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Snake. Most species are nonvenomous and those that have venom use it primarily to kill and subdue prey rather than for self-defense.

Snake

Some possess venom potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by constriction. Etymology 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".[6] The word ousted adder, as adder went on to narrow in meaning, though in Old English næddre was the general word for snake.[7] The other term, serpent, is from French, ultimately from Indo-European *serp- (to creep),[8] which also gave Ancient Greek hérpō (ἕρπω) "I crawl". Evolution The fossil record of snakes is relatively poor because snake skeletons are typically small and fragile, making fossilization uncommon.

Origins Distribution Size. American alligator. The American alligator (Alligator mississippiensis), sometimes referred to colloquially as a gator or common alligator, is a large crocodilian reptile endemic to the southeastern United States.

American alligator

It is one of two living species in the genus Alligator within the family Alligatoridae; it is larger than the other extant alligator species, the Chinese alligator. Adult male American alligators measure 3.4 to 4.6 m (11 to 15 ft) in length, and can weigh 453 kg (999 lb). Females are smaller, measuring around 3 m (9.8 ft). The American alligator inhabits freshwater wetlands, such as marshes and cypress swamps from Texas to North Carolina. It is distinguished from the sympatric American crocodile by its broader snout, with overlapping jaws and darker coloration, and is less tolerant of saltwater but more tolerant of cooler climates than the American crocodile, which is found only in tropical climates. Crocodilia. Large, solidly built, lizard-like reptiles, crocodilians have long flattened snouts, laterally compressed tails, and eyes, ears, and nostrils at the top of the head.

Crocodilia

They swim well and can move on land in a "high walk" and a "low walk", while smaller species are even capable of galloping. Their skin is thick and covered in non-overlapping scales. They have conical, peg-like teeth and a powerful bite. They have a four-chambered heart and, somewhat like birds, a unidirectional looping system of airflow within the lungs, but like other reptiles they are ectotherms. Eight species of crocodilians are known to have attacked humans. Spelling and etymology[edit] The group is often spelled 'Crocodylia' for consistency with the genus Crocodylus (Laurenti, 1768). Morphology and physiology[edit] Mounted skeleton and taxidermy of Nile crocodile Crocodilians, like this spectacled caiman, can hide in water with only their nostrils, eyes and ears at the surface.

Locomotion[edit] Jaws and teeth[edit] Reptile. The earliest known reptiles originated around 315 million years ago during the Carboniferous period, having evolved from advanced reptile-like amphibians that became increasingly adapted to life on dry land.

Reptile

Some early examples include the lizard-like Hylonomus, Casineria and possibly Westlothiana, although the latter may be an advanced land-dwelling amphibian. In addition to the living reptiles, there are many diverse groups that are now extinct, in some cases due to mass extinction events. In particular, the K–Pg extinction wiped out the pterosaurs, plesiosaurs, ornithischians, and sauropods, as well as many species of theropods (e.g. tyrannosaurs and dromaeosaurids), crocodyliforms, and squamates (e.g. mosasaurids). Modern reptiles inhabit every continent with the exception of Antarctica. Several living subgroups are recognized: Reptiles are tetrapod vertebrates, creatures that either have four limbs or, like snakes, being descended from four-limbed ancestors.

Classification[edit]