A new analysis of three skull fragments unearthed at the Gran Dolina cave site in Spain indicates that Homo antecessor had bone thickness closer to that of Neanderthals and modern people than to more archaic hominins.
An artist’s rendering of a Homo antecessor individual known as the Girl of Gran Dolina. Image credit: Tom Björklund.
Homo antecessor is an early hominin that lived in Europe between 1.2 million and 600,000 years ago.
The species was first discovered in 1994 at the Gran Dolina cave site in the Sierra de Atapuerca, a karstic system located approximately 15 km east of Burgos in northern Spain.
Homo antecessor was similar in height to modern humans and was fully bipedal.
“The phylogenetic position of Homo antecessor has been the subject of extensive debate since its initial description,” said Rafael Gallareto-Sande from the National Research Center on Human Evolution (CENIEH) in Spain and his colleagues.
“Originally proposed as the last common ancestor of Neanderthals and modern humans based on a combination of derived facial features and primitive postcranial and dental traits, subsequent morphological and proteomic analyses have refined this position, suggesting instead a stem relationship within that clade.”
“Despite its significance, the cranial morphology of this species remains poorly characterized due to the fragmentary nature of the preserved remains.”
In the new study, the authors analyzed parietal fragments from three adult Homo antecessor individuals found in the TD6 unit of the Gran Dolina cave site.
They found that total cranial vault thickness in these individuals falls within the range seen in modern humans and Neanderthals, and is clearly lower than in Homo erectus and other early Pleistocene hominins — a striking contrast, given that thick skull bone has long been considered a hallmark of more archaic human relatives.
“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,” Gallareto-Sande said.
“This provides extremely valuable information that helps us interpret the evolutionary position of the species.”
Until now, scientists had examined only one Homo antecessor parietal bone in detail, described in 2017, and it belonged to a juvenile.
The three new fragments, cataloged as ATD6-115, ATD6-128 and ATD6-401, are the first from adults, giving the researchers a more reliable picture of how the species compares with other hominins at physical maturity.
Using computed microtomography, they measured each of the skull’s three internal layers separately — the outer table, the spongy diploë, and the inner table — along with vascular channels and small pores on the bone’s surface.
