Specializations of the Body Form and Food Habits of Snakes

Viperid snakes have stouter bodies, larger heads, and longer jaws than snakes in other families; there are no major differences between the two subfamilies of vipers in these features. A suite of morphological characters that facilitates swallowing large prey finds its greatest expression among vipers, but certain elapid and colubrid snakes have converged upon the same body form. The number of jaw movements required to swallow prey is linearly related to the size of a prey item when shape is held constant. Very small and very large prey are not disproportionately difficult for a snake to ingest. Vipers swallow their prey with fewer jaw movements than do colubrids or boids and can swallow prey that is nearly three times larger in relation to their own size. Proteolytic venom assists in digestion of prey, and melanin deposits shield the venom glands from light that would degrade the venom stores. Ancillary effects of the morphological features of vipers, plus the ability to ingest a very large quantity of food in one meal, should produce quantitative and qualitative differences in the ecology and behavior of vipers and other snakes.