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 wide range of primary (dry scrubland, pine-oak forest, oak forest, juniper forest) and secondary habitats (agricultural land, and agave and "Opuntia" fields). Five subspecies of "P. orbiculare" are recognized as being valid, including the nominotypical subspecies. "Nota bene": A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than "Phrynosoma". The subspecific name, "cortezii", is in honor of Spanish "conquistador" Hernán Cortés. The subspecific name, "dugesii", is in honor of French-born Mexican naturalist Alfredo Dugès, who is considered the "father" of Mexican herpetology. Mexican Plateau horned lizard The Mexican Plateau horned lizard (Phrynosoma orbiculare)