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
Mexican Plateau horned lizard Mexican Plateau horned lizard The Mexican Plateau horned lizard (Phrynosoma orbiculare) is a species of horned lizard. It is also known as the Chihuahua Desert horned lizard. The specific epithet, "orbiculare", comes from the Latin adjective "orbis", meaning "circular". "Phrynosoma orbiculare" has a characteristic single row of lateral abdominal fringe scales. This "horned toad" also has two short occipital horns. "P. orbiculare" is found only in the high plateau country of central Mexico. Specifically, it is found in the states of Chihuahua, Durango, and Nuevo León. Its range continues southeast through Morelos, Puebla and Veracruz. "P. orbiculare" occurs in a