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-millimetre (0.63 in) dwarf gecko (Sphaerodactylus ariasae) to the 8-metre (26 ft) green anaconda (Eunectes murinus) and the now-extinct mosasaurs, which reached lengths of 14 metres (46 ft).
Squamates are a monophyletic 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 midd
le Jurassic period, but a mitochondrial phylogeny suggests 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.[1] Because snakes have a faster molecular clock than other squamates,[1] and there are few early snake and snake ancestor fossils,[2] it is difficult to resolve the relationship between snakes and other squamate groups.
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.[3] 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 it 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 e
nclosed 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, such as the komodo dragon, can actually reproduce asexually and undergo parthenogenesis.[4]
Recent research suggests 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 Caenophidia, Anguimorpha, and Iguania, and has been shown to have evolved a single time along these lineages before the three families diverged, because all lineages share nine common toxins.[5] The fossil record shows the divergence between anguimorphs, iguanians, and advanced snakes dates back roughly 200 Mya to the Late Triassic/Early Jurassic.[5]
Hnake venom has been shown to have evolved via a process by which a gene encoding for a normal body protein, typically one involved in key regulatory processes or bioactivity, is duplicated, and the copy is selectively expressed in the venom gland.[6] Previous literature hypothesized venoms were modifications of salivary or pancreatic proteins,[7] but it has been discovered that different toxins have been recruited from numerous different protein bodies and are diverse as the functions themselves.[8]
Natural selection has driven the origination and diversification of the toxins to counter the defenses of their prey. Once toxins have been recruited into the venom proteome, they form large multigene families and evolve via the birth-and-death model of protein evolution,[9] which leads to a diversification of toxins that allows the sit-and-wait predators the ability to attack a wide range of prey.[10] It has been hypothesized that the rapid evolution and diversification is the result of a prey/predator arms race where both are adapting to counter the other.[11]
Map showing global distribution of snakebite morbidity
An estimated 125,000 people a year die from venomous snake bites.[12] In the US alone, more than 8,000 venomous snake bites are reported each year.[13] In addition, large pet constrictors, such as boas and pythons, have been known to kill humans through constriction on rare occasions.[14]
Lizard bites, unlike venomous snake bites, are not fatal. The komodo dragon has been kn
own to kill people due to its size, and recent studies show it may have a passive envenomation system. Recent studies also show the close relatives of the komodo, the monitor lizards, all have a similar envenomation system, but the toxicity of the bites is relatively low to humans.[15]
Conservation
Though they survived the worst changes in Earth's history, many squamate species are endangered now due to habitat loss, hunting and poaching, the pet trade, alien species being introduced to their habitats (which puts native creatures at risk through competition, disease, and 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 and breeders educate people about the importance of snakes and lizards.
Desert iguana from Amboy Crater, Mojave Desert, California
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 (since "lizards" excludes the subclade of snakes). 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[16] suggests 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[16]:
Desert iguana from Amboy Crater, Mojave Desert, California
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 (since "lizards" excludes the subclade of snakes). 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 Amph
isbaenia ? 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[16] suggests 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[16]:
^ ab Kumazawa, Yoshinori (2007). "Mitochondrial genomes from major lizard families suggest their phylogenetic relationships and ancient radiations". Gene388 (1-2): 19?26. doi:10.1016/j.gene.2006.09.026. PMID 17118581.
^ ab Fry, B. G., N. Vidal, J. A. Norman, F. J. Vonk, H. Scheib, S. F. R. Ramjan, S. Kuruppu. 2006. Early evolution of the venom system in lizards and snakes. Nature 439:584-588.
^ Fry, B. G., N. Vidal, L. van der Weerd, E. Kochva, and C. Renjifo. 2009. Evolution and diversification of the toxicofera reptile venom system.Journal of Proteomics 72:127-136.
^ Kochva, E. 1987. The origin of snakes and evolution of the venom apparatus. Toxicon 25:65-106.
^ Fry, B.G. 2005. From genome to "Venome": Molecular origin and evolution of the snake venom proteome inferred from phylogenetic analysis of toxin sequences and related body proteins. Genome Research 15:403-420.
^ Fry, B. G., H. Scheib, L. van der Weerd, B. Young, J. McNaughtan, S. F. R. Ramjan, N. Vidal. 2008. Evolution of an arsenal. Molecular & Cellular Proteomics 7:215-246.
^ Calvete, J. J., L. Sanz, Y. Angulo, B. Lomonte, and J. M. Gutierrez. 2009. Venoms, venomics, antivenomics. Febs Letters 583:1736-1743.
^ Barlow, A., C. E. Pook, R. A. Harrison, and W. Wuster. 2009. Coevolution of diet and prey-specific venom activity supports the role of selection in snake venom evolution. Proceedings of the Royal Society B-Biological Sciences 276:2443-2449.
a href="#cite_note-2">[3] 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 it 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, such as the komodo dragon, can actually reproduce asexually and undergo parthenogenesis.[4]
Recent research suggests 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 Caenophidia, Anguimorpha, and Iguania, and has been shown to have evolved a single time along these lineages before the three families diverged, because all lineages share nine common toxins.[5] The fossil record shows the divergence between anguimorphs, iguanians, and advanced snakes dates back roughly 200 Mya to the Late Triassic/Early Jurass
ic.[5]
Hnake venom has been shown to have evolved via a process by which a gene encoding for a normal body protein, typically one involved in key regulatory processes or bioactivity, is duplicated, and the copy is selectively expressed in the venom gland.[6] Previous literature hypothesized venoms were modifications of salivary or pancreatic proteins,[7] but it has been discovered that different toxin
s have been recruited from numerous different protein bodies and are diverse as the functions themselves.[8]
Natural selection has driven the origination and diversification of the toxins to counter the defenses of their prey. Once toxins have been recruited into the venom proteome, they form large multigene families and evolve via the birth-and-death model of protein evolution,[9] which leads to a diversification of toxins that allows the sit-and-wait predators the ability to attack a wide range of prey.[10] It has been hypothesized that the rapid evolution and diversification is the result of a prey/predator arms race where both are adapting to counter the other.[11]
Map showing global distribution of snakebite morbidity
An
estimated 125,000 people a year die from venomous snake bites.[12] In the US alone, more than 8,000 venomous snake bites are reported each year.[13] In addition, large pet constrictors, such as boas and pythons, have been known to kill humans through constriction on rare occasions.[14]
Lizard bites, unlike venomous snake bites, are not fatal. The komodo dragon has been known to kill people due to its size, and recent studies show it may have a passive envenomation system. Recent studies also show the close relatives of the komodo, the monitor lizards, all have a similar envenomation system, but the toxicity of the bites is relatively low to humans.[15]
Conservation
Though they survived the worst ch
anges in Earth's history, many squamate species are endangered now due to habitat loss, hunting and poaching, the pet trade, alien species being introduced to their habitats (which puts native creatures at risk through competition, disease, and 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 and breeders educate people about the importance of snakes and lizards.
Desert iguana from Amboy Crater, Mojave Desert, California
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 (since "lizards" excludes the subclade of snakes). 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[16] suggests 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[16]:
Desert iguana from Amboy Crater, Mojave Desert, California
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 (since "lizards" excludes the subclade of snakes). 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[16] suggests several fam
ilies 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[16]:
^ ab Kumazawa, Yoshinori (2007). "Mitochondrial genomes from major lizard families suggest their phylogenetic relationships and ancient radiations". Gene388 (1-2): 19?26. doi:10.1016/j.gene.2006.09.026. PMID 17118581.
^ ab Fry, B. G., N. Vidal, J. A. N
orman, F. J. Vonk, H. Scheib, S. F. R. Ramjan, S. Kuruppu. 2006. Early evolution of the venom system in lizards and snakes. Nature 439:584-588.
^ Fry, B. G., N. Vidal, L. van der Weerd, E. Kochva, and C. Renjifo. 2009. Evolution and diversification of the toxicofera reptile venom system.Journal of Proteomics 72:127-136.
^ Kochva, E. 1987. The origin of snakes and evolution of the venom apparatus. Toxicon 25:65-106.
^ Fry, B.G. 2005. From genome to "Venome": Molecular origin and evolution of the snake venom proteome inferred from phylogenetic analysis of toxin sequences and related body proteins. Genome Research 15:403-420.
^ Fry, B. G., H. Scheib, L. van der Weerd, B. Young, J. McNaughtan, S. F. R. Ramjan, N. Vidal. 2008. Evolution of an arsenal. Molecular & Cellular Proteomics 7:215-246.
^ Calvete, J. J., L. Sanz, Y. Angulo, B. Lomonte, and J. M. Gutierrez. 2009. Venoms, venomics, antivenomics. Febs Letters 583:1736-1743.
^ Barlow, A., C. E. Pook, R. A. Harrison, and W.
Wuster. 2009. Coevolution of diet and prey-specific venom activity supports the role of selection in snake venom evolution. Proceedings of the Royal Society B-Biological Sciences 276:2443-2449.
Bebler, John L.; King, F. Wayne (1979). The Audubon Society Field Guide to Reptiles and Amphibians of North Am
erica. 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.
Evans SE. 2003. At the feet of the dinosaurs: the origin, evolution and early diversification of squamate reptiles (Lepidosauria: Diapsida). Biological Reviews, Cambridge 78: 513?551. DOI: 10.1017/S14647931030
06134
Evans SE. 2008. The skull of lizards and tuatara. In Biology of the Reptilia, Vol.20, Morphology H: the skull of Lepidosauria, Gans C, Gaunt A S, Adler K. (eds). Ithica, New York, Society for the study of Amphibians and Reptiles. pp1?344. Weblink to purchase
Evans SE, Jones MEH. 2010. The origin, early history and diversification of lepidosauromorph reptiles. In Bandyopadhyay S. (ed.), New Aspects of Mesozoic Biodiversity, 27 Lecture Notes in Earth Sciences 132, 27-44. DOI 10.1007/978-3-642-10311-7_2
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; Tour?, T (1999). Snake Species of the World: A Taxonomic and Geographic Reference. 1. Herp
etologists' 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.
The Acrochordidae are a monotypic family created for the genus Acrochordus. This is a group of primitive aquatic snakes found in Australia and Indonesia. Currently, 3 species are recognized. [more]
Agamidae
Agamids, lizards of the family Agamidae, include more than 300 species in Africa, Asia, Australia, and a few in Southern Europe. Many species are commonly called dragons or dragon lizards. [more]
Aigialosauridae
Aigialosauridae (Greek, aigialos = "seashore" + sauros= lizard) is family of Late Cretaceous semi-aquatic varanoid lizards, regarded by some paleontologists to form distinct monophyletic group and by others as an adaptive grade within the basal mosasauroids. [more]
Amphisbaenia
The Amphisbaenia (or worm lizards) are a usually legless suborder of squamates closely related to lizards and snakes, comprising over 130 extant species. As many species possess a pink body coloration and scales arranged in rings, they have a superficial resemblance to earthworms. They are very poorly understood, due to their burrowing lifestyle and general rarity. Most species are found in Africa and South America, with a few in other parts of the world. Little is known of them outside of their anatomy, and even that is difficult to study due to the mechanics of dissecting something so small. Most species are less than 6 inches (150 mm) long. [more]
Amphisbaenidae
The Amphisbaenidae are a family of amphisbaenians, commonly known as worm lizards. They are found in North and South America, some Caribbean islands, and in sub-Saharan Africa. One deep branching and somewhat aberrant genus, Blanus, is native to Europe, and may represent a distinct family. [more]
Anguidae
Anguidae is a large and diverse family of lizards native to the northern hemisphere. The group includes the slowworms, glass lizards, and alligator lizards, among others. Anguidae is divided into three subfamilies and contains 94 species in eight genera. Their closest living relatives are the helodermatid lizards. They have hard osteoderms beneath their scales, and many of the species have reduced or absent limbs, giving them a snake-like appearance, although others are fully limbed. [more]
Aniliidae
The Aniliidae are a monotypic family created for the monotypic genus Anilius that contains the species A. scytale, found in South America. This snake possesses a vestigial pelvic girdle that is visible as a pair of cloacal spurs. It is ovoviviparous. The diet consists mainly of amphibians and other reptiles. Currently, two subspecies are recognized, including the typical form described here. [more]
Anniellidae
The family Anniellidae, known as American legless lizards contains two species in a single genus Anniella: A. pulchra, the California Legless Lizard, and the rare, A. geronimensis, Baja California Legless Lizard. [more]
The Anomalepididae are a family of nonvenomous snakes found in Central and South America. They are similar to Typhlopidae, except that some species possess a single tooth in the lower jaw. Currently, 4 genera and 15 species are recognized. [more]
Bipedidae, are a family of amphisbaenians. They are found only in Mexico. Ajolotes are carnivorous, burrowing reptiles, but unlike other species of amphisbaenian, they possess two stubby forelimbs placed far forward on the body. The shovel-like limbs are used to scrape away soil while burrowing through the soil, in a similar manner to a mole. [more]
Boidae
The Boidae are a family of nonvenomous snakes found in America, Africa, Europe, Asia and some Pacific Islands. Relatively primitive snakes, adults are medium to large in size, with females usually larger than the males. Two subfamilies comprising eight genera and 43 species are currently recognized. [more]
Bolyeridae
The Bolyeriidae are a family of snakes native to Mauritius and a few islands around it, especially Round Island. In the past they also occurred on the island of Mauritius, but were extirpated there due to human influence and foraging pigs in particular. These snakes were formerly placed in the Boidae, but are now classed as a separate family. Currently, two monotypic genera are recognized, but only a single species is extant. [more]
Bolyeriidae
The Bolyeriidae are a family of snakes native to Mauritius and a few islands around it, especially Round Island. In the past they also occurred on the island of Mauritius, but were extirpated there due to human influence and foraging pigs in particular. These snakes were formerly placed in the Boidae, but are now classed as a separate family. Currently, two monotypic genera are recognized, but only a single species is extant. [more]
Chamaeleonidae
Chameleons (family Chamaeleonidae) are a distinctive and highly specialized clade of lizards. They are distinguished by their parrot-like zygodactylous feet, their separately mobile and stereoscopic eyes, their very long, highly modified, and rapidly extrudable tongues, their swaying gait, the possession by many of a prehensile tail, crests or horns on their distinctively shaped heads, and the ability of some to change color. Uniquely adapted for climbing and visual hunting, the approximately 160 species of chameleon range from Africa, Madagascar, Spain and Portugal, across south Asia, to Sri Lanka, have been introduced to Hawaii, California and Florida, and are found in warm habitats that vary from rain forest to desert conditions. Chameleons are often kept as household pets. [more]
Cordylidae is a family of small to medium sized lizards that occur in southern and eastern Africa. They are commonly known as "Girdled", Spinytail lizards or Girdle-tail lizards. [more]
Corytophanidae
Corytophanidae is a family of lizards also called casque head lizards or helmeted lizards. They typically have well-developed head crests in the shape of a casque. This crest is a sexually dimorphic characteristic in males of Basiliscus, but is present in both sexes of Corytophanes and Laemanctus (Pough et al. 2003). In Corytophanes, these crests are used in defensive displays where the lateral aspect of the body is brought about to face a potential predator in an effort to look bigger (Pough et al. 2003). There are 9 known species of casque heads from 3 genera. [more]
The Cylindrophiidae are a monotypic family containing the genus Cylindrophis found in Asia. These are burrowing snakes and all have checkered black-and-white bellies. Currently, 8 species are recognized and no subspecies. [more]
Eublepharinae is one of five subfamilies of the Gekkonidae, or geckos. Eublepharinae has 27 species in five genera. Also called eyelid geckos, the Eublepharines have more primitive features than other geckos. In particular, their feet lack the modifications that allow most other geckos to climb sheer surfaces. Unlike other geckos, they also have movable eyelids. They are nocturnal lizards, often preying on insects and similar creatures. They lay a pair of leathery eggs, and, in at least some species, the sex of the young is determined by the temperature of incubation, as in crocodiles. [more]
Gekkonidae
Geckos are lizards belonging to the infraorder Gekkota, found in warm climates throughout the world. They range from 1.6 cm to 60 cm. [more]
Gerrhosauridae
The Gerrhosauridae is a family of lizards native to Africa and Madagascar. Also known as plated lizards, they live in a range of habitats, from rocky crevices to sand dunes. Their form is variable, with some species having four fully developed limbs, and others with vestigial hind limbs only. Most species are believed to be oviparous. [more]
Gymnophthalmidae
Gymnophthalmidae is a family of lizards, sometimes known as spectacled lizards or microteiids. They are called 'spectacled' because of their transparent lower eyelids, so they can still see with closed eyes. Like most lizards, but unlike geckos, these eyelids are movable. [more]
Hydrophiinae, also known as sea snakes, is a group of venomous elapid snakes that inhabit marine environments for most or all of their lives. Though they evolved from terrestrial ancestors, most are extensively adapted to a fully aquatic life and are unable to move on land, except for the genus Laticauda, which retain ancestral characteristics, allowing limited land movement. They are found in warm coastal waters from the Indian Ocean to the Pacific. [more]
Lacertidae is the family of the wall lizards, true lizards, or sometimes simply lacertas, which are native to Europe, Africa, and Asia. The group includes the genus Lacerta, which contains some of the most commonly seen lizard species in Europe. It is a diverse family with hundreds of species in 37 genera. [more]
Lanthanotidae
The earless monitor lizard (Lanthanotus borneensis) is a semi-aquatic, brown lizard native to northern Borneo. It is the only species in the family Lanthanotidae, a group related to the true monitor lizards, as well as to the beaded lizards. [more]
The Leptotyphlopidae (commonly called Slender Blind Snakes or Thread Snakes) are a family of snakes found in North and South America, Africa, and Asia. All are fossorial and adapted to burrowing, feeding on ants and termites. Two genera are recognized comprising eighty-seven species. [more]
Loxocemidae
The Loxocemidae are a monotypic family of snakes created for the monotypic genus Loxocemus that contains the species L. bicolor found in Central America. Loxocemidae is the smallest snake family, having just one species and one genera. No subspecies are currently recognized. [more]
Mosasaurs (from Latin Mosa meaning the 'Meuse river', and Greek sauros meaning 'lizard') are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs are now considered to be the closest relatives of snakes, due to cladistic analyses that have taken into account similarities in jaw and skull anatomies. Mosasaurs were varanoids closely related to terrestrial monitor lizards. They probably evolved from semi-aquatic squamates known as aigialosaurs, which were more similar in appearance to modern-day monitor lizards, in the Early Cretaceous. During the last 20 million years of the Cretaceous Period (Turonian-Maastrichtian), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. [more]
The Opluridae, or Madagascan iguanas, are a family of moderately sized lizards native to Madagascar. There are seven species in two genera, with most of the species being in Oplurus. The family includes species that live amongst rocks, some that live in trees, and one that inhabits sand dunes. All of the species lay eggs, and have teeth that resemble those of the true iguanas. [more]
Phrynosomatidae is a diverse family of lizards, found from Panama to the extreme south of Canada. Many members of the group are adapted to life in hot, sandy deserts, although the spiny lizards prefer rocky deserts or even relatively moist forest edges, and the short-horned lizard lives in prairie or sagebrush environments. The group includes both egg-laying and viviparous species, with the latter being more common in species living at high elevations. [more]
Polychrotidae
Polychrotidae is a family of lizards commonly known as anoles (). NCBI places the anole in subfamily Polychrotinae of the family Iguanidae. Four genera are common: Anolis, Norops, Phenacosaurus, and Polychrus. [more]
Pygopodidae
Pygopodidae (commonly known as legless lizards, snake-lizards or flap-footed lizards) is a family of squamates that have reduced or absent limbs and are related to the geckos. There are at least 35 species in two subfamilies and eight genera. They have unusually long, slender, bodies, giving them a strong resemblance to snakes. Like both snakes and most geckos, they have no eyelids, but unlike snakes, they have external ear-holes and flat, non-forked tongues. They are native to Australia and New Guinea. [more]
Pythonidae
The Pythonidae, commonly known simply as pythons, from the Greek word python (p????), are a family of nonvenomous snakes found in Africa, Asia and Australia. Among its members are some of the largest snakes in the world. Eight genera and 26 species are currently recognized. [more]
Skinks are lizards belonging to the family Scincidae. Together with several other lizard families, including Lacertidae (the "true" or wall lizards), they comprise the superfamily or infraorder Scincomorpha. With about 1200 described species, the Scincidae are the second most diverse family of lizards, exceeded only by the Gekkonidae (or geckos). [more]
The Tropidophiinae, common name dwarf boas, are a subfamily of snakes found from Mexico and the West Indies south to southeastern Brazil. These are small to medium-sized fossorial snakes, some with beautiful and striking color patterns. Currently, 4 living genera containing 22 species and one extinct genus with one species are recognized. [more]
Tropiduridae
The Tropiduridae is a family of iguanid lizards native to South America and the West Indies. Commonly known as Neotropical ground lizards, most are ground-dwelling animals, and the family includes some lizards adapted to relatively cold climates, including those of the Andes mountains and Tierra del Fuego. Several species give birth to live young. [more]
Typhlopidae
The Typhlopidae are a family of blind snakes. They are found mostly in the tropical regions of Africa, Asia, the Americas, and all mainland Australia and various islands. The rostral scale overhangs the mouth to form a shovel like burrowing structure. They live underground in burrows, and since they have no use for vision, their eyes are mostly vestigial. They have light-detecting black eyespots, and teeth occur in the upper jaw. The tail ends with a horn like scale. Most of these species are oviparous. Currently, 6 genera are recognized containing 203 species. [more]
Uropeltidae
The Uropeltidae are a family of primitive burrowing snakes endemic to southern India and Sri Lanka. The name is derived from the Greek words ura ("tail") and pelte ("shield"), indicating the presence of the large keratinous shield at the tip of the tail. Currently, 8 genera are recognized comprising 47 species. These snakes are nonvenomous. [more]
Varanidae
Varanidae is a group of lizards of the superfamily Varanoidea. The family is a group of carnivorous lizards which includes the largest living lizard, the Komodo dragon, and the crocodile monitor. Varanidae contains the living genus Varanus and a number of extinct taxa. Their closest living relatives are the anguid and helodermatid lizards. [more]
Viperidae
The Viperidae are a family of venomous snakes found all over the world, except in Antarctica, Australia, Ireland, Madagascar, Hawaii, various other isolated islands, and above the Arctic Circle. All have relatively long, hinged fangs that permit deep penetration and injection of venom. Four subfamilies are currently recognized. They are commonly known as vipers or viperids. [more]
Xantusiidae
Night lizards (family name Xantusiidae) are a group of very small, viviparous (live-bearing) lizards, averaging from less than 4 cm to over 12 cm long. The family has only three genera, with approximately 23 living species. The genera are divided by geographic range: Xantusia in southwestern North America and Baja California, Cricosaura in Cuba, and Lepidophyma, the most populous night lizard genus, in Central America. [more]
Xenopeltidae
The Xenopeltidae are a monotypic family of snakes created to the genus Xenopeltis, which is found in Southeast Asia. Its members are known for their highly iridescent scales. Currently, two species are recognized and no subspecies. [more]
Xenosauridae
The Xenosauridae is a family of lizards native to Central America and China. Also known as knob-scaled lizards, they have rounded, bumpy scales and osteoderms. Most species prefer moist or semi-aquatic habitats, although they are widespread within their native regions, with some even inhabiting semi-arid scrub environments. They are carnivorous or insectivorous, and give birth to live young. [more]
At least 20 species and subspecies belong to the Family Xenosauridae.
More info about the Family Xenosauridae may be found here.
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Map showing global distribution of snakebite morbidity