Tuatara are reptiles endemic to New Zealand and which, although resembling most lizards, are part of a distinct lineage, the order Rhynchocephalia. The two species of tuatara are the only surviving members of their order, which flourished around 200 million years ago. Tuatara are greenish brown and gray, and measure up to 80 cm from head to tail-tip and weigh up to 1.3 kg with a spiny crest along the back, especially pronounced in males. Their dentition, in which two rows of teeth in the upper jaw overlap one row on the lower jaw, is unique among living species. They are further unusual in having a pronounced photoreceptive eye, the “third eye”, which is thought to be involved in setting circadian and seasonal cycles. They are able to hear, although no external ear is present, and have a number of unique features in their skeleton, some of them apparently evolutionarily retained from fish. Although tuatara are sometimes called “living fossils”, recent anatomical work has shown that they have changed significantly since the Mesozoic era. Adult tuatara are terrestrial and nocturnal reptiles, though they will often bask in the sun to warm their bodies. Tuatara of both sexes defend territories, and will threaten and eventually bite intruders. The bite can cause serious injury. Tuatara will bite when approached, and will not let go easily.
This small “dinosaur” is one of the oldest living animals. 200 million years ago, their relatives walked the earth. They have evolved significantly, but are still the only ones left in their order. Today, their closest living relatives are snakes and lizards.
It is extremely closely related to the S. punctatus and it has been considered that both species should be merged into one. The main differences lie in small physical variations and geographical distribution. The Brothers Island Tuatara lives strictly on the North Brother Island in Cook Straight. S. punctatus is more widely distributed across the Cook Straight. Physical differences include minor color changes, skin patterns, and size (S. guntheri is generally smaller), but there are hardly any genetic variations.
These ancient reptiles still carry features of their extinct ancestors. They have a prominent photoreceptive eye, which has vanished in most reptiles today. Their skeletons also carry some features that link them to fish. They also have certain features that are more similar to crocodiles, birds and turtles, rather than lizards.
Hatchling tuatara (Sphenodon punctatus) bred at Chester Zoo (photo courtesy of the media team), AKA baby Isolde! It has taken decades of work to reach this point; outside its native New Zealand the tuatara has never been bred in captivity before this youngster emerged. It’s named for specialist herpetology keeper Isolde McGeorge, whose 38 year career at the zoo led to the successful mating and hatching.
As Spring warms the earth on the wooded bank where they live, the tuataras at Zealandia come out to bask in the sun at the mouths of their burrows. For @sebohannon who seems to like our “living fossil”.
The tuatara is genus of reptiles found only in New Zealand. The genus contains only two living species - the Brothers Island tuatara (Sphenodonguntheri) and the Northern tuatara (Sphenodon punctatus). When the tuatara was first scientifically classified in 1831 they were assumed to be lizards. In 1867 the order Rhynchocephalia (meaning “beak head”, in reference to the distinctive skull structure) was created by Albert Günther of the British Museum, for the tuatara and its fossil relatives.
The tuatara is often referred to as a living fossil due to several primitive features that they still have, though they have changed significantly since the Mesozoic era.
The brain structure and manner in which tuatara move is more similar of amphibians than reptiles, whilst their heart has the most primitive structure of any reptile and their lungs have only a single chamber and lack bronchi.
The skulls of tuataras also shows their age - it is simple in build with two openings (temporal fenestra) on each side of the skull, with complete arches, and the upper jaw is firmly attached to the skull. This makes for a very rigid, inflexible construction.
The tip of the upper jaw is beak-like and separated from the remainder of the jaw by a notch. There is a single row of teeth in the lower jaw and a double row in the upper, with the bottom row fitting perfectly between the two upper rows when the mouth is closed. This specific tooth arrangement is not seen in any other reptile. The jaws chew with backwards and forwards movements combined with a shearing up and down action. As their teeth wear down, older tuatara have to switch to softer prey such as earthworms, larvae, and slugs, and eventually have to chew their food between smooth jaw bones.
These are just some of the physical features which differentiate tuataras from squamata (lizards and snakes). If you wish to read more just check out the wikipedia page on these amazing animals [x]
A study of Saurian morphology: Lepidosauria (part 1)
Lepidosauria is a reptilian group commonly associated with snakes and lizards, which belong to the subgroup Squamata. The first two images here represent the once diverse subgroup Rhynchocephalia.
Pleurosaurus was an aquatic rhynchocephalian found in Solnhofen formation with streamlined body which probably allowed it to swim rapidly. Meanwhile, Sphenodon is the only surviving member of Rhynchocephalia, endemic to New Zealand.
The first member of Squamata in this series is Eublepharis, a genus known for one pet species, the Leopard Gecko. It belongs to the clade Gekkota, comprising all geckos and a family of limbless lizards, Pygopodidae. Gekkota is also closely related to Dibamia, another family of limbless lizards, showing that leglessness evolved convergently multiple times in Squamata.