Squamata

(vertebrate zoology) An order of reptiles, composed of the lizards and snakes, distinguished by a highly modified skull that has only a single temporal opening, or none, by the lack of shells or secondary palates, and by possession of paired penes on the males.

Family: Angleheads, Calotes, Dragon Lizards, and Relatives
Family: Chameleons
Family: Anoles, Iguanas, and Relatives
Family: Geckos and Pygopods
Family: Blindskinks
Family: Wormlizards
Family: Mole-Limbed Wormlizards
Family: Florida Wormlizards
Family: Spade-Headed Wormlizards
Family: Night Lizards
Family: Wall Lizards, Rock Lizards, and Relatives
Family: Microteiids
Family: Whiptail Lizards, Tegus, and Relatives
Family: Girdled and Plated Lizards
Family: Skinks
Family: Alligator Lizards, Galliwasps, Glass Lizards, and Relatives
Family: Knob-Scaled Lizards
Family: Gila Monsters and Mexican Beaded Lizards
Family: Monitors, Goannas, and Earless Monitors
Family: Early Blindsnakes
Family: Slender Blindsnakes
Family: Blindsnakes
Family: False Blindsnakes
Family: Shieldtail Snakes
Family: Pipe Snakes
Family: False Coral Snakes
Family: Sunbeam Snakes
Family: Neotropical Sunbeam Snakes
Family: Boas
Family: Pythons
Family: Splitjaw Snakes
Family: Woodsnakes and Spinejaw Snakes
Family: File Snakes
Family: Vipers and Pitvipers
Family: African Burrowing Snakes
Family: Colubrids
Family: Cobras, Kraits, Seasnakes, Death Adders, and Relatives

(Lizards and snakes)

Class: Reptilia

Order: Squamata

Number of families: About 42

Number of genera, species: About 1,880 genera; 7,200 species

Evolution and systematics

Squamates are the most diverse living clade of reptiles, including about 1,440 genera and 4,450 species of lizards plus 440 genera and 2,750 species of snakes. Although snakes are commonly considered to constitute their own group, they clearly have descended from lizards and are merely limbless lizards. Squamates exhibit more than 70 shared derived traits, which indicate that they are descendants of a common ancestor, forming a large natural monophyletic group. (Snakes and lizards once were classified as different suborders, but since snakes are embedded within lizards, this classification is no longer tenable under the monophyletic standard of modern phylogenetic systematics.)

Resources

Arnold, E. N. "Cranial Kinesis in Lizards: Variations, Uses, and Origins." Vol. 30, Evolutionary Biology, edited by Max K. Hecht, Ross J. MacIntyre, and Michael T. Clegg. New York: Plenum Press, 1998.

Estes, R. "The Fossil Record and Early Distribution of Lizards." In Advances in Herpetology and Evolutionary Biology, edited by G. J. Rhodin and K. Miyata. Cambridge: Museum of Comparative Zoology, Harvard University, 1983.

Estes, R., K. de Queiroz, and J. Gauthier. "Phylogenetic Relationships Within Squamata." In Phylogenetic Relationships of the Lizard Families, edited by R. Estes and G. Pregill. Stanford, CA: Stanford University Press, 1988.

Greene, Harry W. Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press, 1997.

Pianka, E. R. Ecology and Natural History of Desert Lizards: Analyses of the Ecological Niche and Community Structure. Princeton, NJ: Princeton University Press, 1986.

Pianka, E. R., and L. J. Vitt. Lizards: Windows to the Evolution of Diversity. Berkeley: University of California Press, 2003.

Schwenk, K. "Feeding in Lepidosaurs. In Feeding: Form, Function, and Evolution in Tetrapod Vertebrates, edited by K. Schwenk. San Diego: Academic Press, 2000.

Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd edition. San Diego: Academic Press, 2001.

Autumn, K., Y. A. Liang, S. T. Hsieh, W. Zesch, W. P. Chan, T. W. Kenny, R. Fearing, and R. J. Full. "Adhesive Force of a Single Gecko Foot-Hair." Nature 405 (2000): 681–685.

Gans, C. "The Feeding Mechanism of Snakes and Its Possible Evolution." American Zoologist 1 (1961): 217–227.

Huey, R. B. "Egg Retention in Some High Altitude Anolis Lizards." Copeia 1977 (1977): 373–375.

Huey, R. B., and E. R. Pianka. "Ecological Consequences of Foraging Mode." Ecology 62 (1981): 991–999.

Huey, R. B., and M. Slatkin. "Cost and Benefits of Lizard Thermoregulation." Quarterly Review of Biology 51 (1976): 363–384.

McDowell, S., and C. Bogert. "The Systematic Position of Lanthanotus and the Affinities of the Anguimorphan Lizards." Bulletin of the American Museum of Natural History 105, no. 1 (1954): 1–142.

Patchell, F. C., and R. Shine. "Feeding Mechanisms in Pygopodid Lizards: How Can Lialis Swallow Such Large Prey?" Journal of Herpetology 20 (1986): 59–64.

Savitsky, A. H. "Hinged Teeth in Snakes: An Adaptation for Swallowing Hard-Bodied Prey." Science 212 (1981): 346–349.

Schwenk, K. "Why Snakes Have Forked Tongues." Science 263 (1994): 1573–1577.

Smith, K. K. "Mechanical Significance of Streptostyly in Lizards." Nature 283 (1980): 778–779.

[Article by: Eric R. Pianka, PhD]

The dominant order of living reptiles composed of the lizards and snakes. The group first appeared in Jurassic times and today is found in all but the coldest regions. Various forms are adapted for arboreal, burrowing, or aquatic lives, but most squamates are fundamentally terrestrial. There are about 4700 Recent species: 2200 lizards and 2500 snakes.

The order is readily distinguished from all known reptiles by its highly modified skull; an enlarged and movable quadrate; and a temporal opening that is lost or reduced in many forms. No other reptiles show these modifications, which allow for great kinesis in the lower jaw since it articulates with the quadrate. In addition, the order is distinct from other living reptile groups because its members have no shells or secondary palates and the males possess paired penes.

Traditionally the Squamata have been divided into two major subgroups, the lizards, suborder Sauria, and the snakes, suborder Serpentes. The latter group is basically a series of limbless lizards, and it is certain that snakes are derived from some saurian ancestor. There are many different legless lizards, and it has been suggested that more than one line has evolved to produce those species currently grouped together as snakes.

Sauria

The majority of saurians are insectivorous, but a few feed on plants while others, notably the Varanidae and allies, feed on larger prey including birds and mammals. The largest living lizard is the Komodo dragon (Varanus komodoensis).

The majority of lizards are quadrupedal in locomotion and are usually ambulatory scamperers or scansorial. Some forms are bipedal, at least when in haste. The coloration of each species of lizard is characteristic. Most forms exhibit marked differences in coloration between the sexes, at least during the breeding season, and frequently the young are markedly different from the parents. Color changes occur in rapid fashion among some species, and all are capable of metachrosis or changing color to a certain extent. See also Sexual dimorphism.

There are but two species of venomous lizards, both members of the genus Heloderma, in the family Helodermatidae: the Gila monster (H. suspectum) and the beaded lizard (H. horridum).

The following list indicates the major evolutionary lines and families of lizards. Families indicated by an asterisk contain limbless, snakelike species. All members of the families Pygopodidae, Anelytropsidae, Dibamidae, Amphisbaenidae, Feylinidae, and Anniellidae are snakelike lizards.

Iguania line

     Family: Iguanidae

                     Agamidae

                     Chamaeleontidae

Gekkota line

     Family: Gekkonidae

                     Pygopodidae

Scincomorpha line

     Family: Xantusiidae

                     Teiidae

                     Lacertidae

                     Gerrhosauridae*

                     Scincidae*

                     Anelytropsidae*

                     Dibamidae*

Annulata line

     Family: Amphisbaenidae*

Anguimorpha line

     Family: Anguidae*

                     Anniellidae*

                     Feyliniidae*

                     Xenosauridae

                     Helodermatidae

                     Varanidae

                     Lanthonotidae

Serpentes

Snakes are basically specialized, limbless lizards which probably evolved from burrowing forms but have now returned from subterranean habitats to occupy terrestrial, arboreal, and aquatic situations. The following characteristics are typical of all serpents. There is no temporal arch so that the lower jaw and quadrate are very loosely attached to the skull. This gives the jaw even greater motility than is the case in lizards. The body is elongate with 100–200 or more vertebrae, and the internal organs are elongate and reduced. A spectacle covers the eye.

The largest living snake is the Indian python (Python reticulatus), which reaches 30 ft (9 m) in length and a weight of 250 lb (113 kg). The largest venomous snake is the king cobra (Ophiophagus hannah), of southern Asia, which is known to attain a length of 18 ft (5.5 m).

The senses of snakes are fundamentally similar to those of all terrestrial vertebrates. Great dependence is placed upon olfaction and the Jacobson's organs (olfactory canals in the nasal mucosa). The tongue of all snakes is elongate and deeply bifurcated. When not in use it can be retracted into a sheath located just anterior to the glottis, but it is protrusible and is constantly being projected to pick up samples for the Jacobson's organs from the surrounding environment. Snakes are deaf to airborne sounds and receive auditory stimuli only through the substratum via the bones of the head. The eyes are greatly modified from those in lizards, and there is no color vision. Some groups are totally blind and have vestigial eyes covered by scales or skin.

Four basic patterns of locomotion are found in snakes, and several may be used by a particular individual at different times. The most familiar type is curvilinear. Snakes using rectilinear locomotion move forward in a straight line, without any lateral undulations, by producing wavelike movements in the belly plates. Laterolinear locomotion, or sidewinding, is used primarily on smooth or yielding surfaces and is very complex. Concertina locomotion movement resembles the expansion and contraction of that musical instrument.

The vast majority of living snakes are harmless to humans, although a number are capable of inflicting serious injury with their venomous bites. The venom apparatus has evolved principally as a method of obtaining food, but it is also advantageous as a defense against attackers. Fangs are teeth modified for the injection of venom into the victim, and the venom glands are modified salivary glands connected to the grooved fangs by a duct. Special muscles are present in all proglyphous snakes to force the venom into the wound. The venom itself is a complex substance containing a number of enzymes. Certain of these enzymes attack the blood, others in the nervous system, and some are spreaders.

The following list indicates the major groups of living snakes.

     Family: Typhlopidae

                     Leptotyphlopidae

                     Aniliidae

                     Boidae

                     Colubridae

                     Elapidae

                     Hydrophiida

                     Viperidae

                     Crotalidae

An order of animals, the scaly-bodied reptiles, including snakes and lizards.

Scaled reptiles Fossil range: Jurassic-recent PreЄ Є O S D C P T J K Pg N
Blotched blue-tongued lizard
Scientific classification
Domain:	Eukarya
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata Oppel, 1811
Suborders
see text
black: range of Squamata

This article is about the Squamata order of reptiles. For the Roman scale armour, see Lorica squamata.

Squamata, or the scaled reptiles, is the largest recent order of reptiles, including lizards and snakes. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the braincase. This is particularly visible in snakes, which are able to open their mouths very wide to accommodate comparatively large prey. They are the most variably-sized order of reptiles, ranging from the 16 mm (0.63 in.) Jaragua Sphaero (Sphaerodactylus ariasae) to the 8 m (26 ft.) Green Anaconda (Eunectes murinus).

Contents 1 Classification 2 List of Families 3 Evolution 4 Reproduction 5 Venom 6 Humans and Squamates 6.1 Bites and fatalities 6.2 Conservation 7 Notes 8 References 9 External links

Classification

Classically, the order is divided into three suborders:

• Lacertilia, the lizards;
• Serpentes, the snakes;
• Amphisbaenia, the worm lizards.

Of these, the lizards form a paraphyletic group. In newer classifications the name Sauria is used for reptiles and birds in general, and the Squamata are divided differently:

• Suborder Iguania – (the agamids, chameleons, iguanids. and other New World lizards)
• Suborder Scleroglossa
  • Infraorder Anguimorpha – (the monitors, Gila monster, alligator lizards, galliwasps, slow-worms and others)
  • Infraorder Amphisbaenia – worm lizards
  • Infraorder Gekkota – (the geckos)
  • Infraorder Scincomorpha – (skinks, whiptail lizards and common European lizards)
  • Infraorder Serpentes – (the snakes)

The relationships between these suborders is not yet certain, though recent research^[1] suggests that several families may form a hypothetical venom clade which encompasses a majority (nearly 60%) of Squamate species. Named Toxicofera, it combines the following groups from traditional classification^[1]:

• Suborder Serpentes (snakes)
• Suborder Iguania (agamids, chameleons, iguanids, etc.)
• Infraorder Anguimorpha, consisting of:
  • Family Varanidae (monitor lizards, including the Komodo dragon)
  • Family Anguidae (alligator lizards, glass lizards, etc.)
  • Family Helodermatidae (Gila monster and Mexican beaded lizard)

List of Families

Amphisbaenia
Family	Common Names	Example Species	Example Photo
Amphisbaenidae Gray, 1865	Tropical worm lizards	Darwin's worm lizard (Amphisbaena darwinii)	-
Bipedidae Taylor, 1951	Bipes worm lizards	Mexican mole lizard (Bipes biporus)	-
Rhineuridae Vanzolini, 1951	North American worm lizards	North American worm lizard (Rhineura floridana)
Trogonophidae Gray, 1865	Palearctic worm lizards	Checkerboard worm lizard (Trogonophis wiegmanni)	-
Anguoidea or Diploglossa
Family	Common Names	Example Species	Example Photo
Anguidae Oppel, 1811	Glass lizards	Slow worm (Anguis fragilis)
Anniellidae Gray, 1852	American legless lizards	California legless lizard (Anniella pulchra)
Xenosauridae Cope, 1866	Knob-scaled lizards	Chinese crocodile lizard (Shinisaurus crocodilurus)
Gekkota
Family	Common Names	Example Species	Example Photo
Dibamidae Boulenger, 1884	Blind lizards	Dibamus nicobaricum	-
Gekkonidae Gray, 1825	Geckos	Thick-tailed gecko (Underwoodisaurus milii)
Pygopodidae Boulenger, 1884	Legless lizards	Burton's snake lizard (Lialis burtonis)	-
Iguania
Family	Common Names	Example Species	Example Photo
Agamidae Spix, 1825	Agamas	Eastern bearded dragon (Pogona barbata)
Chamaeleonidae Gray, 1825	Chameleons	Veiled chameleon (Chamaeleo calyptratus)
Corytophanidae Frost & Etheridge, 1989	Casquehead lizards	Plumed basilisk (Basiliscus plumifrons)
Crotaphytidae Frost & Etheridge, 1989	Collared and leopard lizards	Common collared lizard (Crotaphytus collaris)
Hoplocercidae Frost & Etheridge, 1989	Wood lizards or clubtails	Club-tail iguana (Hoplocercus spinosus)	-
Iguanidae	Iguanas	Marine iguana (Amblyrhynchus cristatus)
Leiosauridae Frost et al., 2001	-	Darwin's iguana (Diplolaemus darwinii)	-
Opluridae Frost & Etheridge, 1989	Madagascan iguanas	Chalarodon (Chalarodon madagascariensis)	-
Phrynosomatidae Frost & Etheridge, 1989	Earless, spiny, tree, side-blotched and horned lizards	Greater earless lizard (Cophosaurus texanus)
Polychrotidae Frost & Etheridge, 1989	Anoles	Carolina anole (Anolis carolinensis)
Tropiduridae Frost & Etheridge, 1989	Neotropical ground lizards	(Microlophus peruvianus)
Platynota
Family	Common Names	Example Species	Example Photo
Helodermatidae	Gila monsters	Gila monster (Heloderma suspectum)
Lanthanotidae	Earless monitor	Earless monitor (Lanthanotus borneensis)	-
Varanidae	Monitor lizards	Perentie (Varanus giganteus)
Scincomorpha
Family	Common Names	Example Species	Example Photo
Cordylidae	Spinytail lizards	Girdle-tailed lizard (Cordylus warreni)
Gerrhosauridae	Plated lizards	Sudan plated lizard (Gerrhosaurus major)
Gymnophthalmidae	Spectacled lizards	-	-
Lacertidae Oppel, 1811	Wall or true lizards	Ocellated lizard (Lacerta lepida)
Scincidae Oppel, 1811	Skinks	Western blue-tongued skink (Tiliqua occipitalis)
Teiidae	Tegus or whiptails	Blue tegu (Tupinambis teguixin)
Xantusiidae	Night lizards	Granite night lizard (Xantusia henshawi)
Alethinophidia
Family	Common Names	Example Species	Example Photo
Acrochordidae Bonaparte, 1831[2]	File snakes	Marine file snake (Acrochordus granulatus)
Aniliidae Stejneger, 1907[3]	Coral pipe snakes	Burrowing false coral (Anilius scytale)
Anomochilidae Cundall, Wallach and Rossman, 1993.[4]	Dwarf pipe snakes	Leonard's pipe snake, (Anomochilus leonardi)
Atractaspididae Günther, 1858[5]	Mole vipers	Bibron's burrowing asp (Atractaspis bibroni)
Boidae Gray, 1825[2]	Boas	Amazon tree boa (Corallus hortulanus)
Bolyeriidae Hoffstetter, 1946	Round Island boas	Round Island burrowing boa (Bolyeria multocarinata)
Colubridae Oppel, 1811[2]	Colubrids	Grass snake (Natrix natrix)
Cylindrophiidae Fitzinger, 1843	Asian pipe snakes	Red-tailed pipe snake (Cylindrophis ruffus)
Elapidae Boie, 1827[2]	Cobras, coral snakes, mambas, kraits, sea snakes, sea kraits, Australian elapids	King cobra (Ophiophagus hannah)
Loxocemidae Cope, 1861	Mexican burrowing snakes	Mexican burrowing snake (Loxocemus bicolor)
Pythonidae Fitzinger, 1826	Pythons	Ball python (Python regius)
Tropidophiidae Brongersma, 1951	Dwarf boas	Northern eyelash boa (Trachyboa boulengeri)
Uropeltidae Müller, 1832	Shield-tailed snakes, short-tailed snakes	Cuvier's shieldtail (Uropeltis ceylanica)
Viperidae Oppel, 1811[2]	Vipers, pitvipers, rattlesnakes	European asp (Vipera aspis)
Xenopeltidae Bonaparte, 1845	Sunbeam snakes	Sunbeam snake (Xenopeltis unicolor)
Scolecophidia
Family	Common Names	Example Species	Example Photo
Anomalepidae Taylor, 1939[2]	Dawn blind snakes	Dawn blind snake (Liotyphlops beui)
Leptotyphlopidae Stejneger, 1892[2]	Slender blind snakes	Texas blind snake (Leptotyphlops dulcis)
Typhlopidae Merrem, 1820[6]	Blind snakes	Black blind snake (Typhlops reticulatus)

Evolution

Squamates are a monophyletic group that is a sister group to the tuatara. The squamates and tuatara together are a sister group to crocodiles and birds, the extant archosaurs. Squamate fossils first appear in the early Jurassic, but a mitochondrial phylogeny suggests that they evolved in the late Permian. The evolutionary relationships within the squamates are not yet completely worked out, with the relationship of snakes to other groups being most problematic. From morphological data, Iguanid lizards have been thought to have diverged from other squamates very early, but recent molecular phylogenies, both from mitochondrial and nuclear DNA, do not support this early divergence^[7]. Because snakes have a faster molecular clock than other squamates,^[7] and there are few early snake and snake ancestor fossils,^[8] it is difficult to resolve the relationship between snakes and other squamate groups.

Reproduction

The male members of the group Squamata have a hemipenis. Hemipenes are usually held inverted, within the body, and are everted for reproduction via erectile tissue like that in the human penis.^[9] Only one is used at a time, and some evidence indicates males alternate use between copulations. The hemipenis itself has a variety of shapes, depending on species. Often the hemipenis 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 a seminal groove which seals as the erectile tissue expands. This is also the only reptile group in which can be found both viviparous and ovoviviparous species, as well as the usual oviparous reptiles. Some species, like the Komodo dragon, can actually reproduce asexually and undergo parthenogenesis.^[10]

Venom

Venom is modified saliva, delivered through fangs.^[11] The fangs of 'advanced' venomous snakes like viperids and elapids are hollow to inject venom more effectively, while the fangs of rear-fanged snakes such as the Boomslang merely have a groove on the posterior edge to channel venom into the wound. Snake venoms are often prey specific, its role in self-defense is secondary.^[11] Venom, like all salivary secretions, is a pre-digestant which initiates the breakdown of food into soluble compounds allowing for proper digestion and even "non-venomous" snake bites (like any animal bite) will cause tissue damage.^[12]

Recent research suggests that 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 families Helodermatidae, Elapidae, Viperidae, and some members of the Colubridae. However, all snakes, some agamid lizards and most monitor lizards are now believed by some to have proteins very closely related to venom.^[13][14]

Humans and Squamates

Bites and fatalities

See also: Snakebite

Map showing global distribution of snakebite morbidity.

It is estimated that 125,000 people a year die from venomous snake bites.^[15] In the US alone, more than 8,000 venomous snake bites are reported each year.^[16] In addition, large pet constrictors, like boas and pythons, have been known to kill humans through strangulation on rare occasions.^[17]

Lizard bites, unlike venomous snake bites, are not fatal. The Komodo dragon has been known to kill people due to its size.^[18] The two known venomous species of lizard, the Gila monster and Mexican beaded lizard have never caused a human death by envenomation.

Conservation

Even though they survived the worst changes in Earth's history, today many squamate species are endangered due to habitat loss, hunting and poaching, the pet trade, alien species being introduced to their habitat (which puts native creatures at risk through unfair competition & predation), and many other unnecessary reasons. Because of this, some are in fact extinct with Africa having the most extinct species of squamates. However, breeding programs and wildlife parks are trying to save many endangered reptiles from extinction. Many zoos & breeders educate people about the importance of snakes and lizards.

Notes

1. ^ ^{a b} Fry, B. et al. (February 2006). "Early evolution of the venom system in lizards and snakes" (PDF). Nature 439: 584–588. doi:10.1038/nature04328. http://www.nature.com/nature/journal/v439/n7076/abs/nature04328.html. 
2. ^ ^{a b c d e f g} Cogger(1991), p.23
3. ^ Aniliidae (TSN 209611). Integrated Taxonomic Information System. Retrieved on 12 December 2007.
4. ^ Anomochilidae (TSN 563894). Integrated Taxonomic Information System. Retrieved on 13 December 2007.
5. ^ Atractaspididae (TSN 563895). Integrated Taxonomic Information System. Retrieved on 13 December 2007.
6. ^ Typhlopidae (TSN 174338). Integrated Taxonomic Information System. Retrieved on 13 December 2007.
7. ^ ^{a b} Kumazawa, Yoshinori (2007). "Mitochondrial genomes from major lizard families suggest their phylogenetic relationships and ancient radiations". Gene 388: 19–26. doi:10.1016/j.gene.2006.09.026. 
8. ^ "Lizards & Snakes Alive!". American Museum of Natural History. http://www.amnh.org/exhibitions/lizards/snakes/world.php. Retrieved 2007-12-25. 
9. ^ "Iguana Anatomy". http://www.greenigsociety.org/anatomy.htm. 
10. ^ Morales, Alex. "Komodo Dragons, World's Largest Lizards, Have Virgin Births". Bloomberg Television. http://www.bloomberg.com/apps/news?pid=20601082&sid=apLYpeppu8ag&refer=canada. Retrieved 2008-03-28. 
11. ^ ^{a b} Mehrtens (1987), p.243
12. ^ Mehrtens (1987), p.209
13. ^ "Venom Hunt Finds 'Harmless' Snakes A Potential Danger". Science Daily. http://www.sciencedaily.com/releases/2003/12/031216075937.htm. Retrieved 2007-12-25. 
14. ^ "Lizards' poisonous [sic] secret is revealed". NewScientist. http://www.newscientist.com/article.ns?id=dn8331. Retrieved 2007-12-25. 
15. ^ "Snake-bites: appraisal of the global situation". Who.com. http://www.who.int/bloodproducts/publications/en/bulletin_1998_76(5)_515-524.pdf. Retrieved 2007-12-30. 
16. ^ "First Aid Snake Bites". University of Maryland Medical Center. http://www.umm.edu/non_trauma/snake.htm. Retrieved 2007-12-30. 
17. ^ "Pet boa constrictor chokes owner". BBC News. 2006-12-18. http://news.bbc.co.uk/2/hi/americas/6191305.stm. Retrieved 2007-12-30. 
18. ^ "Komodo dragon kills boy, 8, in Indonesia". msnbc. http://www.msnbc.msn.com/id/19026658/. Retrieved 2007-12-30. 

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References

• Bebler, John L.; King, F. Wayne (1979). The Audubon Society Field Guide to Reptiles and Amphibians of North America. New York: Alfred A. Knopf. pp. 581. ISBN 0394508246. 
• Capula, Massimo; Behler (1989). Simon & Schuster's Guide to Reptiles and Amphibians of the World. New York: Simon & Schuster. ISBN 0671690981. 
• Cogger, Harold; Zweifel, Richard (1992). Reptiles & Amphibians. Sydney, Australia: Weldon Owen. ISBN 0831727861. 
• Conant, Roger; Collins, Joseph (1991). A Field Guide to Reptiles and Amphibians Eastern/Central North America. Boston, Massachusetts: Houghton Mifflin Company. ISBN 0395583896. 
• Ditmars, Raymond L (1933). Reptiles of the World: The Crocodilians, Lizards, Snakes, Turtles and Tortoises of the Eastern and Western Hemispheres. New York: Macmillian. pp. 321. 
• Freiberg, Dr. Marcos; Walls, Jerry (1984). The World of Venomous Animals. New Jersey: TFH Publications. ISBN 0876665679. 
• Gibbons, J. Whitfield; Gibbons, Whit (1983). Their Blood Runs Cold: Adventures With Reptiles and Amphibians. Alabama: University of Alabama Press. pp. 164. ISBN 978-0817301354. 
• McDiarmid, RW; Campbell, JA; Touré, T (1999). Snake Species of the World: A Taxonomic and Geographic Reference. 1. Herpetologists' League. pp. 511. ISBN 1893777006. 
• Mehrtens, John (1987). Living Snakes of the World in Color. New York: Sterling. ISBN 0806964618. 
• Rosenfeld, Arthur (1989). Exotic Pets. New York: Simon & Schuster. pp. 293. ISBN 067147654. 

External links

• Squamata

v • d • e Extant reptile orders by subclass Kingdom: Animalia · Phylum: Chordata · Subphylum: Vertebrata Anapsida Chelonia Testudines Diapsida Lepidosauromorpha Sphenodontia · Squamata Archosauromorpha Crocodilia

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