Atlas of cortical sulcal imprints on Pan endocasts

Abstract

Human brain evolution, explored through the study of fossil endocasts, reveals key insights into changes through time of the cerebral morphology. The genus Pan, being the closest extant relative to humans, provides a crucial comparative basis to identify features that are unique to the human lineage, thereby enriching the understanding of adaptations that have contributed to the human evolutionary history. However, to date, there is no atlas characterising brain imprints in chimpanzee endocasts and documenting variation in their patterns. Utilising micro-focus X-ray Computed Tomography, 21 Pan paniscus and Pan troglodytes dry crania were scanned, and virtual endocasts were automatically reconstructed. Following the automated detection of cortical imprints and manual labelling, advanced statistical methods were applied to generate a density map that documents the distribution of sulcal imprints. Sulci that are critically discussed in palaeoneurology, such as the lunate sulcus, were reliably detected and identified on 21 endocasts, in addition to other sulci of the frontal-, parietal-, temporal-, and occipital lobes, while accessory sulci such as the fronto-marginal sulcus and pre-lunate sulcus showed lower detection rates. This study provides the first comprehensive description of sulcal imprints on extant Pan endocasts and presents invaluable comparative resources for studying brain evolution from the hominin fossil record.