Rhynchocephalia is an order of lizard-like reptiles that includes only two living species of tuatara (Sphenodon punctatus and Sphenodon guntheri), which only inhabit parts of New Zealand. Despite its current lack of diversity, the Rhynchocephalia at one time included a wide array of genera in several families, and represents a lineage stretching back to the Mesozoic Era. Many of the niches occupied by lizards today were then held by sphenodontians. There were even several successful groups of aquatic sphenodontians such as pleurosaurs and the bizarre Ankylosphenodon.