Early and Middle Pleistocene hominins from Atapuerca (Spain) show differences in dental developmental patterns

The Bayesian statistical approach considers teeth as forming a developmental module, as opposed to a tooth-by-tooth analysis. This approach has been employed to analyze Upper Pleistocene hominins, including Neandertals and some anatomically modern humans, but never earlier populations. Here, we show its application on five hominins from the TD6.2 level of the Gran Dolina site (Homo antecessor, Early Pleistocene) and the Sima de los Huesos site (Middle Pleistocene) of the Sierra de Atapuerca (Burgos, northern Spain). Our results show an advanced development of the third molars in both populations with respect to modern Homo sapiens. In addition, the Sima de los Huesos hominins differ from H. sapiens and H. antecessor in the relatively advanced development of their second molar. The relative mineralization of I1/M1 in H. antecessor appears to be similar to that of modern humans, as opposed to that of Neandertals, which appear to be unique. These observations, combined with reduced enamel formation times and the advanced development of the third molars, appear to indicate a shorter ontogenetic period in the hominins from Gran Dolina and Sima de los Huesos in comparison to modern human average.

Crown tissue proportions and enamel thickness distribution in early Pleistocene Homo antecessor maxillary premolars (Atapuerca, Spain)

Objectives Both morphometric and proteomic studies have revealed the close relationship of Homo antecessor with Neanderthals and H. sapiens. Considering this relationship, we aim to characterize the Early Pleistocene Atapuerca-Gran Dolina (TD6) maxillary premolars to test if their pattern of enamel thickness is shared with Neanderthals or H. sapiens. Materials and Methods We employed microcomputed tomography to estimate 2D and 3D tissue proportions in seven H. antecessor maxillary premolars, belonging to two individuals: H1 and H3, and compared them to a sample of extinct and extant Homo populations of African, Asian and European origin (n = 52). Results Our results reveal a different pattern of enamel thickness between the Atapuerca-Gran Dolina two individuals. While TD6-H1 possesses thin-enameled crowns, with a clear affinity with Neanderthals, TD6-H3 exhibits the thick pattern, a trait shared with the majority of fossil hominins and H. sapiens. Discussion This work provides new data on upper premolar enamel thickness in H. antecessor. By documenting both a thin and a thick pattern of enamel thickness in the TD6 sample, we warn about the taxonomic utility of this feature in the characterization of isolated remains. We suggest that the thin enamel condition would have emerged during the Early Pleistocene and it became the most frequent and typical condition in Neanderthals. Possible causes for the pattern observed in TD6 include sexual dimorphism or presence of two populations in the sample; however, population variability is the most plausible explanation with a character expression intermediate between those of Neanderthals and other members of the genus Homo. This interpretation is compatible with the phylogenetic position of H. antecessor close to the ancestor of Neanderthals and H. sapiens.