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
Common collared lizard Collared lizards in the wild have been the subject of a number of studies of sexual selection. In captivity if two males are placed in the same cage they will fight to the death. Males have a blue-green body with a light brown head. Females have a light brown head and body. Two black stripes around the neck give these lizards their name. Common collared lizard The common collared lizard ("Crotaphytus collaris"), also called eastern collared lizard, Oklahoma collared lizard or collared lizard, is a North American lizard that can reach in length (including the tail), with a large head