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 horned lizard Mexican horned lizard The Mexican horned lizard ("Phrynosoma taurus") is a horned lizard species native to Mexico. Horned lizards are sometimes referred to as "horned toads" or "horny toads", although they are not toads. Compared to other members of the horned lizards (genus "Phrynosoma"), little is known about this species. It is known to live in the Sierra Madre del Sur, south and southeast of Mexico City, in the states of Guerrero and Puebla, Mexico. Its range partially overlaps with that of "Phrynosoma braconnieri". The Mexican horned lizard is a terrestrial species found in arid scrub, high desert, and even