The Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) has participated in a paper published in the Journal of Human Evolution, that provides new quantitative data on cranial vault thickness in Homo antecessor, based on the analysis of three parietal fragments recovered from the Gran Dolina site in the Sierra de Atapuerca, Burgos (Spain).

Supported by the Fundación Atapuerca/Reale Foundation and the Atapuerca Project, the research forms part of a doctoral thesis focusing on the cranial microstructure of this species and its comparison with that of other human groups, both living and extinct. The thesis is being undertaken by CENIEH predoctoral researcher Rafael Gallareto-Sande under the supervision of María Martinón-Torres (CENIEH), Emiliano Bruner (MNCN-CSIC) and Palmira Saladié (IPHES).

The results show that the total cranial vault thickness of these adult individuals falls within the range observed in modern humans and Neanderthals and is clearly lower than that found in Homo erectus and other Early Pleistocene hominins.

Layer by layer
Until now, the only Homo antecessor parietal bone studied in detail had been described by Emiliano Bruner and colleagues in 2017 and belonged to a juvenile individual. The three fragments analyzed in the new study—ATD6-115, ATD6-128 and ATD6-401—come from adult individuals.
The analysis was conducted using micro-computed tomography, a technique that makes it possible to measure separately the three layers that make up the cranial bone—the outer table, the diploë and the inner table—and to examine other features of the bone surface in detail, including vascular channels and microforamina.

When the three layers were analyzed separately, the diploë—the spongy tissue within the bone—was the thickest in all the specimens, accounting for between 41% and 50% of the total thickness. This is consistent with the pattern observed in Neanderthals and modern humans.

The Homo antecessor fragments also show different relative proportions in the other two layers: the outer table is relatively thinner and the inner table relatively thicker than in Neanderthals and modern humans.

“This is the first time we have been able to compare the cranial thickness of this species quantitatively, layer by layer, with the available data for other members of the genus Homo. This provides extremely valuable information that helps us interpret the evolutionary position of the species,” says Gallareto-Sande.

A mosaic anatomy
Homo antecessor was originally described on the basis of the remains recovered from level TD6 of Gran Dolina as a species with a mosaic anatomy, combining derived facial and neurocranial features with more primitive postcranial and dental traits. It is now considered a group close to the common evolutionary root of Neanderthals and modern humans.
The results of this study support that characterization, adding the thickness and internal architecture of the parietal bone to the features that define this combination of ancestral and derived traits.

However, the findings point to a trend rather than a definitive conclusion, as the available Homo antecessor sample remains small.“The available sample is still limited and fragmentary, so any new fragment could refine these results. We hope that future excavation campaigns will continue to yield new cranial remains that allow us to test these observations and explore their implications in greater depth,” concludes Gallareto-Sande.