Turtle

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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, aquatic fresh-water turtles also being referred to as terrapins. The term is also used (esp. 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 varieties. About 300 species are alive today. When a turtle is in its egg the temperature determines whether it's male or female: a higher temperature becoming a female, a lower temperature becoming a male.

Related Topics:
Reptile - Bony - Cartilagenous - Shell - North America - Tortoise - Extinct

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Sea turtles grow to large sizes and live in the oceans in the temperate and tropical regions of the earth. Pond turtles (or terrapins) are generally of a much smaller size, while land based terrapins (or tortoises) can be as big as the sea turtles. The measured sizes of turtles varies from a few centimetres (forest/jungle species) to up to two meters (the leatherback and the Galapagos tortoises). All turtles have a protective shell around their bodies. The top part of their case is called the carapace, the underside is the plastron, and the two are connected by the bridge. Turtles generally live a long time; some individuals are known to have lived longer than 150 years. The oldest tortoise on record is known to have lived at least 188 years.

Related Topics:
Sea turtle - Tropical - Carapace - Plastron - Oldest tortoise on record

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The first turtles are believed to have already existed in the era of the dinosaurs, some 200 million years ago. Turtles are the only surviving branch of the even more ancient clade Anapsida, which includes groups such as the procolophonoids, millerettids and pareiasaurs. All anapsid skulls lack a temporal opening. All other extant amniotes have temporal openings (although in mammals the hole has become the zygoid arch). Most of the anapsids became extinct in the late Permian period, with the exception of the procolophonoids and the precursors of the testudines (turtles).

Related Topics:
Dinosaur - Clade - Anapsida - Procolophonoid - Millerettid - Pareiasaur - Mammals - Permian

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However, it has recently been suggested that the anapsid condition of the turtle skull may not be a primitive character reflecting anapsid descent, but rather a case of convergent evolution. More recent phylogenetic studies with this in mind have 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 that affirmed an anapsid ancestry suggests that their inclusion of turtles within Anapsida was due to both the starting assumption that they were anapsid (most prior phylogenies concerned what sort of anapsid they were) and also due to insufficiently broad sampling of fossil and extant taxa for construction of the cladogram. While the issue is far from resolved, most scientists now lean towards a Diapsid origin for turtles.

Related Topics:
Diapsids - Squamata - Archosauria

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Even though they spend large amounts of their lives underwater, turtles are air-breathing reptiles, and must surface at regular intervals to refill their lungs with fresh air. They also spend part of their lives on dry land. 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 (white) contains a different protein than does a bird's egg, such that it will not coagulate when cooked. Turtle eggs prepared to eat would consist mainly of yolk. Turtles are now highly endangered, largely as a result of beach development and over hunting.

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Aquatic respiration in Australian freshwater turtles is currently being studied. Some species have large cloacal cavities that are lined with many finger-like projections. These projections, called "papillae", have a rich blood supply, and serve to increase the surface area of the cloaca. The turtles can take up dissolved oxygen from the water using these papillae, in much the same way that fish use gills to respire.

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The ornate box turtle is the state reptile of Kansas. It is interesting however, that turtles as classroom pets, have been banned in the state, as well as many others.

Related Topics:
Kansas - Pet

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