Don’t be fooled-- that’s no lizard. The (in)famous northern tuatara (Sphenodon punctatus) is the sole living member of the order Rhynchocephalia, which dates all the way back to the Mesozoic era. Tuataras are the only surviving member of their group and, evolutionarily, are older than other squamates like snakes and lizards. For this reason, tuataras are sometimes referred to as living fossils and they have changed little in the 240 million years since the squamate–rhynchocephalian split.
There are several traits that distinguish S. punctatus from other reptiles. Much of their skeletal structure is more primitive than that of squamates-- lizards and snakes-- and their skulls especially show a basic structure that is more similar to dinosaurs. They also have special rib-like bones called gastralia that are considered an ancestral trait of reptiles, and which are also found in crocodiles. Their vertebrae are hourglass shaped and are more comparable to those of amphibians, and unlike other reptiles their teeth are fused directly to their jaws. Like turtles, they lack eardrums and external holes, and their ears are filled with fatty fluid. Conversely, they have almost 500 odour receptors-- about as many as birds. Finally, tuataras have a third eye known as a parietal eye on the top of their head. This eye can only sense changes in light and is usually covered by scales; some scientists think it may help with thermoregulation. Other reptiles also have a parietal eye, but it’s most pronounced in tuataras.
Aside from these unique characteristics, S. punctatus bears a close resemblance to its reptilian relatives. Their scales are hard, granular, and often resemble those of crocodiles or turtles. They can be grey, green, or reddish brown-- or change between all three-- and males have a prominent crest on the back. Males also tend to be slightly larger than females, coming in at 61cm in length and up to 1kg. This also makes it New Zealand’s largest reptile. Like some of its lizard cousins, tuatara have the ability to lose their tails when grabbed by a predator and then regrow it later.
Although they grow rapidly, shedding their skin three or four times a year as juveniles, tuataras live incredibly long lives. They reach sexual maturity at anywhere from 10 to 20 years old and can live to be over 70. Tuatara also reproduce very slowly; females only lay a clutch once every four years. This is because yearly mating occurs in the fall but the eggs aren’t laid until the following spring at the very earliest, and then they must be incubated for another 12-15 months. Like other reptiles, the sex of the hatchlings depends on the temperature during incubation; warmer temperatures produce more males and cooler temperature produce females. There is little evidence to indicate parental care after hatching, and most adults are solitary. They can also be highly territorial, and are known to kill and eat young tuataras.
S. Punctatus is a nocturnal reptile, and they typically sleep in burrows or in a sunny patch nearby during the day. At night they look for food-- namely insects, rodents, or bird eggs. Tuataras have incredibly slow metabolisms, so they only need to eat occasionally. Older tuataras also have more worn down or missing teeth, which makes them unable to hunt as effectively. S. punctatus has no natural predators, but introduced predators include rodents and dogs.
Conservation status: The IUCN rates tuataras as Least Concern, but they are currently listed as Appendix I by the Convention on the International Trade in Endangered Species (CITES), which in effect bans any trade or transport of the species without strict authorization. Their primary threat is habitat loss and low genetic diversity, which provides an additional incentive to prevent removal of the species from their native habitat.
