Abstract:
Endocasts (i.e., replicas of the inner surface of the bony braincase) constitute a critical
proxy for qualifying and quantifying variations in brain shape and organization in
extinct taxa. In the absence of brain tissues preserved in the fossil record, endocasts
provide the only direct evidence of brain evolution. However, debates on whether or
not information inferred from the study of endocasts reflects brain shape and organization
have polarized discussions in paleoneurology since the earliest descriptions
of cerebral imprints in fossil hominin crania. By means of imaging techniques (i.e.,
MRIs and CT scans) and 3D modelling methods (i.e., surface-based comparisons), we
collected consistent morphological (i.e., shape) and structural (i.e., sulci) information
on the variation patterns between the brain and the endocast based on a sample of
extant human individuals (N = 5) from the 3D clinical image database of the Steve
Biko Academic Hospital in Pretoria (South Africa) and the Hôpitaux Universitaires
Pitié Salpêtrière in Paris (France). Surfaces of the brain and endocast of the same
individual were segmented from the 3D MRIs and CT images, respectively. Sulcal
imprints were automatically detected. We performed a deformation-based shape
analysis to compare both the shape and the sulcal pattern of the brain and the endocast.
We demonstrated that there is close correspondence in terms of morphology and organization between the brain and the corresponding endocast with the exception
of the superior region. By comparatively quantifying the shape and organization
of the brain and endocast, this work represents an important reference for paleoneurological
studies.
