The Baby Turtle Free National Geographic Pix

The Baby Turtle Free National Geographic Pix

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

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

Differences can be found in usage of the particular common terms turtle, tortoise, and terrapin, based on the variety of English being utilized. These terms are typical names and do not reflect exact biological or taxonomic distinctions.

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

In North America, all chelonians are usually commonly called turtles. Tortoise is used only within reference to fully terrestrial turtles or, more narrowly, only those members of Testudinidae, your family of modern land tortoises. Terrapin may refer to small semi-aquatic turtles that live in fresh and brackish water, in particular the diamondback terrapin (Malaclemys terrapin). Although the people from the genus Terrapene live mostly on land, these people are known as box turtles rather than tortoises. The particular American Society of Ichthyologists and Herpetologists uses "turtle" to describe all types of the order Testudines, regardless of whether they are land-dwelling or sea-dwelling, and uses "tortoise" like a more specific expression for slow-moving terrestrial species.

In the United Empire, the term turtle is used for water-dwelling species, which includes ones known in the US as terrapins, however, not for terrestrial species, which are known only as tortoises.

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turtles The Wild World of Zoobooks

The word chelonian is usually popular among veterinarians, scientists, and conservationists working with these animals as a catch-all title for any person in the superorder Chelonia, which includes almost all turtles living and extinct, 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 hands, is based on the Latin word for tortoise, testudo. Terrapin comes from an Algonquian word regarding turtle.

Some languages do not have this variation, 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. The sea-dwelling turtle is tortuga marina, a freshwater species tortuga de río, and a tortoise tortuga terrestre.

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, 1000 lb). Freshwater turtles are generally smaller, but along with the largest species, the 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 The united states, which attains a covering 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 other people were relatively widely dispersed around the world into prehistoric times, and they 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 usually on the Seychelles and Galápagos Islands and can grow to over 130 centimeter (51 in) in length, and weigh about 300 kg (660 lb).

The largest ever chelonian was Archelon ischyros, a Past due Cretaceous sea turtle identified to have been up to 4. 6 m (15 ft) long.

River Turtle Life of Sea

The tiniest turtle is the speckled padloper tortoise of South Africa. It measures no more than 8 centimeter (3. 1 in) in length and weighs about 140 g (4. 9 oz). Two other species of small turtles are the particular American mud turtles and musk turtles that live in an area that will ranges from Canada to South America. The shell duration of many species in this group is less than 13 cm (5. 1 in) long.

Turtles are divided into 2 groups, according to how they retract their necks to their shells (something the our ancestors Proganochelys could not do). The mechanism of throat retraction differs phylogenetically: the suborder Pleurodira retracts side to side to the side, anterior to make girdles, while the suborder Cryptodira retracts straight back again, between shoulder girdles. These motions are largely due to the morphology and arrangement of cervical backbone. Of all recent turtles, the cervical column consists of nine joints plus eight vertebrae, which are individually independent. Since these vertebrae are not fused and are rounded, the particular neck is more flexible, being able to flex in the backwards and sideways directions. The major function and evolutionary inference of neck retraction is thought to be regarding feeding rather than protection. Neck retraction and testing 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 morphology suggests the retraction function is for serving purposes as the suction helps catch prey. The particular protection the shell provides the head when it is retracted is consequently not the main function of retraction, thus is usually an exaptation. As for the difference between the two methods of retraction, both Pleurodirans and Cryptodirans use the quick expansion of the neck like a method of predation, therefore the difference in retraction mechanism is not really due to a difference in ecological niche.

Head

Most turtles that spend most associated with their lives on land get their eyes looking down at objects in front of them. Some aquatic turtles, such as nipping turtles and soft-shelled turtles, have eyes closer to the very best of the mind. These species of turtle can hide from predators in shallow water, where they lie entirely submerged except for their eyes plus nostrils. Near their eye, sea turtles possess glands that produce salty holes that rid their body associated with excess salt consumed through the water they drink.

Turtles have rigid beaks and use their teeth to cut and chew food. Instead of having teeth, that they appear to have lost about 150-200 million years ago, the upper and lower teeth 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 reduce through tough plants. They use their tongues to swallow food, but in contrast to most reptiles, they cannot stick out their tongues in order to catch food.

ShellPrimary article: Turtle shellTop of the 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 internal layer of a turtle's shell is made upward of about 60 bone fragments that include portions of the backbone and the particular ribs, meaning the turtle cannot crawl away from its shell. In most turtles, the outer layer from the shell is covered simply by horny scales called scutes which are part of its outer skin, or pores and skin. Scutes comprise of the fibrous protein keratin that also makes up the particular scales of other lizards. These scutes overlap the seams between the covering bones and add strength to the shell. Some turtles do not possess horny scutes; regarding example, the leatherback sea turtle and the soft-shelled turtles have shells covered along with leathery skin instead.

The particular shape of the cover gives helpful clues about how a turtle lives. Many tortoises have a big, dome-shaped shell that can make it difficult for potential predators to crush the covering between their jaws. A single of the few conditions is the African pancake tortoise, which has the flat, flexible shell that will allows it to hide in rock crevices. The majority of aquatic turtles have smooth, streamlined shells, which aid within swimming and diving. American snapping turtles and musk turtles have small, cross-shaped plastrons that give them more efficient leg motion for walking along the bottom of ponds plus streams. Another exception is the Belawan Turtle (Cirebon, West Java), which has sunken-back soft-shell.

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

Tortoises, being land-based, have instead heavy shells. In comparison, aquatic and soft-shelled turtles have lighter shells that will help them avoid settling in water and go swimming faster with more agility. These lighter shells possess large spaces called fontanelles between the shell our bones. The shells of leatherback sea turtles are extremely light because they lack scutes and contain many fontanelles.

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

Names for Pet Turtles and Tortoises

Breathing Turtles

Respiration, for many amniotes, is achieved by the particular contraction and relaxation associated with specific muscle groups (i. electronic. intercostals, abdominal muscles, and/or a diaphragm) attached to an internal rib-cage that can increase or contract the entire body wall thus assisting air flow in and out of the lungs. The ribs of Chelonians, however, are fused with their carapace and exterior 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 had to evolve special modifications for respiration.

Turtle pulmonary ventilation occurs by making use of specific categories of abdominal muscles attached to their viscera and shell that draw the lungs ventrally throughout inspiration, where air will be drawn in via the negative pressure gradient (Boyle's Law). In expiration, the contraction from the transversus abdominis is the driving push by propelling the viscera into the lungs and expelling air under optimistic pressure. Conversely, the calming and flattening of the particular oblique abdominis muscle draws the transversus back down which, once more, draws air flow back into the lung area. Important auxiliary muscles used for ventilatory processes are the pectoralis, which is used in conjunction with the transverse abdominis during motivation, as well as the serratus, which moves using the abdominal oblique associated expiration.

The lungs associated with Testudines are multi-chambered and attached their entire size over the carapace. The number of chambers can vary among taxa, though most often they have three lateral compartments, three medial chambers, and one terminal chamber. As previously mentioned, the act of specific abdominal muscles pulling down the viscera (or pressing back up) is exactly what allows for respiration within turtles. Specifically, it is the turtles large liver organ that pulls or pushes 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 stomach is directly attached to the left lung by the ventral mesopneumonium, that is attached to their liver organ from the ventral mesentery. When the liver is drawn down, inspiration begins. Supporting the lungs is the particular post-pulmonary septum, which is found in all Testudines, and it is thought to prevent the lungs from collapsing.

Types of Turtles Giant Tortoise Reptile Gardens Reptile Gardens

Turtles Skin and molting

As pointed out above, the outer layer of the shell is part of the epidermis; each scute (or plate) on the shell refers to a single altered scale. The remainder of the skin has a lot smaller scales, just like the epidermis of other reptiles. Turtles do not molt their skins all at as soon as as snakes do, yet continuously in small parts. When turtles are kept in aquaria, small bedding of dead skin can be seen in the water (often appearing to be a thin item of plastic) having been sloughed off when the particular animals deliberately rub on their own against an item of wood or stone. Tortoises also shed skin, but dead epidermis is allowed to accumulate directly into thick knobs and plates that provide protection in order to parts of the body outside the shell.

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

Turtles Limbs

Terrestrial tortoises have short, durable feet. Tortoises are famous for moving slowly, simply because of their large, cumbersome shells, which restrict stride length.

Skeleton associated with snapping turtle (Chelydra serpentina)

Amphibious turtles normally possess limbs similar to those of tortoises, except that the particular feet are webbed and often have long paws. These turtles swim making use of all four feet in a way similar in order to the dog paddle, along with the feet on the particular left and right side of the particular 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 whatsoever, preferring to walk along the bottom of the river or lake. As well as webbed feet, turtles have really long claws, used to help them clamber on to riverbanks and floating logs upon which they bask. Male turtles tend in order to have particularly long claws, and these look like utilized to stimulate the female while mating. While most turtles have webbed feet, some, like the pig-nosed turtle, have true flippers, along with the digits being joined into paddles as well as the paws being relatively small. These species swim in the same way as sea turtles do (see below).

Sea turtles are usually almost entirely aquatic and have flippers instead of feet. Sea turtles fly through the water, using the particular up-and-down motion of the front flippers to generate drive; the back feet are not used for propulsion yet can be utilized as rudders for steering. Compared with freshwater turtles, sea turtles have very limited mobility upon land, and apart from the splash from the nest towards the sea as hatchlings, male 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 on their own forwards using their flippers.

Behavior of Turtles

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

Turtles Communication

The particular Arrau turtle has the sizable vocal repertoire.

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

Turtle Intelligence

See furthermore: Animal knowledge

It has been reported that wood turtles are better than white rats at understanding to navigate mazes. Situation studies exist of turtles playing. They actually, however, have got a very low encephalization quotient (relative brain to body mass), and their particular hard shells enable them to live without fast reflexes or elaborate predator prevention strategies. In the lab, turtles (Pseudemys nelsoni) may learn novel operant duties and have demonstrated a long-term memory of at minimum 7. 5 months.

Turtle Mating Techniques

An example of mounting behavior within turtles

Turtles are known for displaying a broad variety of mating behaviours, nevertheless , they are not really 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 regarding the offspring once it can hatched. Females generally outnumber males in various turtle species (such as Green turtles), and as a result, most men will engage in multiple copulation with multiple partners throughout their lifespan. However, because of to the sexual dimorphism present in most turtle species, males must develop different courting strategies or use alternate methods in order to gain access to any mate. Most terrestrial species have males that are larger than females, and battling between males often decides a hierarchical order within which the higher up the order an individual is, the better the particular chance is of the person getting access to a potential mate. For many semi-aquatic species and bottom-walking aquatic species, combat takes place less often. Males belonging to semi-aquatic and bottom-walking species instead often use their larger size benefit to forcibly mate with a female. In fully aquatic species, males are frequently smaller than females and therefore they cannot use the same strategy because their semi-aquatic relatives, which relies on overwhelming the females with strength. Males in this group resort to using courtship displays in an attempt to gain mating entry to a female.

Battling Between Males Turtles

Saddle back again Galapagos tortoise

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

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

Force Mating Turtles

Male (left) and female (right) radiated tortoise

The male scorpion dirt turtle is an instance of a bottom-walking aquatic species that relies on overwhelming females with its larger size as a mating strategy. The male techniques the female from the back, and often resorts in order to aggressive methods like gnawing at the female's tail or hind limbs, followed by a mounting behavior in which usually the male clasps the particular edges of her carapace with his forelimbs plus hind limbs to keep her in position. The man follows this action simply by laterally waving his head and sometimes biting the female's head in a good attempt to get the girl to withdraw her head into her shell. This reveals her cloaca, and with it exposed, the man can attempt copulation simply by seeking to insert his holding tail.

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

Turtles Courtship Shows

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

Ecology and life history of turtles

Sea turtle swimming

Although several turtles spend large quantities of their lives marine, all turtles and tortoises breathe air and should surface at regular periods to refill their lungs. They can also spend much or all associated with their lives on dried out land. Aquatic respiration within Australian freshwater turtles will be currently being studied. A few species have large cloacal cavities that are lined with many finger-like projections. These types of projections, called papillae, possess a rich blood supply and improve the surface area of the cloaca. The particular turtles can take up dissolved oxygen from the particular water using these papillae, within much the same method that fish use gills to respire.

Like other reptiles, turtles lay ovum that are slightly gentle and leathery. The ovum from the most significant species are spherical while the eggs of the rest are elongated. Their albumen is white and contains a different protein from bird ovum, such that it may not coagulate when prepared. Turtle eggs prepared to consume consist mainly of yolk. In some species, temp determines whether an egg cell develops into a man or a female: a higher temperature causes a female, a lower temperature the man. Large numbers of ovum are deposited in openings dug into mud or 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. When the turtles hatch, they squirm their way to the particular surface and head against the water. There are no known species in which the mom cares for her youthful.

Sea turtles lay their own eggs on dry, exotic beaches. Immature sea turtles are not cared regarding by the adults. Turtles can take many years to achieve breeding age, and in many cases, breed every few years ınstead of annually.

Researchers have lately discovered a turtle's internal organs do not steadily break lower or become less efficient over time, unlike most other animals. It has been found that the liver organ, lungs, and kidneys of a centenarian turtle are nearly indistinguishable from those of its immature equal. This has inspired hereditary researchers to start evaluating the turtle genome regarding longevity genes.

A team of turtles is known as a bale.

Turtles Diet

A green ocean turtle grazing on

A turtle's diet differs greatly according to the atmosphere by which it lives. Mature turtles typically eat aquatic plants; (citation needed) invertebrates for example insects, snails, plus worms; and have already been reported to occasionally eat dead marine animals. Many small freshwater species are carnivorous, eating small seafood and a wide variety of aquatic lifestyle. However, protein is important to turtle growth and juvenile turtles are purely carnivorous.

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

Systematics and evolution of Turtles

Primary article: Turtle classification

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

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

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

Dependent on body fossils, the particular first proto-turtles are believed to have existed in the particular late Triassic Period associated with the Mesozoic era, regarding 220 million years back, and their shell, which has remained a incredibly stable body plan, will be thought to have evolved from bony extensions of their backbones and broad ribs that expanded and grew together to form the complete shell that provided protection at every phase of its evolution, also when the bony element of the shell was not complete. This is backed by fossils of the particular freshwater Odontochelys semitestacea or "half-shelled turtle with teeth", from the late Triassic, which have been found near Guangling in south west China. Odontochelys displays the complete bony plastron and an incomplete carapace, comparable to an early stage of turtle embryonic development. Prior to this discovery, the particular earliest-known fossil turtle ancestors, like Proganochelys, were terrestrial together a complete cover, offering no clue to the evolution of this impressive anatomical feature. By the late Jurassic, turtles had extended widely, and their precious history becomes easier to read.

Their precise ancestry has been disputed. It had been believed they are the particular only surviving branch of the ancient evolutionary grade Anapsida, which includes groups like procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporal opening while all additional extant amniotes have temporary openings (although in mammals, the hole has turn out to be the zygomatic arch). The particular millerettids, protorothyrids, and pareiasaurs became extinct in the particular late Permian period plus the procolophonoids during the particular Triassic.

Nevertheless , it was later recommended that this anapsid-like turtle head might be due to reversion rather than to anapsid descent. More recent morphological phylogenetic studies with this particular in mind placed turtles firmly within diapsids, slightly closer to Squamata in order to Archosauria.[55][56] All molecular studies possess 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 performed by Lyson et 's. (2012) recovered turtles as the sister group of lepidosaurs instead. Reanalysis of earlier phylogenies suggests that they will classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) plus because they did not sample fossil and extant taxa broadly enough with regard to constructing the cladogram. Testudines were suggested to get diverged from other diapsids between 200 and 279 million years ago, though the debate is far through settled. Even the conventional placement of turtles outside Diapsida cannot be dominated out at this stage. A combined analysis of morphological and molecular information conducted by Lee (2001) found turtles to end up being anapsids (though a relationship with archosaurs couldn't end up being statistically rejected).[64] Similarly, a morphological research conducted by Lyson ainsi que al.. (2010) recovered them as anapsids most carefully related to Eunotosaurus. A molecular analysis of 248 nuclear genes from 16 vertebrate taxa suggests that turtles are a sister group to birds and crocodiles (the Archosauria).[66] The date of splitting up of turtles and parrots and crocodiles was approximated to be 255 million in years past. The most latest common ancestor of living turtles, corresponding to the split between Pleurodira and Cryptodira, was estimated to have occurred around 157 million yrs ago. The oldest definitive 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 first genomic-scale phylogenetic analysis associated with ultraconserved elements (UCEs) to check into the placement of turtles within reptiles, Crawford ou al. (2012) also recommend that turtles are the sister group to parrots and crocodiles (the Archosauria).

The first genome-wide phylogenetic analysis was completed simply by Wang et al. (2013). Using the draft genomes of Chelonia mydas plus Pelodiscus sinensis, the team used the largest turtle information set to date in their analysis and concluded that turtles are likely the sister group of crocodilians and birds (Archosauria). This particular 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 many advanced turtle traits, and thus probably indicates numerous millions of years associated with preceding turtle evolution; this particular is further supported simply by evidence from fossil tracks from the Early Triassic of the United Declares (Wyoming and Utah) plus from the Middle Triassic of Germany, indicating that will proto-turtles already existed because early as the first Triassic. Proganochelys lacked the opportunity to pull its head into the shell, had a lengthy neck, and had the long, spiked tail finishing in a club. Could body form is comparable to those of ankylosaurs, it resulted from convergent evolution.

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