| Tuatara Fossil range: Triassic-Recent | |
|---|---|
| Scientific classification
| |
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Sphenodontia[1] | |
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Sphenodontidae | |
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Sphenodon | |
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The tuatara is a reptile endemic to New Zealand which, though it resembles most lizards, is actually part of a distinct lineage, order Sphenodontia.[2][3] The two species of tuatara are the only surviving members of its order, which flourished around 200 million years ago during the Triassic period.[3] Their most recent common ancestor with any other extant group is with the squamates (lizards and snakes). For this reason, tuatara 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 also includes birds and crocodiles).
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. The origin of the tuatara probably lies close to the split between the Lepidosauromorpha and the Archosauromorpha. Though tuatara resemble lizards, the similarity is 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.[4]
Cladogram showing relationships of extant members of the Sauria.[5] Numbered items are:
1. Tuatara
2. Lizards
3. Snakes
4. Crocodiles
5. Birds
"Lizards" are paraphyletic. Branch lengths do not indicate divergence times.
Tuatara were originally classified as lizards in 1831 when the British Museum received a skull.[6] The genus 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. Now, most authors prefer to use the more exclusive order name of Sphenodontia for the tuatara and its closest living relatives.[7]
Many disparately related species were subsequently added to the Rhynchocephalia, resulting in what taxonomists call a "wastebasket taxon".[8]Williston proposed the Sphenodontia to include only tuatara and their closest fossil relatives in 1925.[8]Sphenodon is derived from the Greek for "wedge" (σφηνος/sphenos) and "tooth" (δόντι/odon(t)).[9]
Tuatara have been referred to as living fossils.[2] This means that they have remained mostly unchanged throughout their entire history, which is approximately 220 million years.[10] However, taxonomic work[11] on Sphenodontia has shown that this group has undergone a variety of changes throughout the Mesozoic, and a recent molecular study showed that their rate of molecular evolution is faster than of any other animal so far examined.[12][13] Many of the niches occupied by lizards today were then 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 may be unique to tuatara since their sphenodontian ancestors lived in the much warmer climates of the Mesozoic.
Species[]
There are two extant species: Sphenodon punctatus and the much rarer Sphenodon guntheri, or Brothers Island tuatara, which is confined to North Brother Island in Cook Strait.[14] The species name punctatus is Latin for "spotted",[15] and guntheri refers to Albert Günther. S. punctatus was named when only one species was known, and its name is misleading, since both species can have spots. The Brother's Island tuatara (S. guntheri) has olive brown skin with yellowish patches, while the colour of the other species, (S. punctatus), ranges from olive green through grey to dark pink or brick red, often mottled, and always with white spots.[16][17][18] In addition, S. guntheri is considerably smaller.[19] A third, extinct species of Sphenodon was identified in November 1885 by William Colenso, who was sent an incomplete sub-fossil specimen from a local coal mine. Colenso named the new species S. diversum.[20]
References[]
- ^ http://www.doc.govt.nz/conservation/native-animals/reptiles-and-frogs/tuatara/
- ^ a b "Tuatara". New Zealand Ecology: Living Fossils. TerraNature Trust. 2004. http://www.terranature.org/tuatara.htm. Retrieved on 2006-11-10.
- ^ a b "Facts about tuatara". Conservation: Native Species. Threatened Species Unit, Department of Conservation, Government of New Zealand. http://www.doc.govt.nz/templates/page.aspx?id=33163. Retrieved on 2007-02-10.
- ^ "Hylonomus lyelli". Symbols. Province of Nova Scotia. May 2003. http://www.gov.ns.ca/legislature/HOUSE_OF_ASSEMBLY/Symbols/fossil.htm. Retrieved on 2007-05-24.
- ^ Fry B.G., Vidal N., Norman J.A., Vonk F.J., Scheib H., Ramjan R., Kuruppu S., Fung K., Hedges S.B., Richardson M.K., Hodgson W.C., Ignjatovic V., Summerhayes R. and Kochva E. (2005) "Early evolution of the venom system in lizards and snakes." Nature doi:10.1038/nature04328 (online 17 November 2005).
- ^ Lutz 2005, p. 42.
- ^ "Lepidosauromorpha: Lizards, snakes, Sphenodon, and their extinct relatives.". The Tree of Life Web Project. Tree of Life Web Project. 1995. http://tolweb.org/Lepidosauromorpha/14917. Retrieved on 2006-07-27.
- ^ 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.
- ^ ""Sphenodon"". Dictionary.com Unabridged (v 1.1). Random House, Inc. http://dictionary.reference.com/browse/sphenodon. Retrieved on 2007-01-08.
- ^ Russell, Matt (August 1998). "Tuatara, Relics of a Lost Age". Cold Blooded News. Colorado Herpetological Society. http://webspinners.com/coloherp/cb-news/archive/nature/tuatara.php. Retrieved on 2006-05-19.
- ^ 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.
- ^ "Tuatara evolving faster than any other species". Massey University. http://www.massey.ac.nz/massey/about-us/news/article.cfm?mnarticle=tuatara-evolving-faster-than-any-other-species-01-03-2008.
- ^ "Fastest Evolving Creature is 'Living Dinosaur'". LiveScience. 26 March 2008. http://www.livescience.com/animals/080326-fastest-tuatara.html.
- ^ "Tuatara - Sphenodon punctatus". Science and Nature: Animals. bbc.co.uk. Archived from the original on 2012-12-23. https://archive.is/hKQI. Retrieved on 2006-02-28.
- ^ Stearn, William T (1 April 2004). Botanical Latin. Portland, Oregon: Timber Press Inc. pp. 476. ISBN 0881926272. http://books.google.com/books?id=w0hZvTFJUioC&pg=PA476&lpg=PA476&dq=botanical+epithets+punctatus&source=web&ots=9qBJXCKdot&sig=bk7NNo-DkKk_UeUiOCnUj8R-4CA.
- ^ Cite error: Invalid
<ref>tag; no text was provided for refs namedkarori - ^ Cite error: Invalid
<ref>tag; no text was provided for refs namedencyclo - ^ Lutz 2005, p. 16.
- ^ Gill, Brian & Whitaker, Tony. 1996. New Zealand Frogs and reptiles. David Bateman publishing, pp. 22-24. ISBN 1869532643
- ^ Colenso, W. (1885). "Notes on the Bones of a Species of Sphenodon, (S. diversum, Col.,) apparently distinct from the Species already known." (PDF). Transactions and Proceedings of the Royal Society of New Zealand 18: 118–128. http://rsnz.natlib.govt.nz/volume/rsnz_18/rsnz_18_00_000850.pdf.
Further reading[]
- Daugherty, Charles and Cree, Alison. (1990). Tuatara: a survivor from the dinosaur age. New Zealand Geographic 6 (April–June 1990): 60.