The Skull of Tarsius: Functional Morphology, Eyeballs, and the Nonpursuit Predatory Lifestyle The Skull of Tarsius: Functional Morphology, Eyeballs, and the Nonpursuit Predatory Lifestyle

Little is known about the impact of enormous eyeballs on the tarsier's head, apart from facial morphology. I used a biomechanical analysis to compare the cranium of Tarsius with the Eocene fossil Necrolemur, a moderately large-eyed surrogate for ancestral tarsiid cranial morphology. Eyeball hypertrophy has radically influenced the neurocranium and basicranium, driving the evolution of such derived features as recession of orbital fossae, ectopically located eyeballs, uptilted brain and rounded braincase, anteroventrally shifted foramen magnum, enlarged and horizontally leveled nuchal plane, laterally displaced and narrowed tympanic cavities, and shortened external auditory tubes. The gestalt is an adaptation to efficient orthograde head carriage, balanced head-turning movements, and spatial packaging of cranial components, responses to an extreme loading regimen in which the eyes, with a mass approximating twice the bulk of the brain, profoundly eccentrically load the skull. Specializations of the retina and cortex suggest tarsiers have an acutely developed spatial sense, especially adept at detecting and mapping motion. Spanning several anatomical systems, this configuration represents an extreme form of vertical clinging and leaping (XVCL) geared for noiseless, nonpursuit predation, an energyminimizing procurement strategy that may be a trade-off for relying on metabolically expensive, outsized eyeballs, maintained by a highly nutritious, super-specialized, animalivorous food source. A more varied galago-like locomotor profile and Int J Primatol (2010) 31:1032–1054 DOI 10.1007/s10764-010-9447-x A. L. Rosenberger (*) Department of Anthropology and Archaeology , Brooklyn College, The City University of New York CUNY, Brooklyn, NY 11210, USA e-mail: [email protected] A. L. Rosenberger The Graduate Center, The City University of New York, New York, NY, USA A. L. Rosenberger New York Consortium in Primatology (NYCEP), New York, NY, USA A. L. Rosenberger Department of Mammalogy, The American Museum of Natural History, New York, NY 10024, USA Author's personal copy