Turtle Turtle The Illustrated Man Category="Pet reptiles"Category="Reptiles"Category="Turtles"
For other uses, see Turtle (disambiguation).

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Turtles
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Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Reptilia
Order:Testudines
Linnaeus,  1758
Families
See text

Turtles are reptiles of the order 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. Turtles are now highly endangered, largely due to beach development and over-hunting.

Description

All turtles have a protective shell around their bodies. The top part of the shell is called the Carapace, the bottom is called the Plastron, and the two are connected by a bridge.

Sea turtles grow to large sizes and live in the oceans in the Temperate and tropical regions of Earth. Pond turtles (terrapins) are usually much smaller, while some land terrapins (tortoises) are as large as sea turtles. The sizes of turtles vary from a few centimetres (Forest and Jungle species) to two meters (the leatherback turtle and the Galapagos tortoise).

Turtles generally live a long time; some individuals are known to have lived longer than 150 years. The oldest tortoise on record is Tui Malila, known to have lived at least 188 years.

Sea turtles lay their eggs on dry sandy beaches. The eggs of the largest species are spherical, while the eggs of the rest are elongated. Their albumen is White and contains a different Protein than do bird eggs, such that it will not coagulate when cooked. Turtle eggs prepared to eat consist mainly of yolk. In some species, temperature determines whether an egg develops into a male or a female: a higher temperature causes a female, a lower temperature causes a male.

Although they spend large proportions of their lives underwater, turtles are air-breathing reptiles, and must surface at regular intervals to refill their lungs with fresh Air. However, aquatic respiration in Australian freshwater turtles is currently being studied. Some species have large cloacal cavities lined with many finger-like projections. These projections, called "papillae", have a rich blood supply, and increase the surface area of the cloaca. The turtles can take up dissolved Oxygen from the water through these papillae, in much the same way that fish use gills.

Turtles have a gelatinous substance in their upper and lower shell, called calipash and calipee respectively, the calipash being of a dull greenish and the calipee of a light yellow color.

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 Chelonia - Turtles

[image] [image] Suborder Cryptodira [image]

Suborder Pleurodira

Turtles in pop culture

Turtles are depicted in Western culture as, snapping turtles aside, easygoing and patient creatures.

See also

External links

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Wikibooks has a Dichotomous Key related to this taxon:
Testudines