Comparing endocranial form and shape differences in modern humans and Neandertal: a geometric approach

Abstract

Paleoneurology is based on the analysis of the traces left by the brain cortical structures on the endocranial surface of fossil specimens. Although such information is indirect and fragmentary, it may provide useful insights on hu-man brain evolution. Computed tomography and shape analysis deeply improve the toolkit available for paleo-neurological studies. Shape analysis and multivariate approaches suggest that modern humans have undergone a specific evolution of the parietal areas. In this paper the endocranial lateral profiles of two complete specimens (one modern human and one Neandertal) are compared using both form and shape information by means of geometric comparison and coordinate-based maps, integrating superimpositions and Euclidean distance matrix analysis. Using both superimposed (shape) and non-transformed (form) data, the modern endocast is character-ized by a midsagittal enlargement of the parietal and occipito-cerebellar areas, associated with antero-posterior shortening of the fronto-temporal profile. Differences can be quantified and synthesized using simple geometric tools. Modern brain morphology may be the result of both neural changes and structural constraints, in which modularity and integration make the endocranial geometry sensitive to the cranial base dynamics, facial changes, tissue strains, and metabolic/physiological adjustments. Although paleoanthropology often deals with fragments or single specimens, the use of geometrical modelling is a useful and simple tool to standardize, quantify, and describe morphological differences.