Lizard heads called the parietal eye, a basal ("primitive") feature also present in the tuatara. This "eye" has only a rudimentary retina and lens and cannot form images, but is sensitive to changes in light and dark and can detect movement. This helps them detect predators stalking it from above. Until 2006 it was thought that among lizards, only the Gila monster and the Mexican beaded lizard were venomous. However, several species of monitor lizards, including the Komodo dragon, produce powerful venom in their oral glands. Lace monitor venom, for instance, causes swift loss of consciousness and extensive bleeding through its
Greater short-horned lizard widely distributed lizard in North America and occurs in the widest range of habitats: West into central Nevada, East into North and South Dakota, North to Southern Saskatchewan and Alberta and then South into the Texas Panhandle and into central Mexico. This species of lizard is mostly an arid mountain dweller living in the range of 9000–11,300 feet (170–3440 m). It is the only member of its genus in Wyoming, which counts "Phrynosoma" as its state reptile. It is also considered an endangered species in Saskatchewan and Alberta. The greater short-horned lizard occupies ranges from semiarid plains to high elevations