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63-625: The strange creature has the head of a snake , the body of a leopard , the haunches of a lion , and the feet of a hart . Its name comes from the great noise that it emits from its belly, a barking like "thirty couple hounds questing". Glatisant is related to the French word glapissant , 'yelping' or 'barking', especially of small dogs or foxes. The questing beast is a description of the medieval mythological view on giraffes , whose generic name of Camelopardalis originated from their description of being half- camel and half-leopard. Evidence of this

126-547: A stem -squamate, making it the oldest known squamate. The phylogenetic analysis was conducted by performing high-resolution microfocus X-ray computed tomography (micro-CT) scans on the fossil specimen of Megachirella to gather detailed data about its anatomy . These data were then compared with a phylogenetic dataset combining the morphological and molecular data of 129 extant and extinct reptilian taxa . The comparison revealed Megachirella had certain features that are unique to squamates. The study also found that geckos are

189-406: A clade called Toxicofera . Genetic data also suggest that the various limbless groups – snakes, amphisbaenians , and dibamids – are unrelated, and instead arose independently from lizards. The male members of the group Squamata have hemipenes , which are usually held inverted within their bodies, and are everted for reproduction via erectile tissue like that in the mammalian penis . Only one

252-714: A family of giant, primitive, python-like snakes, was around until 50,000 years ago in Australia, represented by genera such as Wonambi . Recent molecular studies support the monophyly of the clades of modern snakes, scolecophidians, typhlopids + anomalepidids, alethinophidians, core alethinophidians, uropeltids ( Cylindrophis , Anomochilus , uropeltines), macrostomatans, booids, boids, pythonids and caenophidians. While snakes are limbless reptiles, evolved from (and grouped with) lizards, there are many other species of lizards that have lost their limbs independently but which superficially look similar to snakes. These include

315-661: A minor component of the North American fauna, but during the Miocene, the number of species and their prevalence increased dramatically with the first appearances of vipers and elapids in North America and the significant diversification of Colubridae (including the origin of many modern genera such as Nerodia , Lampropeltis , Pituophis , and Pantherophis ). There is fossil evidence to suggest that snakes may have evolved from burrowing lizards, during

378-872: A passive envenomation system. Recent studies also show that the close relatives of the Komodo, the monitor lizards, all have a similar envenomation system, but the toxicity of the bites is relatively low to humans. The Gila monster and beaded lizards of North and Central America are venomous, but not deadly to humans. Though they survived the Cretaceous–Paleogene extinction event , many squamate species are now endangered due to habitat loss, hunting and poaching, illegal wildlife trading, alien species being introduced to their habitats (which puts native creatures at risk through competition, disease, and predation), and other anthropogenic causes. Because of this, some squamate species have recently become extinct , with Africa having

441-414: A positive cladistical correlation, although some of these features are shared with varanids. Genetic studies in recent years have indicated snakes are not as closely related to monitor lizards as was once believed—and therefore not to mosasaurs, the proposed ancestor in the aquatic scenario of their evolution. However, more evidence links mosasaurs to snakes than to varanids. Fragmented remains found from

504-460: A seminal groove that seals as the erectile tissue expands. This is also the only reptile group in which both viviparous and ovoviviparous species are found, as well as the usual oviparous reptiles. The eggs in oviparous species have a parchment-like shell. The only exception is found in blind lizards and three families of geckos (Gekkonidae, Phyllodactylidae and Sphaerodactylidae), where many lay rigid and calcified eggs. Some species, such as

567-520: A short tail remains of the caudal vertebrae. However, the tail is still long enough to be of important use in many species, and is modified in some aquatic and tree-dwelling species. Many modern snake groups originated during the Paleocene , alongside the adaptive radiation of mammals following the extinction of (non-avian) dinosaurs . The expansion of grasslands in North America also led to an explosive radiation among snakes. Previously, snakes were

630-721: A symbol of impious churchgoers who disturb the sanctity of Mass by talking. The Beast appears in some other works as well, including stories written in French, Galician , Spanish, and Italian. Snake Snakes are elongated, limbless reptiles of the suborder Serpentes ( / s ɜːr ˈ p ɛ n t iː z / ). Like all other squamates , snakes are ectothermic , amniote vertebrates covered in overlapping scales . Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads ( cranial kinesis ). To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of

693-499: A year die from venomous snake bites. In the US alone, more than 8,000 venomous snake bites are reported each year, but only one in 50 million people (five or six fatalities per year in the USA) will die from venomous snake bites. Lizard bites, unlike venomous snake bites, are usually not fatal. The Komodo dragon has been known to kill people due to its size, and recent studies show it may have

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756-420: Is a finer one, barely visible; the cavities are connected internally, separated only by a membrane with nerves that are extraordinarily attuned to detecting temperature changes between. As in the overlapping vision fields of human eyes, the forward-facing pit on either side of the face combined produces a field of vision: a pit viper can distinguish between objects and their environments, as well as accurately judge

819-415: Is adapted for burrowing and its stomach indicates that it was preying on other animals. It is currently uncertain if Tetrapodophis is a snake or another species, in the squamate order, as a snake-like body has independently evolved at least 26 times. Tetrapodophis does not have distinctive snake features in its spine and skull. A study in 2021 places the animal in a group of extinct marine lizards from

882-476: Is associated with DNA mutations in the Zone of Polarizing Activity Regulatory Sequence (ZRS), a regulatory region of the sonic hedgehog gene which is critically required for limb development. More advanced snakes have no remnants of limbs, but basal snakes such as pythons and boas do have traces of highly reduced, vestigial hind limbs. Python embryos even have fully developed hind limb buds, but their later development

945-441: Is automixis with terminal fusion (see figure), a process in which two terminal products from the same meiosis fuse to form a diploid zygote . This process leads to genome-wide homozygosity , expression of deleterious recessive alleles, and often to developmental abnormalities. Both captive-born and wild-born A. contortrix and A. piscivorus appear to be capable of this form of parthenogenesis. Reproduction in squamate reptiles

1008-461: Is based on morphological characteristics and mitochondrial DNA sequence similarity. Alethinophidia is sometimes split into Henophidia and Caenophidia , with the latter consisting of "colubroid" snakes ( colubrids , vipers , elapids , hydrophiids , and atractaspids ) and acrochordids, while the other alethinophidian families comprise Henophidia. While not extant today, the Madtsoiidae ,

1071-524: Is his family quest to hunt the Questing Beast. Merlin reveals that the Questing Beast had been born of a human woman, a princess who lusted after her own brother. She slept with a devil who had promised to make the boy love her, but the devil manipulated her into accusing her brother of rape. Their father had the brother torn apart by dogs as punishment. Before he died, he prophesied that his sister would give birth to an abomination that would make

1134-459: Is not universal (see Amphisbaenia , Dibamidae , and Pygopodidae ). Living snakes are found on every continent except Antarctica, and on most smaller land masses; exceptions include some large islands, such as Ireland, Iceland, Greenland, and the islands of New Zealand, as well as many small islands of the Atlantic and central Pacific oceans. Additionally, sea snakes are widespread throughout

1197-456: Is ordinarily sexual, with males having a ZZ pair of sex-determining chromosomes, and females a ZW pair. However, the Colombian rainbow boa, Epicrates maurus , can also reproduce by facultative parthenogenesis, resulting in production of WW female progeny. The WW females are likely produced by terminal automixis. When female sand lizards mate with two or more males, sperm competition within

1260-624: Is potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by constriction . The English word snake comes from Old English snaca , itself from Proto-Germanic * snak-an- ( cf. Germanic Schnake 'ring snake', Swedish snok 'grass snake'), from Proto-Indo-European root * (s)nēg-o- 'to crawl to creep', which also gave sneak as well as Sanskrit nāgá 'snake'. The word ousted adder , as adder went on to narrow in meaning, though in Old English næddre

1323-585: Is relatively poor because snake skeletons are typically small and fragile making fossilization uncommon. Fossils readily identifiable as snakes (though often retaining hind limbs) first appear in the fossil record during the Cretaceous period. The earliest known true snake fossils (members of the crown group Serpentes) come from the marine simoliophiids , the oldest of which is the Late Cretaceous ( Cenomanian age) Haasiophis terrasanctus from

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1386-561: Is shown in the Arthuriana paper, showing that the beast comes from a mistranslation of the Arabic word Zaraffa. The wrong form of the word was used, leading to the description of the beast to be described as Zurafa, or docile or graceful. This is shown in the original French text where it is described as "douce". The account from Post-Vulgate Suite du Merlin , which was taken up by Thomas Malory for his seminal Le Morte d'Arthur , has

1449-816: Is stopped by the DNA mutations in the ZRS. There are about 3,900 species of snakes, ranging as far northward as the Arctic Circle in Scandinavia and southward through Australia. Snakes can be found on every continent except Antarctica, as well as in the sea, and as high as 16,000 feet (4,900 m) in the Himalayan Mountains of Asia. There are numerous islands from which snakes are absent, such as Ireland , Iceland , and New Zealand (although New Zealand's northern waters are infrequently visited by

1512-400: Is the largest order of reptiles , comprising lizards and snakes . With over 12,162 species , it is also the second-largest order of extant (living) vertebrates , after the perciform fish . Squamates are distinguished by their skins, which bear horny scales or shields, and must periodically engage in molting . They also possess movable quadrate bones , making possible movement of

1575-729: Is the sound of its offspring who tear the creature apart from the inside; the author takes the Questing Beast as a symbol of Christ , destroyed by the followers of the Old Law, the Twelve Tribes of Israel . Gerbert de Montreuil provides a similar vision of the Beast in his Continuation of Perceval, the Story of the Grail , though he says that it is "wondrously large" and interprets the noise and subsequent gruesome death by its own offspring as

1638-431: Is used at a time, and some evidence indicates that males alternate use between copulations . The hemipenis has a variety of shapes, depending on the species. Often it bears spines or hooks , to anchor the male within the female. Some species even have forked hemipenes (each hemipenis has two tips). Due to being everted and inverted, hemipenes do not have a completely enclosed channel for the conduction of sperm , but rather

1701-588: The Archosauria , the clade that contains crocodiles and birds, and their extinct relatives. Fossils of rhynchocephalians first appear in the Early Triassic , meaning that the lineage leading to squamates must have also existed at the time. A study in 2018 found that Megachirella , an extinct genus of lepidosaurs that lived about 240 million years ago during the Middle Triassic , was

1764-690: The Bathonian age of the Middle Jurassic of the Northern Hemisphere, with the first appearance of many modern groups, including snakes, during this period. Scientists believe crown group squamates probably originated in the Early Jurassic based on the fossil record, with the oldest unambiguous fossils of squamates dating to the Middle Jurassic. Squamate morphological and ecological diversity substantially increased over

1827-479: The Cretaceous Period . An early fossil snake relative, Najash rionegrina , was a two-legged burrowing animal with a sacrum , and was fully terrestrial . Najash , which lived 95 million years ago, also had a skull with several features typical for lizards, but had evolved some of the mobile skull joints that define the flexible skull in most modern snakes. The species did not show any resemblances to

1890-558: The Jurassic and Early Cretaceous indicate deeper fossil records for these groups, which may potentially refute either hypothesis. Both fossils and phylogenetic studies demonstrate that snakes evolved from lizards , hence the question became which genetic changes led to limb loss in the snake ancestor. Limb loss is actually very common in extant reptiles and has happened dozens of times within skinks , anguids , and other lizards. In 2016, two studies reported that limb loss in snakes

1953-570: The Jurassic period, with the earliest known fossils dating to between 143 and 167  Ma ago. The diversity of modern snakes appeared during the Paleocene epoch ( c.  66 to 56 Ma ago, after the Cretaceous–Paleogene extinction event ). The oldest preserved descriptions of snakes can be found in the Brooklyn Papyrus . Most species of snake are nonvenomous and those that have venom use it primarily to kill and subdue prey rather than for self-defense. Some possess venom that

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2016-553: The Komodo dragon , can reproduce asexually through parthenogenesis . Studies have been conducted on how sexual selection manifests itself in snakes and lizards . Snakes use a variety of tactics in acquiring mates. Ritual combat between males for the females with which they want to mate includes topping, a behavior exhibited by most viperids , in which one male twists around the vertically elevated fore body of his opponent and forcing it downward. Neck biting commonly occurs while

2079-534: The West Bank , dated to between 112 and 94 million years old. Based on genomic analysis it is certain that snakes descend from lizards . This conclusion is also supported by comparative anatomy , and the fossil record. Pythons and boas —primitive groups among modern snakes—have vestigial hind limbs: tiny, clawed digits known as anal spurs , which are used to grasp during mating. The families Leptotyphlopidae and Typhlopidae also possess remnants of

2142-681: The most extinct species . Breeding programs and wildlife parks, though, are trying to save many endangered reptiles from extinction. Zoos, private hobbyists, and breeders help educate people about the importance of snakes and lizards. Historically, the order Squamata has been divided into three suborders: Of these, the lizards form a paraphyletic group, since the "lizards" are found in several distinct lineages, with snakes and amphisbaenians recovered as monophyletic groups nested within. Although studies of squamate relationships using molecular biology have found different relationships between some squamata lineagaes, all recent molecular studies suggest that

2205-479: The slowworm , glass snake , and amphisbaenians . Leptotyphlopidae Gerrhopilidae Typhlopidae Xenophidiidae Anomalepididae Aniliidae Tropidophiidae Xenopeltidae Loxocemidae Pythonidae Boidae Bolyeridae Xenophidiidae Uropeltidae Anomochilidae Cylindrophiidae Acrochordidae Xenodermidae Pareidae Viperidae Homalopsidae Colubridae Lamprophiidae Elapidae The fossil record of snakes

2268-478: The tuatara , the last surviving member of the once diverse Rhynchocephalia , with both groups being placed in the clade Lepidosauria . Squamates are a monophyletic sister group to the rhynchocephalians , members of the order Rhynchocephalia. The only surviving member of the Rhynchocephalia is the tuatara . Squamata and Rhynchocephalia form the subclass Lepidosauria , which is the sister group to

2331-537: The upper jaw relative to the neurocranium . This is particularly visible in snakes, which are able to open their mouths very widely to accommodate comparatively large prey . Squamates are the most variably sized living reptiles, ranging from the 16 mm (0.63 in) dwarf gecko ( Sphaerodactylus ariasae ) to the 6.5 m (21 ft) reticulated python ( Malayopython reticulatus ). The now- extinct mosasaurs reached lengths over 14 m (46 ft). Among other reptiles, squamates are most closely related to

2394-434: The yellow-bellied sea snake and the banded sea krait ). The now extinct Titanoboa cerrejonensis was 12.8 m (42 ft) in length. By comparison, the largest extant snakes are the reticulated python , measuring about 6.95 m (22.8 ft) long, and the green anaconda , which measures about 5.21 m (17.1 ft) long and is considered the heaviest snake on Earth at 97.5 kg (215 lb). At

2457-508: The Cretaceous period known as dolichosaurs and not directly related to snakes. An alternative hypothesis, based on morphology , suggests the ancestors of snakes were related to mosasaurs —extinct aquatic reptiles from the Cretaceous —forming the clade Pythonomorpha . According to this hypothesis, the fused, transparent eyelids of snakes are thought to have evolved to combat marine conditions (corneal water loss through osmosis), and

2520-584: The Hox gene expression in the axial skeleton responsible for the development of the thorax became dominant. As a result, the vertebrae anterior to the hindlimb buds (when present) all have the same thoracic-like identity (except from the atlas , axis , and 1–3 neck vertebrae). In other words, most of a snake's skeleton is an extremely extended thorax. Ribs are found exclusively on the thoracic vertebrae. Neck, lumbar and pelvic vertebrae are very reduced in number (only 2–10 lumbar and pelvic vertebrae are present), while only

2583-527: The Indian and Pacific oceans. Around thirty families are currently recognized, comprising about 520 genera and about 3,900 species . They range in size from the tiny, 10.4 cm-long (4.1 in) Barbados threadsnake to the reticulated python of 6.95 meters (22.8 ft) in length. The fossil species Titanoboa cerrejonensis was 12.8 meters (42 ft) long. Snakes are thought to have evolved from either burrowing or aquatic lizards, perhaps during

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2646-422: The Questing Beast appear to the young King Arthur after he has had an affair with his half-sister Morgause and begotten Mordred (they did not know that they were related when the incestuous act occurred). Arthur sees the Questing Beast drinking from a pool just after he wakes from a disturbing dream that foretells Mordred's destruction of the realm. He is then approached by King Pellinore , who confides that it

2709-510: The Questing Beast during the Grail Quest after he, Percival , and Galahad have chased it into a lake. The Questing Beast's story can be interpreted as a symbol of the incest, violence and chaos that eventually destroys Arthur's kingdom. The earlier Perlesvaus , however, offers an entirely different depiction of the Questing Beast. There it is described as pure white, smaller than a fox, and beautiful to look at. The noise from its belly

2772-451: The copy is selectively expressed in the venom gland. Previous literature hypothesized that venoms were modifications of salivary or pancreatic proteins, but different toxins have been found to have been recruited from numerous different protein bodies and are as diverse as their functions. Natural selection has driven the origination and diversification of the toxins to counter the defenses of their prey. Once toxins have been recruited into

2835-516: The course of the Cretaceous , including the appeance of groups like iguanians and varanoids , and true snakes. Polyglyphanodontia , an extinct clade of lizards, and mosasaurs , a group of predatory marine lizards that grew to enormous sizes, also appeared in the Cretaceous. Squamates suffered a mass extinction at the Cretaceous–Paleogene (K–Pg) boundary , which wiped out polyglyphanodontians, mosasaurs, and many other distinct lineages. The relationships of squamates are debatable. Although many of

2898-405: The distance between objects and itself. The heat sensing ability of a pit viper is so great that it can react to a difference as small as one third of a degree Fahrenheit. Other infrared-sensitive snakes have multiple, smaller labial pits lining the upper lip, just below the nostrils. Squamata Squamata ( / s k w æ ˈ m eɪ t ə / , Latin squamatus , 'scaly, having scales')

2961-478: The divergence between anguimorphs, iguanians, and advanced snakes dates back roughly 200 million years ago (Mya) to the Late Triassic / Early Jurassic , but the only good fossil evidence is from the Middle Jurassic. Snake venom has been shown to have evolved via a process by which a gene encoding for a normal body protein, typically one involved in key regulatory processes or bioactivity, is duplicated, and

3024-548: The earliest crown group squamates, not iguanians. However, a 2021 study found the genus to be a lepidosaur of uncertain position, in a polytomy with Squamata and Rhynchocephalia . In 2022, the extinct genus Cryptovaranoides was described from the Late Triassic ( Rhaetian age) of England as a highly derived squamate belonging to the group Anguimorpha , which contains many extant lineages such as monitor lizards , beaded lizards and anguids . The presence of an essentially modern crown group squamate so far back in time

3087-531: The ears. Some primitive snakes are known to have possessed hindlimbs, but their pelvic bones lacked a direct connection to the vertebrae. These include fossil species like Haasiophis , Pachyrhachis and Eupodophis , which are slightly older than Najash . This hypothesis was strengthened in 2015 by the discovery of a 113-million-year-old fossil of a four-legged snake in Brazil that has been named Tetrapodophis amplectus . It has many snake-like features,

3150-407: The evolutionary origin of venom may exist deep in the squamate phylogeny, with 60% of squamates placed in this hypothetical group called Toxicofera . Venom has been known in the clades Caenophidia , Anguimorpha , and Iguania , and has been shown to have evolved a single time along these lineages before the three groups diverged, because all lineages share nine common toxins. The fossil record shows

3213-621: The external ears were lost through disuse in an aquatic environment. This ultimately led to an animal similar to today's sea snakes . In the Late Cretaceous , snakes recolonized land, and continued to diversify into today's snakes. Fossilized snake remains are known from early Late Cretaceous marine sediments, which is consistent with this hypothesis; particularly so, as they are older than the terrestrial Najash rionegrina . Similar skull structure, reduced or absent limbs, and other anatomical features found in both mosasaurs and snakes lead to

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3276-450: The female's reproductive tract may occur. Active selection of sperm by females appears to occur in a manner that enhances female fitness. On the basis of this selective process, the sperm of males that are more distantly related to the female are preferentially used for fertilization, rather than the sperm of close relatives. This preference may enhance the fitness of progeny by reducing inbreeding depression . Recent research suggests that

3339-432: The groups originally recognized on the basis of morphology are still accepted, understanding of their relationships to each other has changed radically as a result of studying their genomes . Iguanians were long thought to be the earliest crown group squamates based on morphological data, but genetic data suggest that geckos are the earliest crown group squamates. Iguanians are now united with snakes and anguimorphs in

3402-437: The head, between the nostrils and the eyes. In fact the pit looks like an extra pair of nostrils. All snakes have the ability to sense warmth with touch and heat receptors like other animals ;however, the highly developed pit of the pit vipers is distinctive. Each pit is made of a pit cavity and an inner cavity, the larger one lies just behind and generally below the level of the nostril, and opens forward. Behind this larger cavity

3465-545: The modern burrowing blind snakes, which have often been seen as the most primitive group of extant forms. One extant analog of these putative ancestors is the earless monitor Lanthanotus of Borneo (though it is also semiaquatic ). Subterranean species evolved bodies streamlined for burrowing, and eventually lost their limbs. According to this hypothesis, features such as the transparent , fused eyelids ( brille ) and loss of external ears evolved to cope with fossorial difficulties, such as scratched corneas and dirt in

3528-575: The other end of the scale, the smallest extant snake is Leptotyphlops carlae , with a length of about 10.4 cm (4.1 in). Most snakes are fairly small animals, approximately 1 m (3.3 ft) in length. Some of the most highly developed sensory systems are found in the Crotalidae, or pit vipers—the rattlesnakes and their associates. Pit vipers have all the sense organs of other snakes, as well as additional aids. Pit refers to special infrared-sensitive receptors located on either side of

3591-515: The other instead of side by side, and most have only one functional lung . Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca . Lizards have independently evolved elongate bodies without limbs or with greatly reduced limbs at least twenty-five times via convergent evolution , leading to many lineages of legless lizards . These resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule

3654-451: The pelvic girdle, appearing as horny projections when visible. Front limbs are nonexistent in all known snakes. This is caused by the evolution of their Hox genes , controlling limb morphogenesis . The axial skeleton of the snakes' common ancestor, like most other tetrapods, had regional specializations consisting of cervical (neck), thoracic (chest), lumbar (lower back), sacral (pelvic), and caudal (tail) vertebrae. Early in snake evolution,

3717-583: The same sounds as the pack of dogs that were about to kill him. Later on in the Post-Vulgate, the Prose Tristan , and the sections of Malory based on those works, Saracen knight Palamedes hunts the Questing Beast. It is at first a futile venture, much like his love for Tristan 's paramour Iseult , offering him nothing but hardship. But his conversion to Christianity allows Palamedes relief from his endless worldly pursuits, and he finally slays

3780-429: The snakes are entwined. Parthenogenesis is a natural form of reproduction in which the growth and development of embryos occur without fertilization. Agkistrodon contortrix (copperhead snake) and Agkistrodon piscivorus (cottonmouth snake) can reproduce by facultative parthenogenesis; they are capable of switching from a sexual mode of reproduction to an asexual mode. The type of parthenogenesis that likely occurs

3843-432: The venom proteome , they form large, multigene families and evolve via the birth-and-death model of protein evolution, which leads to a diversification of toxins that allows the ambush predators the ability to attack a wide range of prey. The rapid evolution and diversification is thought to be the result of a predator–prey evolutionary arms race , where both are adapting to counter the other. An estimated 125,000 people

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3906-575: Was the general word for snake. The other term, serpent , is from French, ultimately from Indo-European * serp- 'to creep', which also gave Ancient Greek ἕρπω ( hérpō ) 'I crawl' and Sanskrit sarpá ‘snake’. All modern snakes are grouped within the suborder Serpentes in Linnean taxonomy , part of the order Squamata , though their precise placement within squamates remains controversial. The two infraorders of Serpentes are Alethinophidia and Scolecophidia . This separation

3969-458: Was unexpected, as their diversification was previously thought to have occurred during the Jurassic and Cretaceous. A 2023 study found that Cryptovaranoides most likely represents an archosauromorph with no apparent squamate affinities, though the original describers maintained their original conclusion that this taxon represents a squamate. The oldest unambiguous fossils of Squamata date to

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