Primate origins: Lessons from a neotropical marsupial

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Abstract
The didelphid Caluromys shows evolutionary convergence towards prosimians in having a relatively large brain, large eyes, small litters, slow development, and agile locomotion. The selection pressures that favored the emergence of primate-like traits in Caluromys from a generalized didelphid ancestor may be analogous to the selection pressures favoring the initial divergence of primates from a primitive nonprimate ancestor, and thus Caluromys provides an independent test of the arboreal hypothesis (Smith: Annual Report of the Board of Regents of the Smithsonian Institution 1912:553–572, 1913), the visual predation hypothesis (Cartmill: The Functional and Evolutionary Biology of Primates, pp. 97–122, 1972), and the angiosperm exploitation hypothesis (Sussman: American Journal of Primatology, in press) of primate origins. Quantitative data on free-ranging C. derbianus in Costa Rica demonstrate that it is highly arboreal, uses visually directed predation to capture arthropod prey, and makes extensive use of terminal branch foraging, where it feeds on small angiosperm products. These observations are consistent with predictions from each model of primate origins, thus suggesting that the hypotheses are not mutually exclusive but are interdependent. The initial divergence of primates probably involved exploitation of the rich angiosperm products and associated insects found in fine terminal branches; visually directed predation may have evolved as an efficient method of insect capture in the terminal branch milieu.