Lordkipanidze of the Georgian National Museum in Tbilisi disagrees with their conclusions, believing that shape similarities among skulls that fit the lower jaws indicate that only one Homo species occupied the site.
Geologic studies show that the Dmanisi fossils are no younger than 1.76 million years old, he adds. However, the new study suggests the accumulation could cover an undetermined period of time.
Most researchers acknowledge the high degree of size and shape differences at Dmanisi, although their interpretations differ.
According to Lordkipanidze and his team, the large variability exhibited by the Dmanisi hominins would lessen the differences used to identify species such as Homo habilis, Homo rudolfensis, Homo ergaster or Homo erectus. All of these would thus belong to the same species, representing regional variants of a single lineage that would have inhabited the Eurasian and African continents during a considerable large period. However, if they belong to the same lineage, Dmanisi hominins would exhibit a sexual size difference greater than that observed in modern humans and chimpanzees.
Requires further exploration
The new study’s authors expect that future discoveries at Dmanisi and revisions of the fossil record will shed light on the interpretation of these hominins, saying the evidence available at present suggests the first dispersion out of Africa was probably more complex than previously supposed, that different ecological niches may have been present in the area where the fossils were found, and that the possibility of there having been two species should be further explored.
Source: Past Horizons: http://www.pasthorizonspr.com/index.php/archives/03/2014/more-than-one-species-at-dmanisi-site-in-georgia