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Turtles are an
order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such as cleanliness a ...
of
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
s known as Testudines, characterized by a
shell Shell may refer to: Architecture and design * Shell (structure)A shell is a type of structural element which is characterized by its geometry, being a three-dimensional solid whose thickness is very small when compared with other dimensions, and ...
developed mainly from their ribs. Modern turtles are divided into two major groups, the side-necked turtles and hidden neck turtles which differ in the way the head retracts. There are 360 living and recently extinct species of turtles, including
tortoise Tortoises () are reptiles Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a ...

tortoise
s and
terrapin Terrapins are one of several small species of turtle Turtles are reptiles of the Order (biology), order Chelonia or Testudines . They are characterized by a special bone, bony or cartilage, cartilaginous animal shell, shell developed fro ...
s. They are found on most continents, some islands and much of the
ocean The ocean (also the sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
. Like other reptiles, birds, and mammals, they breathe air and do not lay eggs underwater, although many species live in or around water. Genetic evidence typically places them in close relation to
crocodilian Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, ...
s and birds. Turtle shells are made mostly of bone; the upper part is the domed
carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
, while the underside is the flatter
plastron The turtle shell is a shield for the ventral and dorsal parts of turtles (the Order (biology), order Testudines), completely enclosing all the vital organs of the turtle and in some cases even the head. It is constructed of modified bony elements ...

plastron
or belly-plate. Its outer surface is covered in scales made of
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin Alpha-keratin, or α-keratin, is a type of keratin Keratin () is one of a family of fibrous structural proteins known as Scleroprot ...

keratin
, the material of hair, horns, and claws. The carapace bones develop from ribs that grow sideways and develop into broad flat plates that join up to cover the body. Turtles are
ectotherm An ectotherm (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...
s or "cold-blooded", meaning that their internal temperature varies with their direct environment. They are generally opportunistic
omnivore An omnivore () is an animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been — ...
s and mainly feed on plants and animals with limited movements. Many turtles
migrate Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum len ...
short distances seasonally.
Sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines Turtles are reptile Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constitut ...

Sea turtle
s are the only reptiles that migrate long distances to lay their eggs on a favored beach. Turtles have appeared in myths and folktales around the world. Some terrestrial and freshwater species are widely kept as pets. Turtles have been hunted for their meat, for use in traditional medicine, and for their shells. Sea turtles are often killed accidentally as
bycatch Bycatch (or by-catch), in the fishing industry The fishing industry includes any industry or activity concerned with taking, culturing, processing, preserving, storing, transporting, marketing or selling fish or fish products. It is defined by ...
in fishing nets. Turtle habitats around the world are being destroyed. As a result of these pressures, many species are threatened with extinction.


Naming and etymology

The word ''turtle'' is derived from the
French
French
or ('turtle,
tortoise Tortoises () are reptiles Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a ...

tortoise
'). It is a
common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is sometimes erroneously referred to as ...
and may be used without knowledge of taxonomic distinctions. In North America, it may denote the order as a whole. In Britain, the name is used for
sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines Turtles are reptile Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constitut ...

sea turtle
s as opposed to freshwater
terrapin Terrapins are one of several small species of turtle Turtles are reptiles of the Order (biology), order Chelonia or Testudines . They are characterized by a special bone, bony or cartilage, cartilaginous animal shell, shell developed fro ...
s and heavy-footed, land-dwelling tortoises. In Australia, which lacks true tortoises (family Testudinidae), non-marine turtles were traditionally called tortoises, but more recently turtle has been used for the entire group. The name of the order, ''Testudines'' (), is based on the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...

Latin
word for tortoise, ; and was coined by German naturalist
August Batsch August Johann Georg Karl Batsch (28 October 1761 – 29 September 1802) was a German naturalist. He was a recognised authority on mushrooms, and also described new species of ferns, bryophytes, and seed plants. Life and career Batsch was born ...

August Batsch
in 1788. The order has also been historically known as ''Chelonii'' ( Latreille 1800) and ''Chelonia'' (Ross and Macartney 1802) which are based on the
Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the diale ...
word for tortoise: (). Testudines is the official order name due to the
Principle of Priority 270px, '' valid name. Priority is a fundamental principle of modern botanical nomenclature and zoological nomenclature. Essentially, it is the principle of recognising the first valid application of a name to a plant or animal. There are two aspec ...
. The term chelonian is used as a formal name for members of the group.


Anatomy and physiology


Size

The largest
living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objects and dead organisms ** extant taxon, Living species, one that is not extinct *Personal life, the course of an individual human ...
species of turtle (and fourth-largest
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
) is the
leatherback turtle The leatherback sea turtle (''Dermochelys coriacea''), sometimes called the lute turtle or leathery turtle or simply the luth, is the largest of all living turtle Turtles are an of s known as Testudines, characterized by a developed ma ...
which can reach over in length and weigh over . The largest known turtle was '''', a
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous The Cretaceous ( ) is a that lasted from about 145 to 66 (Mya). It is the third and final period of the , as well as the longest. At around 79 millio ...

Late Cretaceous
sea turtle up to long, wide between the tips of the front flippers, and estimated to have weighed over . The smallest living turtle is ''
Chersobius signatus ''Chersobius signatus'' is the world's smallest species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined ...
'' of South Africa, measuring no more than in length and weighing .


Shell

The shell of a turtle is unique among
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...
s and serves to protect the animal and provide shelter from the elements. It is primarily made of bone, and consists of two parts: the
carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
which usually contains 50–60 bones and covers the back of the animal while the
plastron The turtle shell is a shield for the ventral and dorsal parts of turtles (the Order (biology), order Testudines), completely enclosing all the vital organs of the turtle and in some cases even the head. It is constructed of modified bony elements ...

plastron
has only 7–11 bones and covers the belly. They are connected by lateral extensions of the plastron. The carapace is fused with the vertebrae and ribs while the plastron is formed from bones of the
shoulder girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle The clavicle, or collarbone, is a slender, S-shaped bone approximately 6 i ...
,
sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, human lung, lungs, and major blood vessels from in ...

sternum
, and
gastralia Image:Tyrannosaurus gastralia.jpg, ''Tyrannosaurus'' gastralia Gastralia (singular gastralium) are dermal bones found in the anatomical terms of location, ventral body wall of modern crocodilians and tuatara. They are found between the sternum and ...
(abdominal ribs). During development, the ribs grow sideways into a carapacial ridge, unique to turtles, entering the
dermis The dermis or corium is a layer of skin between the epidermis (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from s ...
(inner skin) of the back to support the carapace. The development is signaled locally by proteins known as
fibroblast growth factor Fibroblast growth factors (FGF) are a family of cell signalling proteins produced by macrophages; they are involved in a wide variety of processes, most notably as crucial elements for normal development in animal cells. Any irregularities in their ...
s which include
FGF10 Fibroblast growth factor 10 is a protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one location to another. P ...
. The shoulder girdle in turtles is made up of two bones, the scapula and the
coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except theria Theria (; Greek language, Greek: , wild beast) is a Scientific classification, subclass of Mammal, ...
. Both the shoulder and pelvic girdles of turtles are located within the shell and hence are effectively within the rib cage. The trunk ribs grow over the shoulder girdle during development. The outer surface of the shell is covered in epidermal (outer skin) scales known as
scute A scute or scutum (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roma ...
s which are made of
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin Alpha-keratin, or α-keratin, is a type of keratin Keratin () is one of a family of fibrous structural proteins known as Scleroprot ...

keratin
, the same substance that makes up hair and fingernails. Typically, a turtle has 38 scutes on the carapace and 16 on the plastron, giving them 54 in total. Carapace scutes are divided into "marginals" around the margin, "vertebrals" over the vertebral column, though the scute that overlays the neck is called the "cervical". "Pleurals" are present between the marginals and vertebrals. Plastron scutes include gulars (throat), humerals, pectorals, abdominals, and anals.
Side-necked turtles The Pleurodira are one of the two living Suborder (biology), suborders of Testudines, turtles, the other being the Cryptodira. The division between these two suborders represents a very deep evolutionary divide between two very different types of ...
additionally have "intergular" scutes between the gulars. Turtle scutes usually interlock like mosaic tiles, but in some species, like the
hawksbill sea turtle The hawksbill sea turtle (''Eretmochelys imbricata'') is a critically endangered sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven ...

hawksbill sea turtle
, the scutes on the carapace can overlap. The shapes of turtle shells vary with the adaptations of the individual species, and sometimes with sex. Land-dwelling turtles tend to have more domed shells, which appear to make them more resistant to being crushed by large animals. Aquatic turtles have flatter, smoother shells which allow them to cut through the water. Sea turtles in particular have streamlined shells that reduce
drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adja ...
and increase stability in the open ocean. Some turtle species have ridged, lumped, or spiked shells which provide extra protection from predators and
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard The leopard (''Pan ...

camouflage
against the leafy floor. The humps of a tortoise shell may tilt its body when it gets flipped over, allowing it to flip back. In male tortoises, the lead edge of the plastron is thickened and used for butting and ramming during combat. Shells vary in flexibility. In tortoises, the plastron and its extensions lock the sides of the carapace together, giving it even greater crushing resistance. Some species, such as
box turtle Box turtles are North American turtle Turtles are an of s known as Testudines, characterized by a developed mainly from their ribs. Modern turtles are divided into two major groups, the s and which differ in the way the head retracts. ...

box turtle
s, lack the extensions and instead have the carapace bones fully fused or
ankylosed Ankylosis is a stiffness of a joint A joint or articulation (or articular surface) is the connection made between bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. ...
together, creating a single unit. Several species have hinges on their shells, usually on the plastron, which allow them to expand and contract.
Softshell turtle The Trionychidae are a taxonomic family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is t ...

Softshell turtle
s have rubbery edges, due to the loss of bones. The leatherback turtle has hardly any bones in its shell, instead it consists of thick
connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions ...
covered in leathery skin.


Head and neck

The turtle's skull is unique among living
amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; from grc, , ''klados'', "bran ...
s (which includes reptiles, birds and mammals), it is solid and rigid with no openings for muscle attachment ( temporal fenestrae). Muscles instead attach to recesses in the back of the skull. Turtle skulls vary in shape, from the elongated skulls of softshells to the broad and flattened skull of the
mata mata The mata mata, mata-mata, or matamata (''Chelus fimbriata'') is a freshwater turtle species found in South America, primarily in the Amazon basin, Amazon and Orinoco basins. It is one of two extant taxon, extant species in the genus ''Chelus'', t ...
. Some turtle species have developed large and thick heads, allowing for greater muscle mass and stronger bites. Turtles that are carnivorous or
durophagous Durophagy is the eating behavior of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material ...
(eating hard-shelled animals), have the most powerful bites. For example, the durophagous '' Mesoclemmys nasuta'' has a bite force of 432 N. Species that are
insectivorous A robber fly eating a _.html" ;"title="hoverfly ">hoverfly An insectivore is a Carnivore">carnivorous A carnivore , meaning "meat Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since pre ...
,
piscivorous (''Nerodia sipedon'') eating a fish A piscivore is a carnivore, carnivorous animal that eats primarily fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Th ...
(fish-eating), or
omnivorous An omnivore () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular ...
have lower bite forces. Living turtles lack teeth but have beaks made of keratin sheaths lining the edges of the jaws. These sheaths may have sharp edges for cutting meat, serrated ridges for clipping plants, or broad plates for crushing
mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are recognized. The number of fossil species is es ...
. The necks of turtles are highly flexible, possibly to compensate for their rigid shells. Some species, like sea turtles, have short necks while others, such as snake-necked turtles, have very long ones. Despite this, all turtle species have eight , a consistency not found in other reptiles but paralleled in mammals. Some snake-necked turtles have both long necks and large heads and thus have difficulty lifting them when not in water.


Limbs and locomotion

Due to their heavy shells, turtles are slow-moving on land. A
desert tortoise The desert tortoise (''Gopherus agassizii)'', is a species of tortoise in the Family (biology), family Testudinidae. The species is native to the Mojave Desert, Mojave and Sonoran Deserts of the southwestern United States and northwestern Mexico, ...

desert tortoise
moves at only . By contrast, sea turtles can swim at . The limbs of turtles are adapted for various means of locomotion and habits and most have five toes. Tortoises are specialized for terrestrial environments and have column-like legs with elephant-like feet and short toes. The
gopher tortoise The gopher tortoise (''Gopherus polyphemus'') is a species of turtle in the Family (biology), family Testudinidae. The species is native to the southeastern United States. The gopher tortoise is seen as a keystone species because it digs burrows ...
has flattened front limbs for digging in the substrate. Freshwater turtles have more flexible legs and longer toes with
webbing red, blue and black nylon webbing as used in auto racing harnesses Webbing is a strong Textile, fabric weaving, woven as a flat strip or tube of varying width and fibres, often used in place of rope. It is a versatile component used in climbing ...
, giving them thrust in the water. Some of these species, such as snapping turtles and
mud turtle ''Kinosternon'' is a genus of small aquatic turtles from the Americas known commonly as mud turtles. Geographic range They are found in the United States, Mexico, Central America, and South America. The greatest species richness is in Mexico, a ...
s, mainly walk along the water bottom, much as they would on land. Others, such as terrapins, swim by paddling with all four limbs with the simultaneous retraction of the opposing front and hind limbs, helping them maintain their direction while thrusting. Sea turtles and the pig-nosed turtle are the most specialized for swimming. Their front limbs have evolved into flippers while the shorter hind limbs are shaped more like rudders. The front limbs provide most of the thrust for swimming, while the hind limbs serve as stabilizers. Sea turtles such as the
green sea turtle The green sea turtle (''Chelonia mydas''), also known as the green turtle, black (sea) turtle or Pacific green turtle, is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank ...

green sea turtle
rotate the front limb flippers like a bird's wings to generate a propulsive force on both the upstroke and on the downstroke. This is in contrast to similar-sized freshwater turtles (measurements having been made on young animals in each case) such as the Caspian turtle, which uses the front limbs like the oars of a rowing boat, creating substantial negative thrust on the recovery stroke in each cycle. In addition, the streamlining of the marine turtles reduces drag. As a result, marine turtles produce a propulsive force twice as large, and swim six times as fast, as freshwater turtles. The swimming efficiency of young marine turtles is similar to that of fast-swimming fish of open water, like
mackerel Mackerel is a common name applied to a number of different species of pelagic fish Pelagic fish live in the pelagic zone The pelagic zone consists of the water column A water column is a Concept, conceptual column of water from the ...

mackerel
. Compared to other reptiles, turtles tend to have reduced tails, but these vary in both length and thickness among species and between sexes. They are especially large in snapping turtles and the big-headed turtle. The latter uses it for balance while climbing. The
cloaca In animal anatomy, a cloaca (plural cloacae or ) is the posterior that serves as the only opening for the , reproductive, and s (if present) of many animals. All s, s, birds, and a few mammals (s, s, s, and s) have this orifice, from which ...
is at the base of the tail, and the tail itself houses the reproductive organs. Hence, males have longer tails to accommodate the penis. In sea turtles, the tail is longer and also somewhat
prehensile A prehensile tail. Prehensility is the quality of an appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism (from Ancient Greek, Greek: ὀργ ...
and males use it to grasp females when mating. Several turtle species have spines on their tails.


Senses

Turtles make use of
vision Vision or The Vision may refer to: Perception Optical perception * Visual perception Visual perception is the ability to interpret the surrounding environment (biophysical), environment through photopic vision (daytime vision), color visio ...
to find food and mates, avoid predators, and orient themselves. The
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
's light-sensitive cells include both rods for vision in low light, and
cones A cone is a three-dimensional space, three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the Apex (geometry), apex or vertex (geometry), vertex. A cone is fo ...

cones
with three different
photopigment Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore A chromophore is the part of a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunnel ...
s for bright light, where they have full-color vision. There is possibly a fourth type of cone that detects
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
, as hatchling sea turtles respond experimentally to ultraviolet light, but it is unknown if they can distinguish this from longer wavelengths. A freshwater turtle, the
red-eared slider The red-eared slider (''Trachemys scripta elegans'') is a subspecies of the pond slider (''Trachemys scripta''), a semiaquatic turtle belonging to the Family (biology), family Emydidae. It is the most popular pet turtle in the United States, is ...

red-eared slider
, has an exceptional seven types of cone cell. Sea turtles orient themselves on land by night, using visual features detected in dim light. They can use their eyes in clear surface water, muddy coasts, the darkness of the deep ocean, and also above water. Unlike in terrestrial turtles, the
cornea The cornea is the transparent Transparency, transparence or transparent most often refer to transparency and translucency, the physical property of allowing the transmission of light through a material. They may also refer to: Literal uses * ...

cornea
, the curved surface that lets light into the eye, does not help to focus light on the retina, so focusing underwater is handled entirely by the lens, behind the cornea. The cone cells contain oil droplets placed to shift perception towards the red part of the spectrum which improves color discrimination. Visual acuity, studied in hatchlings, is highest in a horizontal band with retinal cells packed about twice as densely as elsewhere. This gives the best vision along the visual horizon. Sea turtles do not appear to use
polarized light Polarization (also Also or ALSO may refer to: *Advanced Life Support in Obstetrics Advanced Life Support in Obstetrics (ALSO) is a program that was developed by the American Academy of Family Physicians (AAFP). This course helps physicians, ce ...
for orientation as many other animals do. The deep-diving leatherback turtle lacks specific adaptations to low light, such as large eyes, large lenses, or a reflective tapetum. It may rely on seeing the
bioluminescence Bioluminescence is the production and emission of light by a living organism. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some Fungus , fungi, microorganisms includ ...
of prey when hunting in deep water. Turtles have no ear openings; the
eardrum In the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
is covered with scales and surrounded by a bony
otic capsule The bony labyrinth (also osseous labyrinth or otic capsule) is the rigid, bony outer wall of the inner ear in the temporal bone. It consists of three parts: the vestibule of the ear, vestibule, semicircular canals, and cochlea. These are cavities ho ...
, which is absent in other reptiles. Their hearing thresholds are high compared to other reptiles, reaching up to 500 Hz in air, but underwater they are more attuned to lower frequencies. The
loggerhead sea turtle The loggerhead sea turtle (''Caretta caretta''), is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often d ...

loggerhead sea turtle
has been shown experimentally to respond to low sounds, with maximal sensitivity between 100 and 400 Hz. Turtles have both
olfactory The sense of smell, or olfaction, is the special sense In medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and managing the diagnosis, prognosis, Preventive medicine, prevention, the ...

olfactory
(smell) and receptors along the nasal cavity, the latter of which are used to detect tiny particles. Experiments on green sea turtles showed they could learn to respond to a selection of different odorant chemicals such as
triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA ...

triethylamine
and
cinnamaldehyde Cinnamaldehyde is an organic compound with the formula C6H5CH=CHCHO. Occurring naturally as predominantly the Cis-trans isomerism, ''trans'' (''E'') isomer, it gives cinnamon its flavor and odor. It is a phenylpropanoid that is naturally synthesize ...

cinnamaldehyde
, which were detected by olfaction in the nose. Such signals could be used in navigation.


Breathing

Amniotes typically breathe by contracting and relaxing specific muscle groups (i.e. intercostals, abdominal muscles, and/or a
diaphragm Diaphragm may refer to: * Diaphragm (anatomy) or thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Diaphragm (optics), a stop in the light path of a lens, having an aperture that regulates the amount of light that pass ...
) attached to a rib cage that can expand and contract the body wall, letting air flow in and out of the lungs. The rigid shell of turtles is not capable of expansion, so they have had to evolve special adaptations for respiration. The lungs of turtles are attached directly to the carapace above while below, connective tissue attaches them to the organs. They have multiple lateral (side) and medial (middle) chambers (the numbers of which vary between species) and one terminal (end) chamber. The lungs are ventilated using specific groups of abdominal muscles attached to the organs which pull and push on them. Specifically, it is the turtle's large liver that compresses the lungs. Underneath the lungs, in the
coelomic cavity The coelom (or celom) is the main body cavity A body cavity is any space or compartment, or potential space in the animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid. The two largest human b ...
, the liver is attached to the right lung by the
root In vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia artēria'' 'windpipe' + φυτά ''phutá'' 'plants'), form a large grou ...
, and the stomach is directly attached to the left lung, which is attached to the liver by a
mesentery The mesentery is an organ that attaches the intestines to the posterior abdominal wall In anatomy, the abdominal wall represents the boundaries of the abdominal cavity The abdominal cavity is a large body cavity in humans and many other anima ...

mesentery
. When the liver is pulled down, inhalation begins. Supporting the lungs is a wall or
septum In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...

septum
, which is thought to prevent them from collapsing. During exhalation, the contraction of the
transversus abdominis muscle The transverse abdominal muscle (TVA), also known as the transverse abdominis, transversalis muscle and transversus abdominis muscle, is a muscle layer of the anterior Standard anatomical terms of location deal unambiguously with the anatomy A ...
propels the organs into the lungs and expels air. Conversely, during inhalation, the relaxing and flattening of the oblique abdominis muscle pulls the transversus back down which allows air back into the lungs. Although many turtles spend large amounts of their lives underwater, all turtles breathe air and must surface at regular intervals to refill their lungs. Depending on the species, immersion periods vary between a minute and an hour. Some species can respire through the cloaca, which contains large sacs that are lined with many finger-like projections which take up dissolved
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
from the water.


Circulation

Turtles share the linked circulatory and pulmonary (lung) systems of vertebrates, where the three-chambered heart pumps deoxygenated blood through the lungs and then pumps the returned
oxygenated blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...
through the body's tissues. The cardiopulmonary system has both structural and physiological adaptations that distinguish it from other vertebrates. Turtles have a large lung volume and can move blood through non-pulmonary blood vessels, including some within the heart, to avoid the lungs while they are not breathing. They can hold their breath for much longer periods than other reptiles and they can tolerate the resulting low oxygen levels. They can moderate the increase in acidity during anaerobic (non-oxygen-based) respiration by chemical buffering and they can lie dormant for months, in
aestivation Aestivation ( la, aestas (summer); also spelled estivation in American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language nativ ...

aestivation
or
brumation Dormancy is a period in an organism's life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the pr ...
. The heart has two
atriaAtria may refer to: *Atrium (heart) The atrium (Latin ātrium, “entry hall”) is the upper chamber through which blood enters the Ventricle (heart), ventricles of the heart. There are two atria in the human heart – the left atrium receives bloo ...
but only one ventricle. The ventricle is subdivided into three chambers. A muscular ridge enables a complex pattern of blood flow so that the blood can be directed either to the lungs via the
pulmonary artery A pulmonary artery is an artery An artery (plural arteries) () is a blood vessel that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are t ...

pulmonary artery
, or to the body via the
aorta The aorta ( ) is the main and largest artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vas ...

aorta
. The ability to separate the two outflows varies between species. The leatherback has a powerful muscular ridge enabling almost complete separation of the outflows, supporting its actively swimming lifestyle. The ridge is less well developed in freshwater turtles like the sliders ('' Trachemys''). Turtles are capable of enduring periods of anaerobic respiration longer than many other vertebrates. This process breaks down sugars incompletely to
lactic acid Lactic acid is an organic acid An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, conta ...

lactic acid
, rather than all the way to
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
and water as in aerobic (oxygen-based) respiration. They make use of the shell as a source of additional buffering agents for combating increased acidity, and as a sink for lactic acid.


Osmoregulation

In sea turtles, the bladder is singular and in most freshwater turtles, it is bi-lobed. Sea turtle bladders have two small accessory bladders, located at the sides to the neck of the urinary bladder and above to the pubis. Arid-living tortoises have bladders that serve as reserves of water, storing up to 20% of their body weight in fluids. The fluids are normally very low in
solute In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence i ...
s, but higher during droughts when the reptile gains
potassium Potassium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, b ...

potassium
salts from its plant diet. The bladder stores these salts until the tortoise finds fresh drinking water. To regulate the amount of salt in their bodies, sea turtles and
diamondback terrapin The diamondback terrapin or simply terrapin (''Malaclemys terrapin'') is a species of turtle native to the Brackish water, brackish coastal tidal marshes of the eastern and southern United States, and in Bermuda. It belongs to the monotypic genus ...
s secrete excess salt in a thick sticky substance from their tear glands. Because of this, sea turtles may appear to be "crying" when on land.


Thermoregulation

Turtles, like other reptiles, have a limited ability to regulate their body temperature. This ability varies between species, and with body size. Small pond turtles regulate their temperature by crawling out of the water and basking in the sun, while small terrestrial turtles move between sunny and shady places to adjust their temperature. Large species, both terrestrial and marine, have sufficient mass to give them substantial thermal inertia, meaning that they heat up or cool down over many hours. The Aldabra giant tortoise weighs up to some and is able to allow its temperature to rise to some on a hot day, and to fall naturally to around by night. Some giant tortoises seek out shade to avoid overheating on sunny days. On Grand Terre Island, food is scarce inland, shade is scarce near the coast, and the tortoises compete for space under the few trees on hot days. Large males may push smaller females out of the shade, and some then overheat and die. Adult sea turtles, too, have large enough bodies that they can to some extent control their temperature. The largest turtle, the leatherback, can swim in the waters off Nova Scotia which may be as cold as , while their body temperature has been measured at up to warmer than the surrounding water. To help keep their temperature up, they have a system of countercurrent heat exchange in the blood vessels between their body core and the skin of their flippers. The vessels supplying the head are insulated by fat around the neck.


Behavior


Diet and feeding

Most turtle species are opportunistic omnivores; land-dwelling species are more Herbivore, herbivorous and aquatic ones more Carnivore, carnivorous. Generally lacking speed and agility, most turtles feed either on plant material or on wikt:sedentary, sedentary animals like mollusks, worms, and insect larvae. Some species, such as the African helmeted turtle and snapping turtles, eat fish, amphibians, reptiles (including other turtles), birds, and mammals. They may take them by ambush predator, ambush but also scavenge. The alligator snapping turtle has a worm-like appendage on its tongue which it Aggressive mimicry, uses to lure fish into its mouth. Tortoises are the most herbivorous group, consuming grasses, leaves, and fruits. Many turtle species, including tortoises, supplement their diet with eggshells, animal bones, hair, and droppings for extra nutrients. Turtles generally eat their food in a straightforward way, though some species have special feeding techniques. The yellow-spotted river turtle and the painted turtle may filter feed by skimming the water surface with their mouth and throat open to collect particles of food. When the mouth closes, the throat constricts and excess water is pushed out through the nostrils and the gap in between the almost closed jaws. Some species employ a "gape-and-suck method" where the turtle opens its jaws and expands its throat widely, sucking the prey in. The diet of an individual within a species may change with age, sex, and season, and may also differ between populations. In many species, juveniles are generally carnivorous but become more herbivorous as adults. With Barbour's map turtle, the larger female mainly eats mollusks while the male eats mostly arthropods. Blanding's turtle may feed mainly on snails or crayfish depending on the population. The European pond turtle has been recorded as being mostly carnivorous much of the year but switching to Nymphaea alba, water lilies during the summer. Some species have developed Generalist and specialist species, specialized diets such as the hawksbill, which eats sponges, the leatherback, which feeds on jellyfish, and the Mekong snail-eating turtle.


Communication and intelligence

While popularly thought of as mute, turtles make various sounds to communicate. Tortoises may bellow when courting and mating. Various species of both freshwater and sea turtles emit short, low-frequency calls from the time they are in the egg to when they are adults. These vocalizations may serve to create group cohesion when Animal migration, migrating. The oblong turtle has a particularly large vocal range; producing sounds described as clacks, clicks, squawks, hoots, various kinds of chirps, wails, ', grunts, growls, blow bursts, howls, and drum rolls. Play behavior has been documented in some turtle species. In the laboratory, Florida red-bellied cooters can learn novel tasks and have demonstrated a long-term memory of at least 7.5 months. Similarly, giant tortoises can learn and remember tasks, and master lessons much faster when trained in groups. Tortoises appear to be able to retain operant conditioning nine years after their initial training.


Defense

When sensing danger, a turtle may flee, freeze or withdraw into its shell. Freshwater turtles flee into the water, though the Sonora mud turtle may take refuge on land as the shallow temporary ponds they inhabit make them vulnerable. When startled, a softshell turtle may dive underwater and bury itself under the sea floor. If a predator persists, the turtle may bite or discharge from its cloaca. Several species produce foul-smelling chemicals from musk glands. Other tactics include threat displays and Bell's hinge-back tortoise can Apparent death, play dead. When attacked, big-headed turtle hatchlings squeal, possibly startling the predator.


Migration

Turtles are the only reptiles that migrate long distances, more specifically the marine species that can travel up to thousands of kilometers. Some non-marine turtles, such as the species of ''Geochelone'' (terrestrial), ''Chelydra'' (freshwater), and ''Malaclemys'' (estuarine), migrate seasonally over much shorter distances, up to around , to lay eggs. Such short migrations are comparable to those of some lizards, snakes, and crocodilians. Sea turtles nest in a specific area, such as a beach, leaving the eggs to hatch unattended. The young turtles leave that area, migrating long distances in the years or decades in which they grow to maturity, and then return seemingly to the same area every few years to mate and lay eggs, though the precision varies between species and populations. This "natal homing" has appeared remarkable to biologists, though there is now plentiful evidence for it, including from genetics. How sea turtles navigate to their breeding beaches remains unknown. One possibility is Imprinting (psychology), imprinting as in salmon, where the young learn the chemical signature, effectively the scent, of their home waters before leaving, and remember that when the time comes for them to return as adults. Another possible cue is the orientation of the earth's magnetic field at the natal beach. There is experimental evidence that turtles have an effective magnetic sense, and that they use this in Animal navigation, navigation. Proof that homing occurs is derived from genetic analysis of populations of loggerheads, hawksbills, leatherbacks, and Olive ridley sea turtle, olive ridleys by nesting place. For each of these species, the populations in different places have their own mitochondrial DNA genetic signatures which persist over the years. This shows that the populations are distinct and that homing must be occurring reliably.


Reproduction and lifecycle

Turtles have a wide variety of mating behaviors but do not form Pair bond, pair-bonds or social groups. In green sea turtles, females generally outnumber males. In terrestrial species, males are often larger than females and fighting between males establishes a dominance hierarchy for access to mates. For most semi-aquatic and bottom-walking aquatic species, combat occurs less often. Males of these species instead may use their size advantage to Sexual coercion among animals, mate forcibly. In fully aquatic species, males are often smaller than females and rely on courtship displays to gain mating access to females.


Courtship and mounting

Courtship varies between species, and with habitat. It is often elaborate in aquatic species, both marine and freshwater, but minimal in the semi-aquatic mud turtles and snapping turtles. A male tortoise bobs his head, then immobilizes the female by biting and butting her before mounting. The male scorpion mud turtle approaches the female from the rear, and often resorts to aggressive methods such as biting the female's tail or hind limbs, followed by a mounting. Female choice is important in some species, and female green sea turtles are not always receptive. As such, they have evolved behaviors to avoid the male's attempts at copulation, such as swimming away, confronting the male followed by biting or taking up a refusal position with her body vertical, her limbs widely outspread, and her plastron facing the male. If the water is too shallow for the refusal position, the females resort to beaching themselves, as the males will not follow them ashore. All turtles fertilize internally; mounting and copulation can be difficult. In many species, males have a concave plastron that fits with the female's carapace. In species like the Russian tortoise, the male has a lighter shell and longer legs. The high, rounded shells of box turtles are particular obstacles for mounting. The male eastern box turtle leans backward into position and hooks onto the back of the female's plastron. Aquatic turtles mount in water, and female sea turtles support the mounting male while swimming and diving. During copulation, the male turtle forces his tail under the females to allow for their cloacas to align and he can insert his penis. Some female turtles can Female sperm storage, store sperm from multiple males and their Clutch (eggs), egg clutches can have multiple sires.


Eggs and hatchlings

Turtles, including sea turtles, lay their eggs on land, although some lay eggs close to or in shallow water which rises and falls in level. While most species build nests and lay eggs where they forage, some travel miles. The common snapping turtle walks on land to lay eggs, while sea turtles travel even further; the leatherback swims some to its nesting beaches. Most turtles prepare a nest for their eggs. Females usually dig a flask-like chamber in the substrate. Other species lay their eggs in vegetation or crevices. Females choose nesting locations based on environmental factors such as temperature and humidity, which are important for developing embryos. Depending on the species, the number of eggs laid varies from 10 to over 100. Larger females can lay eggs that are greater in number or bigger in size. Compared to freshwater turtles, tortoises deposit fewer but larger eggs. Females can lay multiple clutches throughout a season, particularly in species that experience unpredictable monsoons. Most mother turtles do no more in the way of parental care than covering their eggs and immediately leaving, though some species guard their nests for days or weeks. Eggs vary between spherical, oval, elongated, and between hard- and soft-shelled. Most species have their temperature-dependent sex determination, sex determined by temperature. In some species, higher temperatures produce females and lower ones produce males, while in others, intermediate temperatures produce males and both hot and cold extremes produce females. There is experimental evidence that the embryos of ''Mauremys reevesii'' can move around inside their eggs to select the best temperature for development, thus influencing their sexual destiny. In other species, sex is Sex-determination system#Chromosomal systems, determined genetically. The length of incubation for turtle eggs varies from two to three months for temperate species, and four months to over a year for tropical species. Species that live in warm temperate climates can embryonic diapause, delay their development. When ready to hatch, young turtles break out of the shell using an egg tooth, a sharp projection that exists temporarily on their upper beak. Hatchlings dig out of the nest and find cover in vegetation or water. Some species remain in the nest for longer, be it for overwintering or to wait for the rain to soften the soil for them to dig out. Young turtles are highly vulnerable to predators, both in the egg and as hatchlings. Mortality is high during this period but significantly decreases when they reach adulthood. Most species grow rapidly during their early years and slow down when they are mature.


Lifespan

Turtles can live very long lives. The oldest living turtle and land animal is said to be a Seychelles giant tortoise named Jonathan (tortoise), Jonathan, who turned 187 in 2019. A Galápagos tortoise named Harriet (tortoise), Harriet was collected by Charles Darwin in 1835; it died in 2006, having lived for at least 176 years. Most wild turtles do not reach that age. Turtles keep growing new scutes under the previous scutes every year, allowing researchers to estimate how long they have lived. They also negligible senescence, age very slowly. The survival rate for adult turtles can reach 99% per year.


Systematics and evolution


Fossil history

Zoologists have sought to explain the evolutionary origin of the turtles, and in particular of their unique shells. In 1914, Jan Versluys proposed that bony plates in the dermis, called osteoderms, fused to the ribs beneath them, later called the "Polka Dot Ancestor" by Olivier Rieppel. The theory accounted for the evolution of fossil pareiasaurs from ''Bradysaurus'' to ''Anthodon (reptile), Anthodon'', but not for how the ribs could have become attached to the bony dermal plates. More recent discoveries have painted a different scenario for the evolution of the turtle's shell. The Crown group#Stem groups, stem-turtles ''Eunotosaurus'' of the Middle Permian, ''Pappochelys'' of the Middle Triassic, and ''Eorhynchochelys'' of the Late Triassic lacked carapaces and plastrons but have shortened trunks, broadened ribs, and elongated dorsal vertebrae. Also in the Late Triassic, ''Odontochelys'' had a partial shell consisting of a complete bony plastron and an incomplete carapace. The development of a shell reached completion with the Late Triassic ''Proganochelys'', with its fully developed carapace and plastron. The broadening of the ribs may have originally been adapted for digging and a fossorial lifestyle. The oldest known members of the Pleurodira lineage are the Platychelyidae, from the Late Jurassic. The oldest known unambiguous cryptodire is ''Sinaspideretes,'' a close relative of softshell turtles, from the Late Jurassic of China. During the Late Cretaceous and Cenozoic, members of the pleurodire families Bothremydidae and Podocnemididae became widely distributed in the Northern Hemisphere due to their coastal habits. The oldest known soft-shelled turtles and sea turtles appeared during the Early Cretaceous. Tortoises originated in Asia during the Eocene. A late surviving group of stem-turtles, the Meiolaniidae, survived in Australasia into the Pleistocene and Holocene.


External relationships

The turtles' exact ancestry has been disputed. It was believed they were the only surviving branch of the ancient evolutionary grade Anapsida, which includes groups such as Procolophonidae, procolophonids and pareiasaurs. All anapsid skulls lack a temporal opening while all other living amniotes have temporal openings. It was later suggested that the anapsid-like turtle skulls may be due to backward evolution rather than to anapsid descent. Fossil evidence has shown that early stem-turtles possessed small temporal openings. Some early morphological phylogenetics, phylogenetic studies have placed turtles closer to Lepidosauria (tuataras, lizards, and snakes) than to Archosauria (
crocodilian Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, ...
s and birds). By contrast, several Molecular phylogenetics, molecular studies place turtles either within Archosauria, or, more commonly, as a sister group to extant archosaurs, though an analysis conducted by Tyler Lyson and colleagues (2012) recovered turtles as the sister group of lepidosaurs instead. Ylenia Chiari and colleagues (2012) analyzed 248 nuclear genes from 16 vertebrate taxa and suggested that turtles share a most recent common ancestor, more recent common ancestor with birds and crocodilians. The date of separation of turtles and birds and crocodilians was estimated to be during the Permian. Through genomic-scale phylogenetic analysis of ultra-conserved elements (UCEs) to investigate the placement of turtles within reptiles, Nicholas Crawford and colleagues (2012) similarly found that turtles are closer to birds and crocodilians. The first genome-wide phylogenetic analysis was completed by Zhuo Wang and colleagues (2013). Using the draft (unfinished) genome sequences of the green sea turtle and the Chinese softshell turtle, the team again concluded that turtles are likely a sister group of crocodilians and birds. The external phylogeny of the turtles is shown in the cladogram below.


Internal relationships

Modern turtles and their extinct relatives with a complete shell are classified within the clade Testudinata. The most recent common ancestor of living turtles, corresponding to the split between Pleurodira (side-necked species) and Cryptodira (hidden necked species), is estimated to have occurred around during the Late Triassic. Robert Thompson and colleagues (2021) comment that living turtles have very low diversity, given the group's age. Diversity has been constant, according to their analysis, except for a single rapid increase around the Eocene-Oligocene boundary some 30 million years ago, and a major regional extinction at roughly the same time. They suggest that global climate change caused both events, as the cooling and drying caused the land to become arid and turtles to become extinct there, while new continental margins exposed by the climate change provided habitats for other species to evolve. The cladogram, from Nicholas Crawford and colleagues 2015, shows the internal phylogeny of the Testudines down to the level of Family (biology), families. The analysis by Thompson and colleagues in 2021 supports the same structure down to the family level.


Differences between the two suborders

Turtles are divided into two living suborders: Cryptodira and Pleurodira. The two groups differ in the way the neck is retracted for protection. Pleurodirans retract their neck to the side and in front of the shoulder girdles, whereas cryptodirans retract their neck back into their shell. These motions are enabled by the morphology and arrangement of neck vertebrae. Sea turtles (which belong to Cryptodira) have mostly lost the ability to retract their heads. The shape of the head differs between the two suborders, as the jaw musculature is associated with different bones in the two groups. The adductor muscles in the lower jaw create a pulley-like system in both subgroups. However, the bones that the muscles articulate with differ. In Pleurodira, the pulley is formed with the pterygoid bones of the palate, but in Cryptodira the pulley is formed with the otic capsule. Both systems help to vertically redirect the Anatomical terms of motion#Abduction and adduction, adductor muscles and maintain a powerful bite. A further difference between the suborders is the attachment of the pelvis. In Cryptodira, the pelvis is free, linked to the shell with flexible ligaments. In Pleurodira, the pelvis is Suture (anatomy), sutured, joined with bony connections, to the carapace and to the plastron, creating a pair of large columns of bone at the back end of the turtle, linking the two parts of the shell.


Distribution and habitat

Turtles are widely distributed across the world's continents, oceans, and islands with terrestrial, fully aquatic, and semi-aquatic species. Sea turtles are mainly tropical and subtropical, but leatherbacks can be found in temperate areas of the Atlantic and Pacific. Living Pleurodira all live in freshwater and are found only in the Southern Hemisphere. The Cryptodira include terrestrial, freshwater, and marine species, and these range more widely. The world regions richest in non-marine turtle species are the Amazon basin, the Gulf of Mexico Drainage basin, drainages of the United States, and parts of South and Southeast Asia. For turtles in colder climates, their distribution is limited by constraints on reproduction, which is reduced by long hibernations. North American species barely range above the southern Canadian border. Some turtles are found at high altitudes, for example, the species ''Terrapene ornata'' occurs up to in New Mexico. Conversely, the leatherback sea turtle can dive over . Species of the genus ''Gopherus'' can tolerate body temperatures from below freezing to over , though they are most active at .


Conservation

Among vertebrate orders, turtles are second only to primates in the percentage of threatened species. 360 modern species have existed since 1500 AD. Of these, 51–56% are considered threatened and 60% considered threatened or extinct. Turtles face many threats, including habitat destruction, harvesting for consumption, the pet trade, light pollution, and climate change. Asian species have a particularly high extinction risk, primarily due to their long-term unsustainable exploitation for food and medicine, and about 83% of Asia's non-marine turtle species are considered threatened. As of 2021, turtle extinction is progressing much faster than during the Cretaceous-Tertiary extinction. At this rate, all turtles could be extinct in a few centuries. Turtle hatchery, hatcheries can be set up when protection against flooding, erosion, predation, or heavy poaching is required. Chinese markets have sought to satisfy an increasing demand for turtle meat with farmed turtles. In 2007 it was estimated that over a thousand turtle farms operated in China. All the same, wild turtles continue to be caught and sent to market in large numbers, resulting in what conservationists have called "the Asian turtle crisis". In the words of the biologist George Amato, the hunting of turtles "vacuumed up entire species from areas in Southeast Asia", even as biologists still did not know how many species lived in the region. In 2000, all the Asian box turtles were placed on the CITES list of endangered species. Harvesting wild turtles is legal in some American states, and there has been a growing demand for American turtles in Asia. The Florida Fish and Wildlife Conservation Commission estimated in 2008 that around 3,000 pounds of softshell turtles were exported each week via Tampa International Airport. However, the great majority of turtles exported from the US between 2002 and 2005 were farmed. Large numbers of sea turtles are accidentally killed in Longline fishing, longlines, gillnetting, gillnets, and trawling nets as
bycatch Bycatch (or by-catch), in the fishing industry The fishing industry includes any industry or activity concerned with taking, culturing, processing, preserving, storing, transporting, marketing or selling fish or fish products. It is defined by ...
. A 2010 study suggested that over 8 million had been killed between 1990 and 2008; the Eastern Pacific and the Mediterranean were identified as among the areas worst affected. Since the 1980s, the United States has required all Shrimp trawling, shrimp trawlers to fit their nets with turtle excluder devices which prevent turtles from being caught in the net and drowning. More locally, other human activities are affecting marine turtles. In Australia, Queensland's shark culling program, which uses shark nets and drum line (shark control), drum lines, has killed over 5,000 turtles as bycatch between 1962 and 2015; including 719 loggerhead turtles and 33 critically endangered hawksbill sea turtles. Native turtle populations can also be threatened by Invasive species, invasive ones. The central North American red-eared slider turtle has been labeled among the "100 of the World's Worst Invasive Alien Species, world's worst invasive species", being distributed globally due to the pet trade. They appear to compete with native turtle species in eastern and western North America, Europe, and Japan.


Human uses


In culture

File:Kurmavatara (tortoise incarnation of Vishnu), from Garhwa, Allahabad District.jpg, alt=Photograph of temple sculpture in India, 4th-century sculpture of turtle avatar of Vishnu. Garhwa, Garhwa, India File:PSM V10 D562 The hindoo earth.jpg, alt=Lithograph drawing of world resting on 4 elephants standing on a giant turtle, World resting on four elephants on the back of the World Turtle. Western depiction of "The Hindu Earth", 1877 File:Kangxi-Lugou-rebuilding-stele-3581.jpg, alt=Chinese funeral stone held up by a stone tortoise, Bixi (tortoise), Bixi supporting Kangxi Emperor's stele, Beijing, 1698 File:Alice par John Tenniel 34.png, alt=Children's book illustration with turtle figure standing on hind legs, The Mock Turtle in Lewis Carroll's 1865 ''Alice's Adventures in Wonderland'' File:The Turtle 1898 Manhattan Theatre poster.jpg, alt=Painting of a turtle standing on hind legs, with top hat and cane, on theatre poster, Poster for 1898 production of ''The Turtle'' at the Manhattan Theatre, Broadway File:Terrapin Shell Leg Rattles Worn by Lead Woman Dancer, Oconaluftee Village, NC. - NARA - 281630.jpg, alt=Photograph of cloth with four terrapin shell rattles to be tied around a dancer's leg, Terrapin shell leg rattles worn by lead Cherokee woman dancer, 20th century Turtles have featured in human cultures across the world since ancient times. They are generally viewed positively despite not being "cuddly" or flashy; their association with antiquity and old age have contributed to their endearing image. In Hindu mythology, the World Turtle, named Kurma, Kurma or Kacchapa, supports four elephants on his back; they, in turn, carry the weight of the whole world on their backs. The turtle is one of the ten avatars or incarnations of the god Vishnu. The yoga pose Kurmasana is named for the avatar. revised from American Academy of Religions conference, San Francisco, 19 November 2011. World Turtles are found in Native American cultures including the Algonquian peoples, Algonquian, Iroquois, and Lenape. They tell many versions of the creation story of Turtle Island (Native American folklore), Turtle Island. One version has Muskrat pile up earth on Turtle's back, creating the continent of North America. An Iroquois version has the pregnant Sky Woman fall through a hole in the sky between a tree's roots, where she is caught by birds who land her safely on Turtle's back; the Earth grows around her. The turtle here is altruistic, but the world is a heavy burden, and the turtle sometimes shakes itself to relieve the load, causing earthquakes. A turtle was the symbol of the Ancient Mesopotamian god Enki from the 3rd millennium BC onwards. An ancient Greek origin myth told that only the tortoise refused the invitation of the gods Zeus and Hera to their wedding, as it preferred to stay at home. Zeus then ordered it to carry its house with it, ever after. Another of their gods, Hermes, invented a seven-stringed chelys, lyre made with the shell of a tortoise. In China, the turtle was one of the Four Symbols, four sacred animals in Confucianism, while in the Han period, steles were mounted on top of stone turtles, later linked with Bixi, the turtle-shelled son of the Dragon King. Marine turtles feature significantly in Australian Aboriginal art. The army of Ancient Rome used the ' Testudo formation, ("tortoise") formation where soldiers would form a shield wall for protection. In Aesop's Fables, "The Tortoise and the Hare" tells how an unequal race may be won by the slower partner. Lewis Carroll's 1865 ''Alice's Adventures in Wonderland'' features a Mock Turtle, named for Mock turtle soup, a soup meant to imitate the expensive soup made from real turtle meat. In 1896, the French playwright Léon Gandillot wrote a comedy in three acts named ''La Tortue'' that was "a Parisian sensation" in its run in France, and came to the Manhattan Theatre, Broadway, New York in 1898 as ''The Turtle''. A "cosmic turtle" and the island motif reappear in Gary Snyder's 1974 novel ''Turtle Island (book), Turtle Island'', and again in Terry Pratchett's ''Discworld'' series as A'Tuin the Great, starting with the 1983 novel ''The Colour of Magic''. It is supposedly of the species ''Chelys galactica'', the galactic turtle, complete with four elephants on its back to support Discworld. Turtles have been featured in comic books and animations such as the 1984 Teenage Mutant Ninja Turtles.


As pets

Some turtles, particularly small terrestrial and freshwater species, are kept as pets. The popularity of pet turtles increased in the 1950s, and the US became the largest supplier, particularly of farm-bred red-eared sliders, in the international pet trade. The demand for exotic pets has led to an increase in illegal Wildlife trade, wildlife trafficking. It is estimated that 21% of the value of live animal trade is in reptiles, with turtles being the most popular members of the group. Poor husbandry of tortoises can cause chronic rhinitis (nasal swelling), overgrown beaks, hyperparathyroidism (which softens their skeleton), constipation, various reproductive problems, and injuries from dogs. In the early 20th century, people in the United States have organized and gambled on Turtle racing, turtle races.


As food and other uses

The flesh of captured wild turtles continues to be eaten in Asian cultures, while turtle soup was once a popular dish in English cuisine. Gopher tortoise stew has been popular with some groups in Florida. The supposed aphrodisiac or medicinal properties of turtle eggs created a large trade for them in Southeast Asia. Hard-shell turtle plastrons and soft-shell carapaces are widely used in traditional Chinese medicine; Taiwan imported nearly 200 metric tons of hard-shells from its neighbors yearly from 1999 to 2008. A popular medicinal preparation based on herbs and turtle shells is ''guilinggao'' jelly. The substance tortoiseshell, usually from the hawksbill turtle, has been used for centuries to make jewelery, tools, and ornaments around the Western Pacific. Hawksbills have accordingly been hunted for their shells. The trading of tortoiseshell was internationally banned in 1977 by CITES. Some cultures have used turtle shells to make music: Native American shamans made them into ceremonial rattles, while Aztecs, Maya civilization, Mayas, and Mixtecs made ' drums. File:StateLibQld 2 395489 Catching turtles, wood engraving, 1875.jpg, Catching turtles in Australia, 1875, alt=Historic engraving of men catching turtles on a beach File:TurtleSeafood.jpg, Turtles on sale as food in Canada, 2007, alt=photo of turtles on sale as food in a shop File:Turtle plastrons as TCM in Xi'an market.jpg, Turtle plastrons for traditional Chinese medicine, alt=Photograph of a box of turtle plastrons in a market File:Peigne en écaille.jpg, A tortoiseshell comb; the material was expensive and decorative, and widely used for small items., alt=Photograph of a decoratively ridged comb made of tortoiseshell File:Sheldonbasking.JPG, A pet red-eared slider basking on a floating platform under a sun lamp, alt=Photograph of a pet turtle in a terrarium


See also

World Turtle Day


References


General sources

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External links


Turtle Survival Alliance

Turtle Conservancy

Symposium on Turtle Evolution
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