The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


The evolution of global endocast shape in primates

KARI L. ALLEN.

Evolutionary Anthropology, Duke University

Thursday 10:15-10:30, Ballroom C Add to calendar

It has long been suspected that encephalization may be associated with aspects of cranial form that distinguish extant anthropoids from strepsirhine primates. However, it is unknown how encephalization correlates to overall brain shape and cranial form across the primate order. This project addresses these questions using geometric morphometric (GM) shape analyses of both the cranium and endocast of living primates and Oligocene anthropoids from the Fayum deposits of Egypt.

Three-dimensional landmarks were collected on virtual endocasts, segmented from micro-CT scans of thirty-one extant primate species and two fossil anthropoids from the Fayum of Egypt: Parapithecus (DPC18651) and Aegyptopithecus (CGM85785). Fourteen endocast landmarks and twenty-six cranial landmarks were chosen to reflect extant variation in overall cranial and endocranial form. Shape was explored using Principal Component (PC) Analysis of Procrustes-aligned shape variables. PC scores were found to have a high degree of phylogenetic signal (Pagel’s lambda value approaching 1.0). As such, PC scores were examined for correlation to absolute and residual endocranial volume (ECV) using PGLS regression techniques.

PC1 scores from both the endocast (en) and cranial (cr) analyses are significantly correlated with residual ECV (p<0.05), while PC1cr and PC2en are significantly correlated with absolute ECV. The fossil specimens are aligned with living strepsirrhine primates in both endocranial shape (low endovertex, rostrally projecting olfactory bulb, etc.) and size, but more closely resemble modern anthropoids in overall cranial form, thus illustrating that a historical approach is crucial to our understanding of the evolutionary and developmental factors that cause variation in cranial form among primates.

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