Evolution of cranial and endocranial profiles in Homo species: A study in 2D geometric morphometrics

Cranial anatomical features play a prominent part in the definition of extinct Homo taxa and in species identification in fossils. Thus, knowledge of cranial morphology considered within its geochronological framework is essential to the understanding of the evolution, chronology, and dispersal of the genus Homo. The brain is also a valuable object of study for research on human evolution, because of features such as its large size and a high encephalization quotient in some Homo species, as well as the complexity of human cognition. However, the joint evolution of endo- and ectocranial anatomies is still little studied, and landmarks representing cerebral anatomy rather than inner cranial bone anatomy are still rarely used. This exploratory piece of research examines endo- and ectocranial profiles in samples representing 3 Homo taxa: Homo sapiens (fossil and recent specimens), Homo erectus, and Homo neanderthalensis. We used 2D geometric morphometrics to analyze the shape of the endo- and ectocranial vaults, as well as the relationships between selected anatomical features such as the extension of lobes and bones. The shapes of the vaults were computed using both fixed landmarks and sliding semilandmarks. The fixed landmarks used for the endocranium were chosen in order to represent cerebral anatomy, in that they are defined by the imprints left by brain structures on the inner bone surface of the skull, and not by bony structures such as the inferior side of cranial sutures. Among other results, we have shown or confirmed specific features in the shape of the endocranium in Homo sapiens, as well as a few differences in the patterns of interplay between lobes and bones. These data, and any further results obtained with larger samples, may provide new insights into the development of the endocranial anatomical pattern in Homo sapiens and of its variability.