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73-696: A fang is a long, pointed tooth . In mammals , a fang is a modified maxillary tooth, used for biting and tearing flesh. In snakes , it is a specialized tooth that is associated with a venom gland (see snake venom ). Spiders also have external fangs , which are part of the chelicerae . Fangs are most common in carnivores or omnivores, but some herbivores, such as fruit bats , have them as well. They are generally used to hold or swiftly kill prey, such as in large cats. Omnivorous animals, such as bears , use their fangs when hunting fish or other prey, but they are not needed for consuming fruit. Some apes also have fangs, which they use for threats and fighting. However,
146-562: A clade ( monophyletic group) including birds, though the precise definition of this clade varies between authors. Others prioritize the clade Sauropsida , which typically refers to all amniotes more closely related to modern reptiles than to mammals . The earliest known proto-reptiles originated from the Carboniferous period, having evolved from advanced reptiliomorph tetrapods which became increasingly adapted to life on dry land. The earliest known eureptile ("true reptile")
219-447: A temnospondyl ). A series of footprints from the fossil strata of Nova Scotia dated to 315 Ma show typical reptilian toes and imprints of scales. These tracks are attributed to Hylonomus , the oldest unquestionable reptile known. It was a small, lizard-like animal, about 20 to 30 centimetres (7.9 to 11.8 in) long, with numerous sharp teeth indicating an insectivorous diet. Other examples include Westlothiana (for
292-509: A group of tetrapods with an ectothermic ('cold-blooded') metabolism and amniotic development . Living reptiles comprise four orders : Testudines ( turtles ), Crocodilia ( crocodilians ), Squamata ( lizards and snakes ), and Rhynchocephalia (the tuatara ). As of May 2023, about 12,000 living species of reptiles are listed in the Reptile Database . The study of the traditional reptile orders, customarily in combination with
365-715: A month to wear away the same amount. The incisors and cheek teeth of rabbits are called aradicular hypsodont teeth. This is sometimes referred to as an elodent dentition. These teeth grow or erupt continuously. The growth or eruption is held in balance by dental abrasion from chewing a diet high in fiber. Rodents have upper and lower hypselodont incisors that can continuously grow enamel throughout its life without having properly formed roots. These teeth are also known as aradicular teeth, and unlike humans whose ameloblasts die after tooth development , rodents continually produce enamel, they must wear down their teeth by gnawing on various materials. Enamel and dentin are produced by
438-681: A new set of teeth every two weeks to replace worn teeth. Most extant mammals including humans are diphyodonts, but there are exceptions including elephants, kangaroos, and manatees, all of which are polyphyodonts. Rodent incisors grow and wear away continually through gnawing, which helps maintain relatively constant length. The industry of the beaver is due in part to this qualification. Some rodents, such as voles and guinea pigs (but not mice ), as well as lagomorpha ( rabbits , hares and pikas ), have continuously growing molars in addition to incisors. Also, tusks (in tusked mammals) grow almost throughout life. Teeth are not always attached to
511-495: A section of the clade Amniota : The section that is left after the Mammalia and Aves have been hived off. It cannot be defined by synapomorphies , as is the proper way. Instead, it is defined by a combination of the features it has and the features it lacks: reptiles are the amniotes that lack fur or feathers. At best, the cladists suggest, we could say that the traditional Reptilia are 'non-avian, non-mammalian amniotes'. Despite
584-463: A soft mush for them to eat in order to obtain adequate nutrition. Elephants ' tusks are specialized incisors for digging food up and fighting. Some elephant teeth are similar to those in manatees , and elephants are believed to have undergone an aquatic phase in their evolution. At birth, elephants have a total of 28 molar plate-like grinding teeth not including the tusks. These are organized into four sets of seven successively larger teeth which
657-569: A tiny gecko, Sphaerodactylus ariasae , which can grow up to 17 mm (0.7 in) to the saltwater crocodile , Crocodylus porosus , which can reach over 6 m (19.7 ft) in length and weigh over 1,000 kg (2,200 lb). In the 13th century, the category of reptile was recognized in Europe as consisting of a miscellany of egg-laying creatures, including "snakes, various fantastic monsters, lizards, assorted amphibians, and worms", as recorded by Beauvais in his Mirror of Nature . In
730-513: Is a hard, calcified structure found in the jaws (or mouths ) of many vertebrates and used to break down food . Some animals, particularly carnivores and omnivores , also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by gums . Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from
803-479: Is equivalent to the more common definition of Sauropsida, which Modesto and Anderson synonymized with Reptilia, since the latter is better known and more frequently used. Unlike most previous definitions of Reptilia, however, Modesto and Anderson's definition includes birds, as they are within the clade that includes both lizards and crocodiles. General classification of extinct and living reptiles, focusing on major groups. The cladogram presented here illustrates
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#1732765777186876-607: Is known as teething and can be painful. Kangaroos , elephants , and manatees are unusual among mammals because they are polyphyodonts . In aardvarks , teeth lack enamel and have many pulp tubules, hence the name of the order Tubulidentata . In dogs , the teeth are less likely than humans to form dental cavities because of the very high pH of dog saliva, which prevents enamel from demineralizing. Sometimes called cuspids, these teeth are shaped like points (cusps) and are used for tearing and grasping food. Like human teeth, whale teeth have polyp-like protrusions located on
949-503: Is only seen in older whales where the cementum has been worn away to show the underlying enamel. The toothed whale is a suborder of the cetaceans characterized by having teeth. The teeth differ considerably among the species. They may be numerous, with some dolphins bearing over 100 teeth in their jaws. On the other hand, the narwhals have a giant unicorn-like tusk, which is a tooth containing millions of sensory pathways and used for sensing during feeding, navigation, and mating. It
1022-474: Is some variation between species, most notably the venom-injecting fangs of snakes . The pattern of incisors, canines, premolars and molars is found only in mammals, and to varying extents, in their evolutionary ancestors . The numbers of these types of teeth vary greatly between species; zoologists use a standardised dental formula to describe the precise pattern in any given group. The word tooth comes from Proto-Germanic * tanþs , derived from
1095-558: Is the most neurologically complex tooth known. Beaked whales are almost toothless, with only bizarre teeth found in males. These teeth may be used for feeding but also for demonstrating aggression and showmanship. In humans (and most other primates), there are usually 20 primary (also "baby" or "milk") teeth, and later up to 32 permanent teeth. Four of these 32 may be third molars or wisdom teeth , although these are not present in all adults, and may be removed surgically later in life. Among primary teeth, 10 of them are usually found in
1168-490: Is used by molluscs for feeding and is sometimes compared rather inaccurately to a tongue . It is a minutely toothed, chitinous ribbon, typically used for scraping or cutting food before the food enters the oesophagus . The radula is unique to molluscs, and is found in every class of mollusc apart from bivalves . Within the gastropods , the radula is used in feeding by both herbivorous and carnivorous snails and slugs . The arrangement of teeth (also known as denticles) on
1241-479: The Proto-Indo-European * h₁dent- , which was composed of the root * h₁ed- ' to eat ' plus the active participle suffix * -nt , therefore literally meaning ' that which eats ' . The irregular plural form teeth is the result of Germanic umlaut whereby vowels immediately preceding a high vocalic in the following syllable were raised. As the nominative plural ending of
1314-418: The amniotic egg . The terms Sauropsida ("lizard faces") and Theropsida ("beast faces") were used again in 1916 by E.S. Goodrich to distinguish between lizards, birds, and their relatives on the one hand (Sauropsida) and mammals and their extinct relatives (Theropsida) on the other. Goodrich supported this division by the nature of the hearts and blood vessels in each group, and other features, such as
1387-591: The animal 's teeth are related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing and grinding. Carnivores , on the other hand, have canine teeth to kill prey and to tear meat. Mammals, in general, are diphyodont , meaning that they develop two sets of teeth. In humans , the first set (the "baby", "milk", "primary" or " deciduous " set) normally starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth . Normal tooth eruption at about six months
1460-414: The enamel organ , and growth is dependent on the presence of stem cells , cellular amplification , and cellular maturation structures in the odontogenic region . Rodent incisors are used for cutting wood, biting through the skin of fruit, or for defense. This allows for the rate of wear and tooth growth to be at equilibrium. The microstructure of rodent incisor enamel has shown to be useful in studying
1533-477: The maxilla (i.e. upper jaw) and the other 10 in the mandible (i.e. lower jaw). Among permanent teeth, 16 are found in the maxilla and the other 16 in the mandible. Most of the teeth have uniquely distinguishing features. An adult horse has between 36 and 44 teeth. The enamel and dentin layers of horse teeth are intertwined. All horses have 12 premolars, 12 molars, and 12 incisors. Generally, all male equines also have four canine teeth (called tushes) between
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#17327657771861606-540: The thelodonts had scales composed of dentine and an enamel-like compound, suggesting that the origin of teeth was from scales which were retained in the mouth. Fish as early as the late Cambrian had dentine in their exoskeletons, which may have functioned in defense or for sensing their environments. Dentine can be as hard as the rest of teeth and is composed of collagen fibres, reinforced with hydroxyapatite . Though teeth are very resistant, they also can be brittle and highly susceptible to cracking. However, cracking of
1679-1741: The "family tree" of reptiles, and follows a simplified version of the relationships found by M.S. Lee, in 2013. All genetic studies have supported the hypothesis that turtles are diapsids; some have placed turtles within Archosauromorpha, though a few have recovered turtles as Lepidosauromorpha instead. The cladogram below used a combination of genetic (molecular) and fossil (morphological) data to obtain its results. Synapsida ( mammals and their extinct relatives) [REDACTED] † Millerettidae [REDACTED] † Eunotosaurus † Lanthanosuchidae [REDACTED] † Pareiasauromorpha [REDACTED] † Procolophonoidea [REDACTED] † Captorhinidae [REDACTED] † Paleothyris † Araeoscelidia [REDACTED] † Claudiosaurus [REDACTED] † Younginiformes [REDACTED] † Kuehneosauridae [REDACTED] Rhynchocephalia ( tuatara and their extinct relatives) [REDACTED] Squamata ( lizards and snakes ) [REDACTED] [REDACTED] † Eosauropterygia [REDACTED] † Placodontia [REDACTED] † Sinosaurosphargis † Odontochelys † Proganochelys Testudines ( turtles ) [REDACTED] † Choristodera [REDACTED] † Prolacertiformes [REDACTED] † Rhynchosauria [REDACTED] † Trilophosaurus [REDACTED] Archosauriformes ( crocodiles , birds , dinosaurs and extinct relatives) [REDACTED] [REDACTED] The placement of turtles has historically been highly variable. Classically, turtles were considered to be related to
1752-453: The 18th century, the reptiles were, from the outset of classification, grouped with the amphibians . Linnaeus , working from species-poor Sweden , where the common adder and grass snake are often found hunting in water, included all reptiles and amphibians in class "III – Amphibia" in his Systema Naturæ . The terms reptile and amphibian were largely interchangeable, reptile (from Latin repere , 'to creep') being preferred by
1825-484: The French. J.N. Laurenti was the first to formally use the term Reptilia for an expanded selection of reptiles and amphibians basically similar to that of Linnaeus. Today, the two groups are still commonly treated under the single heading herpetology . It was not until the beginning of the 19th century that it became clear that reptiles and amphibians are, in fact, quite different animals, and P.A. Latreille erected
1898-774: The Proto-Germanic consonant stems (to which * tanþs belonged) was * -iz , the root vowel in the plural form * tanþiz (changed by this point to * tą̄þi via unrelated phonological processes) was raised to /œː/, and later unrounded to /eː/, resulting in the tōþ/tēþ alternation attested from Old English . Cf. also Old English bōc/bēċ ' book/books ' and ' mūs/mȳs ' ' mouse/mice ' , from Proto-Germanic * bōks/bōkiz and * mūs/mūsiz respectively. Cognate with Latin dēns , Greek ὀδούς ( odous ), and Sanskrit dát . Teeth are assumed to have evolved either from ectoderm denticles (scales, much like those on
1971-657: The anapsid condition has been found to occur so variably among unrelated groups that it is not now considered a useful distinction. By the early 21st century, vertebrate paleontologists were beginning to adopt phylogenetic taxonomy, in which all groups are defined in such a way as to be monophyletic ; that is, groups which include all descendants of a particular ancestor. The reptiles as historically defined are paraphyletic , since they exclude both birds and mammals. These respectively evolved from dinosaurs and from early therapsids, both of which were traditionally called "reptiles". Birds are more closely related to crocodilians than
2044-421: The beak of birds may have evolved from teeth to allow chicks to escape their shells earlier, and thus avoid predators and also to penetrate protective covers such as hard earth to access underlying food. True teeth are unique to vertebrates, although many invertebrates have analogous structures often referred to as teeth. The organisms with the simplest genome bearing such tooth-like structures are perhaps
2117-421: The class Batracia (1825) for the latter, dividing the tetrapods into the four familiar classes of reptiles, amphibians, birds, and mammals. The British anatomist T.H. Huxley made Latreille's definition popular and, together with Richard Owen , expanded Reptilia to include the various fossil " antediluvian monsters", including dinosaurs and the mammal-like ( synapsid ) Dicynodon he helped describe. This
2190-568: The course of feeding if the prey is struggling. Additionally, amphibians that undergo a metamorphosis develop bicuspid shaped teeth. The teeth of reptiles are replaced constantly throughout their lives. Crocodilian juveniles replace teeth with larger ones at a rate as high as one new tooth per socket every month. Once mature, tooth replacement rates can slow to two years and even longer. Overall, crocodilians may use 3,000 teeth from birth to death. New teeth are created within old teeth. A skull of Ichthyornis discovered in 2014 suggests that
2263-403: The crown from the base of the tooth. Most amphibians exhibit teeth that have a slight attachment to the jaw or acrodont teeth. Acrodont teeth exhibit limited connection to the dentary and have little enervation . This is ideal for organisms who mostly use their teeth for grasping, but not for crushing and allows for rapid regeneration of teeth at a low energy cost. Teeth are usually lost in
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2336-474: The development of fish scales. Study of a tooth plate of a fossil of the extinct fish Romundina stellina showed that the teeth and scales were made of the same tissues, also found in mammal teeth, lending support to the theory that teeth evolved as a modification of scales. Teeth are among the most distinctive (and long-lasting) features of mammal species. Paleontologists use teeth to identify fossil species and determine their relationships. The shape of
2409-554: The early proposals for replacing the paraphyletic Reptilia with a monophyletic Sauropsida , which includes birds, that term was never adopted widely or, when it was, was not applied consistently. When Sauropsida was used, it often had the same content or even the same definition as Reptilia. In 1988, Jacques Gauthier proposed a cladistic definition of Reptilia as a monophyletic node-based crown group containing turtles, lizards and snakes, crocodilians, and birds, their common ancestor and all its descendants. While Gauthier's definition
2482-418: The elephant will slowly wear through during its lifetime of chewing rough plant material. Only four teeth are used for chewing at a given time, and as each tooth wears out, another tooth moves forward to take its place in a process similar to a conveyor belt. The last and largest of these teeth usually becomes exposed when the animal is around 40 years of age, and will often last for an additional 20 years. When
2555-453: The fetus develops within the mother, using a (non-mammalian) placenta rather than contained in an eggshell . As amniotes, reptile eggs are surrounded by membranes for protection and transport, which adapt them to reproduction on dry land. Many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals , with some providing initial care for their hatchlings. Extant reptiles range in size from
2628-460: The food through the stomach for digestion. Molluscs have a structure called a radula , which bears a ribbon of chitinous teeth. However, these teeth are histologically and developmentally different from vertebrate teeth and are unlikely to be homologous . For example, vertebrate teeth develop from a neural crest mesenchyme -derived dental papilla , and the neural crest is specific to vertebrates, as are tissues such as enamel . The radula
2701-412: The foods are abrasive enough to cause attrition, rabbit teeth grow continuously throughout life. Rabbits have a total of six incisors, three upper premolars, three upper molars, two lower premolars, and two lower molars on each side. There are no canines. Dental formula is 2.0.3.3 1.0.2.3 = 28. Three to four millimeters of the tooth is worn away by incisors every week, whereas the cheek teeth require
2774-430: The horse's bit contact. Therefore, wolf teeth are commonly removed. Horse teeth can be used to estimate the animal's age. Between birth and five years, age can be closely estimated by observing the eruption pattern on milk teeth and then permanent teeth. By age five, all permanent teeth have usually erupted. The horse is then said to have a "full" mouth. After the age of five, age can only be conjectured by studying
2847-460: The host. The incision leaves a mark that is an inverted Y inside of a circle. After piercing the skin and injecting anticoagulants ( hirudin ) and anaesthetics , they suck out blood, consuming up to ten times their body weight in a single meal. In some species of Bryozoa , the first part of the stomach forms a muscular gizzard lined with chitinous teeth that crush armoured prey such as diatoms . Wave-like peristaltic contractions then move
2920-466: The hypothesis that turtles belong to a separate clade within Sauropsida , outside the saurian clade altogether. The origin of the reptiles lies about 310–320 million years ago, in the steaming swamps of the late Carboniferous period, when the first reptiles evolved from advanced reptiliomorphs . The oldest known animal that may have been an amniote is Casineria (though it may have been
2993-417: The inner surface of the jaw by one side. In cartilaginous fish , such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw. Monophyodonts are animals that develop only one set of teeth, while diphyodonts grow an early set of deciduous teeth and a later set of permanent or "adult" teeth . Polyphyodonts grow many sets of teeth. For example, sharks , grow
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3066-442: The jaw and are encased in a bony shell separated by soft tissue. Walrus tusks are canine teeth that grow continuously throughout life. Fish , such as sharks , may go through many teeth in their lifetime. The replacement of multiple teeth is known as polyphyodontia . A class of prehistoric shark are called cladodonts for their strange forked teeth. Unlike the continuous shedding of functional teeth seen in modern sharks,
3139-469: The jaw, as they are in mammals. In many reptiles and fish, teeth are attached to the palate or to the floor of the mouth, forming additional rows inside those on the jaws proper. Some teleosts even have teeth in the pharynx . While not true teeth in the usual sense, the dermal denticles of sharks are almost identical in structure and are likely to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, and are not found in
3212-419: The last of these teeth has fallen out, regardless of the elephant's age, the animal will no longer be able to chew food and will die of starvation. Rabbits and other lagomorphs usually shed their deciduous teeth before (or very shortly after) their birth, and are usually born with their permanent teeth. The teeth of rabbits complement their diet, which consists of a wide range of vegetation. Since many of
3285-508: The late 19th century, a number of definitions of Reptilia were offered. The biological traits listed by Lydekker in 1896, for example, include a single occipital condyle , a jaw joint formed by the quadrate and articular bones, and certain characteristics of the vertebrae . The animals singled out by these formulations, the amniotes other than the mammals and the birds, are still those considered reptiles today. The synapsid/sauropsid division supplemented another approach, one that split
3358-508: The latter are to the rest of extant reptiles. Colin Tudge wrote: Mammals are a clade , and therefore the cladists are happy to acknowledge the traditional taxon Mammalia ; and birds, too, are a clade, universally ascribed to the formal taxon Aves . Mammalia and Aves are, in fact, subclades within the grand clade of the Amniota. But the traditional class Reptilia is not a clade. It is just
3431-796: The living reptiles, there are many diverse groups that are now extinct , in some cases due to mass extinction events . In particular, the Cretaceous–Paleogene extinction event wiped out the pterosaurs , plesiosaurs , and all non-avian dinosaurs alongside many species of crocodyliforms and squamates (e.g., mosasaurs ). Modern non-bird reptiles inhabit all the continents except Antarctica. Reptiles are tetrapod vertebrates , creatures that either have four limbs or, like snakes, are descended from four-limbed ancestors. Unlike amphibians , reptiles do not have an aquatic larval stage. Most reptiles are oviparous , although several species of squamates are viviparous , as were some extinct aquatic clades –
3504-443: The majority of stem chondrichthyan lineages retained all tooth generations developed throughout the life of the animal. This replacement mechanism is exemplified by the tooth whorl-based dentitions of acanthodians , which include the oldest known toothed vertebrate, Qianodus duplicis . All amphibians have pedicellate teeth , which are modified to be flexible due to connective tissue and uncalcified dentine that separates
3577-434: The majority of the crown remaining below the gumline in the dental socket. The rest of the tooth will slowly emerge from the jaw, erupting about 3 mm ( 1 ⁄ 8 in) each year, as the horse ages. When the animal reaches old age, the crowns of the teeth are very short and the teeth are often lost altogether. Very old horses, if lacking molars, may need to have their fodder ground up and soaked in water to create
3650-456: The molars and incisors. However, few female horses (less than 28%) have canines, and those that do usually have only one or two, which many times are only partially erupted. A few horses have one to four wolf teeth , which are vestigial premolars, with most of those having only one or two. They are equally common in male and female horses and much more likely to be on the upper jaw. If present these can cause problems as they can interfere with
3723-580: The more primitive jawless fish – while lampreys do have tooth-like structures on the tongue, these are in fact, composed of keratin , not of dentine or enamel, and bear no relationship to true teeth. Though "modern" teeth-like structures with dentine and enamel have been found in late conodonts , they are now supposed to have evolved independently of later vertebrates' teeth. Living amphibians typically have small teeth, or none at all, since they commonly feed only on soft foods. In reptiles, teeth are generally simple and conical in shape, although there
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#17327657771863796-422: The other euryapsids, and given the older name Parapsida. Parapsida was later discarded as a group for the most part (ichthyosaurs being classified as incertae sedis or with Euryapsida). However, four (or three if Euryapsida is merged into Diapsida) subclasses remained more or less universal for non-specialist work throughout the 20th century. It has largely been abandoned by recent researchers: In particular,
3869-428: The outermost embryonic germ layer , the ectoderm . The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The teeth of mammals have deep roots, and this pattern is also found in some fish, and in crocodilians . In most teleost fish, however, the teeth are attached to the outer surface of the bone, while in lizards they are attached to
3942-488: The outside and exposed dentin on the inside, so they self-sharpen during gnawing . On the other hand, continually growing molars are found in some rodent species, such as the sibling vole and the guinea pig. There is variation in the dentition of the rodents, but generally, rodents lack canines and premolars , and have a space between their incisors and molars, called the diastema region. Manatees are polyphyodont with mandibular molars developing separately from
4015-638: The parasitic worms of the family Ancylostomatidae . For example, the hookworm Necator americanus has two dorsal and two ventral cutting plates or teeth around the anterior margin of the buccal capsule. It also has a pair of subdorsal and a pair of subventral teeth located close to the rear. Historically, the European medicinal leech , another invertebrate parasite, has been used in medicine to remove blood from patients. They have three jaws (tripartite) that resemble saws in both appearance and function, and on them are about 100 sharp teeth used to incise
4088-463: The phylogeny and systematics of rodents because of its independent evolution from the other dental traits. The enamel on rodent incisors are composed of two layers: the inner portio interna (PI) with Hunter-Schreger bands (HSB) and an outer portio externa (PE) with radial enamel (RE). It usually involves the differential regulation of the epithelial stem cell niche in the tooth of two rodent species, such as guinea pigs . The teeth have enamel on
4161-416: The primitive anapsid reptiles. Molecular work has usually placed turtles within the diapsids. As of 2013, three turtle genomes have been sequenced. The results place turtles as a sister clade to the archosaurs , the group that includes crocodiles, non-avian dinosaurs, and birds. However, in their comparative analysis of the timing of organogenesis , Werneburg and Sánchez-Villagra (2009) found support for
4234-552: The radula ribbon varies considerably from one group to another as shown in the diagram on the left. Predatory marine snails such as the Naticidae use the radula plus an acidic secretion to bore through the shell of other molluscs. Other predatory marine snails , such as the Conidae , use a specialized radula tooth as a poisoned harpoon . Predatory pulmonate land slugs, such as the ghost slug , use elongated razor-sharp teeth on
4307-404: The radula to seize and devour earthworms . Predatory cephalopods, such as squid , use the radula for cutting prey. In most of the more ancient lineages of gastropods, the radula is used to graze by scraping diatoms and other microscopic algae off rock surfaces and other substrates. Limpets scrape algae from rocks using radula equipped with exceptionally hard rasping teeth. These teeth have
4380-881: The relatively short canines of humans are not considered to be fangs. Certain mythological and legendary creatures such as dragons , gargoyles , demons and yakshas are commonly depicted with prominent fangs. The fangs of vampires are one of their defining characteristics. The iconographic representation of some Hindu deities include fangs, to symbolize the ability to hunt and kill. Two examples are fierce warrior goddess Chamunda and god of death Yama in some iconographic representations. Fangs are also common among guardian figures such as Verupaksha in Buddhism art in China and East Asia, as well as Rangda in Balinese Hinduism . Tooth A tooth ( pl. : teeth )
4453-438: The reptiles into four subclasses based on the number and position of temporal fenestrae , openings in the sides of the skull behind the eyes. This classification was initiated by Henry Fairfield Osborn and elaborated and made popular by Romer 's classic Vertebrate Paleontology . Those four subclasses were: The composition of Euryapsida was uncertain. Ichthyosaurs were, at times, considered to have arisen independently of
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#17327657771864526-430: The root surface of the tooth. These polyps are made of cementum in both species, but in human teeth, the protrusions are located on the outside of the root, while in whales the nodule is located on the inside of the pulp chamber. While the roots of human teeth are made of cementum on the outer surface, whales have cementum on the entire surface of the tooth with a very small layer of enamel at the tip. This small enamel layer
4599-531: The skin of sharks ) that folded and integrated into the mouth (called the "outside–in" theory), or from endoderm pharyngeal teeth (primarily formed in the pharynx of jawless vertebrates ) (the "inside–out" theory). In addition, there is another theory stating that neural crest gene regulatory network , and neural crest-derived ectomesenchyme are the key to generate teeth (with any epithelium , either ectoderm or endoderm). The genes governing tooth development in mammals are homologous to those involved in
4672-427: The stomachs of vertebrate predators. Enamel can be lost by abrasion or spalling, and is lost before dentine or bone are destroyed by the fossilisation process. In such a case, the 'skeleton' of the teeth would consist of the dentine, with a hollow pulp cavity. The organic part of dentine, conversely, is destroyed by alkalis. Reptile See text for extinct groups. Reptiles , as commonly defined, are
4745-461: The strongest known tensile strength of any biological material, outperforming spider silk . The mineral protein of the limpet teeth can withstand a tensile stress of 4.9 GPa , compared to 4 GPa of spider silk and 0.5 GPa of human teeth . Because teeth are very resistant, often preserved when bones are not, and reflect the diet of the host organism, they are very valuable to archaeologists and palaeontologists. Early fish such as
4818-789: The structure of the forebrain. According to Goodrich, both lineages evolved from an earlier stem group, Protosauria ("first lizards") in which he included some animals today considered reptile-like amphibians , as well as early reptiles. In 1956, D.M.S. Watson observed that the first two groups diverged very early in reptilian history, so he divided Goodrich's Protosauria between them. He also reinterpreted Sauropsida and Theropsida to exclude birds and mammals, respectively. Thus his Sauropsida included Procolophonia , Eosuchia , Millerosauria , Chelonia (turtles), Squamata (lizards and snakes), Rhynchocephalia , Crocodilia , " thecodonts " ( paraphyletic basal Archosauria ), non- avian dinosaurs , pterosaurs , ichthyosaurs , and sauropterygians . In
4891-693: The study of modern amphibians , is called herpetology . Reptiles have been subject to several conflicting taxonomic definitions. In Linnaean taxonomy , reptiles are gathered together under the class Reptilia ( / r ɛ p ˈ t ɪ l i ə / rep- TIL -ee-ə ), which corresponds to common usage. Modern cladistic taxonomy regards that group as paraphyletic , since genetic and paleontological evidence has determined that birds (class Aves), as members of Dinosauria , are more closely related to living crocodilians than to other reptiles, and are thus nested among reptiles from an evolutionary perspective. Many cladistic systems therefore redefine Reptilia as
4964-448: The tooth can be used as a diagnostic tool for predicting bite force. Additionally, enamel fractures can also give valuable insight into the diet and behaviour of archaeological and fossil samples. Decalcification removes the enamel from teeth and leaves only the organic interior intact, which comprises dentine and cementine . Enamel is quickly decalcified in acids, perhaps by dissolution by plant acids or via diagenetic solutions, or in
5037-475: The wear patterns on the incisors, shape, the angle at which the incisors meet, and other factors. The wear of teeth may also be affected by diet, natural abnormalities, and cribbing . Two horses of the same age may have different wear patterns. A horse's incisors, premolars, and molars, once fully developed, continue to erupt as the grinding surface is worn down through chewing. A young adult horse will have teeth, which are 110–130 mm (4.5–5 inches) long, with
5110-590: The years following Gauthier's paper. The first such new definition, which attempted to adhere to the standards of the PhyloCode , was published by Modesto and Anderson in 2004. Modesto and Anderson reviewed the many previous definitions and proposed a modified definition, which they intended to retain most traditional content of the group while keeping it stable and monophyletic. They defined Reptilia as all amniotes closer to Lacerta agilis and Crocodylus niloticus than to Homo sapiens . This stem-based definition
5183-650: Was Hylonomus , a small and superficially lizard-like animal which lived in Nova Scotia during the Bashkirian age of the Late Carboniferous , around 318 million years ago . Genetic and fossil data argues that the two largest lineages of reptiles, Archosauromorpha (crocodilians, birds, and kin) and Lepidosauromorpha (lizards, and kin), diverged during the Permian period. In addition to
5256-592: Was close to the modern consensus, nonetheless, it became considered inadequate because the actual relationship of turtles to other reptiles was not yet well understood at this time. Major revisions since have included the reassignment of synapsids as non-reptiles, and classification of turtles as diapsids. Gauthier 1994 and Laurin and Reisz 1995's definition of Sauropsida defined the scope of the group as distinct and broader than that of Reptilia, encompassing Mesosauridae as well as Reptilia sensu stricto . A variety of other definitions were proposed by other scientists in
5329-627: Was not the only possible classification scheme: In the Hunterian lectures delivered at the Royal College of Surgeons in 1863, Huxley grouped the vertebrates into mammals , sauroids, and ichthyoids (the latter containing the fishes and amphibians). He subsequently proposed the names of Sauropsida and Ichthyopsida for the latter two groups. In 1866, Haeckel demonstrated that vertebrates could be divided based on their reproductive strategies, and that reptiles, birds, and mammals were united by
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