Tuatara (Rhynchocephalia)

This group gathers Reptiles subcategory members belonging to the order Rhynchocephalia, represented today by a single living species, the tuatara, found only on a number of small islands off the coast of New Zealand after being wiped out on the mainland by introduced predators. Despite a superficial lizard-like appearance, the tuatara is not a lizard at all: it is the sole surviving member of an ancient reptile lineage that was far more diverse during the age of the dinosaurs, making it one of the most frequently cited living fossils in the animal kingdom, though its lineage has continued to evolve slowly rather than remaining literally unchanged. The tuatara is distinguished from every true lizard and snake by details of its skull and jaw structure, a third, light-sensing "parietal eye" beneath a translucent patch of skin on the skull, an unusually slow metabolism and growth rate, and one of the longest lifespans of any reptile, with wild individuals regularly living past one hundred years.