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Snakes have no external ears, but they retain a few vestiges of an internal ear, which are connected to other skull bones in such a way as to permit the transmission of some earth-borne, and perhaps a few aerial, sound waves of low frequency.
Sdnakes rate of growth in snakes sdnakes correlated with the availability of food and temperatures high enough to permit full metabolic activity. When all factors are optimal, snakes grow surprisingly fast. It has been suggested that all snakes grow rapidly until they reach sexual maturity, after which time growth slows but very seldom stops completely.
For molting in snakes, the replacement cells for the skin grow on the same cycle and cohere sdnakes a complete unit. Snakes differ from other reptiles in being limbless and having a greatly elongated body and tail. Snakes also lack movable eyelids and external ear openings. Classified with lizards in the order Squamata, snakes represent a lizard that, over the course of evolutionhas undergone structural reduction, simplification, and loss as well as specialization.
All snakes lack external limbs, but not all legless reptiles are snakes. Certain burrowing lizards may have only front or hind limbs or be completely legless. Unlike lizards, snakes lack movable eyelids, which in a continuous and often disconcerting stare. Snakes also lack external ear openings. Internally, they have lost the urinary bladder. The visceral organs are elongated, with reduction of the left member in relation to the right; the left lung is greatly reduced or even lost entirely. However, snakes possess increased s of vertebrae and have developed two novelties among vertebrates : a tracheal lung in the neck region and a venom -conducting system for subduing prey.
Snakes are thought to have evolved from terrestrial lizards as early as the Middle Jurassic Epoch The oldest known fossil snake, Eophis underwoodiwas a small snake that lived in southern England about million years ago. Snakes are misunderstood and often maligned, primarily out of ignorance about their true nature and position in the natural world. All snakes are predators, but venomous snakes that is, biting snakes that use their fangs to inject toxins into their victims have given an inaccurate reputation to the entire group, as most people cannot tell the dangerous from the harmless.
Only a small percentage fewer than species are venomous, and of those only about half are capable of inflicting a lethal bite. Although snakebite mortality worldwide is estimated at 80,—, people per year, the majority of deaths occur in Southeast Asiaprincipally because of poor medical treatment, malnutrition of victims, and a large of venomous species. Although there are about 8, venomous snakebites per year in the United Statesthe average of annual fatalities is less than 10 or so per year—fewer than are attributed to bee stings and lightning strikes.
In Mexico10 times as many people die annually from bee stings as from snakebites. Snakes can control the amount of venom they inject and may bite sdnakes for food or defensively for protection. Snakes have a limited amount of venom available at any given time and do not want to waste it on nonprey organisms.
Statistics show that the vast majority of snakebites occur while either catching and handling captive snakes or trying to molest or kill wild ones. In either case, the snake is only defending itself. Rattlesnakesfor example, are venomous, and large ones are sdnakes dangerous owing to sdnakes amount of venom they can inject.
However, most are shy and retreating, and none will attack a person unmolested. When approached or molested, they will coil up and rattle as a warning to be left alone, striking only as a last resort. Even in these scenarios, only two snakes have a reputation as dangerous aggressors: the black mamba Dendroaspis polylepis of Africa and the king cobra Ophiophagus hannah of Southeast Asia.
Nevertheless, snakes are inoffensive under the vast majority of circumstances. People are rarely indifferent about them, generally exhibiting emotions that range from religious awe and superstitious dread to repulsion and uncontrollable fear. It is interesting to note that, although most people profess to fear or hate snakes, one of the most visited areas of any zoo is the snake house—proof that snakes are mysterious and fascinating, even if they are loathed.
Given their exquisite colours, patterns, and graceful movements as they crawl, swim, or climb, some snakes can be considered among the most beautiful animals. Very few snakes are truly poisonous. One of the most common, yet harmless, poisonous snakes in North America is the garter snake Thamnophiswhose body has the ability to absorb and store the toxins of the newtssalamandersand other poisonous prey it eats. Nearly every culture since prehistoric times including various present-day cultures has worshipped, revered, or feared snakes. Serpent worship is one of the earliest forms of veneration, with some carvings dating to 10, bce.
Although Satan is depicted as a serpent sdnakes the biblical of the Creationsnakes are revered by most societies. A vast global compendium of superstitions and mythologies about snakes has sprung up. The hides of six snake species especially pythons s and wart snakes are commonly bought and sold in the skin trade. The of rattlesnakes used for their skins is minor in comparison.
Hundreds of thousands of live snakes are collected for sale in the international pet trade. Nearlyball pythons and 30, boa constrictors are sdnakes annually into the United States. The removal of such enormous s from the wild threatens the survival of these species, and many snake populations are in decline as a result of capture and habitat destruction. The release of nonnative pet snakes into the wild has also sdnakes to the introduction of several invasive speciesincluding the Burmese pythons that have devastated small mammal populations in the Florida Everglades.
Most snakes do not spend much of sdnakes time doing anything but resting. The thermoregulation problem varies with latitude and altitude. The actions and reactions of a snake in temperate North America are distinct from those of one living in the American tropical lowlands but are similar to those of another living at higher altitudes in the Andes of Ecuador.
No matter where they live, snakes are subjected to pressures from the living biotic parts of the environment as well as from the physical, nonliving abiotic parts. But the amount or degree of challenge to the snake from different segments of the environment changes drastically depending upon the region it inhabits. An individual living in the hot, humid tropics of Africa, with comparatively constant temperatures close to optimum throughout the year and ample moisture from both rainfall and the surroundings, faces environmental problems that are overwhelmingly biotic, involving competition with other members of its own species for food, the challenge from other species of snakes and perhaps other vertebrates for possession of the ecological nicheand constant pressure of the predators that find it a tasty morsel.
On the other hand, the common adderor European viper Vipera berusliving north of the Arctic Circle in Europe, is the only snake present in the area and lives practically unchallenged in its niche. However, its survival is challenged continually by its physical environment, and death from overheating, freezing, or dehydration sdnakes a repetitive threat. Sdnakes Snakes and humans Natural history Dormant periods Interactions between individuals Reproduction Mating Egg formation and laying Early development and growth Molt Sdnakes Form and function Vertebrae The skin Sdnakes Skull and sense organs Urogenital system Specializations for securing food.
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Give Feedback External Websites. Let us know if you have suggestions to improve this article requires. External Websites. Articles from Britannica Encyclopedias for elementary and high sdnakes students. By James A. Fast Facts 2-Min Summary. Timber Rattlesnake. See all media. Also Known As: serpent Serpentes Show more.
Full Article. Snakes suborder Serpentes. Sdnakes on an individual drawing to see a larger image. Behold the rattlesnake's rattle, thought to be a warning device to other organisms. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now. Learn how the predatory pilot black snake strikes, suffocates, and consumes whole its rodent prey.
The pilot black snake Elaphe obsoleta suffocates prey such as rats and mice before swallowing them whole. Load Next .Sdnakes
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