Emiliano Bruner, a paleoneurobiologist at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), has coordinated a study published recently in the American Journal of Physical Anthropology, on the relationship between the cranial anatomy and the volume of the temporal lobes in the brains of extant and fossil primates: these areas are involved in many cognitive functions including language, memory, social relationships and spatial orientation.

The temporal lobes are found precisely in the middle cranial fossa within the endocranial cavity. Therefore, in fossils, this fossa is normally used to estimate the volume of the lobes held there, although to date there had not been any evidence that the two measurements, the sizes of the cranial fossa and of the cerebral lobes, were genuinely correlated.

This study analyzed a total of 22 primate species, both extant and fossil, to determine whether the size of the cranial fossae is related to the volume of the temporal lobes, and investigate how this has varied over the course of the evolution of this group.

The shape of the middle fossa in the endocranial cavity is influenced by factors external to the brain, such as the biomechanics of the mandible, the position of the face, and flexing of the cranial base. “Nevertheless, the results show that there is a very strong correspondence between the volume of the temporal lobes and the size of the cranial fossa they occupy, which allows species that have undergone a significant enlargement of this part of the brain, such as our own, to be picked out”, says Bruner.

Alannah Pearson, a predoctoral student at the Australian National University, is the lead author on this study, on which David Polly, of Indiana University (USA), also collaborated.