The only recent species of the order Rhynchocephalia is the tuatara, Sphenodon punctatus, which is native to some islands of New Zealand. It is a unique species—a living fossil—fitting in its ecologic niche with an interesting strategy for 200 million yr.
The tuatara has an unexpectedly low optimum temperature of about 12°C. Also unique is the anatomy of this rare and endangered species. Our study gave a closer view to some very special anatomic structures that could not be found in any other species in the world. We examined nine young animals of both sexes frequently for 3 yr by transcutaneous ultrasonography. A special particularity is a relict structure from a very early step of evolution, the parietal eye. Its situation could be imaged by ultrasonography, as well as the peculiar construction of the skull with its osseous temple bridges. Further, the organs of the gastrointestinal tract and urogenital tract could be visualized.
Ultrasonography was, one more time, a fine tool to investigate covered structures in a not well discovered species. It is one of the best fitting methods of examination in order to get detailed information about anatomy in a non-invasive way, even in such rare species.