Sphenodontidae

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Two extant species in one genus (Sphenodon) comprise Sphenodontidae. Tuataras are currently restricted to small islands off New Zealand, where they live amongst sea bird colonies, and even share burrows with these birds.

Tuataras are rather stout animals, roughly iguana-like in appearance, with dorsal spines on the neck and head and a thick tail. They reach an adult length of between 19 and 28cm from snout to vent, with an overall length less than 80cm, and weigh less than 1kg. The coronoid process of the dentary is prominent, bones in the upper jaw have been modified into teeth-like chisels that overhang the lower jaw, and some of the palatine teeth are enlarged. Tuataras are active at quite low temperatures, and they do bask in open forests although less than many other reptiles. Their "primitive" morphology and physiology led herpetologists in the early twentieth century to consider the tuatara a living fossil and maladapted relic, but more recent work has suggested on the contrary that tuataras are well-adapted to its current habitat.

Tuataras are primarily nocturnal predators of arthropods, especially those associated with sea bird colonies, and tree wetas (giant New Zealand orthopterans). Given the opportunity, they will eat small lizards, amphibians, and juvenile seabirds.

Tuataras and very long-lived for reptiles, continuing to grow for up to 50 years, and have lived in captivity for as long as 77 years. They take up to 20 years to reach sexual maturity, reproducing only once every 3-4 years, and usually mate in the summer (January), but do not lay eggs until the next summer. Clutches of 8-15 eggs are deposited in nests that the females dig, and the hatchlings emerge between a year and 16 months later. Vocalizations within their hearing range suggest that tuataras do aurally communicate with each other, perhaps especially in areas where burrow density reaches a spacing of only 2m.

Tuataras were once widespread in New Zealand, but are now highly endangered, primarily because of human influence. Humans arriving in New Zealand used tuataras as a food source, and perhaps more devastatingly, introduced the rat, which decimated the population by eating eggs and juveniles. Tuataras are currently listed under CITES Appendix I, and by RedList as Vulnerable.

Rhynchocephalian fossils such as Gephrysaurus, Palacrodon, and Polysphenodon are found as early as the middle Triassic, and by the early Jurassic, rhynchocephalians such as Homeosaurus and Opistias had evolved that resemble the modern form of Sphenodon. Also in the Jurassic, rhynchocephalians acquired a diversity of habit and body form, and included herbivorous aquatic forms such as Ankylosphenodon. Mesozoic rhynchocephalians were geographically widespread, and their fossils are found in Europe, North America, and South Africa.

Gans, C. 1983. Is Sphenodon punctatus a maladapted relic? pp. 613-620 in Advances in Herpetology and Evolutionary Biology (A. G. J. Rhodin and K. Miyata, eds.). Harvard University, Cambridge MA.

Reynoso, V. H. 2000. An unusual aquatic sphenodontian (Reptilia: Diapsida) from the Tlayua formation (Albian), Central Mexico. J. Paleo. 74: 133-148.

Zug, G. 1993. Herpetology: An introductory biology of amphibians and reptiles. Academic Press, San Diego CA.

Contributors

Jennifer C. Ast (author).

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

motile

having the capacity to move from one place to another.