The Gila monster is a squat, slow-moving lizard with a bite that releases venom from glands in its lower jaw. Small grooves within needlelike teeth aid the flow of poison into the victim, slowing down prey and stopping predators. The Gila usually eats less than once a month; when it does, it tends to devour prey--lizards, frogs, and birds--in one gulp. The knobs on its skull, also found on crocodiles, thicken the bone, probably for protection.
Reprinted from Skulls, by permission of Black Dog & Leventhal Publishers. Copyright © 2012