Testudines

Taxobox
name = Turtles
fossil_range = Fossil range|210|0Late Triassic - Recent

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image_width = 240px
image_caption = "Chelonia" from Ernst Haeckel's "Kunstformen der Natur", 1904
regnum = Animalia
phylum = Chordata
subphylum = Vertebrata
superclassis = Tetrapoda
classis = Reptilia
subclassis = Anapsida
superordo = Chelonia
superordo_authority = Macartney, 1802
ordo = Testudines
ordo_authority = Linnaeus, 1758
range_

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range_map_width = 240px
range_map_caption = blue: sea turtles, black: land turtles
diversity_link= List of Testudines families
diversity= 14 extant families with ca. 300 species
subdivision_ranks = Suborders
subdivision =
Cryptodira
Pleurodira See text for families.

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 is strictly speaking 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. The oldest fossils of the Testudines actually predate "Australochelys". They are the basal turtle genus "Proganochelys" [Formerly known as "Triassochelys"] which lived in Late Triassic Eurasia about 210 million years ago, making turtles one of the oldest reptile groups, and a much more ancient group than lizards and snakes.

Characteristics

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, coveringcite book |editor=Cogger, H.G. & Zweifel, R.G.|author= Obst, Fritz Jurgen|year=1998|title=Encyclopedia of Reptiles and Amphibians|publisher= Academic Press|location=San Diego|pages= 108-111|isbn= 0-12-178560-2] .

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.

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.

ystematics

There are about 300 living species of testudine, grouped into two suborders and fourteen families [See references in Haaramo (2008)] .

Basal chelonians

* Genus "Australochelys" (basal Chelonia)
* Genus "Proganochelys" (basal Testudines)

uborder Cryptodira

Basal genera
* Genus "Kayentachelys"
* Genus "Indochelys"Infraorder †Paracryptodira
*Basal and "incertae sedis"
**Family †Kallokibotiidae
**Family †Mongolochelyidae
**Family †Pleurosternidae
**Family †Solemydidae
*Superfamily †Baenoidea
**Family †Baenidae
**Family †Macrobaenidae
**Family †NeurankylidaeInfraorder Eucryptodira
* †"Sinemys" wuerhoensis"
* Genus †"Chubutemys" (Meiolaniidae?)
* Genus †"Hangaiemys" (Macrobaenidae?)
* Genus †"Judithemys"
* Genus †"Osteopygis"
* Genus †"Planetochelys"
* Family Chelydridae (snapping turtles)
* Family †Eurysternidae
* Family †Macrobaenidae
* Family †Meiolaniidae (horned turtles)
* Family †Plesiochelyidae
* Family †Sinemydidae
* Family †Xinjiangchelyidae
*Superfamily Chelonioidea (sea turtles)
**Family †Protostegidae
**Family †Thalassemyidae
**Family †Toxochelyidae
**Family Cheloniidae (green sea turtles and relatives)
**Family Dermochelyidae (leatherback turtles)
*Superfamily Testudinoidea
**Family †Haichemydidae
**Family †Lindholmemydidae
**Family †Sinochelyidae
**Family Platysternidae (big-headed turtle)
**Family Emydidae (pond, box and water turtles)
**Family Geoemydidae (Asian river turtles, Asian leaf turtles, Asian box turtles and roofed turtles)
**Family Testudinidae (tortoises)
*Superfamily Trionychoidea
**Family †Adocidae
**Family Carettochelyidae (pignose turtles)
**Family Dermatemydidae (river turtles)
**Family Kinosternidae (mud turtles)
**Family Trionychidae (softshell turtles)

uborder Pleurodira

Basal and "incertae sedis"
*Family †Araripemydidae
*Family †Proterochersidae
*Family Chelidae (Austro-American sideneck turtles)Superfamily Pelomedusoidea
*Family †Bothremydidae
*Family Pelomedusidae (African sideneck turtles)
*Family Podocnemididae (Madagascan big-headed and American sideneck river turtles)

Footnotes

References

* (2008): Mikko's Phylogeny Archive - [http://www.helsinki.fi/~mhaaramo/metazoa/deuterostoma/chordata/reptilia/parareptilia/hallucicrania.html Hallucicrania] . Version of 2008-MAR-11. Retrieved 2008-MAY-07.