The Hawksbill Turtle SNSH
Turtles are diapsids of the particular order Testudines (or Chelonii) characterized by a special bony or cartilaginous shell developed from their ribs plus acting as a protect. "Turtle" may refer in order to the order as a whole (American English) or even to fresh-water and sea-dwelling testudines (British English). The particular order Testudines includes each extant (living) and wiped out species. The earliest known members of this group date from 220 mil years ago, making turtles one of the earliest reptile groups and the more ancient group than snakes or crocodilians. Associated with the 356 known varieties alive today, some are highly endangered.
Turtles are ectotherms—animals commonly called cold-blooded—meaning that their internal temp varies according to the ambient environment. However, since of their high metabolic rate, leatherback sea turtles have a body temp that is noticeably higher than that of the particular surrounding water. Turtles are usually classified as amniotes, together with other reptiles, parrots, and mammals. Like other amniotes, turtles breathe atmosphere and do not lay down eggs underwater, although numerous species live in or around water. The research of turtles is known as cheloniology, following the Greek word for turtle. It will be also sometimes called testudinology, after the Latin name for turtles.
Differences exist in usage of the particular common terms turtle, tortoise, and terrapin, based on the range of English being utilized. These terms are common names and do not reflect precise 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 marine species. Tortoise usually pertains to any land-dwelling, non-swimming chelonian. Terrapin is used to describe several species of small, edible, hard-shell turtles, typically those found in brackish waters.
In Northern America, all chelonians are commonly called turtles. Tortoise is used only within reference to fully terrestrial turtles or, more narrowly, just those members of Testudinidae, the family of modern property tortoises. Terrapin may recommend to small semi-aquatic turtles that live in new and brackish water, particularly the diamondback terrapin (Malaclemys terrapin). Although the users from the genus Terrapene dwell mostly on land, they will 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" as a more specific term for slow-moving terrestrial varieties.
In the United Empire, the term turtle is used for water-dwelling species, which includes ones known in the particular US as terrapins, but not for terrestrial species, which are known only as tortoises.
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The word chelonian will be well-liked by veterinarians, scientists, and conservationists working with these types of animals being a catch-all name for any member of the superorder Chelonia, including almost all turtles living and vanished, as well as their particular immediate ancestors. Chelonia is based on the Greek word for turtles, χελώνη chelone; Greek χέλυς chelys "tortoise" is also used in the formation of medical names of chelonians. Testudines, on the other hands, is based on the particular Latin word for tortoise, testudo. Terrapin comes through an Algonquian word regarding turtle.
Some languages perform not have this distinction, as all of these are known by the particular same name. For instance , within Spanish, the word tortuga is used for turtles, tortoises, and terrapins. The sea-dwelling turtle is tortuga marina, a freshwater varieties tortuga de río, and a tortoise tortuga terrestre.
The largest living chelonian is the leatherback ocean turtle (Dermochelys coriacea), which usually reaches a shell length of 200 cm (6. 6 ft) and can achieve a weight of more than 900 kg (2, 000 lb). Freshwater turtles are generally smaller, but along with the largest species, the particular 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 biggest chelonian in North The united states, which attains a cover length of up in order to 80 cm (2. six ft) and weighs since much as 113. 4 kg (250 lb).
Huge tortoises of the genera Geochelone, Meiolania, and others were relatively widely distributed all over the world into prehistoric occasions, and they are known to have got existed in North and South America, Australia, plus Africa. They became extinct at the same time as the appearance associated with man, and it is assumed humans hunted them for food. The just surviving giant tortoises are usually on the Seychelles plus Galápagos Islands and may grow to over 130 cm (51 in) in size, and weigh about three hundred kg (660 lb).
The particular largest ever chelonian has been Archelon ischyros, a Late Cretaceous sea turtle identified to have been up to 4. 6 m (15 ft) long.
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The smallest turtle is the speckled padloper tortoise of South Africa. It measures simply no more than 8 cm (3. 1 in) long and weighs about 140 g (4. 9 oz). Two other species associated with small turtles are the American mud turtles plus musk turtles that live in an area that will ranges from Canada in order to South America. The cover duration of many species in this group is much less than 13 cm (5. 1 in) in length.
Turtles are divided into two groups, according to the way they retract their necks to their shells (something the our ancestors Proganochelys could not do). The mechanism of neck retraction differs phylogenetically: the suborder Pleurodira retracts laterally to the side, anterior to shoulder girdles, while the suborder Cryptodira retracts straight back, between shoulder girdles. These types of motions are largely due to the morphology plus arrangement of cervical vertebrae. Of all recent turtles, the cervical column is made up of nine joints and eight vertebrae, which are individually independent. Since these vertebrae are not fused and are rounded, the neck is more flexible, being able to bend in the backwards plus sideways directions. The major function and evolutionary implication of neck retraction is thought to be for 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 once the head is thrust forward and the oropharynx is expanded, and this morphology suggests the retraction function is for nourishing purposes as the suction helps catch prey. The particular protection the shell offers the head when it is retracted is therefore not the main functionality of retraction, thus is usually an exaptation. As with regard to the difference between the particular 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 due in order to a difference in environmental niche.
Head
Most turtles that spend most associated with their lives on property get their eyes looking straight down at objects in front side of them. Some aquatic turtles, such as nipping turtles and soft-shelled turtles, have eyes closer to the top of the mind. These types of turtle can hide from predators within shallow water, where they will lie entirely submerged other than for their eyes plus nostrils. Near their eyes, sea turtles possess glands that produce salty tears that rid themselves associated with excess salt taken in through the water they drink.
Turtles have rigid beaks and use their jaws to cut and chew food. Instead of having teeth, that they appear in order 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 possess knife-sharp ridges for slicing through their prey. Herbivorous turtles have serrated-edged side rails that help them cut through tough plants. They use their tongues to swallow food, but as opposed to most reptiles, they can not stay out their tongues to catch food.
ShellMajor article: Turtle shellThe top shell of the turtle is known as the carapace. The particular lower shell that encases the belly is called the plastron. The carapace and plastron are joined up with 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 bones that include portions associated with the backbone and the particular ribs, meaning the turtle cannot crawl from the shell. In most turtles, the outer layer of 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 particular scales of other lizards. These scutes overlap the seams between the shell bones and add power to the shell. Some turtles do not possess horny scutes; with regard to example, the leatherback ocean turtle and the soft-shelled turtles have shells covered with leathery skin instead.
The particular shape of the covering gives helpful clues about how exactly a turtle lives. Most tortoises have a huge, dome-shaped shell that makes it difficult for potential predators to crush the cover between their jaws. One 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 smooth, streamlined shells, which help in 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 plus streams. Another exception is usually the Belawan Turtle (Cirebon, West Java), which has sunken-back soft-shell.
The color of the turtle's shell may vary. Shells are commonly colored brown, black, or olive green. In some species, covers may have red, orange, yellow, or grey markings, often spots, lines, or irregular blotches. Probably the most colourful turtles is the far eastern painted turtle, which consists of a yellow plastron and a black or olive shell with red marks around the rim.
Tortoises, being land-based, have rather heavy shells. In contrast, aquatic and soft-shelled turtles have lighter shells that will help them avoid sinking in water and go swimming faster with more speed. These lighter shells have large spaces called fontanelles between the shell our bones. The shells of leatherback sea turtles are extremely gentle because they lack scutes and contain many fontanelles.
It has been suggested by Jackson (2002) that will the turtle shell may function as pH barrier. To endure through anoxic conditions, such as winter season periods trapped beneath ice or within anoxic mud at the bottom of ponds, turtles utilize two general physical mechanisms. In the situation of prolonged periods of anoxia, it has been shown that the turtle covering both releases carbonate buffers and uptakes lactic acid solution.
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Respiration Turtles
Respiration, for many amniotes, is achieved by the particular contraction and relaxation of specific muscle groups (i. electronic. intercostals, abs, and/or the diaphragm) mounted on an inner rib-cage that can broaden or contract the body wall thus assisting air flow in and out of the lung area. The ribs of Chelonians, however, are fused with their carapace and exterior to their pelvic plus 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 got to evolve special modifications for respiration.
Turtle pulmonary ventilation occurs by making use of specific groups of abdominal muscle groups attached to their viscera and shell that pull the lungs ventrally during inspiration, where air is usually drawn in via a negative pressure gradient (Boyle's Law). In expiration, the particular contraction from the transversus abdominis is the driving push by propelling the viscera into the lungs and expelling air under optimistic pressure. Conversely, the comforting and flattening of the particular oblique abdominis muscle pulls the transversus back down which, once again, draws air back into the lungs. Important auxiliary muscles used for ventilatory processes are the pectoralis, which is used in conjunction with the transverse abdominis during inspiration, as well as the serratus, which moves with the abdominal oblique accompanying expiration.
The lungs associated with Testudines are multi-chambered plus attached their entire duration over the carapace. The amount of chambers can differ among taxa, though most often these people have three lateral compartments, three medial chambers, and something terminal chamber. As mentioned earlier on, the act of particular abdominal muscles pulling lower the viscera (or pressing back up) is what allows for respiration in turtles. Specifically, it is the turtles large liver organ that pulls or pushes on the lungs. Ventral to the lungs, in the coelomic cavity, the liver organ of turtles is connected directly to the right lung, and their stomach is directly attached to the left lung by the ventral mesopneumonium, which is attached to their liver organ with the ventral mesentery. When the liver is drawn down, inspiration begins. Helping the lungs is the particular post-pulmonary septum, that is discovered in all Testudines, and is thought to prevent the lungs from collapsing.
Marine turtles characteristics, key to the 7 marine species, ecology, habitat and range, behavior
Turtles Pores and skin and molting
As described above, the outer layer of the shell is part of the skin; each scute (or plate) on the shell refers to a single modified scale. The remainder of the skin has much smaller scales, just like the pores and skin of other reptiles. Turtles do not molt their own skins all at once as snakes do, yet continuously in small pieces. When turtles are held in aquaria, small sheets of dead skin can be seen in the water (often appearing in order to be a thin piece of plastic) having been sloughed off when the particular animals deliberately rub by themselves against an item of wood or stone. Tortoises also lose skin, but dead skin is permitted to accumulate directly into thick knobs and dishes that provide protection to parts of the body outside the shell.
Simply by counting the rings created by the stack of smaller, older scutes on top of the larger, newer ones, you are able to estimate the age of a turtle, if one knows how many scutes are produced in per year. This method is not very accurate, partly since growth rate is not really constant, but also because some of the scutes eventually fall away through the shell.
Turtles Limbs
Terrestrial tortoises have short, sturdy feet. Tortoises are popular for moving slowly, simply because of their large, cumbersome shells, which limit stride length.
Skeleton associated with snapping turtle (Chelydra serpentina)
Amphibious turtles normally possess limbs similar to the ones from tortoises, except that the feet are webbed plus often have long claws. 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 right and left side of the particular body alternately providing thrust. Large turtles tend to swim less than smaller ones, and the extremely big species, such since alligator snapping turtles, barely swim whatsoever, preferring to walk across the bottom associated with the river or lake. As well as webbed feet, turtles have extremely long claws, used to help them clamber onto riverbanks and floating records upon which they bask. Male turtles tend in order to have particularly long paws, and these seem to be utilized to stimulate the woman while mating. While many turtles have webbed foot, some, such as the pig-nosed turtle, have true flippers, along with the digits being joined into paddles as well as 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 travel through the water, using the particular up-and-down motion of the particular front flippers to create drive; the back feet are not used for propulsion yet can be utilized as rudders with regard to steering. Compared with fresh water turtles, sea turtles have got very limited mobility upon land, and in addition to the splash from the nest towards the sea as hatchlings, male sea turtles normally never ever leave the sea. Females must come back onto land to lay eggs. They move very gradually and laboriously, dragging by themselves forwards using their flippers.
Behavior of Turtles
Senses of Turtles are thought to have exceptional night vision because of the unusually large amount of rod cells within their retinas. Turtles have color vision with a wealth of cone subtypes with sensitivities ranging through the near ultraviolet (UVA) to red. Some property turtles have very bad pursuit movement abilities, which usually are normally found just in predators that search 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.
While typically thought of because mute, turtles make various sounds when communicating. Tortoises may be vocal when dating and mating. Various types of both freshwater plus sea turtles emit numerous types of calls, often short and low frequency, from the time they may be in the egg in order to whenever they are adults. These types of vocalizations may serve to create group cohesion whenever migrating.
Turtle Cleverness
See furthermore: Animal cognition
It offers 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 particular hard shells enable these to live without fast reflexes or elaborate predator avoidance strategies. In the lab, turtles (Pseudemys nelsoni) can learn novel operant jobs and also have demonstrated a extensive memory of at minimum 7. 5 months.
Turtle Mating Techniques
An example of mounting behavior in turtles
Turtles are identified for displaying a wide variety of mating behaviors, nevertheless , they are not really known for forming pair-bonds or for being part of a social group. Once fertilization has happened and an offspring offers been produced, neither mother or father will provide care regarding the offspring once is actually hatched. Females generally outnumber males in various turtle species (such as Green turtles), and as a result, most men will participate in multiple copulation with multiple partners throughout their lifespan. However, due to the sexual dimorphism present in most turtle species, males must develop different courting strategies or use alternate methods to gain access to any mate. Most terrestrial types have males that are usually bigger than females, and combating between males often establishes a hierarchical order in which the higher up the order an person is, the better the particular chance is of the individual getting access to the potential mate. For many 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 using a female. In fully marine species, males are frequently smaller than females plus therefore they cannot use the particular same strategy because their semi-aquatic relatives, which depends on overpowering the females with power. Males in this category resort to using courtship displays in an try to gain mating accessibility to a female.
Battling Between Males Turtles
Saddle back Galapagos tortoise
Wood turtles invariably is an example of the terrestrial species where the males have a hierarchical ranking system based on dominance through fighting, and it's shown that the males with the greatest rank and thus the most wins in battles have the most offspring.
Galapagos tortoises are another example of a types which has a hierarchical rank that is determined simply by dominance displays, and accessibility to food and mates is regulated by this dominance hierarchy. Two male saddle backs most usually compete for access to cactus trees, which is their own source of food. The particular winner is the individual who stretches their throat the highest, which person gets access to the cactus tree, which may attract potential mates.
Push Mating Turtles
Male (left) and female (right) radiated tortoise
The male scorpion mud turtle is an illustration of a bottom-walking aquatic species that relies on overwhelming females with its bigger size as a mating strategy. The male techniques the feminine from the rear, and often resorts to aggressive methods for example gnawing at the female's tail or even hind limbs, then the mounting behavior in which usually 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 by laterally waving his mind and sometimes biting the particular female's head in a good 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 by wanting to insert his holding tail.
Male radiated tortoises will also be known to use the force mating strategy wherein they use around vegetation to trap or prevent females from getting away, then pin them down for copulation.
Turtles Courtship Shows
Red-eared sliders are a good 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 choice is important in this technique, and the females of several species, such as eco-friendly sea turtles, aren't usually receptive. As a result, they've progressed certain behaviors to avoid the male's attempts at copulation, such as going swimming away, confronting the male followed by biting, or even a refusal position within which the female presumes a vertical position with her limbs widely outspread and her plastron dealing with the male. If the particular water is too superficial to perform the refusal position, the females will resort to beaching on their own, which is a verified 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 quantities of their lives marine, all turtles and tortoises breathe air and must surface at regular time periods to refill their lungs. They can also spend much or all of their lives on dried out land. Aquatic respiration within Australian freshwater turtles is usually currently being studied. Some species have large cloacal cavities that are lined numerous finger-like projections. These projections, called papillae, possess a rich blood supply and raise the surface area of the cloaca. The particular turtles can take upward dissolved oxygen from the water providing a few 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 eggs from the major species are spherical while the eggs of the rest are elongated. Their albumen will be white and contains another protein from bird ovum, such that it will certainly not coagulate when prepared. Turtle eggs ready to consume consist mainly of yolk. In some species, temperature determines whether an egg 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 holes dug into mud or sand. They are after that covered and left to incubate on their own. Depending upon the species, the eggs 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 in which the mom cares for her younger.
Sea turtles lay their own eggs on dry, sandy beaches. Immature sea turtles are not cared regarding by the adults. Turtles can take many years to reach breeding age, plus in many cases, breed every few years ınstead of annually.
Researchers have recently uncovered a turtle's organs do not gradually break down or become less efficient over time, unlike many other animals. It has been found that the liver, lungs, and kidneys of a centenarian turtle are practically indistinguishable from individuals of its immature version. This has inspired hereditary researchers to commence examining the turtle genome with regard to longevity genes.
A group of turtles is actually a bale.
Turtles Diet
A green sea turtle grazing on
A turtle's diet varies greatly depending on the environment in which it lives. Grownup turtles typically eat marine plants; (citation needed) invertebrates like insects, snails, plus worms; and have been reported to occasionally consume dead marine animals. Several small freshwater species are usually carnivorous, eating small fish and a wide variety of aquatic life. However, protein is important to turtle growth plus juvenile turtles are purely carnivorous.
Sea turtles usually feed on jellyfish, sponges, and other soft-bodied organisms. Some species with stronger jaws have been observed to eat shellfish, whilst others, such as the green ocean turtle, do not consume meat at all plus, 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 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 late Triassic Period associated with the Mesozoic era, about 220 million years ago, and their shell, which usually has remained a incredibly stable body plan, is usually considered to have evolved through bony extensions of their particular backbones and broad ribs that expanded and increased together to form a complete shell that offered protection at every phase of its evolution, also when the bony element of the shell was not really complete. This is backed by fossils of the particular freshwater Odontochelys semitestacea or even "half-shelled turtle with teeth", from the late Triassic, which have been found near Guangling in south west China. Odontochelys displays a complete bony plastron and an incomplete carapace, similar to an early phase of turtle embryonic growth. Just before this discovery, the earliest-known fossil turtle ancestors, like Proganochelys, were terrestrial and had a complete covering, offering no clue to the evolution of this amazing anatomical feature. By the past due Jurassic, turtles had radiated widely, and their fossil history becomes better to read.
Their precise ancestry has been disputed. It was believed they are the only surviving branch of the ancient evolutionary quality Anapsida, which includes groups such as procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporary opening while all some other extant amniotes have temporary openings (although in mammals, the hole has turn out to be 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 that 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, somewhat 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 inside Archosauria, or, more commonly, as a sister team to extant archosaurs,[58][59][60][61] though an analysis performed by Lyson et 's. (2012) recovered turtles because the sister group of lepidosaurs instead. Reanalysis of earlier phylogenies suggests that these people classified turtles as anapsids both simply because they assumed this particular classification (most of all of them studying what sort of anapsid turtles are) plus 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 mil years ago, though the debate is far through settled. Even the traditional placement of turtles outdoors Diapsida cannot be ruled out at this stage. A combined analysis of morphological and molecular information conducted by Lee (2001) found turtles to be anapsids (though a partnership with archosaurs couldn't end up being statistically rejected).[64] Similarly, a morphological research conducted by Lyson et al.. (2010) recovered them as anapsids most closely related to Eunotosaurus. A molecular analysis of 248 nuclear genes from 16 vertebrate taxa suggests 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 approximated to be 255 million in years past. The most current common ancestor of living turtles, corresponding to the divided between Pleurodira and Cryptodira, was estimated to get occurred around 157 million years ago. The oldest definitive crown-group turtle (member of the modern clade Testudines) may 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 investigate the placement of turtles within reptiles, Crawford et al. (2012) also recommend that turtles are a 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 and Pelodiscus sinensis, the team used the largest turtle information set to date in their particular analysis and concluded that turtles are likely the sister group of crocodilians and birds (Archosauria). This placement within the diapsids suggests that the turtle lineage lost diapsid head characteristics as it now possesses an anapsid-like head.
The earliest known completely shelled member of the particular turtle lineage is the late Triassic Proganochelys. This particular genus already possessed many advanced turtle traits, plus thus probably indicates numerous millions of years of preceding turtle evolution; this is further supported simply by evidence from fossil songs from the Early Triassic of the United States (Wyoming and Utah) and from the Middle Triassic of Germany, indicating that proto-turtles already existed because early as the first Triassic. Proganochelys lacked the ability to draw its head into its shell, had a lengthy neck, and had the long, spiked tail ending in a club. Could body form is comparable to that of ankylosaurs, this resulted from convergent development.
Turtles are divided in to two extant suborders: Cryptodira and Pleurodira. The Cryptodira is the larger of the two groups plus includes all the ocean turtles, the terrestrial tortoises, and lots of of the freshwater turtles. The Pleurodira are sometimes known as the side-necked turtles, a guide to the way they retract their heads to their shells. This smaller group consists primarily of various freshwater turtles.