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44-921: A small stone chamber, the Kitora Tomb is a little over 1 metre in height and width and about 2.4 metres long, just large enough to bury a single person. The four walls are aligned with the cardinal points of the compass, and respectively feature the Black Divine Tortoise of the North, the Azure Dragon of the East, the Red Phoenix of the South, and the White Tiger of the West. On the ceiling of

88-714: 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

132-542: A king of the north who had two generals serving under him, a "Tortoise General" and a "Snake General". This god had a temple in the Wudang Mountains of Hubei and there are now a "Tortoise Mountain" and a "Snake Mountain" on opposite sides of a river near Wuhan , Hubei's capital. Taoist legend has it that Xuanwu was the prince of a Chinese ruler but was not interested in taking the throne, opting instead to leave his parents at age 16 and study Taoism. According to

176-661: 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

220-414: 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

264-520: 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

308-475: A state of hibernation, and thus implies the season of winter. So the English translation Black ~ Dark ~ Mysterious Warrior is a more faithful translation. It represents the north and the winter season, thus it is sometimes called Black Warrior of the North ( Chinese : 北方玄武 ; pinyin : Běifāng Xuánwǔ ). In Japan, the characters 玄武 are pronounced as Genbu . It is said to protect Kyoto on

352-420: 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

396-415: 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

440-476: 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

484-461: 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 ,

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528-459: 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

572-534: Is one of the Four Symbols of the Chinese constellations . It is usually depicted as a tortoise intertwined with a snake . The character '武' can mean 'martial' or 'warrior.' The two characters 玄 and 武 do not have any literal meaning of tortoise and snake. But both tortoise and snake are known to hibernate during winter. The image of intertwined tortoise and snake likely symbolizes a state of inner struggle or

616-624: 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

660-585: 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

704-816: 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

748-479: 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

792-558: 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

836-632: 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

880-447: The Way , he discovered that he must purge himself of all of his past sins to become a god. He learned to achieve this by washing his stomach and intestines in the river. Washing his internal organs, his sins dissolved into the water in a dark, black form. These then formed into a black tortoise and a snake who terrorized the country. Once Xuanwu learned of this, he returned to subdue them as in

924-534: 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

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968-479: 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

1012-434: 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

1056-508: 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

1100-584: 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

1144-527: 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

1188-475: The chamber floor, mixed with grave goods and human bone. A gilded bronze fitting and sword decorations were discovered, both executed with superbly inlaid patterns. Based upon analysis of the bone fragments and items found in the tomb, it is believed the interred was a middle-aged or older male of aristocratic background. The paintings have suffered the ravages of time, and, as National Treasure of Japan and World Heritage , their preservation has been accorded

1232-468: The chamber there is also an astronomical chart that has been the focus of much research and debate by scholars in the field of archaeoastronomy . In addition, the 12 zodiac animals-headed figures with human body are painted on the wall, which may be one of the oldest remaining zodiac murals in East Asia. Fragments of a lacquered wooden coffin, torn apart when the tomb was robbed, lay 5 cm thick on

1276-474: The countryside. However, as the snake and tortoise showed remorse, he did not kill them but instead let them train under him to atone for their wrongdoings. They then became the Tortoise and Snake generals and assisted Xuanwu with his quests (another legend held that the mortal organs were tossed out to become Wuhan's Tortoise and Snake mountains). According to another source, once Xuanwu had begun his study of

1320-531: 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,

1364-621: 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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1408-437: 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

1452-423: The highest priority. The entire tomb has been roofed over, and a series of adjoining antechambers were constructed to isolate the central chamber from temperature and humidity fluctuations, and prevent contamination by airborne mold spores and microorganisms . 34°27′04″N 135°48′18″E  /  34.4512°N 135.8050°E  / 34.4512; 135.8050 Black Tortoise The Black Tortoise

1496-402: The legend, he eventually achieved divine status and was worshiped as a deity of the northern sky. Other Chinese legends also speak of how the "Tortoise General" and a "Snake General" came to be. During Xuanwu's study to achieve enlightenment and divine status, he was told that, in order to fully achieve divinity, he must purge all human flesh from his body. Since he had always eaten the food of

1540-545: 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

1584-526: The north gate of the Taiji Palace , in the north of Chang'an . In ancient China , the tortoise and the serpent were thought to be spiritual creatures symbolizing longevity. The Min people custom of building turtle-shaped tombs may have had to do with the desire to place the grave under the influence of the Black Tortoise. In the classic novel Journey to the West , Xuanwu was

1628-630: The north side, being one of the four guardian spirits that protect the city. It is represented by the Kenkun Shrine , which is located on top of Mount Funaoka in Kyoto. An important Taoist priest also has 玄武 Xuanwu as his clergy name. He is sometimes (as in Journey to the West ) portrayed in the company of a turtle and a snake. During the Han dynasty , people often wore jade pendants that were in

1672-575: 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

1716-515: 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

1760-762: The other story. As with the other three Symbols , there are seven astrological "Mansions" (positions of the Moon ) within the Black Tortoise. The names and determinative stars are: 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

1804-451: 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,

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1848-528: The shape of turtles. Originally, there was a legend that said that turtles could not mate with other turtles, only snakes. This is why the Black Tortoise is depicted with a snake on its back. The northern gates of Chinese palaces were often named after the Xuanwu. Most famously, the Incident at Xuanwu Gate , where Li Shimin killed his brothers Jiancheng and Yuanji and seized power in a coup, took place at

1892-400: The world , despite all his efforts, his stomach and intestines were still human. A god then came and changed his organs with divine ones. Once removed, the original stomach and intestines were said to have become a tortoise and a snake, respectively. The tortoise and snake became demons and terrorized people. Now divine, Xuanwu heard of this and returned to slay the monsters he had unleashed on

1936-575: 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

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