Evolutionary interpretation of the modern human-like facial morphology of the Atapuerca Gran Dolina-TD6 hominins

Abstract

The Early Pleistocene human fossil remains recovered from the TD6 lithostratigraphic unit of the Gran Dolina cave site in the Sierra de Atapuerca, northern Spain, show a mosaic of primitive and derived features. Among the latter, the modern human-like midfacial topography, as well as several synapomorphies shared with some European Middle Pleistocene hominin and Neanderthals, represents a challenge for the phylogenetic interpretation of Homo antecessor. Using an ontogenetic approach of the maxilla ATD6-69, Freidline et al. (Journal of Human Evolution, 65: 404–423 (2013)) have confirmed previous observations that H. antecessor adults had a set of facial features characterizing H. sapiens. However, Freidline and collaborators proposed that the evolution of modern-looking facial morphology occurred independently in Africa, Asia, and Europe and at several times during the Early and the Middle Pleistocene. Following their line of reasoning, the presence in H. antecessor of some features shared with the European Middle Pleistocene hominins and the Neanderthal lineage could also be interpreted as convergences. However, instead of supposing multiple, parallel evolution, we suggest that a more parsimonious interpretation envisages the hypothetical existence of an Early Pleistocene hominin population, from which several hominin lineages originate and inherit particular combinations of derived features. The TD6 hominins probably represent a side branch of this cladogenetic event, which evolved in Western Europe.