Text © DrSc Giuliano Russini – Biologist Zoologist
English translation by Mario Beltramini
The class of the Reptiles (Reptilia), which appeared for the first time between the period of the Upper Carboniferous (or Pennsylvanian in USA) and the Permian period, Paleozoic or Primary era, about 300 million years ago, subdivides into three subclasses: the one of the Anapsids (Anapsida), which considers only the order of the Chelones (Chelonia) one of the most ancient, that of the Archosaurs (Archosauria), which has the order of the Crocodiles (Crocodilia) and that of the Lepidosaurs, or scaled reptiles (Lepidosauria), which has the orders of the Squamates (Squamata), subdividing into the fundamental suborders of the Saurians (Sauria) and Ophids or Snakes (Ophidia or Serpentes) and the archaic one of the Rhynchocephals (Rhynchocephalia), which has the suborder of the Sphenodonts (Sphenodontia), to which leads one species only, the Spehenodon punctatus, a living fossil, or derelict, nowadays endemic to some islets of the north-eastern part of New Zealand, but which, from the finding of fossil remains, probably in the past had a wider geographic distribution, being present in the whole major island and in the southern part of the Australian continent.
Some taxonomical biologists were contemplating, until the first years of the XX century, also a second species: the Sphenodon guntheri, considered by other herpetological and evolutional biologists only as a subspecies or race of the Sphenodon punctatus. The Sphenodon punctatus commonly called tuatara in the Maori language, is on the contrary called atteria by the tribal population of the Tuatara Maori.
As just said before, the rhynchocephalids, in the local New Zealand fauna are represented by one species only: the Sphenodont (Sphenodon punctatus). Contrary to what happens for the other lepidosaurs (that is, saurians and serpents), their phylogenesis is well known, as the family of the Sphenodontians (Sphenodontidae) was already well diversified in the Late Jurassic, with various genera (for instance Opisthias in North America), also very similar to the genus Sphenodon. Furthermore, the paleontological shortcomings of the Tertiary in this case do not have much importance.
The Rhynchocephalids or Sphenodontids (Rhynchocephalidae, Sphenodontidae) come probably from small eosuchia of the Permian and of the early Trias (Triassic) and by the end of the Secondary (Mesozoic) era were practically spread all over the Earth. The suborder of the Rhynchosaurs (Rhynchosauria), more specialized and characterized by the beaked muzzle, has given also huge herbivorous forms, which, in some instances, did reach the 5 metres of length, whilst the sphenodonts have always remained of small size.
For all information about the Biology (Zoogeography, Ecology-Habitat, Morpho-physiology, Ethology-Reproductive Biology) of the sphenodont or tuatara, the only one species composing the family of the Sphenodontids (Sphenodontidae), leading to the order of the Rhynchocephals (Rhynchocephalia), please read the text dedicated to the Sphenodon punctatus.