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

Activity pattern can only be predicted from eye morphology for haplorhine primates among mammals


1Anatomy, Midwestern University, 2Anthropology, University of Texas at Austin, 3School of Human Evolution and Social Change, Arizona State University

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As in many vertebrate groups, eye shape in haplorhine primates varies predictably with activity pattern. Tarsius and Aotus, the single nocturnal anthropoid, have large corneas relative to eye size as an adaptation for increased visual sensitivity. Conversely, diurnal anthropoids generally demonstrate smaller corneas relative to eye size as an adaptation for increased visual acuity. In this sense haplorhines are unique among mammals as several studies have concluded that most non-haplorhine mammals exhibit eye shapes typical of nocturnal haplorhines and other nocturnal vertebrates, regardless of activity pattern. However, a recent study has argued that new statistical methods allow eye shape to accurately predict mammal activity patterns, including cathemeral species. Here, we conduct a rigorous test examining primate and non-primate mammalian eye shape and activity pattern using a broad sample of species. We find that haplorhine primates is the only mammalian clade where activity pattern is clearly differentiated by eye morphology. We find that the eye shapes of cathemeral non-haplorhine primates and other mammals completely overlap with nocturnal and diurnal species. Additionally, most diurnal and cathemeral mammals, including strepsirrhine primates, have eye shapes that are most similar to those of nocturnal birds and lizards.

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