Dietary Correlates of the Origin and Radiation of Snakes

Abstract

Stomach analyses of living families and of a fossil containing prey were used to address possible dietary correlates of the history of snakes. Aniliids, morphologically primitive among living snakes, feed on relatively heavy, elongate vertebrates. Large aniliids eat larger prey than do small individuals but, as in advanced snakes, they also take small items. Living boids, structurally intermediate between aniliids and advanced snakes, feed on relatively heavy prey of a much greater variety of shapes than do aniliids. An Eocene fossil that might be a boid contains a relatively large crocodilian in its gut. These findings, previous studies, and morphological considerations suggest that very early snakes used constriction and powerful jaws to feed on elongate, heavy prey. This would have permitted a shift from feeding often on small items to feeding rarely on heavy items, without initially requiring major changes in jaw structure relative to a lizard-like ancestor. Subsequent morphological changes could then have allowed boids to utilize a broad range of prey types, including many of those currently eaten by advanced snakes. More recent dietary themes include the consumption of even heavier prey by highly venomous elapids and viperids, and frequent feeding on relatively small items by some other advanced snakes.