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
Eastern fence lizard Eastern fence lizard The eastern fence lizard ("Sceloporus undulatus") is a medium-sized species of lizard in the family Phrynosomatidae. The species is found along forest edges, rock piles, and rotting logs or stumps in the eastern United States. It is sometimes referred to as the prairie lizard, fence swift, gray lizard, northern fence lizard or pine lizard. It is also referred to colloquially as the horn-billed lizard. The generic name, "Sceloporus", is derived from the Greek "skelos"/σκελος, meaning "leg", and the Latin "porus", meaning "hole", referring to the enlarged femoral pores found in this genus of lizards. The specific name,