Misplaced Pages

#742257

95-798: Other than mammals, dicynodonts are the only known vertebrates to have true tusks. Tusks have a variety of uses depending on the animal. Social displays of dominance, particularly among males, are common, as is their use in defense against attackers. Elephants use their tusks as digging and boring tools. Walruses use their tusks to grip and haul out on ice. It has been suggested that tusks' structure has evolved to be compatible with extra-oral environments. Elephant tusks are sexually dimorphic , being on average larger in males than in females, and entirely absent in female Asian elephants . Elephants with large tusks each at least 45 kilograms (99 lb) in weight are known as "tuskers", sometimes also called "big tuskers" or "great tuskers". While tuskers are rare today, it

190-574: A bony secondary palate which completely separates the oral and nasal cavities. 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 long ones. Despite this, all turtle species have eight neck vertebrae , a consistency not found in other reptiles but similar to mammals . Some snake-necked turtles have both long necks and large heads, limiting their ability to lift them when not in water. Some turtles have folded structures in

285-568: A dicynodont, and the name Cryptodontia is no longer used. Thomas Henry Huxley revised Owen's Dicynodontia as an order that included Dicynodon and Oudenodon . Dicynodontia was later ranked as a suborder or infraorder with the larger group Anomodontia, which is classified as an order. The ranking of Dicynodontia has varied in recent studies, with Ivakhnenko (2008) considering it a suborder, Ivanchnenko (2008) considering it an infraorder, and Kurkin (2010) considering it an order. Many higher taxa, including infraorders and families, have been erected as

380-513: A hot day, and to fall naturally to around 29 °C (84 °F) 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,

475-458: A large mammal, probably a diprotodontid . With the decline and extinction of the kannemeyerids, there were to be no more dominant large synapsid herbivores until the middle Paleocene epoch (60 Ma) when mammals , distant descendants of cynodonts , began to diversify after the extinction of the non-avian dinosaurs. Dicynodontia was originally named by the English paleontologist Richard Owen . It

570-524: A large variety of ecotypes, including large, medium-sized, and small herbivores and short-limbed mole-like burrowers. Only four lineages are known to have survived the Great Dying ; the first three represented with a single genus each: Myosaurus , Kombuisia , and Lystrosaurus , the latter being the most common and widespread herbivores of the Induan (earliest Triassic ). None of these survived long into

665-711: A means of classifying the large number of dicynodont species. Cluver and King (1983) recognised several main groups within Dicynodontia, including Eodicynodontia (containing only Eodicynodon ), Endothiodontia (containing only Endothiodontidae ), Pristerodontia ( Pristerodontidae , Cryptodontidae , Aulacephalodontidae , Dicynodontidae , Lystrosauridae , and Kannemeyeriidae ), Kingoriamorpha (containing only Kingoriidae ), Diictodontia ( Diictodontidae , Robertiidae , Cistecephalidae , Emydopidae and Myosauridae ), and Venyukoviamorpha . Most of these taxa are no longer considered valid. Kammerer and Angielczyk (2009) suggested that

760-416: 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 . Compared to other reptiles, turtles tend to have reduced tails, but these vary in both length and thickness among species and between sexes. Snapping turtles and the big-headed turtle have longer tails;

855-458: A skull in 2003. This suggested to indicate that dicynodonts survived into the Cretaceous in southern Gondwana . The dicynodont affinity of these specimens was questioned (including a proposal that they belonged to a baurusuchian crocodyliform by Agnolin et al. in 2010), and in 2019 Knutsen and Oerlemans considered this fossil to be of Plio - Pleistocene age, and reinterpreted it as a fossil of

950-404: 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 play dead . When attacked, big-headed turtle hatchlings squeal, possibly startling the predator. Turtles are

1045-461: 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 usually eats 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

SECTION 10

#1732854673743

1140-401: 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

1235-419: A turtle is unique among vertebrates and serves to protect the animal and provide shelter from the elements. It is primarily made of 50–60 bones and consists of two parts: the domed, dorsal (back) carapace and the flatter, ventral (belly) plastron . They are connected by lateral (side) extensions of the plastron. The carapace is fused with the vertebrae and ribs while the plastron is formed from bones of

1330-450: A worm-like appendage on its tongue that it 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

1425-495: Is an extinct clade of anomodonts , an extinct type of non-mammalian therapsid . Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typically toothless beak, unique amongst all synapsids . Dicynodonts first appeared in Southern Pangaea during the mid-Permian , ca. 270–260 million years ago, and became globally distributed and

1520-504: 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 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 delay their development . Hatching young turtles break out of

1615-539: Is high during this period but significantly decreases when they reach adulthood. Most species grow quickly during their early years and slow down when they mature. Turtles can live long lives. The oldest living turtle and land animal is said to be a Seychelles giant tortoise named Jonathan , who turned 187 in 2019. A Galápagos tortoise named 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

1710-399: 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 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

1805-405: Is highly specialised, light but strong, with the synapsid temporal openings at the rear of the skull greatly enlarged to accommodate larger jaw muscles. The front of the skull and the lower jaw are generally narrow and, in all but a number of primitive forms, toothless. Instead, the front of the mouth is equipped with a horny beak, as in turtles and ceratopsian dinosaurs . Food was processed by

1900-400: 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,

1995-639: Is known from the La Belle France cave in South Africa , often conflated with the Dingonek . It may be based on dicynodont fossils. Turtle Turtles are reptiles of the order Testudines , characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked turtles), which differ in

SECTION 20

#1732854673743

2090-473: Is now plentiful evidence for it, including from genetics. How sea turtles navigate to their breeding beaches remains unknown. One possibility is 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

2185-426: Is often complex in aquatic species, both marine and freshwater, but simpler in the semi-aquatic mud turtles and snapping turtles. A male tortoise bobs his head, then subdues 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

2280-453: Is possibly a fourth type of cone that detects 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 , 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,

2375-557: Is thickened and used for butting and ramming during combat. Shells vary in flexibility. Some species, such as box turtles , lack the lateral extensions and instead have the carapace bones fully fused or ankylosed together. Several species have hinges on their shells, usually on the plastron, which allow them to expand and contract. Softshell turtles have rubbery edges, due to the loss of bones. The leatherback turtle has hardly any bones in its shell, but has thick connective tissue and an outer layer of leathery skin. The turtle's skull

2470-584: Is thought that they were more common in the past, prior to human impact on elephant populations. The two record holders for longest and heaviest recorded African bush elephant tusks are around 3.49 metres (11.5 ft) long measured along the outside curve, and 107 kilograms (236 lb) in weight respectively, while the longest and heaviest Asian elephant tusks are 3.26 metres (10.7 ft) long and 73 kilograms (161 lb) respectively. Even larger tusks are known from some extinct proboscideans , such as species of Stegodon , Palaeoloxodon , and mammoths , with

2565-497: Is thought to prevent them from collapsing. During exhalation, the contraction of the transversus abdominis muscle 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, allowing 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

2660-551: Is unique among living amniotes (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 long and narrow skulls of softshells to the broad and flattened skull of the mata mata . Some turtle species have developed large and thick heads, allowing for greater muscle mass and stronger bites. Turtles that are carnivorous or durophagous (eating hard-shelled animals) have

2755-753: Is used in artifacts and jewellery , and formerly in other items such as piano keys. Consequently, many tusk-bearing species have been hunted commercially and several are endangered . The ivory trade has been severely restricted by the United Nations Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Tusked animals in human care may undergo tusk trimming or removal for health and safety concerns. Furthermore, surgical veterinary procedures to remove tusks have been explored to mitigate human-wildlife conflicts. Dicynodont see " Taxonomy " Dicynodontia

2850-503: The Ancient Greek word χελώνη ( chelone ) 'tortoise'. Testudines is the official order name due to the principle of priority . The term chelonian is used as a formal name for members of the group. The largest living species of turtle (and fourth-largest reptile ) is the leatherback turtle , which can reach over 2.7 m (8 ft 10 in) in length and weigh over 500 kg (1,100 lb). The largest known turtle

2945-809: 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

Tusk - Misplaced Pages Continue

3040-705: The Middle Triassic , and Eorhynchochelys of the Late Triassic lacked carapaces and plastrons but had shortened torsos, expanded ribs, and lengthened 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. Adaptations that led to

3135-570: The bioluminescence of prey when hunting in deep water. Turtles have no ear openings; the eardrum is covered with scales and encircled by a bony otic capsule , which is absent in other reptiles. Their hearing thresholds are high in comparison to other reptiles, reaching up to 500 Hz in air, but underwater they are more attuned to lower frequencies. The loggerhead sea turtle has been shown experimentally to respond to low sounds, with maximal sensitivity between 100 and 400 Hz. Turtles have olfactory (smell) and vomeronasal receptors along

3230-403: The brackish -living diamondback terrapin 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. 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

3325-402: The coracoid . 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 shell is covered in epidermal (outer skin) scales known as scutes that are made of keratin , the same substance that makes up hair and fingernails. Typically, a turtle has 38 scutes on

3420-524: The ilium are large and strong. The tail is short. Pentasauropus dicynodont tracks suggest that dicynodonts had fleshy pads on their feet. Mummified skin from specimens of Lystrosaurus in South Africa have numerous raised bumps. Dicynodonts have long been suspected of being warm-blooded animals. Their bones are highly vascularised and possess Haversian canals , and their bodily proportions are conducive to heat preservation. In young specimens,

3515-596: The larynx or glottis that vibrate to produce sound. Other species have elastin -rich vocal cords . Due to their heavy shells, turtles are slow-moving on land. A desert tortoise moves at only 0.22–0.48 km/h (0.14–0.30 mph). By contrast, sea turtles can swim at 30 km/h (19 mph). 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 has flattened front limbs for digging in

3610-422: 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 water is pushed out through the nostrils and the gap in between the 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

3705-400: 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 rotate the front limb flippers like a bird's wings to generate a propulsive force on both

3800-407: The shoulder girdle , sternum , and gastralia (abdominal ribs). During development, the ribs grow sideways into a carapacial ridge, unique to turtles, entering the dermis (inner skin) of the back to support the carapace. The development is signaled locally by proteins known as fibroblast growth factors that include FGF10 . The shoulder girdle in turtles is made up of two bones, the scapula and

3895-465: The "Polka Dot Ancestor" by Olivier Rieppel. The theory accounted for the evolution of fossil pareiasaurs from Bradysaurus to 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 stem -turtles Eunotosaurus of the Middle Permian , Pappochelys of

Tusk - Misplaced Pages Continue

3990-469: The British Museum . By this time, many more dicynodonts had been described. In 1859, another important species called Ptychognathus declivis was named from South Africa. In the same year, Owen named the group Dicynodontia. In his Descriptive and Illustrated Catalogue , Owen honored Bain by erecting Bidentalia as a replacement name for his Dicynodontia. The name Bidentalia quickly fell out of use in

4085-575: The English paleontologist Richard Owen named two species of dicynodonts from South Africa: Dicynodon lacerticeps and Dicynodon bainii . Since Bain was preoccupied with the Corps of Royal Engineers, he wanted Owen to describe his fossils more extensively. Owen did not publish a description until 1876 in his Descriptive and Illustrated Catalogue of the Fossil Reptilia of South Africa in the Collection of

4180-504: The Permian extinction. A 2024 paper posited that rock art of a superficially walrus-like imaginary creature with downcurved tusks created by the San people of South Africa prior to 1835 may have been partly inspired by fossil dicynodont skulls which erode out of rocks in the area. Dicynodonts have been known to science since the mid-1800s. The South African geologist Andrew Geddes Bain gave

4275-826: The Triassic. The fourth group was the Kannemeyeriiformes , the only dicynodonts who diversified during the Triassic. These stocky, pig- to ox-sized animals were the most abundant herbivores worldwide from the Olenekian to the Ladinian age. By the Carnian they had been supplanted by traversodont cynodonts and rhynchosaur reptiles. During the Norian (middle of the Late Triassic), perhaps due to increasing aridity, they drastically declined, and

4370-504: 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 aligns his tail with the female's so he can insert his penis into her cloaca. Some female turtles can store sperm from multiple males and their egg clutches can have multiple sires. Turtles, including sea turtles, lay their eggs on land, although some lay eggs near water that rises and falls in level, submerging

4465-767: The bones are so highly vascularised that they exhibit higher channel densities than most other therapsids. Yet, studies on Late Triassic dicynodont coprolites paradoxically showcase digestive patterns more typical of animals with slow metabolisms. More recently, the discovery of hair remnants in Permian coprolites possibly vindicates the status of dicynodonts as endothermic animals. As these coprolites come from carnivorous species and digested dicynodont bones are abundant, it has been suggested that at least some of these hair remnants come from dicynodont prey. A new study using chemical analysis seemed to suggest that cynodonts and dicynodonts both developed warm blood independently before

4560-449: The carapace and 16 on the plastron, giving them 54 in total. Carapace scutes are divided into "marginals" around the margin and "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 additionally have "intergular" scutes between

4655-436: The darkness of the deep ocean, and also above water. Unlike in terrestrial turtles, the 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 toward the red part of the spectrum, improving color discrimination. Visual acuity, studied in hatchlings,

4750-554: The dominant herbivorous animals in the Late Permian , ca. 260–252 Mya. They were devastated by the end-Permian Extinction that wiped out most other therapsids ca. 252 Mya. They rebounded during the Triassic but died out towards the end of that period. They were the most successful and diverse of the non-mammalian therapsids, with over 70 genera known, varying from rat-sized burrowers to elephant-sized browsers . The dicynodont skull

4845-595: The eggs. While most species build nests and lay eggs where they forage, some travel miles. The common snapping turtle walks 5 km (3 mi) on land, while sea turtles travel even further; the leatherback swims some 12,000 km (7,500 mi) to its nesting beaches. Most turtles create 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

SECTION 50

#1732854673743

4940-446: The entire group. The name of the order, Testudines ( / t ɛ ˈ s tj uː d ɪ n iː z / teh- STEW -din-eez ), is based on the Latin word testudo 'tortoise'; and was coined by German naturalist 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

5035-522: The environment using landmarks and a map-like system resulting in accurate direct routes towards a goal. Navigation in turtles have been correlated to high cognition function in the medial cortex region of the brain. 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,

5130-751: The evolution of the shell may have originally been 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. Turtles became highly diverse during the Cretaceous, as climatic conditions in this period were favourable for their global dispersal. During

5225-525: The females resort to beaching themselves, as the males do not follow them ashore. All turtles fertilize internally; mounting and copulation can be difficult. In many species, males have a concave plastron that interlocks with the female's carapace. In species like the Russian tortoise , the male has a lighter shell and longer legs. The high, rounded shape of box turtles are particular obstacles for mounting. The male eastern box turtle leans backward and hooks onto

5320-580: The first description of dicynodonts in 1845. At the time, Bain was a supervisor for the construction of military roads under the Corps of Royal Engineers and had found many reptilian fossils during his surveys of South Africa. Bain described these fossils in an 1845 letter published in Transactions of the Geological Society of London , calling them "bidentals" for their two prominent tusks. In that same year,

5415-533: The following years, replaced by popularity of Owen's Dicynodontia. Dicynodonts first appeared during the Middle Permian in the Southern Hemisphere, with South Africa being the centre of their known diversity, and underwent a rapid evolutionary radiation , becoming globally distributed and amongst the most successful and abundant land vertebrates during the Late Permian . During this time, they included

5510-471: The gulars. Turtle scutes are usually structured like mosaic tiles, but some species, like the hawksbill sea turtle , have overlapping scutes on the carapace. The shapes of turtle shells vary with the adaptations of the individual species, and sometimes with sex . Land-dwelling turtles are more dome-shaped, which appears to make them more resistant to being crushed by large animals. Aquatic turtles have flatter, smoother shells that allow them to cut through

5605-628: The head are insulated by fat around the neck. Most turtle species are opportunistic omnivores; land-dwelling species are more herbivorous and aquatic ones more carnivorous . Generally lacking speed and agility, most turtles feed either on plant material or on animals with limited movements 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 but also scavenge. The alligator snapping turtle has

5700-399: 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. Studies have shown that turtles can navigate

5795-633: The latter uses it for balance while climbing. The cloaca is found underneath and at the base, and the tail itself houses the reproductive organs. Hence, males have longer tails to contain the penis. In sea turtles, the tail is longer and more prehensile in males, who use it to grasp mates. Several turtle species have spines on their tails. Turtles make use of vision to find food and mates, avoid predators, and orient themselves. The retina 's light-sensitive cells include both rods for vision in low light, and cones with three different photopigments for bright light, where they have full-color vision. There

SECTION 60

#1732854673743

5890-408: The leatherback, can swim in the waters off Nova Scotia , which may be as cold as 8 °C (46 °F), while their body temperature has been measured at up to 12 °C (22 °F) 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

5985-615: The longest tusk ever recorded being that of a specimen of "Mammut" borsoni from Greece, which measures 5.02 metres (16.5 ft) in length, with an estimated weight of 137 kilograms (302 lb) with some mammoth tusks exceeding 4 metres (13 ft) in length and probably 200 kilograms (440 lb) in weight. The largest walrus tusks can reach lengths of over 95 centimetres (3.12 ft). The longest narwhal tusks reach 3 metres (9.8 ft). The upward curving maxillary tusks of babirusa can reach lengths of over 20 centimetres (7.9 in). Tusks are used by humans to produce ivory , which

6080-549: The lungs via the pulmonary artery , or to the body via the 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 , rather than all

6175-447: The lungs, as in other amniotes, 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

6270-508: The most powerful bites. For example, the durophagous Mesoclemmys nasuta has a bite force of 432 lbf (1,920 N). Species that are insectivorous , piscivorous (fish-eating), or omnivorous have lower bite forces. Living turtles lack teeth but have beaks made of keratin sheaths along the edges of the jaws. These sheaths may have sharp edges for cutting meat, serrations for clipping plants, or broad plates for breaking mollusks . Sea turtles, and several extinct forms, have evolved

6365-401: The nasal cavity, the latter of which are used to detect chemical signals. Experiments on green sea turtles showed they could learn to respond to a selection of different odorant chemicals such as triethylamine and cinnamaldehyde , which were detected by olfaction in the nose. Such signals could be used in navigation. The rigid shell of turtles is not capable of expanding and making room for

6460-422: The natal beach. There is experimental evidence that turtles have an effective magnetic sense, and that they use this in navigation . Proof that homing occurs is derived from genetic analysis of populations of loggerheads, hawksbills, leatherbacks, and olive ridleys by nesting place. For each of these species, the populations in different places have their own mitochondrial DNA genetic signatures that persist over

6555-448: The neck of the urinary bladder and above 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 low in solutes , but higher during droughts when the reptile gains 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

6650-410: 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 in fishing nets. Turtle habitats around

6745-476: 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 27 km (17 mi), to lay eggs. Such short migrations are comparable to those of some lizards, snakes, and crocodilians. Sea turtles nest in

6840-406: The organs that 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 liver is connected to the right lung by the root , and the stomach is directly attached to the left lung, and to the liver by a mesentery . When the liver is pulled down, inhalation begins. Supporting the lungs is a wall or septum , which

6935-406: The presence of tusks has been suggested to be sexually dimorphic . Some dicynodonts such as Stahleckeria lacked true tusks and instead bore tusk-like extensions on the side of the beak. The body is short, strong and barrel-shaped, with strong limbs. In large genera (such as Dinodontosaurus ) the hindlimbs were held erect, but the forelimbs bent at the elbow. Both the pectoral girdle and

7030-426: The previous scutes every year, allowing researchers to estimate how long they have lived. They also age slowly . The survival rate for adult turtles can reach 99% per year. 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

7125-470: The problematic taxonomy and nomenclature of Dicynodontia and other groups results from the large number of conflicting studies and the tendency for invalid names to be mistakenly established. Below is a cladogram modified from Angielczyk et al. (2021): Nyaphulia Eodicynodon Colobodectes Lanthanostegus Pylaecephalidae Eumantellidae Brachyprosopus Endothiodontia Emydopoidea Bidentalia A horned serpent cave art

7220-423: 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 or brumation . The heart has two atria 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

7315-478: The retraction of the lower jaw when the mouth closed, producing a powerful shearing action, which would have enabled dicynodonts to cope with tough plant material. Dicynodonts typically had a pair of enlarged maxillary caniniform teeth, analogous to the tusks present in some living mammals. In the earliest genera, they were merely enlarged teeth, but in later forms they independently evolved into ever-growing teeth like mammal tusks multiple times. In some dicynodonts,

7410-444: The returned oxygenated blood 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

7505-539: The role of large herbivores was taken over by sauropodomorph dinosaurs. Fossils of an Asian elephant -sized dicynodont Lisowicia bojani discovered in Poland indicate that dicynodonts survived at least until the late Norian or earliest Rhaetian (latest Triassic); this animal was also the largest known dicynodont species. Six fragments of fossil bone discovered in Queensland , Australia, were interpreted as remains of

7600-405: The shell using an egg tooth , a sharp projection that exists temporarily on their upper beak. Hatchlings dig themselves out of the nest and find safety in vegetation or water. Some species stay in the nest for longer, be it for overwintering or to wait for the rain to loosen the soil for them to dig out. Young turtles are highly vulnerable to predators, both in the egg and as hatchlings. Mortality

7695-413: 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 that take up dissolved oxygen from the water. 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

7790-830: The species, the number of eggs laid varies from one 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 rounded, oval, elongated, and between hard- and soft-shelled. Most species have their sex determined by temperature . In some species, higher temperatures produce females and lower ones produce males, while in others, milder temperatures produce males and both hot and cold extremes produce females. There

7885-424: The substrate. Freshwater turtles have more flexible legs and longer toes with webbing , giving them thrust in the water. Some of these species, such as snapping turtles and mud turtles , mainly walk along the water bottom, as they would on land. Others, such as terrapins, swim by paddling with all four limbs, switching between the opposing front and hind limbs, which keeps their direction stable. Sea turtles and

7980-405: The time they are in the egg to when they are adults. These vocalizations may serve to create group cohesion when migrating . The oblong turtle has a particularly large vocal range; producing sounds described as clacks, clicks, squawks, hoots, various kinds of chirps, wails, hooos , grunts, growls, blow bursts, howls, and drum rolls. Play behavior has been documented in some turtle species. In

8075-620: The upper part is the domed carapace , while the underside is the flatter plastron or belly-plate. Its outer surface is covered in scales made of 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 ectotherms or "cold-blooded", meaning that their internal temperature varies with their direct environment. They are generally opportunistic omnivores and mainly feed on plants and animals with limited movements. Many turtles migrate short distances seasonally. Sea turtles are

8170-468: 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

8265-449: 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 60 kilograms (130 lb) and is able to allow its temperature to rise to some 33 °C (91 °F) on

8360-404: The water. Sea turtles in particular have streamlined shells that reduce drag and increase stability in the open ocean. Some turtle species have pointy or spiked shells that provide extra protection from predators and camouflage against the leafy ground. The lumps of a tortoise shell can tilt its body when it gets flipped over, allowing it to flip back. In male tortoises, the tip of the plastron

8455-453: The way the head retracts. There are 360 living and recently extinct species of turtles, including land-dwelling tortoises and freshwater terrapins . They are found on most continents, some islands and, in the case of sea turtles , much of the ocean. Like other amniotes (reptiles, birds , and mammals ) they breathe air and do not lay eggs underwater, although many species live in or around water. Turtle shells are made mostly of bone ;

8550-403: The way to 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. In sea turtles, the bladder is one unit and in most freshwater turtles, it is double-lobed. Sea turtle bladders are connected to two small accessory bladders, located at the sides to

8645-684: The world are being destroyed. As a result of these pressures, many species are extinct or threatened with extinction. The word turtle is borrowed from the French word tortue or tortre 'turtle, tortoise '. It is a common name 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 turtles as opposed to freshwater terrapins and 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

8740-578: The year but switching to water lilies during the summer. Some species have developed specialized diets such as the hawksbill, which eats sponges , the leatherback, which feeds on jellyfish , and the Mekong snail-eating turtle . While popularly thought of as mute, turtles make various sounds to communicate. One study which recorded 53 species found that all of them vocalized. Tortoises may bellow when courting and mating. Various species of both freshwater and sea turtles emit short, low-frequency calls from

8835-752: The years. This shows that the populations are distinct and that homing must be occurring reliably. Turtles have a wide variety of mating behaviors but do not form 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 mate forcibly . In fully aquatic species, males are often smaller than females and rely on courtship displays to gain mating access to females. Courtship varies between species, and with habitat. It

8930-415: Was Archelon ischyros , a Late Cretaceous sea turtle up to 4.5 m (15 ft) long, 5.25 m (17 ft) wide between the tips of the front flippers, and estimated to have weighed over 2,200 kg (4,900 lb). The smallest living turtle is Chersobius signatus of South Africa, measuring no more than 10 cm (3.9 in) in length and weighing 172 g (6.1 oz). The shell of

9025-419: Was erected as a family of the order Anomodontia and included the genera Dicynodon and Ptychognathus . Other groups of Anomodontia included Gnathodontia , which included Rhynchosaurus (now known to be an archosauromorph ) and Cryptodontia , which included Oudenodon . Cryptodonts were distinguished from dicynodonts from their absence of tusks. Although it lacks tusks, Oudenodon is now classified as

#742257