General features ( reptile )

Importance

The economic and ecological importance of reptiles to humans is not as great as the other major vertebrate groups birds, fishes, and mammals. Locally, some species are eaten on occasion, if not regularly. The green turtle (Chelonia mydas) is the most widely eaten species of reptile. The giant Galápagos tortoise was especially popular as food among 19th-century seafarers and, for this reason, nearly became extinct. Among the lizards, iguanas are perhaps the most popular as a local food. Leather goods, including luggage, gloves, belts, handbags, and shoes, are made from the skins of lizards, crocodilians, and snakes. This has led to the virtual extinction of several species of crocodilians and to severe reduction of populations of large lizards, snakes, and turtles. As living subjects for biological research, lizards in particular have been useful to the scientist. Venomous species constitute little hazard to humans except in limited rural areas.

Size range

Although persistent but unsubstantiated reports have been made of 12-metre (40-foot) anacondas, this gigantic South American snake, while it probably is the largest living species, does not usually exceed nine metres (30 feet) in length. The reticulated python of Southeast Asia and the East Indies has been recorded at 8.4 metres (27.6 feet). The rock python (Python sebae) of Africa reaches 7.5 metres (24.6 feet). No other group of living snakes approaches the pythons and boas in weight, although the king cobra of Asia and the East Indies comes close in length (5.4 metres, or 17.7 feet) and is the longest venomous snake. The heaviest venomous snake is probably the eastern diamondback rattlesnake (Crotalus adamanteus; see photograph), which, though not exceeding 2.4 metres (7.9 feet), may weigh as much as 15.5 kilograms (34 pounds). The largest of the common nonvenomous snakes of the family Colubridae is probably the Oriental rat snake, Ptyas carinatus (3.73 metres; 12.2 feet). Four living species of crocodilians grow larger than six metres (20 feet): the American crocodile (Crocodilus acutus), the Orinoco crocodile (C. intermedius), the saltwater crocodile (C. porosus), and the gavial (Gavialis gangeticus). The last two may approach nine metres (30 feet).

The giant among living turtles is the marine leatherback (Dermochelys), which reaches a total length of about 2.7 metres (8.9 feet) and a weight of about 680 kilograms (1,500 pounds). The largest of the land turtles is a Galápagos tortoise weighing 255 kilograms (560 pounds). The largest modern lizard is a monitor, the Komodo dragon of the East Indies; it attains a length of three metres (10 feet). Two or three other species of monitors reach 1.8 metres (5.9 feet). The common iguana comes close to that size, but no other lizard does. None of the living reptiles, with the possible exception of snakes, is as large as the largest extinct representative of its particular group. The 2.7-metre leatherback turtle is smaller than the extinct 3.6-metre (11.8-foot) marine turtle Archelon, and no modern crocodile approaches the estimated 15-metre (49-foot) length of Phobosuchus. The Komodo dragon does not compare with the six-metre (20-foot) or more mosasaur Tylosaurus. Lengths exceeding 30 metres (100 feet) and weights of 91,000 kilograms (200,000 pounds) or more may have been achieved by some browsing, quadruped dinosaurs. The smallest reptiles are the geckos, some of which grow no longer than three centimetres (slightly more than one inch). Certain blind snakes (Typhlopidae) are less than 10 centimetres (four inches) in length when fully grown. The smallest turtles weigh less than 450 grams (one pound) and reach a maximum length of 12.5 centimetres (about five inches). The smallest crocodilians are the dwarf crocodile (Osteolaemus tetraspis) and the smooth-fronted caiman (Paleosuchus), about 1.7 metres (5.6 feet) in length.

Distribution and ecology

North Temperate Zone

Although living reptiles, which number some 6,000 species, are primarily tropical animals, many inhabit the temperate zones. The northernmost ranges are those of the lacertid lizard (Lacerta vivipara) and the common viper (Vipera berus), both of Europe and Asia. These ovoviviparous (live-bearing, but the unborn snakes develop within eggs) species live north of the Arctic Circle, at least in Scandinavia. Two other lizards, the slowworm (Anguis fragilis) and the sand lizard (Lacerta agilis), and two snakes, the grass snake (Natrix natrix) and the smooth snake (Coronella austriaca), reach 60° N in Europe. Of the six northern species, all but the grass snake are ovoviviparous. Across Siberia only Lacerta vivipara and Vipera berus live north of 60°. In North America no reptile reaches the 60th parallel. Two species of garter snakes live as far north as 55° in western Canada. In North America and Eurasia the northern limit of turtles is about 55° N. It is only south of 40° Ν that reptiles become abundant. In the eastern United States and eastern Asia, water snakes (Natrix), rat snakes (Elaphe), racers (Coluber), green snakes (Opheodrys), northern skinks (Eumeces), glass “snakes” (lizards of the genus Ophisaurus), and soft-shelled turtles (Trionyx) are common. One of the two living species of Alligator lives in southeastern United States; the other lives in China. Even though both regions are characterized by many species of emydid turtles (family Emydidae), the genera to which the species belong are found in only one region or the other. Many lizards of temperate Eurasia belong to the families Agamidae and Lacertidae, which do not occur at all in the Americas. On the other hand, many lizards of North America are in the families Iguanidae and Teiidae, which do not live in Eurasia. The fauna of the eastern United States is almost as distinct from that of the western United States and northern Mexico (which is faunistically part of the same region) as it is from that of eastern Asia. The eastern United States has many genera and species of emydid turtles; the western United States (defined by a diagonal line running southeast to northwest through Texas, then northward along the Continental Divide) has only four or five species. Few genera and species of iguanid lizards inhabit the eastern United States, whereas the western United States has many. Although the eastern United States has more species of water snakes, the western United States contains more garter snakes. More species of snakes appear in the eastern United States than in the western areas, while the converse is true of lizard species. Reptiles of the North Temperate Zone include many ecological types. Aquatic groups are represented in both hemispheres by the water snakes, many emydid turtles, and the two alligators. Terrestrial groups include tortoises, ground-dwelling snakes, and many genera of lizards. Arboreal snakes are few, and arboreal lizards are almost nonexistent. Burrowing snakes are common. Specialized burrowing lizards are few.

Central and South America

In Central America the reptile fauna becomes richer. Besides several turtle families found in the eastern United States, Central America has three genera of turtles (Dermatemys, Claudius, and Staurotypus) not living elsewhere. Crocodilians become more numerous both in species and individuals. Lizards and snakes are particularly more abundant. Many of the genera of iguanid lizards occurring in the western United States have species in Mexico; one genus of spiny lizards (Sceloporus) reaches its peak of numbers of species in Mexico. South of Mexico the North American iguanid genera disappear and are replaced by tropical groups such as the black iguanas (Ctenosaura), the helmeted iguanids (Corythophanes), the casque-headed iguanids (Laemanctus), and the basilisks (Basiliscus). The lizard family Teiidae, though represented in the United States by the race-runner genus (Cnemidophorus), is tropical, and its real development begins in Central America with the large, conspicuous, and active ameivas (Ameiva) and several small genera that live in concealment. Among snakes, the fer-de-lance genus Bothrops, the coral snakes (Micrurus), the rear-fanged snakes such as the cat-eyed snakes (Leptodeira), and nonvenomous genera such as the tropical green snakes (Leptophis) either appear for the first time or begin their proliferation of species in Central America.

Reptiles become increasingly numerous in northern South America. Vine snakes (Oxybelis and Imantodes), false coral snakes (Erythrolamprus), slender ground snakes (Drymobius), and the burrowing spindle snakes (Atractus) are most abundant there. Most of the genera of the lizard family Teiidae occur in this area. Iguanid lizards of the anole genus (Anolis) are represented in northern South America by approximately 165 species. Other iguanid genera e.g., the long legged Polychrus make their appearance. Crocodilians, in terms of species, are more numerous in South than in Central America, and turtles are also abundant. Some of the North American groups for example, the mud turtles (Kinosternon) and sliders (Chrysemys) are represented, but the majority of species are members of genera and even families (e.g., the side-necked turtles, families Pelomedusidae and Chelidae) unknown in temperate North America. Several groups that form important, if not dominant, elements of the fauna of the Eastern Hemisphere are largely or completely absent from the American tropics: the lizard families Scincidae, Lacertidae, Chamaeleontidae, and Agamidae and the snakes of the cobra (Naja) and water snake (Natrix) genera. South of the tropics, in the temperate zone of South America, the reptilian fauna diminishes rapidly. Crocodilians and turtles do not occur south of northern Argentina. An ovoviviparous pit viper reaches almost 50° S there; two iguanid lizards range almost to 55° S.

Asia

Apart from the genera of reptiles listed above as common to the eastern United States and eastern Asia, the temperate zone of Eurasia is noted for its many lizards of the families Agamidae, Lacertidae, and to lesser degrees Gekkonidae and Scincidae. Most of the lizards are terrestrial; extremely specialized burrowers include desert-dwelling skinks (Ophiomorphus and Scincus). Most of the snakes characteristic of this vast area are also terrestrial. Arboreal snakes are represented almost exclusively by the rat snakes (Elaphe). The leaf-nosed snakes (Lyterhynchus) and the sand boas (Eryx) are the distinctive burrowing snakes of the region. Except for the Chinese alligator and the Indian gavial, temperate Eurasia lacks crocodilians. A few species of turtles are found. A few types characteristic of the Oriental tropics extend into the temperate zone e.g., several rear-fanged snakes (Boiga trigonata and Psammodynastes), a cobra or two (Naja), several species of soft-shelled turtles (Trionyx), and some species of true chameleons (Chamaeleo).

In the Oriental tropics the reptilian fauna is extremely rich in species and diverse types. Aquatic groups are represented by snakes of various genera (e.g., Natrix, Enhydris, Acrochordus), several groups of lizards (Tropidophorus among the skinks and Hydrosaurus among the agamids), many emydid and soft-shelled turtles, and five species of crocodiles. The numerous terrestrial reptiles include the small kukri snakes (Oligodon), the big Oriental rat snakes (Ptyas), cobras, monitor lizards (Varanus), many species and genera of skinks, some geckos, and several land turtles (Cuora, Geochelone). Specialized burrowing snakes (e.g., the family Uropeltidae and the colubrid genus Calamaria) and lizards (e.g., the family Dibamidae and the skink genus Brachymeles) are also abundant. The distinctive life-forms of reptiles in tropical Asia are arboreal. They include pythons and Oriental pit vipers (Trimeresurus), vine snakes (Ahaetulla), slug-eating snakes (Pareas), “flying” snakes (Chrysopelea), and tree racers (Gonyosoma). Some lizards climb only with the aid of claws (e.g., the monitors), a few with the help of prehensile, or grasping, tails (e.g., the deaf agamids, Cophotis), and many with the help of clinging pads under the digits (e.g., many geckos). The most striking arboreal reptiles of this area are the flying lizards (Draco) and the parachuting gecko (Ptychozoon), which has fully webbed digits, a fringed tail, and wide flaps of skin along its sides. Because New Guinea, although geographically part of the East Indies, has a reptilian fauna more akin to that of Australia, the two areas are considered here as one. The Australian region is the only area in the world in which venomous species of snakes outnumber harmless ones. The family Colubridae, comprising the majority of the nonvenomous or slightly venomous snakes of the world, is poorly represented in Australia, which has only 12 species. The Australian region has many snakes of the cobra family (family Elapidae), but no vipers. The fauna also include several pythons and minute blind snakes (family Typhlopidae); a variety of geckos, skinks, and agamid lizards; side-necked turtles; and three species of crocodiles.

Africa

The reptilian fauna of Africa forms two main divisions. The first, the fauna of the North African coast, is akin to that of central and southwestern Asia and southern Europe and is therefore mainly a temperate-zone fauna. The racers, the burrowing sand skink (Scincus), and the emydid turtle (Mauremys caspica) are elements of temperate fauna in North Africa. Some species of the great tropical fauna lying south of the Sahara Desert occur in North Africa and in Southwest Asia. Examples are the sand snakes (Psammophis), cobras, and chameleons (family Chamaeleontidae). As is true of the temperate fauna of Eurasia, the North African reptiles, though representing many families, are principally terrestrial and burrowing. Many lacertid and agamid lizards scamper over rocks and sand by day; they are replaced at night by small geckos and are preyed upon by the racers (Coluber) and sand snakes (Psammophis). In addition to cobras, the venomous snakes of North Africa include the common vipers, the saw-scaled viper (Echis carinatus), and the horned vipers (Cerastes). The last two are true desert animals. Land tortoises (Testudo) are common in the semi-arid land. The second and much larger division of the African fauna is the great tropical assemblage that ranges from the Sahara southward to the Cape of Good Hope. In common with tropical Asia, this vast area has cobras, many skinks, and many geckos. Its fauna differs from that of Asia in the absence of pit vipers (subfamily Crotalinae), the near absence of emydid turtles, and the poor representation of agamid lizards. These groups are replaced in tropical Africa by the many true vipers (subfamily Viperinae), the side-necked turtles (family Pelomedusidae), and the lacertid and cordylid lizards. Chameleons and land tortoises are abundant. Three species of crocodiles occur in Africa. In Africa are found all of the diverse reptilian types characteristic of a tropical area: aquatic turtles, crocodiles, and snakes; terrestrial turtles, snakes, and lizards; burrowing snakes of the blunt-headed and auger types; limbless and virtually blind burrowing lizards; and a profusion of arboreal snakes and lizards. The large island of Madagascar, off the eastern coast of Africa, has a peculiar fauna that appears in part as a collection of castoffs, groups that in Africa have not been able to meet the competition of more advanced forms. With few exceptions the reptiles of Madagascar belong to genera found only there.

[tags]reptiles, animal[/tags]

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