Common snapping turtle Wikipedia

Common snapping turtle Wikipedia

Turtles are diapsids of the particular order Testudines (or Chelonii) seen as a a special bony or cartilaginous shell developed from their ribs and acting as a protect. "Turtle" may refer to the order as a whole (American English) or to fresh-water and sea-dwelling testudines (British English). The order Testudines includes each extant (living) and vanished species. The earliest identified members of this team date from 220 million years ago, making turtles one of the oldest reptile groups and a more ancient group compared to snakes or crocodilians. Associated with the 356 known types alive today, some are usually highly endangered.

Turtles are ectotherms—animals commonly called cold-blooded—meaning that their internal temperature varies according to the ambient environment. However, since of their high metabolic rate, leatherback sea turtles have a body temperature that is noticeably increased than that of the particular surrounding water. Turtles are classified as amniotes, along with other reptiles, parrots, and mammals. Like some other amniotes, turtles breathe air and do not lay down eggs underwater, although numerous species live in or around water. The research of turtles is called cheloniology, after the Greek term for turtle. It is usually also sometimes called testudinology, after the Latin title for turtles.

Differences exist in usage of the common terms turtle, tortoise, and terrapin, according to the range of English being used. These terms are common names and don't reflect exact biological or taxonomic variations.

Turtle may either relate to the order since a whole, or to particular turtles that create up a form taxon which is not monophyletic, or may be restricted to only aquatic species. Tortoise usually relates to any land-dwelling, non-swimming chelonian. Terrapin can be used in order to describe several species of small, edible, hard-shell turtles, typically those found within brackish waters.

In North America, all chelonians are commonly called turtles. Tortoise is used only within mention of the fully terrestrial turtles or, more narrowly, only those members of Testudinidae, the family of modern land tortoises. Terrapin may relate to small semi-aquatic turtles that live in fresh and brackish water, specifically the diamondback terrapin (Malaclemys terrapin). Although the users of the genus Terrapene dwell mostly on land, they are known as box turtles rather than tortoises. The American Society of Ichthyologists and Herpetologists uses "turtle" to describe all species of the order Testudines, whether or not they are land-dwelling or sea-dwelling, and uses "tortoise" being a more specific expression for slow-moving terrestrial types.

In the United Kingdom, the word turtle is used for water-dwelling species, including ones known in the particular US as terrapins, but not for terrestrial species, that are known only as tortoises.

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The word chelonian is usually popular among veterinarians, scientists, plus conservationists working with these types of animals like a catch-all name for any person in the superorder Chelonia, which includes almost all turtles living and wiped out, as well as their own immediate ancestors. Chelonia will be based on the Ancient greek word for turtles, χελώνη chelone; Greek χέλυς chelys "tortoise" is also utilized in the formation of scientific names of chelonians. Testudines, on the other hand, is based on the Latin word for tortoise, testudo. Terrapin comes through an Algonquian word with regard to turtle.

Some languages do not have this distinction, as all of these are referred to by the particular same name. For instance , in Spanish, the word tortuga is used for turtles, tortoises, and terrapins. A sea-dwelling turtle is tortuga marina, a freshwater types tortuga de río, plus a tortoise tortuga terrestre.

The largest living chelonian is the leatherback sea turtle (Dermochelys coriacea), which usually reaches a shell length of 200 cm (6. 6 ft) and can achieve a weight of over 900 kg (2, 500 lb). Freshwater turtles are usually generally smaller, but along with the largest species, the particular Asian softshell turtle Pelochelys cantorii, a few people have been reported upward to 200 cm (6. 6 ft). This dwarfs even the better-known alligator snapping turtle, the biggest chelonian in North America, which attains a shell length of up to 80 cm (2. six ft) and weighs as much as 113. four kg (250 lb).

Giant tortoises of the overal Geochelone, Meiolania, and others were relatively widely distributed all over the world into prehistoric times, and they are known to have got existed in North and South America, Australia, plus Africa. They became wiped out at the same time as the appearance of man, and it will be assumed humans hunted them for food. The just surviving giant tortoises are usually on the Seychelles and Galápagos Islands and can grow to over 130 cm (51 in) in duration, and weigh about 300 kg (660 lb).

The largest ever chelonian was Archelon ischyros, a Late Cretaceous sea turtle recognized to have been as much as 4. 6 m (15 ft) long.

Health and Illnesses in Pet Turtles Pets4Homes

The tiniest turtle is the speckled padloper tortoise of South Africa. It measures no more than 8 cm (3. 1 in) long and weighs about a hundred and forty g (4. 9 oz). Two other species of small turtles are the American mud turtles and musk turtles that live in an area that will ranges from Canada in order to South America. The covering duration of many species within this group is less than 13 cm (5. 1 in) in length.

Turtles are divided into 2 groups, according to how they retract their necks to their shells (something the ancestral Proganochelys could not do). The mechanism of throat retraction differs phylogenetically: the suborder Pleurodira retracts laterally aside, anterior to glenohumeral joint girdles, while the suborder Cryptodira retracts straight back again, between shoulder girdles. These motions are largely because of to the morphology plus arrangement of cervical backbone. Of all recent turtles, the cervical column is made up of nine joints plus eight vertebrae, which are usually individually independent. Since these vertebrae are not joined and are rounded, the particular neck is more flexible, being able to bend in the backwards plus sideways directions. The major function and evolutionary implication of neck retraction is usually thought to be with regard to feeding rather than security. Neck retraction and reciprocal extension allows the turtle to reach out further to capture prey while going swimming. Neck expansion creates suction when the head is thrust forward and the oropharynx is expanded, and this particular morphology suggests the retraction function is for serving purposes as the suction helps catch prey. The protection the shell provides the head when it is retracted is as a result not the main function of retraction, thus is an exaptation. As with regard to the difference between the two methods of retraction, both Pleurodirans and Cryptodirans use the quick expansion of the neck being a method of predation, therefore the difference in retraction mechanism is not really due in order to a difference in environmental niche.

Head

Most turtles that spend most associated with their lives on land have their eyes looking down at objects in front side of them. Some marine turtles, such as snapping turtles and soft-shelled turtles, have eyes closer to the top of the mind. These species of turtle can hide from predators within shallow water, where they lie entirely submerged other than for their eyes plus nostrils. Near their eye, sea turtles possess glands that produce salty holes that rid their body of excess salt taken in through the water they consume.

Turtles have rigid beaks and use their teeth to cut and munch food. Instead of getting teeth, that they appear to have lost about 150-200 million years ago, the upper and lower jaws of the turtle are usually covered by horny side rails. Carnivorous turtles usually have knife-sharp ridges for cutting through their prey. Herbivorous turtles have serrated-edged ridges that help them cut through tough plants. They use their tongues to swallow food, but in contrast to most reptiles, they can not stick out their tongues in order to catch food.

ShellPrimary article: Turtle shellThe upper shell of the turtle is called the carapace. The lower shell that encases the belly is known as the plastron. The carapace and plastron are joined up with together on the turtle's sides by bony buildings called bridges. The inner layer of a turtle's shell is made upward of about 60 our bones that include portions associated with the backbone and the ribs, meaning the turtle cannot crawl out of its shell. In most turtles, the outer layer from the shell is covered by horny scales called scutes that are part of the outer skin, or epidermis. Scutes comprise of the fibrous protein keratin that also makes up the scales of other lizards. These scutes overlap the particular seams between the covering bones and add strength towards the shell. Some turtles do not possess horny scutes; with regard to example, the leatherback sea turtle and the soft-shelled turtles have shells covered with leathery skin instead.

The shape of the covering gives helpful clues about how a turtle lives. Many tortoises have a huge, dome-shaped shell that makes it difficult for predators to crush the shell between their jaws. 1 of the few conditions is the African hot cake tortoise, which has the flat, flexible shell that will allows it to conceal in rock crevices. Most aquatic turtles have flat, streamlined shells, which help within swimming and diving. American snapping turtles and musk turtles have small, cross-shaped plastrons that give all of them more efficient leg motion for walking along the bottom of ponds and streams. Another exception will be the Belawan Turtle (Cirebon, West Java), which has sunken-back soft-shell.

The color of a turtle's shell may vary. Shells are commonly coloured brown, black, or olive green. In certain species, shells may have red, fruit, yellow, or grey marks, often spots, lines, or even irregular blotches. Probably the most vibrant turtles is the eastern painted turtle, which contains a yellow plastron and a black or olive shell with red markings around the rim.

Tortoises, being land-based, have instead heavy shells. In contrast, aquatic and soft-shelled turtles have lighter shells that will help them avoid going in water and go swimming faster with more speed. These lighter shells have got large spaces called fontanelles between the shell bone fragments. The shells of leatherback sea turtles are extremely gentle because they lack scutes and contain many fontanelles.

It has been recommended by Jackson (2002) that the turtle shell can function as pH barrier. To endure through anoxic conditions, such as winter periods trapped beneath snow or within anoxic mud at the end of ponds, turtles utilize two general physical mechanisms. In the situation of prolonged periods of anoxia, it has already been shown that the turtle shell both releases carbonate buffers and uptakes lactic acid solution.

Sea Turtle Species Sea Turtle Exploration

Breathing Turtles

Respiration, for many amniotes, is achieved by the particular contraction and relaxation of specific muscle groups (i. electronic. intercostals, abdominal muscles, and/or the diaphragm) attached with an inner rib-cage that can increase or contract the body wall thus assisting airflow out and in of the lung area. The ribs of Chelonians, however, are fused with their carapace and external to their pelvic and pectoral girdles, a function unique among turtles. This particular rigid shell is not capable of expansion, plus by rendering their rib-cage immobile, Testudines have experienced to evolve special modifications for respiration.

Turtle pulmonary ventilation occurs by using specific groups of abdominal muscle tissue attached to their viscera and shell that draw the lungs ventrally during inspiration, where air is usually drawn in via the negative pressure gradient (Boyle's Law). In expiration, the particular contraction from the transversus abdominis is the driving force by propelling the viscera into the lungs plus expelling air under positive pressure. Conversely, the relaxing and flattening of the oblique abdominis muscle pulls the transversus back down which, once more, draws air flow back into the lung area. Important auxiliary muscles utilized for ventilatory processes would be the pectoralis, which is used in conjunction with the transverse abdominis during inspiration, as well as the serratus, which movements with all the abdominal oblique associated expiration.

The lungs associated with Testudines are multi-chambered plus attached their entire size throughout the carapace. The amount of chambers may differ among taxa, though most commonly they have three lateral compartments, three medial chambers, and another terminal chamber. As previously mentioned, the act of specific abdominal muscles pulling down the viscera (or pushing back up) is exactly what allows for respiration within turtles. Specifically, it is usually the turtles large liver that pulls or forces on the lungs. Ventral to the lungs, within the coelomic cavity, the liver organ of turtles is attached directly to the right lung, and their belly is directly attached to the left lung by the ventral mesopneumonium, that is attached to their liver organ by the ventral mesentery. Whenever the liver is drawn down, inspiration begins. Assisting the lungs is the post-pulmonary septum, which is discovered in all Testudines, and it is thought to prevent the lungs from collapsing.

Edge Of The Plank: Cute Animals: Baby Sea Turtles

Turtles Pores and skin and molting

As described above, the outer coating of the shell will be part of the epidermis; each scute (or plate) on the shell refers to a single revised scale. The remainder associated with the skin has much smaller scales, similar to the pores and skin of other reptiles. Turtles do not molt their own skins all at as soon as as snakes do, yet continuously in small items. When turtles are kept in aquaria, small sheets of dead skin may be seen in the water (often appearing in order to be a thin piece of plastic) having already been sloughed off when the animals deliberately rub on their own against an item of wood or even stone. Tortoises also shed skin, but dead skin is allowed to accumulate into thick knobs and dishes that provide protection to parts of the entire body outside the shell.

By counting the rings created by the stack of smaller, older scutes along with the larger, newer ones, you are able to estimate the age group of a turtle, if one knows the number of scutes are produced in a year. This method is not very accurate, partly since growth rate is not really constant, but also since some of the scutes eventually fall away through the shell.

Turtles Limbs

Terrestrial tortoises have short, durable feet. Tortoises are popular for moving slowly, simply because of their heavy, cumbersome shells, which limit stride length.

Skeleton of snapping turtle (Chelydra serpentina)

Amphibious turtles normally have got limbs similar to the ones from tortoises, except that the particular feet are webbed plus often have long claws. These turtles swim using all four feet within a way similar to the dog paddle, with the feet on the right and left side of the body alternately providing drive. Large turtles tend to swim less than smaller sized ones, and the very big species, such because alligator snapping turtles, barely swim whatsoever, preferring in order to walk along the bottom of the river or river. As well as webbed feet, turtles have extremely long claws, used in order to help them clamber onto riverbanks and floating logs upon which they bask. Male turtles tend to have particularly long paws, and these look like utilized to stimulate the female while mating. While most turtles have webbed ft, some, like the pig-nosed turtle, have true flippers, with the digits being joined into paddles and the claws being relatively small. These species swim in the same way because sea turtles do (see below).

Sea turtles are almost entirely aquatic and have flippers instead associated with feet. Sea turtles take flight through the water, using the particular up-and-down motion of the particular front flippers to create thrust; the back feet are not used for propulsion yet can be used as rudders for steering. Compared with freshwater turtles, sea turtles have very limited mobility upon land, and in addition to the splash from the nest to the sea as hatchlings, man sea turtles normally in no way leave the sea. Females must come back on to land to lay eggs. They move very slowly and laboriously, dragging themselves forwards with their flippers.

Habits of Turtles

Senses of Turtles are thought to get exceptional night vision because of the unusually large quantity of rod cells in their retinas. Turtles possess color vision with a wealth of cone subtypes with sensitivities ranging through the near ultraviolet (UVA) to red. Some property turtles have very poor pursuit movement abilities, which are normally found just in predators that hunt quick-moving prey, but carnivorous turtles are able to move their heads rapidly to snap.

Turtles Communication

The Arrau turtle has a sizable vocal repertoire.

Whilst typically thought of since mute, turtles make various sounds when communicating. Tortoises might be vocal when courting and mating. Various species of both freshwater plus sea turtles emit numerous types of calls, often short and low regularity, from the time they are in the egg in order to whenever they are adults. These vocalizations may serve to create group cohesion when migrating.

Turtle Cleverness

See furthermore: Animal knowledge

It has been reported that wood turtles are better compared to white rats at learning to navigate mazes. Situation studies exist of turtles playing. They are doing, however, have got a very low encephalization quotient (relative brain to body mass), and their hard shells enable these to live without fast reflexes or elaborate predator avoidance strategies. In the laboratory, turtles (Pseudemys nelsoni) may learn novel operant jobs and have demonstrated a extensive memory of at least 7. 5 months.

Turtle Mating Methods

An instance of mounting behavior in turtles

Turtles are known for displaying a broad variety of mating actions, nevertheless , they are not known for forming pair-bonds or for being component of a social team. Once fertilization has occurred and an offspring has been produced, neither parent will provide care with regard to the offspring once it's hatched. Females generally outnumber males in various turtle species (such as Eco-friendly turtles), and as a result, most men will engage in multiple copulation with multiple partners all through their lifespan. However, because of to the sexual dimorphism present in most turtle species, males must develop different courting strategies or even use alternate methods in order to gain access to a potential mate. Most terrestrial varieties have males that are larger than females, and battling between males often establishes a hierarchical order within which the higher upward the order an person is, the better the particular chance is of the person getting access to the potential mate. For the majority of semi-aquatic species and bottom-walking aquatic species, combat occurs less often. Males belonging to semi-aquatic and bottom-walking species instead often make use of their larger size benefit to forcibly mate with a female. In fully marine species, males are frequently smaller than females and therefore they can not use the particular same strategy as their semi-aquatic relatives, which relies on overwhelming the females with power. Males in this class resort to using courtship displays in an try to gain mating accessibility to a female.

Fighting Between Males Turtles

Saddle back again Galapagos tortoise

Wood turtles are an example of a terrestrial species where the particular males have a hierarchical ranking system based on dominance through fighting, plus it's shown that the particular males with the greatest rank and thus the particular most wins in fights have the most offspring.

Galapagos tortoises are another example of a species which has a hierarchical rank which is determined by dominance displays, and accessibility to food and friends is regulated by this dominance hierarchy. Two man saddle backs most usually compete for access in order to cactus trees, that is their particular source of food. The winner is the person who stretches their neck of the guitar the highest, which individual gets access to the cactus tree, which can attract potential mates.

Pressure Mating Turtles

Male (left) and female (right) radiated tortoise

The male scorpion dirt turtle is an example of a bottom-walking marine species that depends on overpowering females with its bigger size as a mating strategy. The male approaches the female from the back, and often resorts in order to aggressive methods like biting the female's tail or hind limbs, then the mounting behavior in which the male clasps the particular edges of her carapace with his forelimbs and hind limbs to keep the girl in position. The man follows this action simply by laterally waving his head and sometimes biting the particular female's head in an attempt to get her to withdraw her go to her shell. This reveals her cloaca, and along with it exposed, the male can attempt copulation simply by wanting to insert his grasping tail.

Male radiated tortoises will also be known to use the force mating technique wherein they use surrounding vegetation to trap or even prevent females from getting away, then pin them lower for copulation.

Turtles Courtship Displays

Red-eared sliders are an sort of a fully aquatic species where the male performs a courtship behavior. Within this case the man extends his forelegs with all the palms facing out plus flutters his forelegs within the female's face. Female options are important in this technique, as well as the females of several species, such as green sea turtles, aren't usually receptive. Therefore, they've progressed certain behaviors to avoid the male's attempts from copulation, such as swimming away, confronting the male followed by biting, or a refusal position within which the female presumes a vertical position along with her limbs widely outspread and her plastron facing the male. If the water is too shallow to perform the refusal position, the females may resort to beaching themselves, which is a confirmed deterrent method, as the particular males will not follow them ashore.

Ecology and life history of turtles

Ocean turtle swimming

Although several turtles spend large amounts of their lives underwater, all turtles and tortoises breathe air and should surface at regular time periods to refill their lungs. They can also invest much or all associated with their lives on dry land. Aquatic respiration within Australian freshwater turtles will be currently being studied. Some species have large cloacal cavities that are lined numerous finger-like projections. These projections, called papillae, have a rich blood supply and increase the surface area of the cloaca. The particular turtles can take up dissolved oxygen from the water providing a few papillae, in much the same way that fish use gills to respire.

Like additional reptiles, turtles lay ovum that are slightly gentle and leathery. The eggs of the largest species are usually spherical while the eggs of the rest are usually elongated. Their albumen will be white and contains a different protein from bird eggs, such that it will certainly not coagulate when cooked. Turtle eggs prepared to eat consist mainly of yolk. In some species, temp determines whether an egg cell develops into a male or even a female: a higher temperature the female, a lower temperature the man. Large numbers of eggs are deposited in openings dug into mud or even sand. They are then covered and left in order to incubate on their own. Depending on the species, the ovum will typically take 70–120 days to hatch. Once the turtles hatch, they squirm their way to the surface and head against the water. You will find no known species where the mother cares for her young.

Sea turtles lay their particular eggs on dry, sandy beaches. Immature sea turtles are not cared with regard to by the adults. Turtles can take many yrs to reach breeding age, and in many cases, breed of dog every few years instead of annually.

Researchers have lately uncovered a turtle's organs do not slowly but surely break lower or become less effective over time, unlike the majority of other animals. It has been found that the liver organ, lungs, and kidneys of a centenarian turtle are practically indistinguishable from those of its immature counterpart. This has inspired hereditary researchers to start examining the turtle genome with regard to longevity genes.

A team of turtles is actually a bale.

Turtles Diet

A green ocean turtle grazing on

A turtle's diet varies greatly according to the atmosphere by which it lives. Grownup turtles typically eat aquatic plants; (citation needed) invertebrates such as insects, snails, and worms; and have already been reported to occasionally consume dead marine animals. Several small freshwater species are carnivorous, eating small seafood and many aquatic lifestyle. However, protein is essential to turtle growth and juvenile turtles are solely carnivorous.

Sea turtles usually feed on jellyfish, sponges, and other soft-bodied microorganisms. Some species with more robust jaws have been noticed to eat shellfish, whilst others, such as the green sea turtle, do not eat meat at all and, instead, have a diet mainly made up of algae.

Systematics and evolution of Turtles

Main article: Turtle classification

See|Observe|Notice} also: List of Testudines families

Life restoration of Odontochelys semitestacea, the oldest known turtle relative with a partial shell

"Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904

Dependent on body fossils, the first proto-turtles are believed to have existed in the particular late Triassic Period of the Mesozoic era, regarding 220 million years ago, and their shell, which has remained a amazingly stable body plan, is usually considered to have evolved through bony extensions of their backbones and broad ribs that expanded and increased together to form a complete shell that offered protection at every phase of its evolution, actually when the bony element of the shell was not really complete. This is supported by fossils of the freshwater Odontochelys semitestacea or even "half-shelled turtle with teeth", from the late Triassic, which have been discovered near Guangling in southwest China. Odontochelys displays the complete bony plastron plus an incomplete carapace, similar to an early stage of turtle embryonic development. Just before this discovery, the particular earliest-known fossil turtle forefathers, like Proganochelys, were terrestrial and had a complete covering, offering no clue in order to the evolution of this amazing anatomical feature. By the late Jurassic, turtles had radiated widely, and their fossil history becomes easier to go through.

Their actual ancestry has been disputed. It had been believed they are the particular only surviving branch associated with the ancient evolutionary grade Anapsida, which includes groups for example procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporal opening while all some 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 plus the procolophonoids during the particular Triassic.

However , it was later recommended the anapsid-like turtle skull might 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 in order to Archosauria.[55][56] All molecular studies have got strongly upheld the placement of turtles within diapsids; some place turtles within Archosauria, or, more frequently, as a sister group to extant archosaurs,[58][59][60][61] though an analysis conducted by Lyson et 's. (2012) recovered turtles as the sister group of lepidosaurs instead. Reanalysis of earlier phylogenies suggests that they classified turtles as anapsids both simply because they assumed this classification (most of them studying what sort associated with anapsid turtles are) and because they did not sample fossil and extant taxa broadly enough regarding constructing the cladogram. Testudines were suggested to get diverged from other diapsids in between 200 and 279 million years ago, though the particular debate is far through settled. Even the conventional placement of turtles outside Diapsida cannot be ruled out at this point. A combined analysis associated with morphological and molecular data conducted by Lee (2001) found turtles to end up being anapsids (though a relationship with archosaurs couldn't be statistically rejected).[64] Similarly, a morphological study conducted by Lyson et al.. (2010) recovered them as anapsids most closely related to Eunotosaurus. The molecular analysis of 248 nuclear genes from sixteen vertebrate taxa shows that turtles are a sister team to birds and crocodiles (the Archosauria).[66] The date of splitting up of turtles and birds and crocodiles was estimated to be 255 mil years ago. The most recent common ancestor of residing turtles, corresponding towards the divided between Pleurodira and Cryptodira, was estimated to have occurred around 157 million yrs ago. The oldest conclusive crown-group turtle (member of the modern clade Testudines) will be the species Caribemys oxfordiensis through the late Jurassic period (Oxfordian stage). Through utilizing the very first genomic-scale phylogenetic analysis of ultraconserved elements (UCEs) to check into the placement of turtles within reptiles, Crawford et al. (2012) also recommend that turtles are the sister group to parrots and crocodiles (the Archosauria).

The first genome-wide phylogenetic analysis was completed by Wang et al. (2013). Using the draft genomes of Chelonia mydas and Pelodiscus sinensis, the group used largest turtle data started date in their analysis and concluded that turtles are likely a sister group of crocodilians and birds (Archosauria). This placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics as it right now possesses an anapsid-like skull.

The earliest known fully shelled member of the turtle lineage is the late Triassic Proganochelys. This genus already possessed numerous advanced turtle traits, and thus probably indicates numerous millions of years of preceding turtle evolution; this is further supported by evidence from fossil tracks from the Early Triassic of the United Declares (Wyoming and Utah) and from the Middle Triassic of Germany, indicating that will proto-turtles already existed since early as the first Triassic. Proganochelys lacked the ability to draw its head into the shell, had a lengthy neck, and had the long, spiked tail ending in a club. While this body form is similar to those of ankylosaurs, it resulted from convergent advancement.

Turtles are divided into two extant suborders: Cryptodira and Pleurodira. The Cryptodira is the larger of the two groups plus includes all the sea turtles, the terrestrial tortoises, and many of the freshwater turtles. The Pleurodira are usually sometimes known as the particular side-necked turtles, a reference to how they retract their heads to their shells. This smaller group consists primarily of various freshwater turtles.