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?Turtles
Fossil range: Template:Fossil rangeLate Triassic - Recent
"Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904
"Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Superclass: Tetrapoda
Class: Reptilia
Subclass: Anapsida
Superorder: Chelonia
Macartney, 1802
Order: Testudines
Linnaeus, 1758
Diversity
14 extant families with ca. 300 species
blue: sea turtles, black: land turtles
blue: sea turtles, black: land turtles
Suborders

Cryptodira
Pleurodira
and see text

Turtles, tortoises, and terrapins are ectothermic reptiles, most of whose body is shielded by a special bony or cartilagenous shell developed from their ribs. They belong to an anapsid lineage, as can be seen from their solid skullcap. About 300 species are alive today; some are highly endangered.

The order to which the turtles belong is usually called Testudines. Sometimes Chelonia is given as a junior synonym, but this might strictly speaking be incorrect. For most purposes, the differences are minor however: The Chelonia are simply the Testudines plus the "proto-turtle" Australochelys africanus, a turtlelike anapsid from the Jurassic which lacked some of the Testudines' apomorphies but is overall of very uncertain placement due to the lack of material. If Murrhardtia staeschei (known from a rather complete shell) and Palaeochersis talampayensis are close relatives of Australochelys, the Chelonia and Testudines are indeed likely to be effectively synonymous in content – though the former would remain a valid superorder, to which any turtle ancestors to be found in the future would be assigned.

The oldest fossils of the Testudines actually predate Australochelys. They are the basal turtle genera Chinlechelys, Odontochelys and Proganochelys[1] which lived in Late Triassic Eurasia about 220-210 million years ago. This makes turtles one of the oldest "reptile" groups, and a much more ancient group than lizards and snakes. Priscochelys, about 230 million years old, was initially believed to represent the most ancient turtle, but actually appears to be a cyamodontoid placodont.

CharacteristicsEdit

The defining feature of the testudines is the presence of a bony shell comprising an upper carapace and a lower plastron, both composed of solid bony plates. In most families, this bony shell is further covered by a layer of thick horny scales, which form the visible part of the shell, but some have a softer, leathery, covering.[2]

Living testudines lack teeth, having a horny beak, which is sharpened or serrated to cut flesh or plant matter. Testudines also have strong limbs to lift their heavy bodies. The shape of the limb is variable, however, with land dwelling species typically fusing the toes into a solid clump, freshwater species having distinct, but webbed, toes, and marine species having powerful flippers.[2]

Testudines lay eggs in a nest chamber, but no species displays parental care. Instead, the young are left to fend for themselves from the moment they hatch. Incubation time varies greatly between species, but two to three months is typical.[2]

SystematicsEdit

Main article: List of Testudines families

There are about 300 living species of Testudines, grouped into two living suborders with fourteen living and many more extinct families, and one entirely prehistoric suborder which is somewhat disputed and might just be a paraphyletic assemblage of basal Testudines.[3].

Basal and incertae sedis cheloniansEdit

Suborder †ProganochelydiaEdit

File:Proganochelys Quenstedti.jpg

Suborder CryptodiraEdit

Basal genera

Infraorder †Paracryptodira

Infraorder Eucryptodira

Suborder PleurodiraEdit

FootnotesEdit

  1. Formerly known as Triassochelys
  2. 2.0 2.1 2.2 Obst (1998)
  3. See references in Haaramo (2008)

ReferencesEdit

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Wikimedia Commons has media related to:
  • Haaramo, Mikko (2008): Mikko's Phylogeny Archive - Hallucicrania. Version of 2008-MAR-11. Retrieved 2008-MAY-07.
  • Obst, Fritz Jürgen (1998): [Testudines]. In: Cogger, H.G. & Zweifel, R.G. (eds.): Encyclopedia of Reptiles and Amphibians: 108-111. Academic Press, San Diego. ISBN 0-12-178560-2

Template:Reptiles

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