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The tuatara has gastralia, rib-like bones also called gastric or abdominal ribs, the presumed ancestral trait of diapsids. It is found in some [[lizard]]s (in lizards they are mostly made of cartilage), crocodiles and the tuatara, and are not attached to the spine or thoracic ribs.
The tuatara has gastralia, rib-like bones also called gastric or abdominal ribs, the presumed ancestral trait of diapsids. It is found in some [[lizard]]s (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.<ref name = "Lutz">{{cite book | last=Lutz | first=Dick | year=2005 | title=Tuatara: A Living Fossil | publisher=DIMI PRESS | id=ISBN 0-931625-43-2}}</ref> This feature is also present in birds. The tuatara is the only living [[tetrapod]] with well developed gastralia and uncinate processes.
The real ribs are small projections, with small, hooked bones, called uncinate processes, found on the rear of each rib.<ref>{{Harvnb|Lutz|2005|p=27}}.</ref> 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 [[clavicle]]s (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.{{cite needed}}
In the early tetrapods, the gastralia and ribs with uncinate processes, together with bony elements such as bony plates in the skin (osteoderms) and [[clavicle]]s (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.{{cite needed}}
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[[Image:Brueckenechse.jpg|thumb|250px|Tuatara juvenile]]
[[Image:Brueckenechse.jpg|thumb|250px|Tuatara juvenile]]
Tuatara reproduce very slowly, taking ten years to reach sexual maturity. Mating occurs in midsummer; females mate and lay [[Egg (biology)|egg]]s once every four years.<ref>{{cite journal| author = Cree et al| year = 1992 | title = Reproductive cycles of male and female tuatara (''Sphenodon punctatus'') on Stephens Island, New Zealand| journal = Journal of Zoology| volume = 226| pages = 199-217}}</ref> 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. <ref> {{cite journal | author=C. Gand, J.C. Gillingham and D.L. Clark | year = 1984 | title = Courtship, mating and male combat in Tuatara, ''Sphenodon punctatus'' | journal = Journal of Herpetology | volume = 18(2) | pages = 194-197}} </ref> 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, much like the mating process in birds.<ref name=Lutz />
Tuatara reproduce very slowly, taking ten years to reach sexual maturity. Mating occurs in midsummer; females mate and lay [[Egg (biology)|egg]]s once every four years.<ref>{{cite journal| author = Cree et al| year = 1992 | title = Reproductive cycles of male and female tuatara (''Sphenodon punctatus'') on Stephens Island, New Zealand| journal = Journal of Zoology| volume = 226| pages = 199-217}}</ref> 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. <ref> {{cite journal | author=C. Gand, J.C. Gillingham and D.L. Clark | year = 1984 | title = Courtship, mating and male combat in Tuatara, ''Sphenodon punctatus'' | journal = Journal of Herpetology | volume = 18(2) | pages = 194-197}} </ref> 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, much like the mating process in birds.<ref>{{Harvnb|Lutz|2005|p=19}}.</ref>


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.<ref name=encyclo /> The sex of a hatchling depends on the temperature of the egg, with warmer eggs tending to produce male tuatara, and cooler eggs producing females. Eggs incubated at 21°&nbsp;C have an equal chance of being male or female. However, at 22°&nbsp;C, 80% are likely to be males, and at 20°&nbsp;C, 80% are likely to be females; at 18°&nbsp;C all hatchlings will be females.<ref name="KCC" /> There is some evidence that sex determination in tuatara is determined by both genetic and environmental factors.<ref>{{cite web | title=Tuatara Sex Debate | url=http://coloherp.org/cb-news/Vol-29/cbn-0204/Tuatara.php | accessdate=2006-03-02}}</ref>
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.<ref name=encyclo /> The sex of a hatchling depends on the temperature of the egg, with warmer eggs tending to produce male tuatara, and cooler eggs producing females. Eggs incubated at 21°&nbsp;C have an equal chance of being male or female. However, at 22°&nbsp;C, 80% are likely to be males, and at 20°&nbsp;C, 80% are likely to be females; at 18°&nbsp;C all hatchlings will be females.<ref name="KCC" /> There is some evidence that sex determination in tuatara is determined by both genetic and environmental factors.<ref>{{cite web | title=Tuatara Sex Debate | url=http://coloherp.org/cb-news/Vol-29/cbn-0204/Tuatara.php | accessdate=2006-03-02}}</ref>
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==Bibliography==
==Bibliography==
*{{Harvard reference
| Surname = Lutz
| Given = Dick
| Year = 2005
| Title = Tuatara: A Living Fossil
| Publisher = Salem, Oregon: DIMI PRESS
| ID = ISBN 0-931625-43-2}}
*{{cite book | last=McKintyre | first=Mary | year=1997 | title=Conservation of the Tuatara | publisher=Victoria University Press | id=ISBN 0-86473-303-8 }}
*{{cite book | last=McKintyre | first=Mary | year=1997 | title=Conservation of the Tuatara | publisher=Victoria University Press | id=ISBN 0-86473-303-8 }}
*{{cite book | last=Parkinson | first=Brian | year=2000 | title=The Tuatara | publisher=Reed Children’s Books | id=ISBN 1-86948-831-8}}
*{{cite book | last=Parkinson | first=Brian | year=2000 | title=The Tuatara | publisher=Reed Children’s Books | id=ISBN 1-86948-831-8}}

Revision as of 19:09, 24 May 2007

For the experimental music band, see Tuatara (band).

Tuatara
Male tuatara
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Sauropsida
Order:
Sphenodontia
Family:
Sphenodontidae
Genus:
Sphenodon

Gray, 1831
Species
black: range (northern New Zealand)

The tuatara is a reptile of the family Sphenodontidae, endemic to New Zealand. The two species are the only surviving members of the Sphenodontians who flourished around 200 million years ago.[1] Tuatara 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. Tuatara, 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,[2] until the first mainland release into the heavily fenced and monitored Karori Wildlife Sanctuary in 2005.[3]

Taxonomy and evolution

Tuatara, and their sister group Squamata (which includes lizards, snakes and amphisbaenians), belong to the superorder Lepidosauria, the only surviving taxon within Lepidosauromorpha. Squamates and tuatara both show caudal autotomy (loss of the tail-tip when threatened), and have a transverse cloacal slit.[4] 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.

Tuatara 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 "wastebasket taxon".[5] Sphenodontia was proposed by Williston in 1925.[5] Now, most authors prefer to use the more exclusive order name of Sphenodontia for the tuatara and its closest living relatives.[6]


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.[7] The Brothers Island tuatara has 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.[2]

Tuatara have been referred to as living fossils.[8] This means that they have remained mostly unchanged throughout their entire history, which is approximately 200 million years.[8] However, taxonomic work[9] 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 tuatara. Tuatara show cold weather adaptations that allow them to thrive on the islands of New Zealand; these adaptations are probably unique to tuatara and not present in extinct sphenodontians, which lived in much warmer climates.[citation needed]

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.[10] 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 colour ranges from olive green to brown to orange-red[3], and it can change colour over its lifetime. It sheds its skin at least once per year, usually 3 or 4 times as juveniles.

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.[citation needed]
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.[4]

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 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 jaw, with the bottom row fitting perfectly between the two upper rows when the mouth is closed.[4] 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.[4] The double-row arrangement provides a self-sharpening mechanism.[citation needed] The tuatara's teeth are not replaced, since they are not separate structures like real teeth, but sharp projections of the jaw bone.[citation needed] 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.[citation needed]

Sensory organs

In tuatara, 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

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.[4] Its purpose is unknown, but it may be useful in absorbing ultraviolet rays to manufacture vitamin D,[11] as well as to determine light/dark cycles, and help with thermoregulation.[4] Of all extant tetrapods, the parietal eye is most pronounced in the tuatara. The parietal eye is part of the pineal complex, another part of which is the pineal gland, which in tuatara secretes melatonin at night.[4]

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 fibres, 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.[12]

Spine and ribs

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 tuatara 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.[13] 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.[citation needed]

Natural history

Adult tuatara 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. Tuatara thrive in temperatures much lower than those tolerated by most reptiles, and hibernate during winter.[14] 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.[15] 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.[16] The low body temperature results in a slower metabolism.

Burrowing seabirds such as petrels, prions and shearwaters share the tuatara's island habitat during the bird's nesting season. The tuatara use the bird's burrows for shelter when available, or dig their own. The seabirds' guano helps to maintain invertebrate populations that tuatara 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.[4]

Tuatara juvenile

Tuatara reproduce very slowly, taking ten years to reach sexual maturity. Mating occurs in midsummer; females mate and lay eggs once every four years.[17] 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. [18] 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, much like the mating process in birds.[19]

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.[4] The sex of a hatchling depends on the temperature of the egg, with warmer eggs tending to produce male tuatara, 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.[11] There is some evidence that sex determination in tuatara is determined by both genetic and environmental factors.[20]

Tuatara probably have the slowest growth rates of any reptile,[4] continuing to grow larger for the first 35 years of their lives.[11] The average lifespan is about 60 years, but they can live to be over 100 years old.[11]

Conservation status

Tuatara, 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.[2] A mainland release occurred in 2005 in the heavily fenced and monitored Karori Wildlife Sanctuary.[3]

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.[4]

A Tuatara at Invercargill's museum

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 tuatara for release into the wild. The Victoria University of Wellington maintains a research programme into the captive breeding of tuatara, 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".[11] Tuatara feature in a number of indigenous legends, and are held as ariki (God forms). Tuatara are regarded as the messengers of Whiro, the god of death and disaster, and Māori women are forbidden to eat them.[21] The tuatara was featured on one side of the New Zealand 5 cent coin, which was phased out in October 2006.[22]

Sphenodon is derived from the Greek for "wedge" (sphenos) and "tooth" (odon(t));[23] punctatus is Latin for "spotted";[24] guntheri alludes to Albert Günther, keeper of Zoology at the British Museum in London.

References

  1. ^ Burnie, David (2001). Animal: The Definitive Visual Guide to the World's Wildlife. New York, New York: DK Publishing, Inc. p. 375. ISBN 0-7894-7764-5. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ a b c "New Zealand Department of Conservation - Facts about tuatara". Retrieved 2007-02-10.
  3. ^ a b c Tuatara Facts Retrieved on February 21, 2007.
  4. ^ a b c d e f g h i j k Cree, Alison. 2002. Tuatara. In: Halliday, Tim and Adler, Kraig (eds.), The new encyclopedia of reptiles and amphibians, Oxford University Press, Oxford, pp. 210-211. ISBN 0-19-852507-9
  5. ^ a b Fraser, Nicholas; Sues, Hans-Dieter; (eds) (1994). "Phylogeny" In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cambridge University Press. ISBN 0-521-45242-2. {{cite book}}: |author= has generic name (help)CS1 maint: multiple names: authors list (link)
  6. ^ "Lepidosauromorpha". Retrieved 2006-07-27.
  7. ^ "Fact Sheet on BBC website". Retrieved 2006-02-28.
  8. ^ a b "New Zealand Ecology--Living Fossils". Retrieved 2006-11-10.
  9. ^ Wu, Xiao-Chun (1994). "Late Triassic-Early Jurassic sphenodontians from China and the phylogeny of the Sphenodontia" in Nicholas Fraser & Hans-Dieter Sues (eds) In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cambridge University Press. ISBN 0-521-45242-2.
  10. ^ Russell, Matt (1998). "Tuatara, Relics of a Lost Age". Matt Russell, Dallas Zoo. Retrieved 2006-05-19.
  11. ^ a b c d e "Tuatara on Kiwi Conservation Club". Retrieved 2006-04-22.
  12. ^ Kaplan, Melissa (2003-09-06). "Reptile Hearing". Melissa Kaplan's Herp Care Collection. Retrieved 2006-07-24. {{cite web}}: Check date values in: |date= (help)
  13. ^ Lutz 2005, p. 27.
  14. ^ http://www.southlandmuseum.com/tuatara_-_facts.htm
  15. ^ "Animal Diversity Web: Tuatara - Habitat". Retrieved 2006-04-22.
  16. ^ Thompson MB and Daugherty CH (1998). "Metabolism of tuatara, Sphenodon punctatus". Comparative biochemistry and physiology A. 119: 519–522.
  17. ^ Cree; et al. (1992). "Reproductive cycles of male and female tuatara (Sphenodon punctatus) on Stephens Island, New Zealand". Journal of Zoology. 226: 199–217. {{cite journal}}: Explicit use of et al. in: |author= (help)
  18. ^ C. Gand, J.C. Gillingham and D.L. Clark (1984). "Courtship, mating and male combat in Tuatara, Sphenodon punctatus". Journal of Herpetology. 18(2): 194–197.
  19. ^ Lutz 2005, p. 19.
  20. ^ "Tuatara Sex Debate". Retrieved 2006-03-02.
  21. ^ http://www.waitangi-tribunal.govt.nz/doclibrary/public/wai262/matauranga_maori/Chapt06.pdf
  22. ^ "Five Cents for the Tuatara". Retrieved 2006-10-11.
  23. ^ Sphenodon URL accessed January 8, 2007.
  24. ^ Dictionary of Botanical Epithets: pulchellus - purpureus URL accessed January 8, 2007.

Bibliography

  • Template:Harvard reference
  • McKintyre, Mary (1997). Conservation of the Tuatara. Victoria University Press. ISBN 0-86473-303-8.
  • Parkinson, Brian (2000). The Tuatara. Reed Children’s Books. ISBN 1-86948-831-8.
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