International Journal of Primatology

, Volume 31, Issue 6, pp 1032–1054 | Cite as

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 energy-minimizing 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 foraging habit was common among fossil tarsiiforms and preadaptive to this lifestyle, partly by canalizing the forward orientation of the tarsier's predatory gaze in VCL mode. Tarsier ecomorphology evolved to minimize the costs of being extraordinarily “top heavy,” carrying a heavy load that is roughly equivalent to 3 brains.


Adaptation Biomechanics Eyes Locomotion Predation Primates Skull Tarsiers 



The research was partially supported by grants from PSC-CUNY and the Tow Travel Research Fund, Brooklyn College. For access to collections I thank authorities and colleagues at the American Museum of Natural History; the United States National Museum; the San Diego Museum of Man; Yale Peabody Museum; Museum of Comparative Zoology, University of California, Berkeley; Museum National d’Histoire Naturelle, Paris; British Museum, London. I express special thanks to Emily Rosenberger for scientific assistance, Julia Zichello for help with illustration, Mark Dow for developing and producing Fig. 1, and to Carsten Neimitz. I thank Siobhan Cooke and anonymous reviewers with deep expertise in tarsier biology for thoughtful comments that improved the manuscript.


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Authors and Affiliations

  1. 1.Department of Anthropology and Archaeology Brooklyn College, The City University of New York CUNYBrooklynUSA
  2. 2.The Graduate CenterThe City University of New YorkNew YorkUSA
  3. 3.New York Consortium in Primatology (NYCEP)New YorkUSA
  4. 4.Department of MammalogyThe American Museum of Natural HistoryNew YorkUSA

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