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Tuatara

2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and
Fish

                     iTuatara
   Male tuatara
   Male tuatara

                             Conservation status

   Vulnerable (VU)
            Scientific classification

   Kingdom: Animalia
   Phylum:  Chordata
   Class:   Sauropsida
   Order:   Sphenodontia
   Family:  Sphenodontidae
   Genus:   Sphenodon
            Gray, 1831

                                   Species

     * Sphenodon punctatus (Gray, 1842)
     * Sphenodon guntheri Buller, 1877
     * Sphenodon diversum (extinct)

   The tuatara is a reptile of the family Sphenodontidae, endemic to New
   Zealand. The two species are the only surviving members of the
   Sphenodontians. The tuataras resemble lizards, but are equally related
   to lizards and snakes, which are their closest living relatives. For
   this reason, they are of great interest in the study of the evolution
   of lizards and snakes, and for the reconstruction of the appearance and
   habits of the earliest diapsids (the group that additionally includes
   birds and crocodiles).

   The tuatara has been classified as an endangered species since 1895.
   Tuataras, like many of New Zealand's native animals, are threatened by
   habitat loss and introduced species, such as mustelids and rats. They
   were extinct on the mainland, with the remaining populations confined
   to 32 offshore islands, until the first mainland release into the
   heavily fenced and monitored Karori Wildlife Sanctuary in 2005.

Taxonomy and evolution

   Tuataras, and their sister group Squamata (which includes lizards,
   snakes and amphisbaenians), belong to the superorder Lepidosauria, the
   only surviving taxon within Lepidosauromorpha. Squamates and tuataras
   both show caudal autotomy, loss of the tail-tip when threatened, and
   have a transverse cloacal slit. The origin of the tuatara probably lies
   close to the split between the Lepidosauromorpha and the
   Archosauromorpha. Though tuatara resemble lizards, the similarity is
   mostly superficial, since the family has several characteristics unique
   among reptiles. The typical lizard shape is very common for the early
   amniotes; the oldest known fossil of a reptile, the Hylonomus,
   resembles a modern lizard.

   Tuataras were originally classified as lizards in 1831 when the British
   Museum received a skull. The species remained misclassified until 1867,
   when Albert Günther of the British Museum noted features similar to
   birds, turtles and crocodiles. He proposed the order Rhynchocephalia
   (meaning "beak head") for the tuatara and its fossil relatives.

   During the years since the inception of the Rhynchocephalia, many
   disparately related species have been added to this order. This has
   resulted in turning the rhynchocephalia into what taxonomists call a "
   wastebin taxon". Sphenodontia was proposed by Williston in 1925. Now,
   most authors prefer to use the more exclusive order name of
   Sphenodontia for the tuatara and its closest living relatives.

   There are two extant species of tuatara: Sphenodon punctatus and the
   much rarer Sphenodon guntheri, or Brothers Island tuatara, which is
   confined to The Brothers Islands in Cook Strait. The Brothers Island
   tuatara have olive skin with yellowish patches. Sphenodon punctatus has
   two subspecies: the Cook Strait tuatara (unnamed subspecies), which
   lives on other islands in and near Cook Strait, and the northern
   tuatara (Sphenodon punctatus punctatus), which lives on the Bay of
   Plenty, and some islands further north.

   Tuataras have been referred to as living fossils. This means that they
   have remained mostly unchanged throughout their entire history, which
   is approximately 200 million years. However, taxonomic work on
   Sphenodontia has shown that this group has undergone a variety of
   changes throughout the Mesozoic. Many of the niches normally associated
   with lizards were instead held by sphenodontians. There was even a
   successful group of aquatic sphenodontians known as pleurosaurs, which
   differed markedly from living tuataras. Tuataras show cold weather
   adaptations that allow them to thrive on the islands of New Zealand;
   these adaptations are probably unique to tuataras and not present in
   extinct sphenodontians, which lived in much warmer climates.

Physical description

   The tuatara is considered the most unspecialised living amniote; the
   brain and mode of locomotion resemble that of amphibians and the heart
   is more primitive than any other reptile. Adults are about 50
   centimetres (20 in) long and weigh between 0.5 and 1 kilogram
   (1.1-2.2 lb). They display sexual dimorphism, as the males are larger,
   weighing up to 1 kilogram (2.2 lb), almost twice the weight reached by
   females. The spiny crest on their back, made of triangular soft folds
   of skin, is bigger in males than in females, and can be stiffened for
   display. The male abdomen is narrower than the female's. The tuatara's
   color ranges from olive green to brown to orange-red, and it can change
   colour over its lifetime. It sheds its skin once a year.

Skull

   In the course of evolution, the skull has been modified in most
   diapsids from the original version evident in the fossil record.
   However, in the tuatara, all the original features are preserved: it
   has two openings (temporal fenestrae) on each side of the skull, with
   complete arches. In addition, in the tuatara, the upper jaw is firmly
   attached to the skull. This makes for a very rigid, inflexible
   construction.
   Testudines (turtle and tortoise) skulls were once believed to be the
   most primitive among amniotes, but newer research suggests this is not
   the case, as they might have lost the temporal holes in the skull
   secondarily rather than never having had them.
   In the tuatara, two rows of teeth in the upper jaw close over one row
   in the lower jaw
   Enlarge
   In the tuatara, two rows of teeth in the upper jaw close over one row
   in the lower jaw

   The tip of the upper jaw is beaklike 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 jaw, with the bottom row fitting
   perfectly between the two upper rows when the mouth is closed. This is
   a tooth arrangement not seen in any other reptiles; although most
   snakes also have a double row of teeth in their upper jaw, their
   arrangement and function is different from the tuatara's. The jaws,
   joined by ligament, chew with backwards and forwards movements combined
   with a shearing up and down action. The force of the bite is suitable
   for shearing chitin and bone. The double-row arrangement provides a
   self-sharpening mechanism. The tuatara's teeth are not replaced, since
   they are not separate structures like real teeth, but sharp projections
   of the jaw bone. As their teeth wear down, older tuataras have to
   switch to softer prey such as earthworms, larvae, and slugs, and
   eventually have to chew their food between smooth jaw bones.

Sensory organs

   In tuataras, both eyes can focus independently, and are specialized
   with a "duplex retina" that contains two types of visual cells for
   vision by both day and night , and a tapetum lucidum which reflects on
   to the retina to enhance vision at night. There is also a third eyelid
   on each eye, the nictitating membrane.
   Tuatara at Hamilton Zoo
   Enlarge
   Tuatara at Hamilton Zoo

   The tuatara has a third eye on the top of its head called the parietal
   eye. It has its own lens, cornea, retina with rod-like structures and
   degenerated nerve connection to the brain, suggesting it evolved from a
   real eye. The parietal eye is only visible in hatchlings, which have a
   translucent patch at the top centre of the skull. After four to six
   months it becomes covered with opaque scales and pigment. Its purpose
   is unknown, but it may be useful in absorbing ultraviolet rays to
   manufacture vitamin D, as well as to determine light/dark cycles, and
   help with thermoregulation. Of all extant tetrapods, the parietal eye
   is most pronounced in the tuatara.

   Together with turtles, the tuatara has the most primitive hearing
   organs among the amniotes. There is no eardrum, and the middle ear
   cavity is filled with loose tissue, mostly adipose tissue. The stapes
   comes into contact with the quadrate (which is immovable) as well as
   the hyoid and squamosal. The hair cells are unspecialized, innervated
   by both afferent and efferent nerve fibers, and respond only to low
   frequencies. Even though the hearing organs are poorly developed and
   primitive with no visible external ears, they can still show a
   frequency response from 100-800 Hz, with peak sensitivity of 40 dB at
   200 Hz.

Spine and ribs

   Adult tuatara on a rock
   Enlarge
   Adult tuatara on a rock

   The tuatara spine is made up of hour-glass shaped amphicoelous
   vertebrae, concave both before and behind. This is the usual condition
   of fish vertebrae and some amphibians, but is unique to tuataras within
   the amniotes.

   The tuatara has gastralia, rib-like bones also called gastric or
   abdominal ribs, the presumed ancestral trait of diapsids. It is found
   in some lizards (in lizards they are mostly made of cartilage),
   crocodiles and the tuatara, and are not attached to the spine or
   thoracic ribs.

   The real ribs are small projections, with small, hooked bones, called
   uncinate processes, found on the rear of each rib. This feature is also
   present in birds. The tuatara is the only living tetrapod with well
   developed gastralia and uncinate processes.

   In the early tetrapods, the gastralia and ribs with uncinate processes,
   together with bony elements such as bony plates in the skin
   (osteoderms) and clavicles (collar bone), would have formed a sort of
   exo-skeleton around the body, protecting the belly and helped to hold
   in the guts and inner organs. These anatomical details most likely
   evolved from structures involved in locomotion even before the
   vertebrates migrated onto land. It is also possible the gastralia were
   involved in the breathing process in primitive and extinct amphibians
   and reptiles. The pelvis and shoulder girdles are arranged differently
   than in lizards, as is the case with other parts of the internal
   anatomy and its scales.

Natural history

   Adult tuataras are terrestrial and nocturnal reptiles, though they will
   often bask in the sun to warm their bodies. Hatchlings hide under logs
   and stones, and are diurnal, likely because adults are cannibalistic.
   Tuataras survive in temperatures much lower than those tolerated by
   most reptiles, and hibernate during winter. They can maintain normal
   activities at temperatures as low as 7°  C, while temperatures over
   28° C are generally fatal. The optimal body temperature for the tuatara
   is from 16 to 21° C, the lowest of any reptile. The body temperature of
   tuatara is lower than that of other reptiles ranging from 5.2–11.2° C
   over a day, whereas most reptiles have body temperatures around 20° C.
   The low body temperature results in a slower metabolism.

   Burrowing seabirds such as petrels, prions and shearwaters share the
   tuataras' island habitat during the bird's nesting season. The tuataras
   use the bird's burrows for shelter when available, or dig their own.
   The seabirds' guano helps to maintain invertebrate populations that
   tuataras predominantly prey on; including beetles, crickets and
   spiders. Their diet also consists of frogs, lizards and bird's eggs and
   chicks. Seabirds may provide beneficial fatty acids.
   Tuatara juvenile
   Enlarge
   Tuatara juvenile

   Tuataras reproduce very slowly; taking ten years to reach sexual
   maturity. Mating occurs in midsummer; females mate and lay eggs once
   every four years. During courtship, a male makes his skin darker,
   raises his crests and parades toward the female. He circles himself
   around the female while slowly walking with stiffened legs. The female
   will either submit, and allow the male to mount her, or retreat to her
   burrow. Males do not have a penis; they reproduce by the male lifting
   the tail of the female and placing his vent over hers. The sperm is
   then transferred into the female.

   Tuatara eggs have a soft, parchment-like shell. It takes the females
   between one and three years to provide eggs with yolk, and up to seven
   months to form the shell. It then takes between 12 and 15 months from
   copulation to hatching. This means reproduction occurs at 2 to 5 year
   intervals, the slowest in any reptile. The sex of a hatchling depends
   on the temperature of the egg, with warmer eggs tending to produce male
   tuataras, and cooler eggs producing females. Eggs incubated at 21° C
   have an equal chance of being male or female. However, at 22° C, 80%
   are likely to be males, and at 20° C, 80% are likely to be females; at
   18° C all hatchlings will be females. There is some evidence that sex
   determination in tuataras is determined by both genetic and
   environmental factors.

   Tuataras probably have the slowest growth rates of any reptile,
   continuing to grow larger for the first 35 years of their lives. The
   average lifespan is about 60 years, but they can live to be over 100
   years old.

Conservation status

   Tuataras, like many native New Zealand animals, are threatened by
   habitat loss, and introduced species such as mustelids and rats. They
   were long confined to 32 offshore islands free of mammals. A mainland
   release occurred in 2005 in the heavily fenced and monitored Karori
   Wildlife Sanctuary.

   Sphenodon guntheri is present naturally on one small island with a
   population of approximately 400, and has been reintroduced to two
   others. Sphenodon punctatus naturally occurs on 29 islands and its
   population is estimated to be over 60,000 individuals.

   There are several Tuatara breeding programmes within New Zealand.
   Southland Museum and Art Gallery in Invercargill, was the first to have
   a tuatara breeding programme; they breed Sphenodon punctatus. Hamilton
   Zoo and Wellington Zoo also breed tuataras for release into the wild.
   The Victoria University of Wellington maintains a research programme
   into the captive breeding of tuataras, and the National Wildlife Centre
   at Pukaha Mount Bruce keeps a pair and juvenile. The WildNZ Trust has a
   tuatara breeding enclosure at Ruawai.

Etymology and cultural significance

   The name "tuatara" derives from the Māori language, meaning "peaks on
   the back". Tuataras feature in a number of indigenous legends, and are
   held as ariki (God forms). Tuataras are regarded as the messengers of
   Whiro, the god of death and disaster, and Māori women are forbidden to
   eat them. The tuatara was featured on one side of the New Zealand 5
   cent coin, which was phased out in October 2006 .

   Sphenodon is derived from the Greek language for "wedge" (sphenos) and
   "tooth" (odon(t)); punctatus is Latin for "spotted"; guntheri alludes
   to Albert Günther, keeper of Zoology at the British Museum in London.
   Retrieved from " http://en.wikipedia.org/wiki/Tuatara"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
