Encyclopaedia of Babies of Beautiful Wild Animals: The Baby Turtle
Turtles are diapsids of the order Testudines (or Chelonii) characterized by a special bony or cartilaginous shell developed from their ribs and acting as a shield. "Turtle" may refer to the order as the whole (American English) or even to fresh-water and sea-dwelling testudines (British English). The order Testudines includes each extant (living) and vanished species. The earliest recognized members of this group date from 220 million years ago, making turtles one of the oldest reptile groups and the more ancient group compared to snakes or crocodilians. Of the 356 known species alive today, some are usually highly endangered.
Turtles are ectotherms—animals commonly called cold-blooded—meaning that their internal temp varies according to the particular ambient environment. However, since of their high metabolic rate, leatherback sea turtles have a body heat that is noticeably higher than that of the surrounding water. Turtles are classified as amniotes, along with other reptiles, birds, and mammals. Like other amniotes, turtles breathe air flow and do not place eggs underwater, although several species live in or even around water. The research of turtles is known as cheloniology, after the Greek term for turtle. It will be 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, depending on the range of English being utilized. These terms are typical names , nor reflect exact biological or taxonomic variations.
Turtle may either refer to the order as a whole, or to particular turtles that create up a form taxon that 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 to describe several species of small, edible, hard-shell turtles, typically those found within brackish waters.
In North America, all chelonians are commonly called turtles. Tortoise is used only in mention of the fully terrestrial turtles or, more narrowly, just those members of Testudinidae, the family of modern property tortoises. Terrapin may relate to small semi-aquatic turtles that live in new and brackish water, particularly the diamondback terrapin (Malaclemys terrapin). Although the members of the genus Terrapene live mostly on land, they will are referred to as box turtles rather than tortoises. The particular 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" like a more specific phrase for slow-moving terrestrial types.
In the United Empire, the word turtle is utilized 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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What do Turtles Eat
The word chelonian is popular among veterinarians, scientists, and conservationists working with these types of animals as a catch-all name for any member of the particular superorder Chelonia, which includes almost all turtles living and extinct, as well as their immediate ancestors. Chelonia is based on the Ancient 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 regarding turtle.
Some languages do not have this distinction, as all of these types of are known by the same name. For example , in Spanish, the word tortuga is used for turtles, tortoises, and terrapins. A sea-dwelling turtle is tortuga marina, a freshwater varieties tortuga de río, plus a tortoise tortuga terrestre.
The largest living chelonian is the leatherback sea turtle (Dermochelys coriacea), which usually reaches a shell length of 200 cm (6. 6 ft) and can achieve a weight of over 900 kg (2, 500 lb). Freshwater turtles are usually generally smaller, but 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 America, which attains a shell length of up to 80 cm (2. 6 ft) and weighs because much as 113. four kg (250 lb).
Huge tortoises of the genera Geochelone, Meiolania, and other people were relatively widely dispersed all over the world into prehistoric times, and are known to have existed in North and South America, Australia, and Africa. They became vanished at the same period as the appearance associated with man, and it is usually assumed humans hunted them for food. The only surviving giant tortoises are usually on the Seychelles plus Galápagos Islands and can develop to over 130 cm (51 in) in size, and weigh about three hundred kg (660 lb).
The particular largest ever chelonian was Archelon ischyros, a Late Cretaceous sea turtle recognized to have been as much as 4. 6 m (15 ft) long.
Baby turtles wallpapers Baby Animals
The tiniest turtle is the speckled padloper tortoise of South Africa. It measures no more than 8 centimeter (3. 1 in) long and weighs about a hundred and forty g (4. 9 oz). Two other species of small turtles are the particular American mud turtles and musk turtles that reside in an area that ranges from Canada in order to South America. The cover duration of many species within this group is much less than 13 cm (5. 1 in) long.
Turtles are divided into 2 groups, according to the way they retract their necks to their shells (something the ancestral Proganochelys could not do). The mechanism of neck of the guitar 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 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 usually 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 main function and evolutionary implication of neck retraction will be thought to be with regard to feeding rather than safety. Neck retraction and reciprocal extension allows the turtle to reach out further to capture prey while swimming. Neck expansion creates suction once the head is drive forward and the oropharynx is expanded, and this particular morphology suggests the retraction function is for nourishing purposes as the suction helps catch prey. The protection the shell provides the head when it is retracted is therefore not the main function of retraction, thus is an exaptation. As for the difference between the two methods of retraction, both Pleurodirans and Cryptodirans use the quick extension of the neck like a method of predation, so the difference in retraction mechanism is just not due to a difference in ecological niche.
Head
Most turtles that spend most of their lives on property get their eyes looking lower at objects in front side of them. Some marine turtles, such as snapping turtles and soft-shelled turtles, have eyes closer to the very best of the head. These types of turtle can hide from predators in 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 consumed from the water they consume.
Turtles have rigid beaks and use their jaws to cut and chew food. Instead of having teeth, which they appear in order to have lost about 150-200 million years ago, the particular upper and lower jaws of the turtle are usually covered by horny ridges. Carnivorous turtles usually have 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 in order to swallow food, but as opposed to most reptiles, they cannot stick out their tongues in order to catch food.
ShellMain article: Turtle shellThe upper 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 became a member of together on the turtle's sides by bony buildings called bridges. The inner layer of a turtle's shell is made up of about 60 bones that include portions of the backbone and the particular ribs, meaning the turtle cannot crawl away from the shell. In most turtles, the outer layer of the shell is covered by horny scales called scutes which are part of its outer skin, or skin. Scutes comprise of the particular fibrous protein keratin that will also makes up the scales of other reptiles. These scutes overlap the particular seams between the cover bones and add strength towards the shell. Some turtles do not possess horny scutes; with regard to example, the leatherback sea turtle as well as the soft-shelled turtles have shells covered along with leathery skin instead.
The particular shape of the covering gives helpful clues about how a turtle lives. The majority of tortoises have a huge, dome-shaped shell that can make it difficult for predators to crush the shell between their jaws. 1 of the few exclusions is the African hot cake tortoise, which has a flat, flexible shell that will allows it to conceal in rock crevices. The majority of aquatic turtles have flat, streamlined shells, which help in swimming and diving. American snapping turtles and musk turtles have small, cross-shaped plastrons that give them more efficient leg movement for walking along the bottom of ponds and streams. Another exception is the Belawan Turtle (Cirebon, West Java), that has sunken-back soft-shell.
The color of a turtle's shell may differ. Shells are commonly coloured brown, black, or olive green. In certain species, shells may have red, orange, yellow, or grey markings, often spots, lines, or irregular blotches. One of the most colourful turtles is the eastern painted turtle, which consists of a yellow plastron and a black or olive shell with red markings 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 going in water and swim faster with more agility. These lighter shells have got large spaces called fontanelles between the shell bones. The shells of leatherback sea turtles are extremely lighting because they lack scutes and contain many fontanelles.
It has been suggested by Jackson (2002) that the turtle shell can function as pH buffer. To endure through anoxic conditions, such as winter periods trapped beneath glaciers or within anoxic mud at the end of ponds, turtles utilize two general physiological mechanisms. In the situation of prolonged periods associated with anoxia, it has been shown that this turtle cover both releases carbonate buffers and uptakes lactic acidity.
Turtles Survive Frigid Hibernations By Breathing Through Their Butts Dbrief
Breathing Turtles
Respiration, for many amniotes, is achieved by the particular contraction and relaxation of specific muscles (i. electronic. intercostals, abdominal muscles, and/or the diaphragm) mounted on an internal rib-cage that can expand or contract the entire body wall thus assisting airflow in and out of the lungs. The ribs of Chelonians, however, are fused with their carapace and external to their pelvic plus pectoral girdles, a function unique among turtles. This rigid shell is not really 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 pull the lungs ventrally during inspiration, where air is drawn in via a negative pressure gradient (Boyle's Law). In expiration, the contraction of the transversus abdominis is the driving push by propelling the viscera into the lungs and expelling air under positive pressure. Conversely, the calming and flattening of the oblique abdominis muscle draws the transversus back straight down which, once again, draws air back into the lung area. Important auxiliary muscles utilized for ventilatory processes would be the pectoralis, which is used in conjunction with the particular transverse abdominis during inspiration, as well as the serratus, which movements with all the abdominal oblique accompanying expiration.
The lungs associated with Testudines are multi-chambered and attached their entire length over the carapace. The amount of chambers can vary in between taxa, though most commonly they will have three lateral chambers, three medial chambers, and one terminal chamber. As mentioned earlier on, the act of specific abdominal muscles pulling down the viscera (or pushing back up) is exactly what allows for respiration within turtles. Specifically, it is the turtles large liver that pulls or forces 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 abdomen is directly attached to the left lung simply by the ventral mesopneumonium, which is attached to their liver from the ventral mesentery. When the liver is taken down, inspiration begins. Assisting the lungs is the particular post-pulmonary septum, which is found in all Testudines, and it is thought to prevent the particular lungs from collapsing.
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Turtles Epidermis and molting
As pointed out above, the outer level of the shell is usually part of the pores and skin; each scute (or plate) on the shell corresponds to a single revised scale. The remainder associated with the skin has a lot smaller scales, like the skin of other reptiles. Turtles do not molt their skins all at once as snakes do, yet continuously in small items. When turtles are kept in aquaria, small linens of dead skin may be seen in the particular water (often appearing in order to be a thin item of plastic) having already been sloughed off when the particular animals deliberately rub on their own against some wood or even stone. Tortoises also lose skin, but dead epidermis is allowed to accumulate in to thick knobs and dishes that provide protection to parts of the body outside the shell.
By counting the rings created by the stack of smaller, older scutes on top of the larger, newer ones, it is possible to estimate the age group of a turtle, when one knows the number of scutes are produced in per year. This method is not very accurate, partly because 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, durable feet. Tortoises are well-known for moving slowly, simply because of their heavy, cumbersome shells, which limit stride length.
Skeleton of snapping turtle (Chelydra serpentina)
Amphibious turtles normally possess limbs similar to those of tortoises, except that the particular feet are webbed plus often have long paws. These turtles swim using all four feet within a way similar in order to the dog paddle, along with the feet on the particular left and right side of the body alternately providing drive. Large turtles tend in order to swim less than smaller sized ones, and the really big species, such since alligator snapping turtles, barely swim whatsoever, preferring to walk across 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 records upon which they bask. Male turtles tend in order to have particularly long paws, and these appear to be used to stimulate the women while mating. While the majority of 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 claws being relatively small. These species swim in the same manner because sea turtles do (see below).
Sea turtles are usually almost entirely aquatic plus have flippers instead of feet. Sea turtles fly through the water, using the up-and-down motion of the particular front flippers to create drive; the back feet are certainly not used for propulsion yet may be used as rudders regarding steering. Compared with freshwater turtles, sea turtles have got very limited mobility upon land, and apart from the dash from the nest towards the sea as hatchlings, man sea turtles normally never leave the sea. Females must come back on to land to lay eggs. They move very slowly and laboriously, dragging by themselves forwards with their flippers.
Behavior of Turtles
Senses of Turtles are thought to get exceptional night eyesight due to the unusually large amount of rod cells in their retinas. Turtles possess color vision with the wealth of cone subtypes with sensitivities ranging from the near ultraviolet (UVA) to red. Some land turtles have very bad pursuit movement abilities, which usually are normally found only in predators that hunt quick-moving prey, but carnivorous turtles are able in order to move their heads quickly to snap.
Turtles Communication
The particular Arrau turtle has a sizable vocal repertoire.
While typically thought of since mute, turtles make different sounds when communicating. Tortoises might be vocal when dating and mating. Various types of both freshwater plus sea turtles emit several types of calls, usually short and low rate of recurrence, from the time these are in the egg in order to whenever they are adults. These vocalizations may serve in order to create group cohesion whenever migrating.
Turtle Intelligence
See furthermore: Animal cognition
It offers been reported that wood turtles are better compared to white rats at understanding to navigate mazes. Case 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 prevention strategies. In the laboratory, turtles (Pseudemys nelsoni) can learn novel operant tasks and have demonstrated a long lasting memory of at minimum 7. 5 months.
Turtle Mating Methods
An example of mounting behavior within turtles
Turtles are known for displaying a broad variety of mating behaviours, however , they are not known for forming pair-bonds or for being component of a social group. Once fertilization has occurred and an offspring offers been produced, neither parent will provide care with regard to the offspring once it's hatched. Females generally outnumber males in various turtle species (such as Eco-friendly turtles), and as a result, most males will engage in multiple copulation with multiple partners all through their lifespan. However, because of to the sexual dimorphism present in most turtle species, males must create different courting strategies or use alternate methods to gain access to a potential mate. Most terrestrial species have males that are larger than females, and battling between males often establishes a hierarchical order within which the higher upward the order an person is, the better the particular chance is of the individual getting access to a 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 advantage to forcibly mate with a female. In fully marine species, males are frequently smaller than females plus therefore they cannot use the particular same strategy as their semi-aquatic relatives, which relies on overpowering the females with power. Males in this category resort to using courtship displays in an try to gain mating access to a female.
Battling Between Males Turtles
Saddle back again Galapagos tortoise
Wood turtles invariably is an example of a terrestrial species where the particular 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 battles have the most children.
Galapagos tortoises are an additional example of a species which has a hierarchical rank that is determined simply by dominance displays, and entry to food and friends is regulated by this particular dominance hierarchy. Two man saddle backs most frequently compete for access to cactus trees, that is their own source of food. The winner is the person who stretches their throat the highest, and that individual gets access to the cactus tree, which can attract potential mates.
Pressure Mating Turtles
Male (left) plus female (right) radiated tortoise
The male scorpion dirt turtle is an example of a bottom-walking marine species that depends on overpowering females with its bigger size as a mating strategy. The male techniques the feminine from the back, and often resorts to aggressive methods such as biting the female's tail or hind limbs, followed by the mounting behavior in which usually the male clasps the edges of her carapace with his forelimbs plus hind limbs to keep the girl in position. The male follows this action by laterally waving his mind and sometimes biting the female's head in an attempt to get the girl to withdraw her head into her shell. This exposes her cloaca, and along with it exposed, the man can attempt copulation by trying 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 even prevent females from escaping, then pin them straight down for copulation.
Turtles Courtship Displays
Red-eared sliders are a good sort of a fully aquatic species where the male performs a courtship behavior. Within this case the male 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, as well as the females of some species, such as eco-friendly sea turtles, aren't constantly receptive. As such, they've developed certain behaviors to avoid the male's attempts from 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 along 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 on their own, which is a confirmed deterrent method, as the particular males is not going to follow them ashore.
Ecology and life history of turtles
Sea turtle swimming
Although numerous 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 invest much or all associated with their lives on dry land. Aquatic respiration within Australian freshwater turtles is usually currently being studied. A few species have large cloacal cavities that are covered with many finger-like projections. These projections, called papillae, have got a rich blood supply and raise the surface region of the cloaca. The particular turtles can take upward dissolved oxygen from the water using these papillae, in much the same method that fish use gills to respire.
Like some other reptiles, turtles lay eggs that are slightly smooth and leathery. The ovum of the largest species are usually spherical while the ovum of the rest are usually elongated. Their albumen is usually white and contains a different protein from bird ovum, such that it may not coagulate when cooked. Turtle eggs ready to consume consist mainly of yolk. In some species, temp determines whether an egg cell develops into a male or perhaps a female: a increased temperature the female, the lower temperature causes a man. Large numbers of eggs are deposited in holes dug into mud or even sand. They are then covered and left to incubate by themselves. Depending upon the species, the ovum will typically take 70–120 days to hatch. Once the turtles hatch, they squirm their way to the particular surface and head toward the water. You can find no known species where the mom cares for her youthful.
Sea turtles lay their particular eggs on dry, sandy beaches. Immature sea turtles are not cared for by the adults. Turtles can take many many years to reach breeding age, and in many cases, breed every few years ınstead of annually.
Researchers have lately learned a turtle's internal organs usually do not little by little break lower or become less effective over time, unlike many other animals. It has been found that the liver organ, lungs, and kidneys of a centenarian turtle are usually nearly indistinguishable from individuals of its immature counterpart. This has inspired hereditary researchers to start examining the turtle genome with regard to longevity genes.
A team of turtles is actually a bale.
Turtles Diet
A green sea turtle grazing on
A turtle's diet varies greatly determined by the environment by which it lives. Adult turtles typically eat marine plants; (citation needed) invertebrates for example insects, snails, plus worms; and have been reported to occasionally consume dead marine animals. A number of small freshwater species are carnivorous, eating small fish and many aquatic lifestyle. However, protein is essential to turtle growth and juvenile turtles are solely carnivorous.
Sea turtles usually feed on jellyfish, sponges, and other soft-bodied organisms. Some species with better jaws have been noticed to eat shellfish, while others, for example the green ocean turtle, do not consume meat at all and, instead, possess a diet mainly 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
Centered on body fossils, the first proto-turtles are thought to have existed in the late Triassic Period of the Mesozoic era, about 220 million years back, and their shell, which usually has remained a incredibly stable body plan, will be thought to have evolved from bony extensions of their particular backbones and broad ribs that expanded and grew together to form the complete shell that offered protection at every phase of its evolution, also when the bony component 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 plus an incomplete carapace, similar to an early phase of turtle embryonic development. Just before this discovery, the particular earliest-known fossil turtle ancestors, like Proganochelys, were terrestrial and had a complete cover, offering no clue in order to the evolution of the amazing anatomical feature. By the late Jurassic, turtles had radiated widely, and their fossil history becomes easier to study.
Their exact ancestry provides been disputed. It was believed they are the particular only surviving branch associated with the ancient evolutionary quality Anapsida, which includes groups such as procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporary opening while all additional extant amniotes have temporary 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.
However , it was later suggested that this anapsid-like turtle skull 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, somewhat closer to Squamata in order to Archosauria.[55][56] All molecular studies have got strongly upheld the positioning of turtles within diapsids; some place turtles inside Archosauria, or, more commonly, as a sister group to extant archosaurs,[58][59][60][61] though an analysis performed by Lyson et 's. (2012) recovered turtles since the sister group of lepidosaurs instead. Reanalysis of before phylogenies suggests that these people classified turtles as anapsids both simply 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 regarding constructing the cladogram. Testudines were suggested to get diverged from other diapsids between 200 and 279 mil years ago, though the particular debate is far through settled. Even the traditional placement of turtles outside Diapsida cannot be dominated out at this point. A combined analysis associated with morphological and molecular data conducted by Lee (2001) found turtles to end up being anapsids (though a connection with archosaurs couldn't end up being statistically rejected).[64] Similarly, a morphological study conducted by Lyson ainsi que al.. (2010) recovered all of them as anapsids most carefully related to Eunotosaurus. The 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 separation of turtles and parrots and crocodiles was approximated to be 255 million in years past. The most current common ancestor of residing turtles, corresponding to the split between Pleurodira and Cryptodira, was estimated to get occurred around 157 million many years ago. The oldest conclusive crown-group turtle (member from the modern clade Testudines) may be the species Caribemys oxfordiensis from the late Jurassic period (Oxfordian stage). Through utilizing the very first genomic-scale phylogenetic analysis of ultraconserved elements (UCEs) to check into the placement of turtles within reptiles, Crawford ainsi que al. (2012) also suggest that turtles are a sister group to 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 information started date in their analysis and concluded that turtles are likely a sister group of crocodilians and birds (Archosauria). This placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics as it right now possesses an anapsid-like head.
The earliest known fully shelled member of the particular turtle lineage is the late Triassic Proganochelys. This genus already possessed many advanced turtle traits, plus thus probably indicates several millions of years associated with 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 will proto-turtles already existed because early as the first Triassic. Proganochelys lacked the opportunity to pull its head into its shell, had a long neck, and had the long, spiked tail finishing in a club. While this body form is similar to that of ankylosaurs, it resulted from convergent advancement.
Turtles are divided into two extant suborders: Cryptodira and Pleurodira. The Cryptodira is the larger of the two groups plus includes all the marine turtles, the terrestrial tortoises, and several of the fresh water turtles. The Pleurodira are sometimes known as the particular side-necked turtles, a reference to the way they retract their own heads to their shells. This smaller group consists primarily of various freshwater turtles.