1Anatomy and Neurobiology, Washington University Medical School, 2Anthropology, Washington University in St. Louis, 3Evolutionary Anthropology, Duke University
April 16, 2016 , Atrium Ballroom A/B
Extant primate suborders Strepsirrhini and Haplorhini display distinct endocranial shape differences that are correlated with suborder differences in encephalization and brain proportions. However, endocranial shape possesses a strong allometric component that may confound suborder differences, as modern anthropoids occupy a greater body size range than do extant strepsirrhines. Large-bodied subfossil lemurs expand the range of strepsirrhine body size and ecological diversity to greater overlap with haplorhines, allowing us to more fully evaluate the relationship between phylogenetic, allometric, and ecological correlates of endocranial diversity within and between primate suborders.
Virtual endocasts were reconstructed from micro-CT scans of subfossil lemur crania from the Duke Lemur Center (Mesopropithecus, Archaeolemur, Babakotia, and Hapalemur). A 3D morphometric analysis was conducted including a comparative sample of 54 extant primate species. Principal Component (PC) scores from Procrustes-aligned landmark sets were tested for correlation to endocast volume (ECV), body size (reconstructed from craniodental dimensions), and diet category (estimated from upper molar shear quotients).
Despite their large bodies and—in the case of Archaeolemur—relatively large brains for lemuroids, the subfossils are distinctly strepsirrhine-like in endocast shape. PC1 separates strepsirrhines and haplorhines, and is correlated with residual ECV (RSquare=0.33, p<0.001). PC2 weakly correlates with body mass (RSquare=0.12, p=0.04), indicating that strepsirrhine and haplorhine endocasts “get big” in somewhat the same fashion, while retaining key characteristics that are diagnostic of their suborder and related to brain proportions rather than overall size. Finally, residual ECV estimates for subfossil lemurs are not consistent with a strict relationship between diet and encephalization among strepsirrhines.
Support for this research was provided by NSF BCS#1232534 (DDIG for K.L. Allen, PI: Rich Kay).