Turtle
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? Turtles |
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Families
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| Testudines, Chelonia |
Turtles are reptiles of the order Testudines (all living turtles belong to the crown group Chelonia), most of whose body is shielded by a special bony or cartilagenous shell developed from their ribs. The term turtle is usually used for the aquatic species, though aquatic fresh water turtles are also called terrapins. The term is sometimes used (esp. in North America) to refer to all members of the order, including tortoises, which are predominantly land-based. The order of Testudines includes both extant (living) and extinct species. About 300 species are alive today. Some species of turtles are highly endangered.
Evolution
The first turtles are believed to have existed in the era of the dinosaurs, 200 million years ago. Their exact ancestry is disputed. It was believed that they are the only surviving branch of the ancient clade Anapsida, which includes groups such as procolophonoids, millerettids, protorothyrids and pareiasaurs. All Anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygoid arch). Most anapsids became extinct in the late Permian period, except procolophonoids and possibly the precursors of the testudines (turtles).
However, it was recently suggested that the Anapsid-like turtle skull may be due to convergent evolution rather than to anapsid descent. More recent phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. All molecular studies have strongly upheld this new phylogeny, though some place turtles closer to Archosauria. Re-analysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa were broadly enough for constructing the cladogram. While the issue is far from resolved, most scientists now lean towards a Diapsid origin for turtles.
Order Testudines - Turtles
Suborder
Paracryptodira
(extinct)
Suborder Cryptodira
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- Family Chelydridae ( Snapping Turtles)
- Superfamily Testudinoidea
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- Family Haichemydidae (extinct)
- Family Sinochelyidae (extinct)
- Family Lindholmemydidae (extinct)
- Family Testudinidae (Tortoises)
- Family Bataguridae (Asian River Turtles, Leaf and Roofed Turtles, Asian Box Turtles)
- Family Emydidae (Pond Turtles/Box and Water Turtles)
- Superfamily Trionychoidea
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- Family Adocidae (extinct)
- Family Carettochelyidae (Pignose Turtles)
- Family Trionychidae (Softshell Turtles)
- Superfamily Kinosternoidea
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- Family Dermatemydidae (River Turtles)
- Family Kinosternidae (Mud and Musk Turtles)
- Family Platysternidae (Big-headed Turtles)
- Superfamily Chelonioidea
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- Family Toxochelyidae (extinct)
- Family Cheloniidae ( Sea Turtles)
- Family Thalassemyidae (extinct)
- Family Dermochelyidae (Leatherback Turtles)
- Family Protostegidae (extinct)
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Suborder Pleurodira
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- Family Proterochersidae (extinct)
- Family Chelidae (Austro-American Sideneck Turtles)
- Family Araripemydidae (extinct)
- Superfamily Pelomedusoidea
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- Family Pelomedusidae (Afro-American Sideneck Turtles)
- Family Bothremydidae (extinct)
- Family Podocnemididae (Madagascan Big-headed and American Sideneck River Turtles)
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