Encyclopaedia of Babies of Beautiful Wild Animals: The Baby Turtle
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 to fresh-water and sea-dwelling testudines (British English). The particular order Testudines includes both extant (living) and wiped out species. The earliest known members of this team date from 220 million years ago, making turtles one of the oldest reptile groups and the more ancient group than 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 heat varies according to the ambient environment. However, because of their high metabolic rate, leatherback sea turtles have a body heat that is noticeably increased than that of the surrounding water. Turtles are classified as amniotes, together with other reptiles, birds, and mammals. Like other amniotes, turtles breathe air and do not lay 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 name for turtles.
Differences can be found in usage of the common terms turtle, tortoise, and terrapin, according to the variety of English being used. These terms are common names and do not reflect accurate biological or taxonomic variations.
Turtle may either relate to the order as a whole, or in order to particular turtles that make 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 can be used in order to describe several species associated with small, edible, hard-shell turtles, typically those found in brackish waters.
In Northern America, all chelonians are usually commonly called turtles. Tortoise is used only within mention of the fully terrestrial turtles or, more narrowly, just those members of Testudinidae, your family of modern property tortoises. Terrapin may recommend to small semi-aquatic turtles that live in refreshing and brackish water, specifically the diamondback terrapin (Malaclemys terrapin). Although the people of the genus Terrapene live mostly on land, they are referred to as box turtles rather than tortoises. The American Society of Ichthyologists and Herpetologists uses "turtle" to describe all types of the order Testudines, regardless of whether they are land-dwelling or even sea-dwelling, and uses "tortoise" being a more specific term for slow-moving terrestrial types.
In the United Kingdom, the term turtle is utilized for water-dwelling species, including ones known in the particular US as terrapins, although not for terrestrial species, which are known only as tortoises.
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The word chelonian is well-liked by veterinarians, scientists, and conservationists working with these types of animals like a catch-all title for any member of the superorder Chelonia, including all turtles living and vanished, as well as their particular immediate ancestors. Chelonia will be based on the Greek word for turtles, χελώνη chelone; Greek χέλυς chelys "tortoise" is also utilized in the formation of medical names of chelonians. Testudines, on the other hand, is based on the Latin word for tortoise, testudo. Terrapin comes from an Algonquian word for turtle.
Some languages do not have this variation, as all of these types of are referred to by the 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, 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 over 900 kg (2, 1000 lb). Freshwater turtles are generally smaller, but 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 largest chelonian in North The united states, which attains a cover length of up to 80 cm (2. 6 ft) and weighs because much as 113. 4 kg (250 lb).
Large tortoises of the overal Geochelone, Meiolania, and others were relatively widely dispersed all over the world into prehistoric periods, and they are known to possess existed in North plus South America, Australia, and Africa. They became extinct at the same period as the appearance of man, and it will be assumed humans hunted all of them for food. The only surviving giant tortoises are usually on the Seychelles plus Galápagos Islands and may grow to over 130 centimeter (51 in) in size, and weigh about three hundred kg (660 lb).
The particular largest ever chelonian had been Archelon ischyros, a Late Cretaceous sea turtle recognized to have been as much as 4. 6 m (15 ft) long.
Bonaire’s Sea Turtles – Sea Turtle Conservation Bonaire
The smallest turtle is the speckled padloper tortoise of South Africa. It measures no more than 8 cm (3. 1 in) in length and weighs about 140 g (4. 9 oz). Two other species associated with small turtles are the particular American mud turtles plus musk turtles that live in an area that will ranges from Canada to South America. The covering duration of many species in 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 our ancestors Proganochelys could not do). The mechanism of neck of the guitar retraction differs phylogenetically: the particular suborder Pleurodira retracts laterally to the side, anterior to shoulder girdles, while the suborder Cryptodira retracts straight back, between shoulder girdles. These motions are largely due to the morphology and arrangement of cervical backbone. Of all recent turtles, the cervical column is made up of nine joints plus eight vertebrae, which are individually independent. Since these vertebrae are not fused and are rounded, the neck is more versatile, being able to flex in the backwards and sideways directions. The major function and evolutionary implication of neck retraction is thought to be for feeding rather than safety. Neck retraction and reciprocal extension allows the turtle to reach out further in order 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 feeding 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 usually an exaptation. As for the difference between the particular two methods of retraction, both Pleurodirans and Cryptodirans use the quick extension of the neck being a method of predation, therefore the difference in retraction mechanism is not really due in order to a difference in ecological niche.
Head
Most turtles that spend most associated with their lives on property get their eyes looking lower at objects in front of them. Some marine turtles, such as nipping turtles and soft-shelled turtles, have eyes closer to the very best of the head. These species of turtle may hide from predators within shallow water, where these people lie entirely submerged other than for their eyes and nostrils. Near their eye, sea turtles possess glands that produce salty holes that rid their body associated with excess salt taken in through the water they drink.
Turtles have rigid beaks and use their jaws to cut and munch food. Instead of having teeth, that they appear to have lost about 150-200 million years ago, the particular 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 ridges that help them reduce through tough plants. These people use their tongues in order to swallow food, but in contrast to most reptiles, they cannot stick out their tongues in order to catch food.
ShellMain article: Turtle shellThe top shell of the turtle is known as 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 constructions called bridges. The internal layer of a turtle's shell is made upward of about 60 our bones that include portions of the backbone and the ribs, meaning the turtle cannot crawl away from its 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 scales of other lizards. These scutes overlap the particular seams between the shell bones and add power to the shell. Some turtles do not possess horny scutes; regarding example, the leatherback sea turtle as well as the soft-shelled turtles have shells covered along with leathery skin instead.
The shape of the cover 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 cover between their jaws. One of the few conditions is the African hot cake tortoise, which has a flat, flexible shell that allows it to hide in rock crevices. Most aquatic turtles have smooth, streamlined shells, which help within swimming and diving. American snapping turtles and musk turtles have small, cross-shaped plastrons that give them more efficient leg movement for walking along the bottom of ponds and streams. Another exception is the Belawan Turtle (Cirebon, West Java), that has sunken-back soft-shell.
The color of a turtle's shell may vary. Shells are commonly coloured brown, black, or olive green. In some species, covers may have red, orange, yellow, or grey marks, often spots, lines, or irregular blotches. One of the most colorful turtles is the eastern painted turtle, which consists of a yellow plastron plus a black or olive shell with red markings around the rim.
Tortoises, being land-based, have rather heavy shells. In contrast, aquatic and soft-shelled turtles have lighter shells that help them avoid settling in water and swim 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 lighting because they lack scutes and contain many fontanelles.
It has been recommended by Jackson (2002) that the turtle shell can function as pH buffer. To endure through anoxic conditions, such as winter season periods trapped beneath snow or within anoxic mud at the end of ponds, turtles utilize two general physiological mechanisms. In the case of prolonged periods associated with anoxia, it has been shown that the turtle covering both releases carbonate buffers and uptakes lactic acid.
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Breathing Turtles
Respiration, for many amniotes, is achieved by the particular contraction and relaxation associated with specific muscle groups (i. electronic. intercostals, abs, and/or a diaphragm) attached with an internal rib-cage that can increase or contract the body wall thus assisting air flow out and in of the lungs. The ribs of Chelonians, however, are fused along with their carapace and exterior to their pelvic and pectoral girdles, a feature 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 adaptations for respiration.
Turtle pulmonary ventilation occurs by making use of specific categories of abdominal muscle tissue attached to their viscera and shell that draw the lungs ventrally during inspiration, where air is usually drawn in via a negative pressure gradient (Boyle's Law). In expiration, the contraction of the transversus abdominis is the driving pressure by propelling the viscera into the lungs and expelling air under good pressure. Conversely, the relaxing and flattening of the particular oblique abdominis muscle draws the transversus back down which, once more, draws atmosphere back into the lungs. Important auxiliary muscles utilized for ventilatory processes would be the pectoralis, which is used in conjunction with the transverse abdominis during motivation, as well as the serratus, which movements using the abdominal oblique associated expiration.
The lungs associated with Testudines are multi-chambered plus attached their entire duration over the carapace. The number of chambers can vary in between taxa, though most commonly they will have three lateral chambers, three medial chambers, and something terminal chamber. As previously mentioned, the act of particular abdominal muscles pulling straight down 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, within the coelomic cavity, the liver of turtles is attached directly to the right lung, and their abdomen is directly attached in order to the left lung by the ventral mesopneumonium, which is attached to their liver organ with the ventral mesentery. Whenever the liver is pulled down, inspiration begins. Assisting the lungs is the post-pulmonary septum, which is found in all Testudines, and is thought to prevent the lungs from collapsing.
turtle The Ocean Enthusiast
Turtles Pores and skin and molting
As pointed out above, the outer coating of the shell is usually part of the pores and skin; each scute (or plate) on the shell corresponds to a single altered scale. The remainder of the skin has a lot smaller scales, just like the pores and skin of other reptiles. Turtles do not molt their skins all at as soon as as snakes do, but continuously in small items. When turtles are kept in aquaria, small linens of dead skin may be seen in the water (often appearing to be a thin piece of plastic) having already been sloughed off when the animals deliberately rub themselves against an item of wood or stone. Tortoises also lose 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.
By counting the rings formed by the stack of smaller, older scutes on top of the larger, newer types, 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 really very accurate, partly since growth rate is not really constant, but also due to the fact some of the scutes eventually fall away from the shell.
Turtles Braches
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 have got limbs similar to the ones from tortoises, except that the feet are webbed and often have long claws. These turtles swim using all four feet within a way similar to the dog paddle, along with the feet on the particular right and left side of the particular body alternately providing drive. Large turtles tend to swim less than smaller sized ones, and the extremely 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 very 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 claws, and these seem to be utilized to stimulate the women while mating. While many turtles have webbed ft, some, such as the pig-nosed turtle, have true flippers, along with the digits being joined into paddles as well as the paws being relatively small. These types of species swim in the same way because sea turtles do (see below).
Sea turtles are usually almost entirely aquatic and have flippers instead associated with feet. Sea turtles take flight with the water, using the up-and-down motion of the front flippers to generate thrust; the back feet are not used for propulsion yet can be utilized as rudders regarding steering. Compared with fresh water turtles, sea turtles possess very limited mobility on land, and in addition to the dash from the nest to the sea as hatchlings, man sea turtles normally never leave the sea. Females must come back on to land to lay ovum. They move very gradually and laboriously, dragging themselves forwards using their flippers.
Behavior of Turtles
Senses of Turtles are believed to get exceptional night eyesight because of the unusually large number of rod cells in their retinas. Turtles have got color vision with the wealth of cone subtypes with sensitivities ranging through the near ultraviolet (UVA) to red. Some property turtles have very poor pursuit movement abilities, which usually are normally found only in predators that quest quick-moving prey, but carnivorous turtles are able to move their heads rapidly to snap.
Turtles Communication
The Arrau turtle has the sizable vocal repertoire.
While typically thought of as mute, turtles make different sounds when communicating. Tortoises might be vocal when dating and mating. Various species of both freshwater plus sea turtles emit numerous types of calls, usually short and low frequency, from the time they may be in the egg in order to whenever they are adults. These vocalizations may serve in order to create group cohesion when migrating.
Turtle Cleverness
See also: Animal cognition
It offers been reported that wooden turtles are better than white rats at studying to navigate mazes. Case studies exist of turtles playing. They are doing, however, have got a very low encephalization quotient (relative brain in order to body mass), and their particular hard shells enable them to live without fast reflexes or elaborate predator prevention strategies. In the laboratory, turtles (Pseudemys nelsoni) can learn novel operant jobs and have demonstrated a long-term memory of at least 7. 5 months.
Turtle Mating Strategies
An example of mounting behavior within turtles
Turtles are recognized for displaying a broad variety of mating behaviors, nevertheless , they are not really known for forming pair-bonds or for being component of a social group. Once fertilization has happened and an offspring has been produced, neither mother or father will provide care regarding the offspring once it's 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 create different courting strategies or even use alternate methods to gain access to a potential mate. Most terrestrial species have males that are usually bigger than females, and combating 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 the potential mate. For the majority of semi-aquatic species and bottom-walking aquatic species, combat happens less often. Males that belong 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 usually smaller than females and therefore they cannot use the particular same strategy as their semi-aquatic relatives, which depends on overwhelming the females with strength. Males in this class resort to using courtship displays in an try to gain mating accessibility to a female.
Combating Between Males Turtles
Saddle back Galapagos tortoise
Wood turtles invariably is an example of a terrestrial species where the males have a hierarchical ranking system based on dominance through fighting, and it's shown that the males with the highest rank and thus the most wins in arguements have the most children.
Galapagos tortoises are one more example of a varieties which has a hierarchical rank which is determined simply by dominance displays, and entry to food and partners is regulated by this dominance hierarchy. Two male saddle backs most frequently compete for access to cactus trees, which is their particular source of food. The particular winner is the person who stretches their neck the highest, which individual gets access to the particular cactus tree, which may attract potential mates.
Push Mating Turtles
Male (left) and female (right) radiated tortoise
The male scorpion dirt turtle is an illustration of a bottom-walking marine species that relies on overpowering females with its bigger size as a mating strategy. The male approaches the feminine from the rear, and often resorts in order to aggressive methods such as gnawing at the female's tail or hind limbs, then the mounting behavior in which usually the male clasps the particular edges of her carapace with his forelimbs plus hind limbs to hold 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 head into her shell. This exposes her cloaca, and with it exposed, the man can attempt copulation by wanting to insert his holding tail.
Male radiated tortoises are also known to make use of the force mating technique wherein they use encircling vegetation to trap or prevent females from getting away, then pin them down for copulation.
Turtles Courtship Displays
Red-eared sliders are an sort of a fully aquatic species in which the male works a courtship behavior. Within this case the male extends his forelegs using the palms facing out and flutters his forelegs in the female's face. Female options are important in this technique, and the females of a few species, such as green sea turtles, aren't usually receptive. As a result, they've evolved certain behaviors to prevent the male's attempts in copulation, such as swimming away, confronting the man followed by biting, or even 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 superficial to perform the refusal position, the females will resort to beaching on their own, which is a proven deterrent method, as the males is not going to follow them ashore.
Ecology and life history of turtles
Ocean turtle swimming
Although numerous 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 dried out land. Aquatic respiration within Australian freshwater turtles will be currently being studied. Several species have large cloacal cavities that are covered with many finger-like projections. These projections, called papillae, possess a rich blood provide and boost the surface region of the cloaca. The turtles can take up dissolved oxygen from the particular water using these papillae, within much the same way that fish use gills to respire.
Like other reptiles, turtles lay eggs that are slightly gentle and leathery. The eggs of the major species are usually spherical while the eggs of the rest are elongated. Their albumen will be white and contains an alternative protein from bird ovum, such that it will not coagulate when prepared. Turtle eggs ready to eat consist mainly of yolk. In some species, temp determines whether an egg cell develops into a man or a female: a higher temperature the female, the lower temperature the man. Large numbers of eggs are deposited in holes dug into mud or even sand. They are then covered and left in order to incubate by themselves. Depending on 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 simply no known species in which the mother cares for her young.
Sea turtles lay their own eggs on dry, exotic beaches. Immature sea turtles are not cared with regard to by the adults. Turtles can take many years to achieve breeding age, and in many cases, breed every few years , rather than annually.
Researchers have lately learned a turtle's internal organs do not gradually break down or become less efficient over time, unlike most other animals. It was found that the liver, lungs, and kidneys of a centenarian turtle are almost indistinguishable from those of its immature equal. This has inspired genetic researchers to commence analyzing the turtle genome with regard to longevity genes.
A group 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. Grownup turtles typically eat aquatic plants; (citation needed) invertebrates such as insects, snails, plus worms; and have already been reported to occasionally consume dead marine animals. Many small freshwater species are carnivorous, eating small fish and many aquatic existence. However, protein is important to turtle growth and juvenile turtles are purely carnivorous.
Sea turtles usually feed on jellyfish, sponges, and other soft-bodied microorganisms. Some species with more powerful jaws have been observed to eat shellfish, whilst others, like the green ocean turtle, do not consume meat at all and, instead, have a diet mostly made up of algae.
Systematics and evolution of Turtles
Primary article: Turtle classification
See|Observe|Notice} also: List of Testudines family members
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 thought to have existed in the late Triassic Period associated with the Mesozoic era, regarding 220 million years ago, and their shell, which usually has remained a incredibly stable body plan, will be considered to have evolved from bony extensions of their own 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 component of the shell was not complete. This is backed by fossils of the 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 plus an incomplete carapace, similar to an early phase of turtle embryonic advancement. Just before this discovery, the earliest-known fossil turtle forefathers, like Proganochelys, were terrestrial and had a complete shell, offering no clue to the evolution of this exceptional anatomical feature. From the late Jurassic, turtles had extended widely, and their precious history becomes much easier to study.
Their precise ancestry provides been disputed. It was believed they are the particular only surviving branch of the ancient evolutionary grade Anapsida, which includes groupings such as procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporary opening while all additional extant amniotes have temporal openings (although in mammals, the hole has become the zygomatic arch). The particular millerettids, protorothyrids, and pareiasaurs became extinct in the late Permian period plus the procolophonoids during the particular Triassic.
Nevertheless , it was later suggested that this anapsid-like turtle skull may 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 than to Archosauria.[55][56] All molecular studies have got strongly upheld the positioning of turtles within diapsids; some place turtles within Archosauria, or, more frequently, as a sister team to extant archosaurs,[58][59][60][61] though an analysis performed by Lyson et al. (2012) recovered turtles as the sister group of lepidosaurs instead. Reanalysis of before phylogenies suggests that they classified turtles as anapsids both simply because they assumed this classification (most of all of them studying what sort associated with 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 particular debate is far from settled. Even the conventional placement of turtles outdoors Diapsida cannot be dominated out at this point. A combined analysis of morphological and molecular data conducted by Lee (2001) found turtles to become anapsids (though a connection 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 group to birds and crocodiles (the Archosauria).[66] The date of splitting up of turtles and wild birds and crocodiles was approximated to be 255 mil years ago. The most current common ancestor of living turtles, corresponding to the divided between Pleurodira and Cryptodira, was estimated to get happened around 157 million years ago. The oldest conclusive crown-group turtle (member of the modern clade Testudines) is the species Caribemys oxfordiensis through the late Jurassic period (Oxfordian stage). Through utilizing the first genomic-scale phylogenetic analysis of ultraconserved elements (UCEs) to investigate the placement of turtles within reptiles, Crawford et al. (2012) also recommend that turtles are a sister group to wild birds 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 data 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 head characteristics as it right now possesses an anapsid-like skull.
The earliest known fully shelled member of the particular turtle lineage is the particular late Triassic Proganochelys. This particular genus already possessed many advanced turtle traits, plus thus probably indicates many millions of years associated with preceding turtle evolution; this is further supported simply by evidence from fossil tracks from the Early Triassic of the United States (Wyoming and Utah) plus from the Middle Triassic of Germany, indicating that proto-turtles already existed as early as the Early Triassic. Proganochelys lacked the opportunity to pull its head into its shell, had a long neck, and had the long, spiked tail ending in a club. Could body form is comparable to those of ankylosaurs, it resulted from convergent development.
Turtles are divided in to two extant suborders: Cryptodira and Pleurodira. The Cryptodira is the larger associated with the two groups and includes all the sea turtles, the terrestrial tortoises, and many of the freshwater turtles. The Pleurodira are usually sometimes known as the side-necked turtles, a reference to how they retract their own heads into their shells. This smaller group consists mainly of various freshwater turtles.