Dietary Correlates of the Origin and Radiation of Snakes

Stomach analyses of living families and of a fossil containingprey were used to address possible dietary correlates of thehistory of snakes. Aniliids, morphologically primitive amongliving 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 shapesthan do aniliids. An Eocene fossil that might be a boid containsa relatively large crocodilian in its gut. These findings, previousstudies, and morphological considerations suggest that veryearly snakes used constriction and powerful jaws to feed onelongate, heavy prey. This would have permitted a shift fromfeeding often on small items to feeding rarely on heavy items,without initially requiring major changes in jaw structure relativeto a lizard-like ancestor. Subsequent morphological changescould then have allowed boids to utilize a broad range of preytypes, including many of those currently eaten by advanced snakes.More recent dietary themes include the consumption of even heavierprey by highly venomous elapids and viperids, and frequent feedingon relatively small items by some other advanced snakes.