May 2011 Home Pet Care
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 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 both extant (living) and extinct species. The earliest recognized members of this group date from 220 million years ago, making turtles one of the oldest reptile groups and a more ancient group compared to snakes or crocodilians. Of the 356 known species alive today, some are 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 temp that is noticeably increased than that of the particular surrounding water. Turtles are usually classified as amniotes, along with other reptiles, parrots, and mammals. Like additional amniotes, turtles breathe air flow and do not place eggs underwater, although numerous species live in or even around water. The study of turtles is known as cheloniology, following the Greek word for turtle. It is usually 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, according to the variety of English being used. These terms are common names and don't reflect exact biological or taxonomic distinctions.
Turtle may either refer to the order because a whole, or to particular turtles that make up a form taxon which is not monophyletic, or might be limited to only marine species. Tortoise usually refers to any land-dwelling, non-swimming chelonian. Terrapin can be used to describe several species associated with small, edible, hard-shell turtles, typically those found within brackish waters.
In Northern 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 land tortoises. Terrapin may refer to small semi-aquatic turtles that live in fresh and brackish water, in particular the diamondback terrapin (Malaclemys terrapin). Although the users from the genus Terrapene dwell 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 species of the order Testudines, whether or not they are land-dwelling or even sea-dwelling, and uses "tortoise" like a more specific phrase for slow-moving terrestrial varieties.
In the United Kingdom, the word turtle is used for water-dwelling species, which includes ones known in the US as terrapins, although not for terrestrial species, which are known only as tortoises.
Rangking: 29
Size: 80.2KB
Width: 1134
Height: 756
Edge Of The Plank: Cute Animals: Baby Sea Turtles
The word chelonian will be popular among veterinarians, scientists, and conservationists working with these animals being a catch-all title for any member of the superorder Chelonia, which includes almost all turtles living and vanished, as well as their immediate ancestors. Chelonia will be based on the Ancient greek word for turtles, χελώνη chelone; Greek χέλυς chelys "tortoise" is also used in the formation of technological 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 do not have this variation, as all of these are referred to by the particular same name. For instance , in Spanish, the word tortuga is used for turtles, tortoises, and terrapins. A sea-dwelling turtle is tortuga marina, a freshwater species 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 reach a weight of more than 900 kg (2, 000 lb). Freshwater turtles are usually generally smaller, but with the largest species, the Asian softshell turtle Pelochelys cantorii, a few people have been reported up 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 in order to 80 cm (2. six ft) and weighs as much as 113. four kg (250 lb).
Large tortoises of the overal Geochelone, Meiolania, and others were relatively widely dispersed around the world into prehistoric periods, and they are known to have existed in North plus South America, Australia, and Africa. They became wiped out at the same period as the appearance associated with man, and it is usually assumed humans hunted them for food. The just surviving giant tortoises are usually on the Seychelles and Galápagos Islands and can develop to over 130 cm (51 in) in size, and weigh about 300 kg (660 lb).
The largest ever chelonian has been Archelon ischyros, a Past due Cretaceous sea turtle identified to have been as much as 4. 6 m (15 ft) long.
Turtles that live on land Pets4Homes
The smallest turtle is the speckled padloper tortoise of South Africa. It measures simply 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 American mud turtles and musk turtles that reside in an area that ranges from Canada to South America. The shell duration of many species in this group is less than 13 cm (5. 1 in) long.
Turtles are divided into two groups, according to how they retract their necks to their shells (something the ancestral Proganochelys could not do). The mechanism of throat retraction differs phylogenetically: the suborder Pleurodira retracts laterally to the side, anterior to glenohumeral joint 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 backbone. Of all recent turtles, the cervical column consists of nine joints plus eight vertebrae, which are usually individually independent. Since these types of vertebrae are not fused and are rounded, the neck is more flexible, being able to flex in the backwards plus sideways directions. The major function and evolutionary inference of neck retraction is usually thought to be with regard to feeding rather than protection. Neck retraction and testing extension allows the turtle to reach out further to capture prey while going swimming. Neck expansion creates suction 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 therefore not the main functionality of retraction, thus is usually an exaptation. As with regard to the difference between the two methods of retraction, both Pleurodirans and Cryptodirans use the quick expansion of the neck being a method of predation, therefore the difference in retraction mechanism is not due in order to a difference in ecological niche.
Head
Most turtles that spend most associated with their lives on land get their eyes looking lower at objects in front side of them. Some aquatic turtles, such as nipping turtles and soft-shelled turtles, have eyes closer in order to the top of the head. These types of turtle can hide from predators within shallow water, where these people lie entirely submerged except for their eyes and nostrils. Near their eyes, sea turtles possess intrigue that produce salty holes that rid themselves of excess salt consumed in from the water they drink.
Turtles have rigid beaks and use their teeth to cut and chew food. Instead of having teeth, that they appear to have lost about 150-200 million years ago, the particular upper and lower jaws 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 cut through tough plants. They will use their tongues to swallow food, but unlike most reptiles, they can not stay out their tongues in order to catch food.
ShellPrimary article: Turtle shellThe upper shell of the turtle is known as the carapace. The particular lower shell that encases the belly is known as the plastron. The carapace and plastron are joined 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 that are part of its outer skin, or pores and skin. Scutes are made up of the particular fibrous protein keratin that will also makes up the scales of other lizards. These scutes overlap the seams between the cover bones and add power towards the shell. Some turtles do not have horny scutes; regarding example, the leatherback ocean turtle and the soft-shelled turtles have shells covered along with leathery skin instead.
The particular shape of the shell gives helpful clues about how a turtle lives. The majority of tortoises have a large, dome-shaped shell that can make it difficult for predators to crush the cover between their jaws. One of the few conditions is the African pancake tortoise, which has the flat, flexible shell that allows it to hide in rock crevices. Many aquatic turtles have flat, streamlined shells, which aid in swimming and diving. United states snapping turtles and musk turtles have small, cross-shaped plastrons that give all of them more efficient leg movement for walking along the bottom of ponds plus streams. Another exception will be 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, shells may have red, orange, yellow, or grey markings, often spots, lines, or even irregular blotches. One of the most colorful 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 rather heavy shells. In contrast, aquatic and soft-shelled turtles have lighter shells that will help them avoid settling in water and go swimming faster with more speed. These lighter shells have got large spaces called fontanelles between the shell bone fragments. The shells of leatherback sea turtles are extremely lighting because they lack scutes and contain many fontanelles.
It has been recommended by Jackson (2002) that the turtle shell may function as pH barrier. To endure through anoxic conditions, such as winter periods trapped beneath snow 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 already been shown that the turtle cover both releases carbonate buffers and uptakes lactic acid.
Lets Learn about Green sea turtles. – Journal Edge
Respiration Turtles
Respiration, for many amniotes, is achieved by the contraction and relaxation associated with specific muscles (i. electronic. intercostals, abs, and/or the diaphragm) mounted on an inner rib-cage that can expand or contract the entire body wall thus assisting air flow in and out of the lung area. 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 rigid shell is not really 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 draw the lungs ventrally during inspiration, where air is usually drawn in via the negative pressure gradient (Boyle's Law). In expiration, the particular contraction of the transversus abdominis is the driving pressure by propelling the viscera into the lungs and expelling air under optimistic pressure. Conversely, the relaxing and flattening of the oblique abdominis muscle drags the transversus back lower which, once again, draws air back into the lung area. Important auxiliary muscles utilized for ventilatory processes are the pectoralis, which is used in conjunction with the particular transverse abdominis during inspiration, and the serratus, which movements using the abdominal oblique associated expiration.
The lungs of Testudines are multi-chambered and attached their entire length down the carapace. The amount of chambers can differ in between taxa, though most often they will have three lateral compartments, three medial chambers, and another terminal chamber. As earlier mentioned, the act of particular abdominal muscles pulling straight down the viscera (or pressing back up) is exactly what allows for respiration within turtles. Specifically, it will be 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 in order to the left lung simply by the ventral mesopneumonium, which is attached to their liver from the ventral mesentery. When the liver is drawn down, inspiration begins. Helping the lungs is the particular post-pulmonary septum, which is discovered in all Testudines, and is thought to prevent the lungs from collapsing.
Common snapping turtle Wikipedia
Turtles Epidermis and molting
As pointed out above, the outer level of the shell will be part of the epidermis; each scute (or plate) on the shell refers to a single modified scale. The remainder of the skin has much smaller scales, like the pores and skin of other reptiles. Turtles do not molt their own skins all at as soon as as snakes do, yet continuously in small parts. When turtles are held in aquaria, small linens of dead skin can be seen in the particular 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 a piece of wood or stone. Tortoises also drop skin, but dead pores and skin is permitted to accumulate directly into thick knobs and dishes that provide protection to parts of the body outside the shell.
By counting the rings created by the stack associated with smaller, older scutes on top of the larger, newer types, you are able to estimate the age group of a turtle, if one knows the number of scutes are produced in per year. This method is not very accurate, partly because growth rate is not constant, but also because some of the scutes eventually fall away through the shell.
Turtles Braches
Terrestrial tortoises have short, sturdy feet. Tortoises are well-known for moving slowly, simply because of their heavy, cumbersome shells, which limit stride length.
Skeleton associated with snapping turtle (Chelydra serpentina)
Amphibious turtles normally have got limbs similar to those of tortoises, except that the particular feet are webbed and often have long claws. These turtles swim using all four feet within a way similar in order to the dog paddle, with the feet on the right and left side of the body alternately providing thrust. Large turtles tend to swim less than smaller ones, and the extremely big species, such since alligator snapping turtles, hardly swim whatsoever, preferring to walk across the bottom of the river or lake. As well as webbed feet, turtles have really long claws, used to help them clamber on to riverbanks and floating records upon which they bask. Male turtles tend in order to have particularly long paws, and these appear to be utilized to stimulate the woman while mating. While most turtles have webbed feet, some, like the pig-nosed turtle, have true flippers, along with the digits being joined into paddles as well as the paws being relatively small. These species swim in the same manner because sea turtles do (see below).
Sea turtles are almost entirely aquatic and have flippers instead of feet. Sea turtles take flight through the water, using the particular up-and-down motion of the particular front flippers to generate drive; the back feet are certainly not used for propulsion yet can be utilized as rudders for steering. Compared with fresh water turtles, sea turtles possess very limited mobility upon land, and apart from the splash from the nest to the sea as hatchlings, male sea turtles normally in no way leave the sea. Females must come back on to land to lay ovum. They move very gradually and laboriously, dragging themselves forwards with their flippers.
Habits of Turtles
Senses of Turtles are thought to get exceptional night eyesight due to the unusually large quantity 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 search 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 because mute, turtles make various sounds when communicating. Tortoises might be vocal when dating and mating. Various types of both freshwater and sea turtles emit many types of calls, often short and low frequency, from the time they may be in the egg in order to when they are adults. These vocalizations may serve to create group cohesion whenever migrating.
Turtle Cleverness
See also: Animal knowledge
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 own hard shells enable these to live without fast reflexes or elaborate predator prevention strategies. In the lab, turtles (Pseudemys nelsoni) may learn novel operant duties and have demonstrated a long-term memory of at least 7. 5 months.
Turtle Mating Strategies
An example of mounting behavior within turtles
Turtles are identified for displaying a broad variety of mating behaviours, however , they are not really known for forming pair-bonds or for being part of a social group. Once fertilization has happened and an offspring has been produced, neither parent will provide care for the offspring once it's hatched. Females generally outnumber males in various turtle species (such as Green turtles), and as a result, most males will take part in multiple copulation with multiple partners throughout their lifespan. However, due 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 types have males that are larger than females, and fighting between males often establishes a hierarchical order in which the higher upward the order an individual is, the better the chance is of the person getting access to a potential mate. For most semi-aquatic species and bottom-walking aquatic species, combat happens less often. Males that belong to semi-aquatic and bottom-walking species instead often make use of their larger size advantage to forcibly mate having a female. In fully marine species, males are often smaller than females and therefore they can not use the same strategy because their semi-aquatic relatives, which relies on overpowering the females with power. Males in this category resort to using courtship displays in an attempt 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 particular males have a hierarchical ranking system based upon dominance through fighting, plus it's shown that the particular males with the highest rank and thus the most wins in arguements have the most offspring.
Galapagos tortoises are one more example of a species which has a hierarchical rank that is determined simply by dominance displays, and entry to food and partners is regulated by this dominance hierarchy. Two male saddle backs most often compete for access in order to cactus trees, which is their source of food. The winner is the individual who stretches their neck of the guitar 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 dirt turtle is an example of a bottom-walking marine species that relies on overwhelming females with its bigger size as a mating strategy. The male methods the feminine from the rear, and often resorts to aggressive methods for example gnawing at the female's tail or hind limbs, accompanied by a mounting behavior in which usually the male clasps the particular edges of her carapace with his forelimbs plus hind limbs to hold her in position. The male follows this action by laterally waving his mind and sometimes biting the particular female's head in an attempt to get the girl to withdraw her go to her shell. This unearths her cloaca, and along with it exposed, the male can attempt copulation simply by wanting to insert his holding tail.
Male radiated tortoises will also be known to use the force mating technique wherein they use around vegetation to trap or even prevent females from escaping, then pin them down for copulation.
Turtles Courtship Displays
Red-eared sliders are an example of a fully aquatic species in which the male works a courtship behavior. In this case the man extends his forelegs with the palms facing out and flutters his forelegs in the female's face. Female options are important in this method, as well as the females of several species, such as eco-friendly sea turtles, aren't constantly receptive. Therefore, they've progressed certain behaviors to prevent the male's attempts at copulation, such as swimming away, confronting the male followed by biting, or a refusal position in which the female presumes a vertical position along with her limbs widely outspread and her plastron facing 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 proven deterrent method, as the particular males will never follow all of them ashore.
Ecology and life history of turtles
Ocean turtle swimming
Although numerous turtles spend large quantities of their lives marine, all turtles and tortoises breathe air and should surface at regular periods to refill their lung area. They can also spend much or all associated with their lives on dried out land. Aquatic respiration in Australian freshwater turtles is usually currently being studied. Several species have large cloacal cavities that are covered numerous finger-like projections. These projections, called papillae, possess a rich blood provide and raise the surface area of the cloaca. The turtles can take upward dissolved oxygen from the particular water providing a few papillae, within much the same way that fish use gills to respire.
Like other reptiles, turtles lay eggs that are slightly smooth and leathery. The eggs from the largest species are spherical while the eggs of the rest are elongated. Their albumen is white and contains a different protein from bird ovum, such that it may not coagulate when prepared. Turtle eggs ready to eat consist mainly of yolk. In some species, temperature determines whether an egg cell develops into a man or perhaps a female: a increased temperature the female, the lower temperature causes a man. Large numbers of eggs are deposited in openings dug into mud or sand. They are then covered and left in order to incubate on their own. Depending on the species, the ovum will typically take 70–120 days to hatch. When the turtles hatch, they squirm their way to the surface and head against the water. There are simply no known species in which the mom cares for her younger.
Sea turtles lay their particular eggs on dry, sandy beaches. Immature sea turtles are not cared with regard to by the adults. Turtles can take many yrs to achieve breeding age, plus in many cases, breed of dog every few years rather than annually.
Researchers have recently found out a turtle's organs tend not to little by little break down or become less effective over time, unlike many other animals. It was found that the liver organ, lungs, and kidneys of a centenarian turtle are virtually indistinguishable from all those of its immature version. This has inspired hereditary researchers to start analyzing the turtle genome for longevity genes.
A team of turtles is known as a bale.
Turtles Diet
A green sea turtle grazing on
A turtle's diet varies greatly determined by the atmosphere in which it lives. Grownup turtles typically eat aquatic plants; (citation needed) invertebrates for example insects, snails, and worms; and have already been reported to occasionally eat dead marine animals. A number of small freshwater species are carnivorous, eating small fish and an array of aquatic life. However, protein is essential to turtle growth plus juvenile turtles are solely carnivorous.
Sea turtles typically feed on jellyfish, sponges, and other soft-bodied organisms. Some species with stronger jaws have been observed to eat shellfish, whilst others, for example the green ocean turtle, do not consume meat at all and, instead, have a diet largely made up of algae.
Systematics and evolution of Turtles
Major article: Turtle classification
See|Observe|Notice} also: List of Testudines family members
Life restoration of Odontochelys semitestacea, the oldest known turtle relative along with a partial shell
"Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904
Based on body fossils, the particular first proto-turtles are thought to have existed in the particular late Triassic Period of the Mesozoic era, regarding 220 million years back, and their shell, which has remained a remarkably stable body plan, will be considered to have evolved from bony extensions of their particular backbones and broad ribs that expanded and grew together to form a complete shell that provided protection at every stage of its evolution, actually when the bony element of the shell was not really complete. This is supported by fossils of the particular freshwater Odontochelys semitestacea or "half-shelled turtle with teeth", from the late Triassic, which have been found near Guangling in southwest China. Odontochelys displays the complete bony plastron plus an incomplete carapace, comparable to an early phase of turtle embryonic development. Just before this discovery, the earliest-known fossil turtle forefathers, like Proganochelys, were terrestrial together a complete cover, offering no clue in order to the evolution of the impressive anatomical feature. With the past due Jurassic, turtles had radiated widely, and their precious history becomes much easier to study.
Their precise ancestry has been disputed. It has been believed they are the particular only surviving branch associated with the ancient evolutionary grade Anapsida, which includes groupings such as procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporal opening while all other extant amniotes have temporary openings (although in mammals, the hole has become the zygomatic arch). The millerettids, protorothyrids, and pareiasaurs became extinct in the particular late Permian period plus the procolophonoids during the particular Triassic.
Nevertheless , it was later suggested that this anapsid-like turtle head may be due to reversion rather than to anapsid descent. More recent morphological phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria.[55][56] All molecular studies have got strongly upheld the placement of turtles within diapsids; some place turtles within Archosauria, or, more commonly, as a sister group to extant archosaurs,[58][59][60][61] though an analysis conducted by Lyson et 's. (2012) recovered turtles as the sister group of lepidosaurs instead. Reanalysis of prior phylogenies suggests that these people 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 have diverged from other diapsids among 200 and 279 mil years ago, though the debate is far from settled. Even the traditional placement of turtles outdoors Diapsida cannot be ruled out at this point. A combined analysis of morphological and molecular data 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 carefully 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 separation 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 split between Pleurodira and Cryptodira, was estimated to have occurred around 157 million yrs ago. The oldest defined crown-group turtle (member of the modern clade Testudines) may be the species Caribemys oxfordiensis from 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 ainsi que al. (2012) also recommend that turtles are the sister group to parrots and crocodiles (the Archosauria).
The first genome-wide phylogenetic analysis was completed by Wang et al. (2013). Using the draft genomes of Chelonia mydas plus Pelodiscus sinensis, the group used the largest turtle information set to date in their analysis and concluded that will 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 now possesses an anapsid-like skull.
The earliest known fully shelled member of the turtle lineage is the late Triassic Proganochelys. This particular genus already possessed numerous advanced turtle traits, plus thus probably indicates numerous millions of years associated with preceding turtle evolution; this particular is further supported by evidence from fossil tracks from the Early Triassic of the United Says (Wyoming and Utah) and from the Middle Triassic of Germany, indicating that will proto-turtles already existed since early as the Early Triassic. Proganochelys lacked the ability 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 that of ankylosaurs, it resulted from convergent development.
Turtles are divided directly into two extant suborders: Cryptodira and Pleurodira. The Cryptodira is the larger of the two groups and includes all the ocean turtles, the terrestrial tortoises, and lots of of the freshwater turtles. The Pleurodira are sometimes known as the particular side-necked turtles, a research to how they retract their own heads to their shells. This particular smaller group consists primarily of various freshwater turtles.