Turtle

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For other uses, see Turtle (disambiguation).
Turtles
Temporal range: Late Triassic – Holocene, 215–0Ma
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Florida box turtle Terrapene carolina
Scientific classification e
Kingdom:Animalia
Phylum:Chordata
Clade:Sauropsida
(unranked):incertae sedis
Order:Testudines (=Chelonii)
Linnaeus, 1758 [1]
Suborders
Cryptodira
Pleurodira
†Proganochelydia
and see text
Diversity
14 extant families with ca. 300 species
blue: sea turtles, black: land turtles
Sea turtle at Henry Doorly Zoo, Omaha NE
Turtles are reptiles of the order Chelonii[2] or Testudines characterised by a special bony or cartilaginous shell developed from their ribs and acting as a shield.[3] The scientific term turtle embraces the species known in general usage as tortoises, sea turtles and terrapins as well as all turtles, which term is commonly used to refer only to swimming species.
The order Chelonii or Testudines includes both extant (living) and extinct species. The earliest known turtles date from 220 million years ago,[4] making turtles one of the oldest reptile groups and a more ancient group than lizards, snakes or crocodiles. Of the many species alive today, some are highly endangered.[5]
Like all other extant reptiles, turtles are ectotherms—their internal temperature varies according to the ambient environment, commonly called cold-blooded. However, because of their high metabolic rate, leatherback sea turtles have a body temperature that is noticeably higher than that of the surrounding water.
Like other amniotes (reptiles, dinosaurs, birds, and mammals), they breathe air and do not lay eggs underwater, although many species live in or around water.

Turtle, tortoise, or terrapin

The use of the terms turtle, tortoise, and terrapin is not straightforward.[6] All animals with a shell and backbone are scientifically classified as turtles, and the word turtle is used to describe all members.[7][8] In general use, the term tortoise usually refers to any non-swimming turtle,[8] and scientifically tortoises are the Testudinidae family, only one of the 14 extant turtle families.[9] Terrapin is an Algonquian word for turtle and is used for several species of small, edible, hard-shell turtles, typically those found in brackish waters,[10][7] which do not form a coherent group.
The word chelonian is popular among veterinarians, scientists, and conservationists working with these animals as a catch-all name for any member of the superorder Chelonia, which includes all turtles living and extinct, as well as their immediate ancestors.[citation needed] Chelonia is based on the Greek word kelone,[11] for armour or interlocking shields.[12] "Turtle" may either refer to the order as a whole, or to particular turtles which make up a form taxon that is not monophyletic.
Some languages do not have this problem, as all of these are referred to by the same name. For example, in Spanish, the word tortuga is used for turtles, tortoises, and terrapins, although the type they belong to is usually specified and added to the name, as marina for sea turtles, de río for freshwater species, and terrestre for tortoises.[citation needed]

Anatomy and morphology

Chelonia mydas in Kona, Hawaii
The largest living chelonian is the leatherback sea turtle (Dermochelys coriacea), which reaches a shell length of 200 cm (6.6 ft) and can reach a weight of over 900 kg (2,000 lb). Freshwater turtles are generally smaller, but with the largest species, the Asian softshell turtle Pelochelys cantorii, a few individuals have been reported up to 200 cm (6.6 ft). This dwarfs even the better-known alligator snapping turtle, the largest chelonian in North America, which attains a shell length of up to 80 cm (2.6 ft) and weighs as much as 113.4 kg (250 lb).[13] Giant tortoises of the genera Geochelone, Meiolania, and others were relatively widely distributed around the world into prehistoric times, and are known to have existed in North and South America, Australia, and Africa. They became extinct at the same time as the appearance of man, and it is assumed humans hunted them for food. The only surviving giant tortoises are on the Seychelles and Galápagos Islands, and can grow to over 130 cm (51 in) in length, and weigh about 300 kg (660 lb).[14]
The largest ever chelonian was Archelon ischyros, a Late Cretaceous sea turtle known to have been up to 4.6 m (15 ft) long.[15]
The smallest turtle is the speckled padloper tortoise of South Africa. It measures no more than 8 cm (3.1 in) in length and weighs about 140 g (4.9 oz). Two other species of small turtles are the American mud turtles and musk turtles that live in an area that ranges from Canada to South America. The shell length of many species in this group is less than 13 cm (5.1 in) in length.
A red-eared slider turtle with eyes closer to the end of the head, keeping only the nostrils and the eyes above the water surface
African spurred tortoise in the zoo of Sharm el-Sheikh
African spurred tortoise at a zoo in the Czech Republic

Neck folding

Turtles are divided into two groups, according to how they evolved a solution to the problem of withdrawing their necks into their shells (something the ancestral Proganochelys could not do): the Cryptodira, which can draw their necks in while contracting it under their spine; and the Pleurodira, which contract their necks to the side.

Head

Most turtles that spend most of their lives on land have their eyes looking down at objects in front of them. Some aquatic turtles, such as snapping turtles and soft-shelled turtles, have eyes closer to the top of the head. These species of turtles can hide from predators in shallow water, where they lie entirely submerged except for their eyes and nostrils. Near their eyes, sea turtles possess glands that produce salty tears that rid their body of excess salt taken in from the water they drink.
Turtles are thought to have exceptional night vision due to the unusually large number of rod cells in their retinas. Turtles have color vision with a wealth of cone subtypes with sensitivities ranging from the near ultraviolet (UV A) to red. Some land turtles have very poor pursuit movement abilities, which are normally found only in predators that hunt quick-moving prey, but carnivorous turtles are able to move their heads quickly to snap.
Turtles have rigid beaks, and use their jaws to cut and chew food. Instead of having teeth, the upper and lower jaws of the turtle are covered by horny ridges. Carnivorous turtles usually have knife-sharp ridges for slicing through their prey. Herbivorous turtles have serrated-edged ridges that help them cut through tough plants. They use their tongues to swallow food, but unlike most reptiles, they cannot stick out their tongues to catch food.

Shell

Main article: Turtle shell
The upper shell of the turtle is called the carapace. The lower shell that encases the belly is called the plastron. The carapace and plastron are joined together on the turtle's sides by bony structures called bridges. The inner layer of a turtle's shell is made up of about 60 bones that include portions of the backbone and the ribs, meaning the turtle cannot crawl out of its shell. In most turtles, the outer layer of the shell is covered by horny scales called scutes that are part of its outer skin, or epidermis. Scutes are made up of the fibrous protein keratin that also makes up the scales of other reptiles. These scutes overlap the seams between the shell bones and add strength to the shell. Some turtles do not have horny scutes. For example, the leatherback sea turtle and the soft-shelled turtles have shells covered with leathery skin, instead.
The rigid shell means turtles cannot breathe as other reptiles do, by changing the volume of their chest cavities via expansion and contraction of the ribs. Instead, they breathe in two ways. First, they employ buccal pumping, pulling air into their mouths, then pushing it into their lungs via oscillations of the floor of the throat. Secondly, when the abdominal muscles that cover the posterior opening of the shell contract, the internal volume of the shell increases, drawing air into the lungs, allowing these muscles to function in much the same way as the mammalian diaphragm.
The shape of the shell gives helpful clues about how a turtle lives. Most tortoises have a large, dome-shaped shell that makes it difficult for predators to crush the shell between their jaws. One of the few exceptions is the African pancake tortoise, which has a flat, flexible shell that allows it to hide in rock crevices. Most aquatic turtles have flat, streamlined shells which aid in swimming and diving. American snapping turtles and musk turtles have small, cross-shaped plastrons that give them more efficient leg movement for walking along the bottom of ponds and streams.
The color of a turtle's shell may vary. Shells are commonly colored brown, black, or olive green. In some species, shells may have red, orange, yellow, or grey markings, often spots, lines, or irregular blotches. One of the most colorful turtles is the eastern painted turtle, which includes a yellow plastron and a black or olive shell with red markings around the rim.
Tortoises, being land-based, have rather heavy shells. In contrast, aquatic and soft-shelled turtles have lighter shells that help them avoid sinking in water and swim faster with more agility. These lighter shells have large spaces called fontanelles between the shell bones. The shells of leatherback sea turtles are extremely light because they lack scutes and contain many fontanelles.
It has been suggested by Jackson (2002) that the turtle shell can function as pH buffer. To endure through anoxic conditions, such as winter periods trapped beneath ice or within anoxic mud at the bottom of ponds, turtles utilize two general physiological mechanisms. In the case of prolonged periods of anoxia, it has been shown that the turtle shell both releases carbonate buffers and uptakes lactic acid.[16]

Skin and molting

Snapping turtle tail, Blue Hills Reservation, Massachusetts
As mentioned above, the outer layer of the shell is part of the skin; each scute (or plate) on the shell corresponds to a single modified scale. The remainder of the skin is composed of skin with much smaller scales, similar to the skin of other reptiles. Turtles do not molt their skins all at once, as snakes do, but continuously, in small pieces. When turtles are kept in aquaria, small sheets of dead skin can be seen in the water (often appearing to be a thin piece of plastic) having been sloughed off when the animals deliberately rub themselves against a piece of wood or stone. Tortoises also shed skin, but dead skin is allowed to accumulate into thick knobs and plates that provide protection to parts of the body outside the shell.
By counting the rings formed by the stack of smaller, older scutes on top of the larger, newer ones, it is possible to estimate the age of a turtle, if one knows how many scutes are produced in a year.[17] This method is not very accurate, partly because growth rate is not constant, but also because some of the scutes eventually fall away from the shell.

Limbs

Terrestrial tortoises have short, sturdy feet. Tortoises are famous for moving slowly, in part because of their heavy, cumbersome shells, which restrict stride length.
Skeleton of snapping turtle (Chelydra serpentina)
Amphibious turtles normally have limbs similar to those of tortoises, except the feet are webbed and often have long claws. These turtles swim using all four feet in a way similar to the dog paddle, with the feet on the left and right side of the body alternately providing thrust. Large turtles tend to swim less than smaller ones, and the very big species, such as alligator snapping turtles, hardly swim at all, preferring to walk along the bottom of the river or lake. As well as webbed feet, turtles have very long claws, used to help them clamber onto riverbanks and floating logs upon which they bask. Male turtles tend to have particularly long claws, and these appear to be used to stimulate the female while mating. While most turtles have webbed feet, some, such as the pig-nosed turtle, have true flippers, with the digits being fused into paddles and the claws being relatively small. These species swim in the same way as sea turtles do (see below).
Sea turtles are almost entirely aquatic and have flippers instead of feet. Sea turtles fly through the water, using the up-and-down motion of the front flippers to generate thrust; the back feet are not used for propulsion, but may be used as rudders for steering. Compared with freshwater turtles, sea turtles have very limited mobility on land, and apart from the dash from the nest to the sea as hatchlings, male sea turtles normally never leave the sea. Females must come back onto land to lay eggs. They move very slowly and laboriously, dragging themselves forwards with their flippers.

Ecology and life history

Sea turtle swimming
Although many turtles spend large amounts of their lives underwater, all turtles and tortoises breathe air, and must surface at regular intervals to refill their lungs. They can also spend much or all of their lives on dry land. 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 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.[18]
Like other reptiles, turtles lay eggs which are slightly soft and leathery. 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 from 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. Large numbers of eggs are deposited in holes dug into mud or sand. They are then covered and left to incubate by themselves. Depending on the species, the eggs will typically take 70-120 days to hatch.[19] When the turtles hatch, they squirm their way to the surface and head toward the water. There are no known species in which the mother cares for the young.
Sea turtles lay their eggs on dry, sandy beaches. Immature sea turtles are not cared for by the adults. Turtles can take many years to reach breeding age, and in many cases breed every few years rather than annually.
Researchers have recently discovered a turtle’s organs do not gradually break down or become less efficient over time, unlike most other animals. It was found that the liver, lungs, and kidneys of a centenarian turtle are virtually indistinguishable from those of its immature counterpart. This has inspired genetic researchers to begin examining the turtle genome for longevity genes.[20]
A group of turtles is known as a bale.[citation needed]

Diet

A Green sea turtle grazing on seagrass at Akumal, Mexico
A turtle's diet varies greatly depending on the environment in which it lives. Adult turtles typically eat aquatic plants;[citation needed] invertebrates such as insects, snails and worms; and have been reported to occasionally eat dead marine animals. Several small freshwater species are carnivorous, eating small fish and a wide range of aquatic life. However, protein is essential to turtle growth and juvenile turtles are purely carnivorous.
Sea turtles typically feed on jellyfish, sponge and other soft-bodied organisms. Some species of sea turtle with stronger jaws have been observed to eat shellfish while some species, such as the green sea turtle do not eat any meat at all and, instead, have a diet largely made up of algae.[21]

Systematics and evolution

See also: List of Testudines families
Odontochelys is the oldest known turtle genus
"Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904
The first proto-turtles are believed to have existed in the late Triassic Period of the Mesozoic era, about 220 million years ago, and their shell, which has remained a remarkably stable body plan, is thought to have evolved from bony extensions of their backbones and broad ribs that expanded and grew together to form a complete shell that offered protection at every stage of its evolution, even when the bony component of the shell was not complete. This is supported by fossils of the freshwater Odontochelys semitestacea or "half-shelled turtle with teeth", from the late Triassic, which have been found near Guangling in southwest China. Odontochelys displays a complete bony plastron and an incomplete carapace, similar to an early stage of turtle embryonic development.[4] Prior to this discovery, the earliest-known fossil turtles were terrestrial and had a complete shell, offering no clue to the evolution of this remarkable anatomical feature. By the late Jurassic, turtles had radiated widely, and their fossil history becomes easier to read.
Their exact ancestry has been disputed. It was believed they are the only surviving branch of the ancient evolutionary grade Anapsida, which includes groups such as procolophonids, 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 zygomatic arch). The millerettids, protorothyrids, and pareiasaurs became extinct in the late Permian period, and the procolophonoids during the Triassic.[22]
However, it was later suggested the anapsid-like turtle skull may be due to reversion rather than to anapsid descent. More recent morphological phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria.[23][24] All molecular studies have strongly upheld the placement of turtles within diapsids; some place turtles within Archosauria,[25] or, more commonly, as a sister group to extant archosaurs,[26][27][28][29] though an analysis conducted by Lyson et al. (2012) recovered turtles as the sister group of lepidosaurs instead.[30] Reanalysis of prior phylogenies suggests 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 broadly enough for constructing the cladogram. Testudines were suggested to have diverged from other diapsids between 200 and 279 million years ago, though the debate is far from settled.[23][26][31] Even the traditional placement of turtles outside Diapsida cannot be ruled out at this point. A combined analysis of morphological and molecular data conducted by Lee (2001) found turtles to be anapsids (though a relationship with archosaurs couldn't be statistically rejected).[32] Similarly, a morphological study conducted by Lyson et al. (2010) recovered them as anapsids most closely related to Eunotosaurus.[33] A molecular analysis of 248 nuclear genes from 16 vertebrate taxa suggests that turtles are a sister group to birds and crocodiles (the Archosauria).[34] The date of separation of turtles and birds and crocodiles was estimated to be 255 million years ago. The most recent common ancestor of living turtles, corresponding to the split between Pleurodira and Cryptodira, was estimated to have occurred around 157 million years ago. This last estimate may conflict with the fossil record depending on whether the genus Kayentachelys, whose fossils date to around 190 million years ago, is the earliest known member of Cryptodira[35] or lies outside the least inclusive clade containing Cryptodira and Pleurodira.[36][37] Through utilizing the first genomic-scale phylogenetic analysis of ultraconserved elements (UCEs) to investigate the placement of turtles within reptiles, Crawford et al. (2012) also suggest that turtles are a sister group to birds and crocodiles (the Archosauria).[38]
The earliest known fully shelled turtle is the late-Triassic Proganochelys. The genus species already had many advanced turtle traits, and thus probably had in its ancestry many millions of years of preceding turtle evolution and species. It did lack the ability to pull its head into its shell (and it had a long neck), and had a long, spiked tail ending in a club, a body form similar to that of ankylosaurs, resulting from convergent evolution.
Turtles are divided into two extant suborders: the Cryptodira and the Pleurodira. The Cryptodira is the larger of the two groups and includes all the marine turtles, the terrestrial tortoises, and many of the freshwater turtles. The Pleurodira are sometimes known as the side-necked turtles, a reference to the way they withdraw their heads into their shells. This smaller group consists primarily of various freshwater turtles.
Chart of the two extant suborders, extinct groups that existed within these two suborders are shown as well

Turtle genera with basal or uncertain phylogenetic position

Suborder †Proganochelydia

Fossil of Proganochelys quenstedti, it is one of the oldest true turtles presently known. Unlike modern Testudines, Proganochelys was not able to hide its head under the shell.

Suborder Cryptodira

The African helmeted turtle (Pelomedusa subrufa) is a pleurodire. Pleurodires hide their head sideways.
Basal genera
Infraorder †Paracryptodira
Infraorder Eucryptodira

Suborder Pleurodira

Distribution

Seven species of marine turtles are found worldwide. Of these, five have been recorded in Europe.[41]

Fossil record

Turtle fossils of hatchling and nestling size have been documented in the scientific literature.[42] Paleontologists from North Carolina State University have found the fossilized remains of the world's largest turtle in a coal mine in Colombia. The specimen named as Carbonemys cofrinii is around 60 million years old and nearly 8 ft long.[43]
On a few rare occasions, paleontologists have succeeded in unearthing large numbers of Jurassic or Cretacious turtle skeletons accumulated in a single area (the Nemegt Formation in Mongolia, the Turtle Graveyard in North Dakota, or the Black Mountain Turtle Layer in Wyoming). The most spectacular find of this kind to date occurred in 2009 in Shanshan County in Xinjiang, where over a thousand ancient freshwater turtles apparently died after the last water hole in an area dried out during a major drought.[44][45]

Genomics

Turtles possess diverse chromosome numbers (2N = 28-66) and a myriad of chromosomal rearrangements have occurred during evolution.[46]

As pets

Red-eared slider basking on a floating platform under a sun lamp
Turtles, particularly small terrestrial and freshwater turtles, are commonly kept as pets. Among the most popular are Russian tortoises, spur-thighed tortoises, and red-eared sliders.[47]
In the United States, due to the ease of contracting salmonellosis through casual contact with turtles, the U.S. Food and Drug Administration (FDA) established a regulation in 1975 to discontinue the sale of turtles under 4 in (100 mm).[48] It is illegal in every state in the U.S. for anyone to sell any turtles under 4 inches (10 cm) long. Many stores and flea markets still sell small turtles due to a loophole in the FDA regulation which allows turtles under 4 in (100 mm) to be sold for educational purposes.[49][50]
Some states have other laws and regulations regarding possession of red-eared sliders as pets because they are looked upon as invasive species or pests where they are not native, but have been introduced through the pet trade. As of July 1, 2007, it is illegal in Florida to sell any wild type red-eared slider. Unusual color varieties such as albino and pastel red-eared sliders, which are derived from captive breeding, are still allowed for sale.[51]

As food, traditional medicine, and cosmetics

Left: The window of a restaurant serving guilinggao, decorated with a 龜 ("turtle") character
Right: Turtle plastrons among other plants and animals parts are used in traditional Chinese medicines. (Other items in the image are dried lingzhi, snake, luo han guo, and ginseng)
The flesh of turtles, calipash or calipee, was, and still is, considered a delicacy in a number of cultures.[5] Turtle soup has been a prized dish in Anglo-American cuisine,[52] and still remains so in some parts of Asia.[which?] Gopher tortoise stew was popular with some groups in Florida.[53]
Turtles remain a part of the traditional diet on the island of Grand Cayman, so much so that when wild stocks became depleted, a turtle farm was established specifically to raise sea turtles for their meat. The farm also releases specimens to the wild as part of an effort to repopulate the Caribbean Sea.[54]
Fat from turtles is also used in the Caribbean and in Mexico as a main ingredient in cosmetics, marketed under its Spanish name crema de tortuga.[55]
Turtle plastrons (the part of the shell that covers a tortoise from the bottom) are widely used in traditional Chinese medicine; according to statistics, Taiwan imports hundreds of tons of plastrons every year.[56] A popular medicinal preparation based on powdered turtle plastron (and a variety of herbs) is the guilinggao jelly;[57] these days, though, it is typically made with only herbal ingredients.

Conservation status

In February 2011, the Tortoise and Freshwater Turtle Specialist Group published a report about the top 25 species of turtles most likely to become extinct, with a further 40 species at very high risk of becoming extinct. This list excludes sea turtles, however both the leatherback and the Kemp's ridley would make the top 25 list. The report is due to be updated in four years time allowing to follow the evolution of the list. Between 48 to 54% of all 328 of their species considered threatened, turtles and tortoises are at a much higher risk of extinction than many other vertebrates. Of the 263 species of freshwater and terrestrial turtles, 117 species are considered Threatened, 73 are either Endangered or Critically Endangered and 1 is Extinct. Of the 58 species belonging to the Testudinidae family, 33 species are Threatened, 18 are either Endangered or Critically Endangered, 1 is Extinct in the wild and 7 species are Extinct. 71% of all tortoise species are either gone or almost gone. Asian species are the most endangered, closely followed by the five endemic species from Madagascar. Turtles face many threats, including habitat destruction, harvesting for consumption, and the pet trade. The high extinction risk for Asian species is primarily due to the long-term unsustainable exploitation of turtles and tortoises for consumption and traditional Chinese medicine, and to a lesser extent for the international pet trade.[58]
Efforts have been made by Chinese entrepreneurs to satisfy increasing demand for turtle meat as gourmet food and traditional medicine with farmed turtles, instead of wild-caught ones; according to a study published in 2007, over a thousand turtle farms operated in China.[59][60] Turtle farms in Oklahoma and Louisiana raise turtles for export to China as well.[60]
Turtles on tree branch over a lake in New Jersey.
Nonetheless, wild turtles continue to be caught and sent to market in large number (as well as to turtle farms, to be used as breeding stock[59]), resulting in a situation described by conservationists as "the Asian turtle crisis".[61] In the words of the biologist George Amato, "the amount and the volume of captured turtles... vacuumed up entire species from areas in Southeast Asia", even as biologists still did not know how many distinct turtle species live in the region.[62] About 75% of Asia's 90 tortoise and freshwater turtle species are estimated to have become threatened.[60]
Harvesting wild turtles is legal in a number of states in the USA.[60] In one of these states, Florida, just a single seafood company in Fort Lauderdale was reported in 2008 as buying about 5,000 pounds of softshell turtles a week. The harvesters (hunters) are paid about $2 a pound; some manage to catch as many as 30–40 turtles (500 pounds) on a good day. Some of the catch gets to the local restaurants, while most of it is exported to Asia. The Florida Fish and Wildlife Conservation Commission estimated in 2008 that around 3,000 pounds of softshell turtles were exported each week via Tampa International Airport.[63]
Nonetheless, the great majority of turtles exported from the USA are farm raised. According to one estimate by the World Chelonian Trust, about 97% of 31.8 million animals harvested in the U.S. over a three-year period (November 4, 2002 – November 26, 2005) were exported.[60][64] It has been estimated (presumably, over the same 2002–2005 period) that about 47% of the US turtle exports go to People's Republic of China (predominantly to Hong Kong), another 20% to Taiwan, and 11% to Mexico.[65][66]

See also

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Notes

  1. ^ "Testudines". Integrated Taxonomic Information System. 
  2. ^ Dubois & Bour 2010
  3. ^ Hutchinson 1996
  4. ^ a b Li et al. 2008
  5. ^ a b Barzyk 1999
  6. ^ Ernst & Lovich 2009, p. 2
  7. ^ a b Ernst & Lovich 2009, p. 3
  8. ^ a b Fergus 2007
  9. ^ Iverson, Kimerling & Kiester 1999
  10. ^ Marshall Cavendish 2001, p. 1513 (no such page)
  11. ^ Stone 2006, p. 85
  12. ^ Brennessel 2006, p. 10
  13. ^ National Geographic 2011.
  14. ^ Connor 2009
  15. ^ Everhart 2012
  16. ^ Jackson 2002
  17. ^ Pet Education 2012.
  18. ^ Priest & Franklin 2002
  19. ^ Librarian50 (June 2007). "How long does it take turtle eggs to hatch once the female turtle has buried them?". Askville by Amazon. Retrieved 31 May 2013. 
  20. ^ Angier 2012
  21. ^ "What Do Turtles Eat?". what-do-turtles-eat.info. Retrieved 31 May 2013. 
  22. ^ Laurin 1996
  23. ^ a b Rieppel & DeBraga 1996
  24. ^ Müller 2004
  25. ^ Mannen & Li 1999
  26. ^ a b Zardoya & Meyer 1998
  27. ^ Iwabe et al. 2004
  28. ^ Roos, Aggarwal & Janke 2007
  29. ^ Katsu et al. 2010
  30. ^ Lyson et al. 2012
  31. ^ Benton 2000
  32. ^ Lee 2001
  33. ^ Lyson et al. 2010
  34. ^ Chiari et al. 2012
  35. ^ a b Gafney et al. 1987
  36. ^ a b c d e Joyce 2007
  37. ^ a b c d e Anquetin 2012
  38. ^ Crawford et al. 2012
  39. ^ a b Gaffney, Tong & Meylan 2006
  40. ^ Gaffney 1996
  41. ^ King & Berrow 2009
  42. ^ Tanke & Brett-Surman 2001, pp. 206–18
  43. ^ Maugh II 2012
  44. ^ Wings et al. 2012
  45. ^ Gannon 2012
  46. ^ Valenzuela & Adams 2011
  47. ^ Alderton 1986
  48. ^ CDC 2007.
  49. ^ GCTTS 2007.
  50. ^ FDA 2012.
  51. ^ "Turtle ban begins today; New state law". newszap.com. 2007-07-01. Retrieved 2007-07-06. [dead link]
  52. ^ Turtle Soup Recipe 1881.
  53. ^ Smithonian Magazine 2001.
  54. ^ "Cayman Islands Turtle Farm". Retrieved 2009-10-28. [dead link]
  55. ^ NOAA 2003.
  56. ^ Chen, Chang & Lue 2009
  57. ^ Dharmananda 2011
  58. ^ Rhodin et al. 2011
  59. ^ a b Fish Farmer 2007.
  60. ^ a b c d e Hylton 2007
  61. ^ Cheung & Dudgeon 2006
  62. ^ Amato 2007
  63. ^ Pittman 2008
  64. ^ World Chelonian Trust: Totals 2006.
  65. ^ World Chelonian Trust: Destinations 2006.
  66. ^ World Chelonian Trust: Observations 2006.

References

Further reading

  • Iskandar, DT (2000). Turtles and Crocodiles of Insular Southeast Asia and New Guinea. Bandung: Palmedia – ITB. 
  • Pritchard, Peter Charles Howard (1979). Encyclopedia of turtles. Neptune, NJ: T.F.H. Publications. ISBN 0-87666-918-6. 

External links

The Wikibook Animal Care has a page on the topic of: Turtle

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