Turtles can vary widely in size, colors and lifestyle but are easily distinguished from all other reptiles by their external shell. All turtles have a bony shell on both the ventral (plastron) and dorsal (carapace) sides, unlike all other modern reptiles such as crocodilians, lizards and snakes. The carapace usually has a second armor, the horned carapace. The dorsal shield is connected to the abdominal armor by a leg bridge on either side of the body.
Turtles usually reproduce annually and are egg-laying without exception. They grow rapidly when young but develop very slowly. Larger turtles mature only after several decades; however, such species can also grow very old. The menu includes both animal and plant matter, depending on the species.
There are about 355 different species of turtles, divided into fourteen families. Turtles are found throughout the world, with the exception of the poles, in a variety of biotopes, including forests, grasslands, marshes and seas. Dozens of species are seriously threatened by human activities. The main threats are habitat destruction and the collection of wild turtles for consumption or the pet trade.
Distribution and habitat
Turtles are found on almost all continents, but only in tropical and subtropical areas. Especially in Africa many species live, in Europe turtles live only in the south around the Mediterranean, in Asia only in the southern part. Only a few of the land-dwelling species are found in temperate regions. In North America, turtles are found in the south and center, in South America, turtles are missing only in the far western coastal belt. In Oceania, turtles inhabit much of its associated islands, but not New Zealand. In Australia, turtles are found everywhere except a large desert area in central Australia. In the Arabian Peninsula, species live in both the north and extreme south, but are absent from most of the central part. The only areas where turtles are not found today are the North and South Poles. The distribution map on the right shows the global distribution of turtles in black, and the distribution of marine turtles in blue.
In terms of habitat, turtles are roughly divided into terrestrial, marsh-dwelling and marine turtles. However, this division has no scientific basis; for example, marine-dwelling species belong to different families. There are also species that belong to the marsh turtles but have adapted to a life on land, an example being box turtles.
A turtle’s habitat can consist of almost all possible biotopes, from sparse areas such as savannahs and semi-deserts to in forests, grasslands and swamps. Only in large lakes and in very hot deserts or cold mountain areas without shelters and vegetation are turtles not found. Turtles, like all reptiles, are cold-blooded, that is, dependent on ambient temperature. Most species live in freshwater in marshy areas and regularly come on land to eat and sunbathe, but stay near water to escape into it when in danger and to rest. Sea turtles live permanently in the world’s oceans; some marsh turtles are also occasionally found in salt water, but only along the coast and in mangrove forests, not in the open sea.
Many turtles are good swimmers that use surface water for shelter. Some species, such as the mollusk turtles, are so water-adapted that they rarely enter land. However, there are also species that drown instantly in too deep water, particularly land turtles.
Characteristics of turtles
In addition to a large and sturdy shell, turtles have an egg-shaped, clearly distinguishable head and always four legs and a tail. In land turtles, all limbs can be fully retracted into the shell; in sea turtles, this is not always the case. However, the head is not always retractable in tortoises, and tortoises are even divided into groups according to the ability to retract the head. The legs have a modified shape depending on their function, the tail no longer has any real function.
Turtles are clearly distinguishable from all other animals by the round to oval, dome-shaped shell that contains most of the body. The head and front legs protrude through an opening at the front, the tail and hind legs through an opening at the rear. The carapace consists of a flat lower part, the abdominal armor or plastron, and a usually convex upper part, the dorsal shield or carapace. These two parts are connected by a leg bridge on either side of the carapace between the front and back legs. There are also turtles in which the carapace is bordered by a broad strip of skin, such as the mollusks.
The inside of the carapace consists of skin bones or bony plates, which are formed from the ribs and protrusions of the thoracic vertebrae. The bony plates are formed from bone tissue of the internal skeleton. The horn plates consist of keratin, which is a hard and horn-like substance that provides protection against external parasites. The scales of turtles (and all other reptiles) are also composed of keratin. The horny scales lie against each other; the edges of the horny scales overlap those of the bony plates, which increases strength. The bony plates are fused to the thoracic vertebrae of the spine, preventing a turtle from leaving its shell.
On the outside, the skin is reinforced with horny shields or horny plates (laminae) that originate in the epidermis. The bony plates give the carapace its shape. The shape of the carapace is often about the same in different genera. The horny plates give the carapace its often species-dependent color and markings. Because the shield shape and markings are generally characteristic of the species, they are important determination characteristics. The color and markings are often even slightly different for each individual, this is like the fingerprint of a turtle. A land-dwelling turtle has a spherical shell, a water-bound turtle has a lighter, flat shell for better swimming. Sea turtles, in addition to a relatively light shell, have a highly streamlined shell shape that ends pointed at the rear. This is due to better hydrodynamics to suit the permanent swimming lifestyle.
All turtles have bony plates, but not all species have developed horny shells, the family of mollusks (Trionychidae) lacks them as well as some other freshwater species, and the marine leatherback turtle also lacks external horny shells. The skin of both mollusks and leatherbacks is leathery; the leatherback turtle has skin that contains many oily substances. These make the shell lighter and have an insulating function to protect the turtle from the lower temperatures of the around polar regions very low water temperatures.
The horned shields on the dorsal shield vary slightly among species, and the shield shape may vary more widely among families. However, all turtles have a uniform basic structure regarding shield construction. The shields at the center of the carapace are called vertebral shields (vertebral), the surrounding shields rib shields (costal) and the horn shields at the edge edge edge shields (marginal). A narrow shield is present at the front, the neck shield (nuchal), at the rear are the anal shields (anal). The abdominal armor consists of six back-to-back double rows of shields and the intermediate throat shield (intergular), which lies between the neck shields (gular). The intergular shield is the only non-paired abdominal shield. In halswenders, an unpaired carapace is always present between the anterior two ventral shields.
Some turtles have distinctive modifications to the carapace to be better protected from enemies. Box turtles have abdominal armor that is hinged on both the front and back and can be folded up. In box turtles, the rear of the dorsal shell can be folded down, see also the heading defense. Some turtles, such as the alligator snapping turtle (Macrochelys temminckii), have greatly reduced abdominal armor that covers only a small part of the abdomen.
In addition to defense, the shell also serves other purposes, such as insulating heat that makes a turtle less likely to cool down, and the bony plates perform a function as a calcium supply, which is useful for pregnant females for egg production.
Due to their large shield with hardened horny shells, only part of the body surface consists of flexible skin, only on the head, legs and tail. The shell of the turtle is also covered with skin; each horned shell consists of a single, greatly enlarged scale. Between the bony plates and the horn shields is a thin layer of dermis, in which the horn shields are formed. This layer is highly perfused and provided with nerves, the carapace of turtles is sensitive which can be noticed if one touches the seams between the horny shields. The turtle will then retreat into its shell in irritation.
The stretchy skin that covers the rest of the body consists, as in all reptiles, of a scaly epidermis. Most of the scales are small; those on the head are often larger and thicker for protection. In land turtles, the front of the front legs often have greatly enlarged scales that serve a defensive function, a turtle brings the legs in front of the retracted head when threatened.
Most turtles are a dark green to brown color with camouflaging markings such as lighter to yellow or red stripes, dots, spots or map drawings. A few turtles have particularly colorful markings especially on the neck and head, such as the diadem turtle, yellow-cheeked turtle and red-cheeked turtle.
The scaly skin must be replaced regularly; this occurs during molting or ecdysis. This is when the top layer of the scale lets go, below which a new hardened scale is already present. As in crocodilians, the scales let go one by one and not in fragments as in lizards or all at once, as is the case in snakes. The horned scales on the back are also shed individually; the released plates are thin and almost transparent. In captive tortoises, inexperienced people sometimes think that the animals are sick; in younger specimens, however, regular molting is normal. After each molt, the horny shells get an additional ridge, so the horny shells show how many moults the animal has undergone. Older animals, however, molt less frequently than juveniles, so the number of layers on the horny shells tells at most something about the relative age of the turtle and not its age in years.
Head and neck
The head of turtles is round/evoid; the neck is relatively long and highly mobile. The head can usually be retracted under the shell. This is not the case in all species, and turtles are even divided into two groups. Turtles that retract the head directly under the shell belong to the Cryptodira or halsbergers. By far the majority of turtles belong to this group. There are two exceptions that belong to the halsbergers but do not retract the head. The species in the bite turtle family have heads that are too large to retract. The sea turtles are also neckbergers but all species have lost the ability to retract the head.
The other group of turtles has a relatively long neck and bends it together with the head under the shell edge, these families belong to the Pleurodira or halswenders. In some species the neck is longer than the carapace. The long neck of the latter group has the advantage that the turtle can live in somewhat deeper water.
Turtles are the only reptiles without teeth. Instead, they have sharp, cornified edges on the beak, much like birds, which allow them to cut off bite-sized chunks of food. The shape of the beak is beak-like. A few species have a very strongly downward-curved, parrot-like beak. The bite of many species is very powerful.
The eyes are usually small and always positioned on the side of the head. They have a rounded pupil and a green, gray or orange to red iris.
A turtle always has four legs, the legs are relatively short and curved, they are on the side of the body as in lizards. The legs are strongly paddle-like flattened in water-loving species so that the turtle can swim better. Many freshwater turtles have skin membranes between the toes that serve a similar function; they increase the surface area of the paw and thus efficiency. During swimming all four legs are used, many aquatic turtles are poor swimmers despite their aquatic lifestyle and walk on the bottom of the water, examples are the matamata and the bite turtle. Sea turtles in particular have highly modified, very flat but wide legs to increase surface area and efficiency. The legs are transformed into flippers; this is also found in the New Guinea pig-nosed turtle (Carettochelys insculpta), a large freshwater species. The front legs, which are used for propulsion, are much longer in these species than the hind legs that serve to steer. On land, however, such legs are not useful, making sea turtles here very slow and vulnerable when moving on land to deposit eggs. Land-dwelling species have four short, roughly equal legs that are massive and round and have a flat underside to stand firmly on. The weight of larger species of land turtles can reach hundreds of pounds, and they must lift the body to propel themselves forward.
The legs are used not only for locomotion but also to tear off food. The mouth is used to hold and cut the food, then the sharp claws are used to tear off parts into bite-sized chunks. Another function of the legs is digging the nest; the hind legs are always used for this purpose. Many aquatic turtles, while taking a sunbath, maneuver themselves into a position where they catch as much sunlight as possible, the front legs are flattened and the hind legs tucked back. The twisted legs create a larger body surface area that traps more sunlight.
The legs often bear nails that serve to climb on land. In many species, males have longer nails than females, this is because they need to hoist themselves onto the female when mating. The longer nails of males are also a secondary sex characteristic; they serve to impress females.
Some turtles can climb trees to sunbathe, using the beak as a grasping organ. Only trees suspended above the water are climbed. This keeps the turtle from crashing if the animal drops to escape when disturbed but ends up in the water and is able to escape. Examples of species that have been described as sometimes climbing trees include the big-headed turtle (Platysternon megacephalum) and some species in the family mud and musk turtles (Kinosternidae).
A turtle always has a tail, in many species it remains small but the tail can also be almost as long as the shell. The tail has no real function anymore; a turtle cannot run fast like a lizard, which uses the tail for balance. The tail is also useless when swimming, unlike a crocodile, which uses the tail as a paddle. In many species of turtles, males can be distinguished from females by a longer and thicker tail.
The big-headed turtles have a tail that is about half the length of the body and bears many triangular bony plates. The tail of these species somewhat resembles that of a crocodilian.
Turtles differ greatly physiologically from all other reptiles, the shell formed by bone tissue, the position of the shoulder girdle and the shape of the mouth. Anatomically, the differences are smaller; turtles have the same organs as other reptiles and a similar circulatory, digestive and respiratory system. Turtles always have two lungs, unlike many snakes, and are in possession of a urinary bladder, which is lacking in some groups of reptiles.
Skeleton and skull
From snout to tail tip, the skeleton of a turtle consists of the skull, cervical vertebrae, shoulder girdle and forelimbs, thoracic vertebrae with the strongly flattened ribs, pelvic girdle with hind limbs and finally the tail vertebrae. On the underside of the carapace is the plastron that protects the abdomen.
Many reptiles have “holes” in the skull, more scientifically called fanestrae or windows, which serve as attachment points for the jaw muscles. Turtles, however, lack these, which is why the group was long counted among the Anapsida, which freely translated means windowless. Other reptiles are counted among the Diapsida (two-window animals), but it is suspected that turtles also belong to this group and that the windows have grown shut.
The various skull bones of turtles differ from those of other reptiles, for example, the square bone is hollow, protruding from the back of the head and visible from the side of the head. The square bone, like the bone quadrato jugal, is quite large, the scaly cranial bone or squamosum is positioned at the top of the head. In contrast, in most primitive reptiles, mammals and birds, quadrato jugal and quadrato jugal are quite small and are covered on the outside by a large scaly cranial bone.
A turtle always has eight cervical vertebrae, which are highly mobile. When retracting the head into the shell, in turtles belonging to the neck wenders (Pleurodira), the neck is first bent after which the head is retracted sideways, the neck is bent along the shell edge. In this process, the cervical vertebrae are bent in an S-shape and can bend either left or right. In cervids (Cryptodira), the neck and head can be retracted directly into the carapace; the cervical vertebrae are then located within the shoulder girdle.
A modification unique to vertebrates is the position of the shoulder girdle, it is located between the ribs in the carapace, as is the pelvic girdle. The bones of the forelimbs and hindlimbs are curved and oriented sideways. The thoracic vertebrae are fused with the bony plates and are part of the carapace; a turtle always has ten thoracic vertebrae.
Finally, a turtle has two sacral vertebrae (which form the sacrum) and about twenty to thirty caudal vertebrae. These are the smallest, the tail is more mobile especially at the base but is otherwise relatively stiff. The tail is never directly retracted like the head but is always salvaged under the shield rim.
Turtles have lungs and need to breathe regularly. Many species have a long neck to live in deeper water, and a few species even have an extended, stalk-like nose. Virtually all turtles can swim well but do not sustain it for long; in too deep water, a turtle may even drown.
A turtle, unlike other animals, cannot increase its body volume because of its hard shell; this prevents the lungs from expanding greatly, which limits its breathing capacity. In fact, when threatened, a turtle must first force all the air out of its lungs in order to retract its head and legs.
The lungs of turtles are relatively large and, like other reptiles, contain windpipe branches (bronchioles) that end in alveoli (lungs). This is in contrast to frogs, for example, which have lungs similar to an empty sac. The alveoli significantly increase the contact area, making gas exchange more efficient. Muscles at the forelimbs are used to further expand the lungs, muscles against the lung surface serve to empty the lungs. To complement lung breathing, many turtles have oxygen-absorbing mucous membranes in other parts of the body, such as the throat. There are also species with such adaptations in the cloaca, water is pumped in and out of the cloaca extracting oxygen from the water. A paired bladder is present at the end of the rectum, the whole thing is referred to as the anal bladder. Aquatic species can use the highly perfused walls of these bladders to absorb oxygen from the water. They can thus hibernate on the bottom of the water while it is covered with a layer of ice. An example of such a species is the fitzroy turtle (Rheodytes leukops).
Turtles can move the air in their lungs from one lung to another in a controlled manner. This is used by water-dwelling species as a balance to change their center of gravity. This is similar to the swim bladder of fish. Aquatic turtles can survive in oxygen-free conditions for relatively long periods, this is especially true of sea turtles such as specimens that end up in fishing nets.
Because of the lack of teeth, turtles cannot grind food. They cut food with the sharp, horny edge of the mouth into bite-sized chunks that are swallowed all at once. To aid digestion, turtles swallow small stones that help grind the food in the stomach. These “stomach stones” are called gastroliths. Swallowing stones also occurs in other reptiles such as crocodilians, and ratites.
The digestive system is adapted to the menu; species that eat a lot of plants have a small intestine that can be much longer than their body length. They are able to digest about 30% of the cellulose present in food. Typical carnivores have a relatively short small intestine. All turtles have a particularly large liver. It is the largest internal organ. The liver not only supports digestion by producing bile but also plays a role when the turtle enters an environment of very low temperature. This occurs in turtles wintering on land. The liver then secretes compounds that have an action similar to antifreeze.
Turtles, like many lizards, have a urinary bladder, which is lacking in other reptiles such as crocodilians and snakes. Like feces, urine is excreted through the cloacal cavity, which is located at the base of the tail and positioned transverse to the body axis.
Turtles are to some extent able to survive severe injuries because they have a well-developed capacity for regeneration; replacing damaged parts such as the shell. Turtles are exposed to dangers that even the hard shell does not protect them from, such as bites from crocodilians or birds of prey that drop the turtle from a great height to crack the animal. Cracks in the shell are a common injury, and although healing is slow, turtles can heal completely from such damage, although the crack often remains visible on the shell.
Forest fires can also cause extensive damage to the carapace. If the living skin layer between the leg shells and the horny shells is not too badly damaged, the horny shells grow back in whole or in part.
A turtle, if a leg is bitten off by a shark, for example, cannot regrow the entire leg but is able to allow such severe injuries to heal and continue living without visible difficulty. A remarkable observation was made by Deraniyagala, who described that the horned shells of hawksbill turtles, after being dipped in boiling water and removed from the shell, grew back completely when the turtle was young.
Turtles have good eyesight; the eyes are complex. Because turtles, like birds and other reptiles, have four types of cones in the retina, they can perceive parts in the ultraviolet and infrared spectrum in addition to colors. Turtles can also see well at night due to the high number of rods on the retina. They can also see potential enemies approaching on the shore underwater. Vision is an important sense for locating food and enemies at a distance. Many aquatic turtles have excellent vision underwater; on land, however, vision is limited.
In particular, aquatic turtles have a well-developed sense of smell to detect food. Both live prey animals and in-water carcasses of other animals are detected, many aquatic turtles have carrion on their menu. During the reproductive period, the sense of smell is used to search for a conspecific of the opposite sex. In aquatic species, this allows turtles to locate each other over long distances. Turtles, like many other vertebrates, have a Jacobson’s organ; however, this olfactory organ has a different construction compared to other reptiles.
Turtles do not have good hearing because they have internal ear bones but no external auditory opening. The eardrum is covered by the skin. The stirrup (stapes) is straight and rod-shaped. Turtles rely mainly on vibrations in the ground to locate potential enemies and conspecifics. The vibrations travel through the hind legs and shell to the inner ear. A turtle can detect mainly low-pitched sounds.
A number of turtle species have small tactile senses on the chin that are similar to the bearded threads of fish. These are used to orient themselves in the water.
Turtles have a relatively small brain that is, however, highly developed. Especially well developed are the parts of the brain that deal with smell, vision and balance. Turtles are in possession of a good memory and captive specimens show that they can also learn. Sea turtles are known to always return to the beach where they themselves were born. Like migratory birds, they can orient themselves over long distances but the mechanism behind this is not exactly known.
Thermoregulation and annual and diurnal activity.
Turtles, like all other reptiles, are cold-blooded or more specifically ectothermic; they cannot produce their own body heat. This is the reason why almost all species cannot survive in cold areas and most turtles are found in subtropical to tropical regions. Many turtles are active during the day but must take shelter during the hottest part of the day or are forced to hide for some time during a very hot or cool period.
Species that live in more temperate regions such as central Europe or North America hibernate. Turtles become increasingly sluggish as temperatures drop in the fall and eat less and less. Just before the animals visit their summer or winter quarters they stop eating completely, they are still active for some time during which the last food remains are excreted. This prevents the remains from rotting, a turtle hibernates with an empty stomach and feeds on its reserves. The turtle’s metabolism is at a lower level during this time.
This is also why many species prefer to reproduce as early in the year as possible. This way, the offspring has longer time to develop and thus build up plenty of reserves to survive the following winter. Aquatic turtles crawl away in the mud of the water where the temperature is rarely below 4 degrees, they are sometimes active as early as 8 degrees water temperature.
Tortoises must burrow deep to avoid freezing; they awaken only at higher temperatures. If freezing of the body occurs, the tissue dies and the turtle will not awaken. However, many species have various tricks to prevent this from happening. One example is the four-toed tortoise (Testudo horsfieldii), which has antifreeze-like substances in its blood that allow it to survive sub-zero temperatures.
Turtles are often diurnal, but there are some exceptions. Examples include many mud and musk turtles and the matamata. These species are twilight or nocturnal and retreat during the day. The gopher tortoise is also a twilight-active species, living in very hot areas. This turtle retreats to self-dug burrows during the day.
Many day-active species that live in cool or temperate areas like to take sunbaths. Water turtles are very tolerant in this regard; the animals often crawl on top of each other which is tolerated by the lower animals. To promote heat absorption, the body is turned toward the sun with the front legs flattened. The hind legs are extended and held with the flat side toward the sun’s heat. The neck is also turned to expose as much body surface area to the sun as possible.
Taking a sun bath makes turtles faster and more active. In addition, as with all reptiles, a higher body temperature significantly speeds up digestion. Due to the insulating effect of the shell, heat can be stored for a while, however, the effect of this is small.
A special species is the leatherback turtle (Dermochelys coriacea), which, thanks to its permanently swimming lifestyle, has an elevated body temperature relative to its environment. This allows the turtle to search for food even in polar waters.
Turtles cannot sweat to cool off due to their scaly skin and must seek coolness in the water or shelter in a burrow underground when the heat is hot. Land-dwelling species often dig their own burrows; aquatic turtles usually seek out the water in hot conditions. Land turtles like to take mud baths to cool off, this also serves to get rid of parasites. When food is not available during prolonged hot periods due to dry conditions, some species retreat to a burrow for several weeks to months. This period of dormancy is called over-summering or aestivation.
Reproduction and development.
Tortoises have a fairly uniform mode of reproduction and development. All species lay eggs that are buried after which the juveniles hatch some time later and develop relatively slowly. Unlike other reptiles such as crocodilians and some lizards, no species has any form of brood care, leaving the juveniles on their own.
Males and females can be distinguished by some different characteristics that are not always easy to see, however. Male turtles generally remain smaller and lighter than females. In turtles, a color change in males during the mating season as in lizards does not occur in principle. A rare exception is the callagur tortoise, whose male develops a white head with red and blue spots.
Typical sex distinguishing characteristics that apply to most species are;
- Males have a thicker and longer tail.
- Males have a sort of pit in the abdominal armor, females a flat abdominal armor; this allows the male to easily stay on the female when mating, with flat abdominal armor he would slide off.
- Males have longer nails; this too serves, among other things, to better climb on the female when mating.
- In some species, males have spurs on the inside of the thighs; these are small, spiny protrusions that females lack.
Turtles have internal fertilization, where the male inserts his sperm directly into the female orifice. All species lay eggs without exception.
A turtle’s reproduction time is species-specific. Before mating takes place, rival males often fight by bashing each other. Turtles have a courtship that again varies by species. In many aquatic turtles, males have very long nails on the front legs, which they use to fan toward the female. Land dwellers chase each other, with the males biting the females. This aggressive behavior does occur in more reptiles such as the lizards, which hold the female with the mouth like this during mating. In turtles, however, biting the male is rewarded with better access to the female’s cloaca.
Simply put, a turtle is a shell with a body inside, which is similar to a balloon: when one side is squeezed, the other side bulges out. When the female retracts her head and neck at the front, this makes her cloaca easier to access.
Males almost always have a single penis; only mollusks have a slightly forked penis for better access to the female’s cloaca. A fully cleft penis or “hemipenis,” incidentally, is normal in other reptiles such as snakes and lizards.
Mating of water-dwelling turtles takes place in the water, strictly land-dwelling species mate on land. When mating in land-dwelling turtles, the male stands on his hind legs and partially hoists himself onto the female with his front legs. The pose most closely resembles the posture called the doggie pose in humans. The male makes jerking movements and opens the mouth during mating. Also, especially in the larger species, panting, growling or even loud screaming sounds are made that are highly unusual for reptiles. The female, on the other hand, usually makes a resigned impression, sometimes walking on during copulation and thus literally taking the male in tow, females that spend copulation while eating have also been described.
Turtles, without exception, are oviparous, or egg-laying. Because producing eggs requires a lot of energy from a female, offspring are not always produced every year as in most vertebrates. The eggs are almost always buried in the soil, almost always seeking a sandy location. Usually a shallow pit is dug into which the eggs are deposited and the pit is then plugged with the hind legs. If the ground is too dry, some species moisten it with fluids from the gut.
Many species of sea turtles migrate to certain beaches each year to deposit eggs. This is also called arribada. These are always the same beaches, because the animals are very strict it is easy to predict when they will come back ashore. They first dig a hole to hide in during egg deposition, then they dig the nest. While laying, the females are in a kind of trance where they are easy to approach and very vulnerable.
In sea turtles, the juveniles leave the nest simultaneously to increase the chances of survival; however, this is not the case in all species. It is also known that the juveniles of Chrysemys picta can overwinter in the egg.
The eggs of turtles are oval to spherical in shape and white to whitish-yellow in color. They may have a very soft shell or a more calcified shell. The eggs of all species have a porous shell so that oxygen can be extracted from the environment and water can be excreted. Turtle eggs are usually deposited on land because the embryos need oxygen and cannot extract it from the water. However, there are exceptions; for example, Chelodina kuchlingi lays eggs underwater from drying pools of water. Other eggs actually hatch underwater, such as those of the New Guinea pig-nosed turtle (Carettochelys insculpta). As a result, the eggs hatch synchronized during the rainy season.
Some turtles, like all sea turtles, produce large clutches. Other turtles, such as species from the genera Homopus and Pyxis, lay only one egg per clutch. Both tactics serve to maximize offspring survival. In species that deposit only a single egg, the embryo is more advanced than in species with many eggs. In species that deposit many eggs, the shape of the egg is round; in species that produce few eggs, the egg is more oval in shape. Turtles can produce several clutches per season, up to more than ten per year in some sea turtles.
Turtles do not have sex chromosomes; sex is determined by ambient temperature during the incubation period. A lower temperature results in a male, a higher one in a female; this is called temperature-dependent sex determination. However, there are known exceptions where sex is not determined by ambient temperature.
Several weeks to months after eggs are deposited, hatchlings crawl out of the egg and burrow out. Turtles have what is known as an egg tooth when they hatch, which serves only to open the egg and then soon releases. Species that live on land disperse across the land, species that live in water seek the water as quickly as possible.
Among the turtles, it is striking that sometimes the young do not resemble the parents at all. The shell is always flatter, but also the shape of the shell and the drawings on both shell and skin can be very different. The shell edge in many species has thorn-like protrusions on the back of the shell and often has raised longitudinal keels, these features fade as the turtle grows and ages. In fact, some turtles were long thought to be two different species because of the vast difference in juvenile and adult forms. Food is also often different, the juveniles almost always eat more animal material than the adults, this is because they grow faster and as a result require more animal protein.
Once a turtle reaches adulthood, the animal continues to grow throughout its life, although very old specimens grow very slowly. The shell shape often continues to change but no longer so drastically. Very old turtles often have a flatter and longer shell than recently mature specimens, although this varies somewhat among species. Some turtles, on the contrary, develop a more bulgy carapace, the center of each hump being formed by the middle of a horn plate. Older animals lose the clarity of coloration and often have a somewhat weathered shell, which often bears scars from attacks by enemies such as birds of prey or crocodilians.
Turtles take a very long time to mature and reproduce. This makes turtles relatively vulnerable. However, they can become very old, the smallest species easily reaching an age of twenty to forty years. Larger species can live more than a hundred years, and the very oldest specimens known became over 150 years old.
Food and hunting
Turtles can be carnivorous (carnivorous), herbivorous (herbivorous), or omnivorous (omnivorous). Many aquatic turtles live primarily on animal matter, such as fish, snails, insects, worms, small crustaceans, and amphibians. Only a few species can be considered particularly predatory, such as the snapping turtle, which also grabs waterfowl if the opportunity arises. Bait is also prized by many turtles. Most turtles eat plant parts such as leaves, fruits, seeds and roots in addition to animal material.
Sometimes a strong food specialization occurs such as the leatherback turtle that lives mainly on jellyfish, the hawksbill turtle eats mainly sponges. Many species have a high preference for certain prey animals, such as the madagascar shin plate turtle (Erymnochelys madagascariensis), which lives mainly on the slender knobbed horned snail, a pointed snail.
Tortoises are the only group of turtles that live mainly on plants; they mostly eat grasses, herbaceous plants and fruits. Tortoises have a very well-developed digestive system, which allows some species to live on dried grasses alone, see also under the heading digestion. Snails and other invertebrates living in them are also eaten, these animals are probably not “bycatch” but are an essential part of the menu. Bait (necrophagy) and dung (coprophagy) have also been described from some species.
Because turtles are cold-blooded and their physiology and behavior are set to move as little as possible, they can survive in environments with little food. Young turtles, on the other hand, have yet to grow and require more animal protein. As they get older and larger they start to eat more and more plants, this is also common among lizards, an example being the green iguana. Especially young but also older turtles need a lot of calcium to build up the skeleton such as the bone plates of the shell.
The turtle obtains food by actively foraging and scours the environment for food, using its well-developed sense of sight and smell. A few species have developed special ways to obtain food:
- The forest stream turtle (Glyptemys insculpta) is known to make vibrations that are transmitted to the ground by its forelimbs. Subterranean invertebrates, such as earthworms, thereby become under the impression that it is raining and quickly rise above ground where they are eaten by the turtle.
- The alligator turtle (Macrochelys temminckii) has a tongue with two worm-like appendages, which are very thin and pink in color. The turtle lies on the bottom of a river with its mouth open and moves the appendages of the tongue, attracting fish that like to eat worms and swimming toward the turtle’s mouth. Once the fish is within reach, the turtle clenches its mouth shut and the prey is caught.
- Many aquatic turtles such as the matamata (Chelus fimbriatus) can expand the throat quickly and strongly to suck in prey animals.
Enemies and defense
The turtle’s main enemy is obviously humans; for non-natural threats, see the heading Threats from humans.
Turtles’ eggs are dug up by a variety of enemies, from crabs and ants to burrowing mammals and some lizards. Young turtles are also preyed upon by all sorts of things because they do not yet have a large, hard shell. Various animals such as fish, aquatic mammals and birds like to peck one out of the water. Adult specimens, however, do not have many natural enemies because of their developed shell. Only crocodilians have jaws powerful enough to crack the very hard shell of large freshwater turtles. An example is the diamondback crocodile (Crocodylus rhombifer), which lives largely off of marsh turtles. The teeth in the back of the mouth of this crocodile are wider than the teeth in the front of the mouth, which is an adaptation to cracking the shell. In many older freshwater turtles that live in regions that are also home to crocodilians, the shell bears the scars of confrontations with this important enemy. Sometimes turtles are killed and eaten by large predators such as canines and felines, examples being coyotes and panthers. Sea turtles are mainly preyed upon by sharks and the sea crocodile, which tear the turtle to pieces.
The shell is too hard for many predatory birds such as crows. Turtles are sometimes killed by birds of prey such as the American bald eagle. Since even these birds are unable to crack the shell, the turtle is picked up and taken into the air. The bird drops its prey at a great height after which the turtle crashes and the bird can reach the meat. According to tradition, the Greek poet Aischylos is said to have met his end by a falling turtle that struck his head.
In addition to predators, turtles fall prey to parasites such as worms, mites, ticks and lower organisms such as fungi and bacteria. Healthy turtles suffer little from these; only in sick or weakened specimens can parasites be dangerous. Notorious are parasites on turtles caught in the wild and sold as pets. Parasites, like the carrier, are placed in an artificial environment and find ideal conditions there. There, they are not inhibited in their growth and development and, especially in specimens weakened by poor housing, can proliferate and lead to rapid death of the turtle. The owner is also not immune from dangerous parasites, see also the heading Turtles in captivity.
During their evolution, turtles have invested mainly in developing a good defense, which has resulted in the relatively very strong shell that can be cracked by very few enemies. Aquatic turtles have a weaker armored shell and are generally very shy animals. They lead a hidden lifestyle and do not show themselves much, a number of species are nocturnal. Day-active species that sunbathe a lot always do so in close proximity to surface water and dive into the water at the slightest disturbance. Most species swim to the bottom and shelter here for a while before later carefully raising their heads above water and carefully exploring the area before re-entering land.
Tortoises are often less shy; many larger species have no natural predators due to their size and weight. Smaller land turtles have a very hard shell and can often retreat completely so that an enemy cannot reach the turtle. The head is retracted and the front legs are folded in front of the head for protection. The most highly developed forms are found in the valve turtles, hatchlings and box turtles. Flap chested turtles (genus Kinixys) have a hinged carapace, the back of the dorsal shell can be folded down. In this way, the hind legs and tail are well protected; it most closely resembles the visor of a helmet that can be folded down. Box turtles (families Pelomedusidae and Podocnemididae) have a hinged abdominal armor that can be folded up at the front, which serves to protect the head and front legs in case of danger.
Box turtles go even further; in these species the abdominal armor is hinged on both sides: front and rear. The abdominal armor is folded up on both sides, so that both the hind legs and tail and the front legs and head are completely stowed in the shell and hidden from view. There are two genera of box turtles, Terrapene and Cuora, which belong to different families so convergent evolution probably occurred.
The slit turtle (Malacochersus tornieri) is one of the few species that has a very flat carapace and is therefore also called pancake turtle. This species can anchor itself with its shell in a rock crevice so that the animal is inaccessible to enemies.
Turtles release a watery liquid when they are picked up to deter the attacker. This liquid does not consist of feces or urine as is often thought, but comes from the anal bladders.
In addition, many turtles have scent glands that secrete a terribly smelly substance to keep attackers at bay. Incidentally, this musky odor is also used to detect a mate during the reproductive season. The best known example of this is the species of the genus Sternotherus, which got their name from this and are known as the musk turtles. In some species, the scent glands are already active in the egg.
Besides hinged valves and foul odors, turtles have a sharp mouth (turtles have no teeth) and strong jaw muscles that can be used to deliver a bite that will be remembered for a long time. The bite of even the smallest species can cause bloody injuries to humans. Turtles extend their necks as far as possible during the bite reflex, allowing them to bite an enemy unexpectedly because the range is greater than estimated by the attacker.
Larger species can take a hefty bite from tissue that can hit veins and arteries leading to dangerous blood loss. Very large species, such as sea turtles, can bite off a finger with their bite. A notorious species is the bite turtle (Chelydra serpentina), which, due to its disproportionately large head and very powerful jaws, can easily bite off a finger or even a hand. The warana (Lepidochelys olivacea) also has a very notorious bite and was called Deraniyagala dog turtle by the biologist for this reason.
Turtles and humans
Turtles are generally considered peaceful and endearing while most people are afraid of other reptiles such as lizards and snakes. As a rule, turtles are not aggressive and retreat into their shells when in danger; however, there are biting exceptions.
Turtles are additionally seen as sluggish, like the turtle in the story of the hare and tortoise. In reality, many species can get out of the way amazingly quickly or swim away very quickly, although they don’t last long.
Turtles have long played a role in human life; for example, turtles have been hunted since time immemorial in order to eat their meat. In different cultures, turtles play a role, for example, in China the Yangtze Week turtle (Rafetus swinhoei) is seen as the god Kim Qui. In Hinduism, Vishnu appeared in the second avatara in the form of the turtle Koerma. In Terry Pratchett’s books, the disk world rests on the shell of a giant soup turtle.
From earlier times, many utensils are known to have been made from the horned shells of turtles. Once polished, the fabric was very popular because of the colorful colors and the often flamed color pattern of the shell, turtle horn has therefore always been very precious. Examples include combs, amulets and jewelry, furniture pieces such as picture frames and cabinets were also plated with tortoiseshell horn for decoration. In particular, the hawksbill turtle shell (Eretmochelys imbricata) and the false hawksbill turtle (Caretta caretta) are popular. Since the 1960s, the manufacture of turtle products has been banned.
Turtles in modern culture
Turtles play a role in various (cartoon) movies and stories. Some well-known fictional turtles are:
- Teenage Mutant Ninja Turtles, four mutant turtles who fight against injustice and love pizza.
- Franklin, the main character from the originally Canadian cartoon series.
- Toon Turtle, a character from Disney, befriends Brother Rabbit.
- Stoffel “I feel appullug” the Turtle from The Fabeltjeskrant, who frequently suffers from ailments.
A more famous turtle was the Galapagos giant tortoise “Lonesome George,” being the last of his species. With his death on June 24, 2012, the species became extinct. Harriet was also a curiosity at the Australian zoo until her death in 2006 because of her advanced age of about 175 years. This Galapagos giant tortoise was long considered a male and carried the name Harry until the discovery that it was a female. Another very old turtle was Tu’i Malila, a radiated turtle that died in 1965 and was 188 or 192 years old at the time.
Turtles, because of their slow metabolism, can grow very heavy, large and, most importantly, very old. Sea turtles are record holders when it comes to fastest swimming quadrupeds, they can reach speeds of 35 kilometers per hour. Some well-known turtle records are:
- Oldest turtle: The oldest turtle whose age has been confirmed is Tu’i Malila, who reached an age of at least 188. Another very old specimen is Adwaitya, this was a seychelles giant tortoise that is said to have reached an age of 255. However, there is no hard evidence for this.
- Largest turtle: The leatherback turtle can grow more than 1.5 meters long and is the largest species. The record is a specimen of 2.74 meters.
- Heaviest turtle: the leatherback turtle is also the heaviest species, on average this turtle grows to 450 pounds, the heaviest specimen weighed 863 pounds.
- Largest turtle in the Netherlands: the Dutch record stands at 2.44 meters total length (shell 1.58 meters). This was another leatherback turtle that washed ashore on Ameland.
- Smallest turtle: the flat turtles of the genus Homopus remain the smallest of all land turtles, the very smallest being the serrated flat turtle with an average shell length of 9.6 centimeters.
- Smallest sea turtle: this is Kemps sea turtle (Lepidochelys kempii), which reaches about 65 centimeters in length. It is also the rarest sea turtle.
- Rarest turtle: the loggerhead turtle has a very small range , there are only 100-200 specimens left in the wild, most of which are not yet mature.
Threat and protection
There are about 355 species of turtles today, many of which are not doing so well, mainly due to human activity. To give the most endangered species some more attention, the organization Turtle Conservation Fund (TCF) has compiled a list of the 25 most endangered species of turtles.
Threats from humans
There are many species that are declining in numbers and range mainly due to habitat destruction, pollution, desiccation and especially the capture of specimens in the wild for the exotic animal trade or for processing into food or goods such as souvenirs and jewelry. The carved shell of turtles is called tortoise or karet.
The trade in exotic animals has a much greater impact on turtles than many other animals. This is because turtles take a relatively very long time to mature. In the wild, this is compensated for by the fact that once mature, specimens can also become relatively very old and reproduce throughout their lives. This makes turtles vulnerable because populations cannot recover well if many adults disappear. The population is insufficiently replenished with juveniles, causing it to become smaller or even disappear altogether.
Many Chinese species have become very rare. This is caused by large-scale illegal capture for the exotic animal trade. When a turtle becomes rarer, a kind of vicious circle is created because the species is worth more money. Due to the price and emerging economy of many Asian countries, turtles have become a luxury item and are increasingly eaten as a delicacy rather than out of food shortage (bushmeat). Several dozen species have been pushed to the brink of extinction as a result. Of the world’s 25 most endangered species, 12 live in Asia. This problem is also known as the Asian Turtle Crisis. The main problem is that when the import of a turtle species is banned, it skyrockets in price and, in addition, other species suffer because they are now seen as alternatives. The fact that the three-striped-water box turtle is now in trouble is probably due to the slow disappearance of another species, the Ambonese box turtle (Cuora amboinensis).
Another disadvantage of turtles in the pet trade is the dumping or escape of specimens into the wild, allowing the animals to compete with local species as exotics. In temperate countries such as the Netherlands, where turtles do not naturally occur, turtles can survive but cannot reproduce. In warmer countries, however, at worst these species develop into invasive species, replacing other species. An example is the presence of the red-cheeked turtle in Australia, which poses a major threat to native species. Along with the infamous giant toad and carp, the turtle is one of Australia’s most damaging invasive species.
Some turtles are bred in turtle farms, as are many crocodilians but the latter are bred for skin and meat, the turtles particularly for trade. Breeding turtles in captivity serves two purposes; both commercial and ecological. In the wild, mortality is very high among juveniles, as it is among crocodilians, but in a nursery there are hardly any losses, which means that a relatively small number need to be released to replenish the populations. This leaves a relatively large number available for the pet trade. In the case of turtles, moreover, farming in farms is practiced on a limited scale compared to crocodilians.
Because of all these threats, turtles are one of the most highly endangered animal groups in the world. Some species, such as the green turtle, are even used by conservation organizations as icons for endangered species.
In addition to direct threats such as landscape change or killing the reptiles, the introduction of domesticated animals also sometimes harms turtles. Several species of giant tortoises of the Galapagos Islands have greatly declined in numbers because grazing animals such as goats ate the vegetation, leaving too little food for the tortoises.
Many species of turtles are even threatened with extinction because of their tasty meat, the best known example being the soup turtle. Turtles are not associated with food in Europe, but in other cultures turtle meat is an important part of traditional cuisine. It is known from finds in the Olduvai Gorge that turtles were eaten as early as 2 million years ago. Considered a delicacy, turtle meat is made into turtle soup, among other things. The soup turtle got its name from its tasty meat. Unlike other sea turtles, adults live exclusively on sea grass, which makes the meat taste much less tart. Another species known for its tasty meat is the bite turtle from North America, this species was already eaten by the Indians and the American colonists also liked to eat turtle meat.
Especially in Asia, there are many traditional dishes that incorporate turtles. An example is “Turtle Bacon Belly” from China, in which turtle meat is mixed with other types of meat (beef, pork) and fish. Even the blood of turtles is consumed in Asia. In some regions, the eggs of turtles are considered a delicacy and are collected for consumption. While turtle eggs are edible, they do not become hard inside after cooking, as is the case with a chicken egg. This is because there are different proteins in the egg than in bird eggs. Also, the shell of the egg is less hard than the shell of a bird’s egg.
An important outlet for wild-caught turtles is traditional Chinese cuisine and a firm belief in alternative medicine. Turtles such as the three-striped box turtle (Cuora trifasciata) are attributed beneficial properties by the Chinese, eating the meat is even said to be effective against cancer, and many products are attributed with potency-boosting properties. Various parts of the turtle are used as traditional medicine, such as the meat, blood or bile. Also considered effective are the head, shell, bones, meat, eggs and some intestines, among others. Consuming the shell is said to “soothe the liver” and cure coughs, night sweats, kidney disorders and absence of menstruation, among other things. The gallbladder, according to the Chinese, helps against hypersensitivity; shield eggs are good against diarrhea and dysentery. The shell or horned shells are decorated and used as amulets. In ancient China, turtles were considered one of the 5 sacred animals and played a role as an oracle.
Research has never shown these assumptions to be correct. Nevertheless, from around the world, turtles of various species are being captured in large quantities and shipped to Asian food markets to meet the rapidly increasing demand.
Scientists suspect that a large proportion of turtles will disappear within a few decades as a result of human activity. To prevent this, turtles, especially the highly endangered species, are protected at both local and international levels. Turtle protection consists of prohibiting the capture and trade of endangered species. A number of nesting beaches of marine turtles are monitored. Of highly endangered species, eggs are collected and reared in an incubator. The most endangered species can only be viewed in zoos because the natural population has disappeared or consists of only a few individuals.
Many countries have developed legislation regulating the keeping of species in captivity and the trade in turtles. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is the main international treaty that protects turtles worldwide. In addition, other measures are being taken that protect the turtles, such as posting warning signs for traffic. The nets of fishing vessels at sea, which often catch sea turtles as bycatch, are being modified to spare the animals. These are called turtle excluder devices, or TEDs for short, which can be freely translated as turtle-resistant trapping methods. This is somewhat similar to other protected marine animals such as dolphins, for which more animal-friendly trapping methods have also been developed to prevent bycatch.
In particular, the family of sea turtles (Cheloniidae) are known to the general public as endangered, in part due to intensive campaigns by conservation organizations; of the six species, 5 are endangered. However, compared to other turtles, sea turtles are not too bad; of the 25 most highly endangered turtle species, not one belongs to this group. One of the species on the brink of extinction and already absent from the wild is the Yangtze Box Turtle (Rafetus swinhoei). Six individuals of this species are still held in captivity; the most recent wild-caught specimen was fished out in 1972.
Besides large-scale projects, often supported by the government, there are also many private initiatives to protect turtles, for example, in 2004 members of the Dutch-Belgian Turtle Society (NSV) donated 2450 euros to the Cuc Phuong Turtle Conservation Centre in Vietnam. Here the eggs of, among others, the Annam water turtle (Mauremys annamensis), the Asian spiny turtle (Cuora mouhotii), the giant loggerhead turtle (Heosemys grandis), the hind end box turtle (Cuora galbinifrons) and the yellow-headed land turtle (Indotestudo elongata) are hatched.
Tortoises in captivity
Tortoises are widely kept in zoos, parks and as pets; some species are very popular. However, care is often underestimated by private individuals, causing the animals to languish and die. Food is not always cheap; juvenile specimens in particular need a lot of food and vitamins. If they do not get enough of these, it causes blindness (vitamin A deficiency) or the carapace does not develop properly which is soon fatal (calcium deficiency). Moreover, animals caught in the wild are often already weakened by transport and stress and are not infrequently infected with parasites that can multiply explosively in an artificial habitat. Not only is this dangerous for the turtle, but also for the owner. One notorious parasite is Salmonella, which can be dangerous to people with weakened immune systems, children and pregnant women.
Like all reptiles, turtles are cold-blooded. They are set up to move as little as possible, so they quickly become boring in captivity. Very young turtles may be more active and swim around busily, but this behavior soon disappears. Also, the private buyer is often unaware that turtles can easily live to be 20 years old, tortoises even a multiple of this.
Most animals offered in the trade are wild-caught specimens, also known as wild-caught. Almost all species of turtles are no longer common and many species are even threatened in their survival. Purchasing a wild-caught animal has a direct negative impact on the natural population. Animals born in captivity are called offspring and are often more accustomed to humans, free of parasites, and the purchase of offspring does not harm natural populations.
The exotic animal trade, along with the Asian turtle crisis and global habitat destruction, is considered the biggest threat to turtles. On the other hand, more and more captive tortoises are being professionally kept and successfully bred. Meanwhile, this industry is proving to be a major contributor to species conservation, creating an ex situ population that can serve as a backup for endangered wildlife populations. The maintenance of stud books helps maintain genetic variation. Trade in turtles is regulated internationally by agreements, which are contained in the CITES (Convention on International Trade in Endangered Species of Wild Flora and Fauna). Regarding the way turtles are kept in zoos and parks, they can be divided into three groups.
This is by far the most popular and well-known group, to which most species offered belong. Bog turtles live in the water, but often come out to sunbathe making them fairly active compared to other species. Bog turtles generally do not grow very large, but there are exceptions. Because of this, the turtle’s enclosure is often estimated to be much too small. The animals, even when very small, are best housed in a large aqua terrarium. It is true that most species stay small in an enclosure that is too small, but this is not good for the turtle. As they grow larger (to about 20-30 centimeters) another enclosure should be sought. The aqua terrarium should have a land area that is shone on by a lamp for sunbathing; some species do not sunbathe, by the way. Turtles are sensitive to drafts and can get sick from them, bog turtles are especially sensitive to this because they live in water as well as on land. Also, changing the water very regularly is very important, because the animals are carnivores and do their needs in the water it quickly becomes dirty and stinks. Contaminated water causes infections to the eyes, respiratory tract and carapace, among others. Again, poor care is dangerous not only for the turtle, but also for the caregiver.
Known species: Yellow-cheeked turtle – Spurious loggerhead turtle – Yellow-bellied turtle – Red-bellied turtle – Red-cheeked turtle (endangered) – Loggerhead turtle – Moorish brook turtle – Muskhead turtle (nocturnal) – Bite turtle (dangerous) – Diamondback turtle – Floridian turtle – Indian roofed turtle – Chinese three-horned turtle – Caspian brook turtle – Japanese water turtle.
Tortoises can be kept in a spacious enclosed terrarium, but are usually housed in a large glass tank on the floor, open at the top. Tortoises have a great need for heat but it is difficult to dissipate it in a closed container. The tank is placed so that drafts have no chance. Tortoises can also be housed in an outdoor enclosure but this can present some dangers. Examples include stray dogs and cats and theft. Tortoises are very pricey; juveniles of the affordable species already cost hundreds of dollars each. Lights are installed above the enclosure for needed warmth; almost all tortoises live in warm to desert-like areas. Tortoises have the advantage that they usually have poor resistance to moisture and live in a dry environment, making the enclosure easy to keep clean. They are also almost all herbivores living on grasses and leaves, other foods such as fruits and meat are also accepted but are not good for the turtle.
Known species: Coal-burner turtle – Panther turtle – Spurred flat turtle – Yellow-headed land turtle – Spiny-ribbon turtle – Slit turtle – Egyptian land turtle – Four-toed land turtle – Greek land turtle – Moorish land turtle – Bell tortoise – Brazilian giant tortoise.
A number of turtles are so highly adapted to water that they never come out of it, even for sunbathing. These species often have specialized lifestyles and are best not acquired by a novice. Typical aquatic inhabitants are the mollusk turtles, which, because of their weak carapace and short legs, never venture onto land except for egg deposition. Some neck turtles or Pleurodira, the group of turtles with very long necks, do not often come out of the water, such as the snake-necked turtles. Almost all aquatic turtles can or should be kept in deeper water in a large aquarium. There are strict water quality requirements that depend on the species. Some species live in cooler or stagnant water, others in warmer or flowing water. Particularly widely varying temperatures quickly lead to disease. Many species are nocturnal and rest during the day. Changing and keeping the water clean is very important.
Known species: Red-bellied loggerhead turtle – Brazilian snake-necked turtle – Long-necked snake-necked turtle – Spiny-eared week turtle – Argentinean snake-necked turtle – Matamata.
Turtles, like other animals, are classified into various groups and subgroups, such as families, subfamilies and genera. However, with the discovery of new (genetic) traits, this classification changes regularly. There are currently 356 known species of turtles and more than 450 subspecies. Subspecies of some species are actually better known, the red-cheeked and yellow-cheeked turtles being an example. They are two subspecies of the same species: the letter tortoise.
The various species are divided into families, which may vary slightly in appearance in shape, size and colors but are all clearly recognizable as turtles. A number of families are relatively unknown, some families are somewhat better known such as the soft-shelled soft-shelled turtles and the land turtles that sometimes grow very large.
The order turtles today consists of two suborders, five superfamilies and fourteen families. It should be noted that the superfamily to which the family snake-necked turtles (Chelidae) belongs does not yet have an accepted name. All species from a third suborder, Paracryptodira, are extinct. Not all modern families are recognized as such, and sometimes subfamilies, on the contrary, are considered family. An example is the families of shin plate turtles and pelomedusas, which were long considered a single family.