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
Isthmian alligator lizard Isthmian alligator lizard The isthmian alligator lizard ("Gerrhonotus rhombifer") is a species of lizard of the Anguidae family. "G. rhombifer" is found in both Costa Rica and Panama. Unlike many lizards near its habitat, individuals have lateral folds. They give birth to live young. "Gerrhonotus rhombifer" had not been seen for fifty years, prior to being rediscovered in 2000 near Golfito, and is one of the rarest species of lizard in Costa Rica. "G. rhombifer" is a broad-headed, long-bodied lizard, which is similar to "Diploglossus monotropis". An adult measures from in total length, with the tail making up approximately two-thirds