Squamata

Superregnum: Eukaryota
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Cladus: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Classis: Reptilia
Cladus: Eureptilia
Cladus: Romeriida
Subclassis: Diapsida
Cladus: Sauria
Infraclassis: Lepidosauromorpha
Superordo: Lepidosauria
Ordo: Squamata
Clades (7): Dibamia – Gekkota – Scincomorpha – Laterata – Iguania – Anguimorpha – Serpentes
[circumscription following Burbrink et al. (2020)]
Genera incertae sedis: †Chmoetokadmon – †Eolacerta – †Hongshanxi – †Jucaraseps – †Liushusaurus – †Megachirella – †Meyasaurus – †Sakurasaurus – †Scandensia – †Yabeinosaurus

Name

Squamata Oppel, 1811: 14
References
Primary references

Oppel, M. 1811. Die Ordnungen, Familien und Gattungen der Reptilien als Prodrom einer Naturgeschichte derselben. Joseph Lindauer: München. XII + 86 pp. BHL Reference page.

Additional references

Camp, C.L. 1923. Classification of the lizards. Bulletin of the American Museum of Natural History 48: 289–480. hdl: 2246/898 Open access Reference page.
Townsend, T.M., Larson, A., Louis, E. & Macey, J.R. 2004. Molecular phylogenetics of Squamata: The position of snakes, amphisbaenians, and dibamids, and the root of the squamate tree. Systematic Biology 53(5): 735–757. DOI: 10.1080/10635150490522340 Open access Reference page.
Vidal, N. & Hedges, S.B. 2005. The phylogeny of squamate reptiles (lizards, snakes, and amphisbaenians) inferred from nine nuclear protein-coding genes. Comptes Rendus Biologies 328(10–11): 1000–1008. DOI: 10.1016/j.crvi.2005.10.001 Paywall Reference page.
Conrad, J.L. 2008. Phylogeny and systematics of squamata (Reptilia) based on morphology . Bulletin of the American Museum of Natural History 310: 1–182. hdl: 2246/5915 Open access Reference page.
Vidal, N. & Hedges, S.B. 2009. The molecular evolutionary tree of lizards, snakes, and amphisbaenians. Comptes Rendus Biologies 332(2-3): 129–139. DOI: 10.1016/j.crvi.2008.07.010 Open access Reference page.
Wiens, J.J., Kuczynski, C.A., Townsend, T., Reeder, T.W., Mulcahy, D.G. & Sites Jr., J.W. 2010. Combining Phylogenomics and Fossils in Higher-Level Squamate Reptile Phylogeny: Molecular Data Change the Placement of Fossil Taxa. Systematic Biology 59(6): 674–688. DOI: 10.1093/sysbio/syq048 Open access Reference page.
Losos, J.B., Hillis, D.M. & Greene, H.W. 2012. Evolution. Who speaks with a forked tongue? Science 338(6113): 1428–1429. DOI: 10.1126/science.1232455 Paywall Reference page.
Gauthier, J.A., Kearney, M., Maisano, J.A., Rieppel, O. & Behlke, A.D.B. 2012. Assembling the Squamate Tree of Life: Perspectives from the Phenotype and the Fossil Record. Bulletin of the Peabody Museum of Natural History 53(1): 3–308. DOI: 10.3374/014.053.0101 Paywall Reference page.
Wiens, J.J., Hutter, C.R., Mulcahy, D.G., Noonan, B.P., Townsend, T.M., Sites, J.W. & Reeder, T.W. 2012. Resolving the phylogeny of lizards and snakes (Squamata) with extensive sampling of genes and species. Biology Letters 8(6): 1043–1046. DOI: 10.1098/rsbl.2012.0703 Open access Reference page.
Pyron, R.A., Burbrink, F.T. & Wiens, J.J. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology 13: 93. DOI: 10.1186/1471-2148-13-93 Open access Reference page.
Reeder, T.W., Townsend, T.M., Mulcahy, D.G., Noonan, B.P., Wood Jr., P.L., Sites Jr., J.W. & Wiens, J.J. 2015. Integrated analyses resolve conflicts over squamate reptile phylogeny and reveal unexpected placements for fossil taxa. PLoS One 10: e0118199. DOI: 10.1371/journal.pone.0118199 Open access Reference page.
Zheng, Y. & Wiens, J.J. 2016. Combining phylogenomic and supermatrix approaches, and a time-calibrated phylogeny for squamate reptiles (lizards and snakes) based on 52 genes and 4162 species. Molecular Phylogenetics and Evolution 94(Part B): 537–547. DOI: 10.1016/j.ympev.2015.10.009 Paywall Reference page.
Pyron, R.A. 2017. Novel Approaches for Phylogenetic Inference from Morphological Data and Total-Evidence Dating in Squamate Reptiles (Lizards, Snakes, and Amphisbaenians). Systematic Biology 66(1): 38–56. DOI: 10.1093/sysbio/syw068 Open access Reference page.
Streicher, J.W. & Wiens, J.J. 2017. Phylogenomic analyses of more than 4000 nuclear loci resolve the origin of snakes among lizard families. Biology Letters 13(9): 20170393. DOI: 10.1098/rsbl.2017.0393 Open access Reference page.
Burbrink, F.T., Grazziotin, F.G., Pyron, R.A., Cundall, D., Donnellan, S., Irish, F., Keogh, J.S., Kraus, F., Murphy, R.W., Noonan, B., Raxworthy, C.J., Ruane, S., Lemmon, A.R., Lemmon, E.M. & Zaher, H. 2020. Interrogating Genomic-Scale Data for Squamata (Lizards, Snakes, and Amphisbaenians) Shows no Support for Key Traditional Morphological Relationships. Systematic Biology 69(3): 502–520. DOI: 10.1093/sysbio/syz062 Open access Reference page.

Vernacular names
беларуская: Лускаватыя
čeština: Šupinatí
Deutsch: Schuppenkriechtiere
English: Scaled Reptiles
español: Escamosos
français: Squamates
magyar: Pikkelyesbőrűek
հայերեն: Թեփուկավորներ
日本語: 有鱗目
한국어: 유린목(有鱗目), 뱀목
norsk: Skjellkrypdyr
polski: Łuskonośne
português: Escamados
русский: Чешуйчатые
Türkçe: Pullular
українська: Лускаті

Squamata (/skwæˈmeɪtə/, Latin squamatus (“scaly, having scales”)) is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species,[3] it is also the second-largest order of extant (living) vertebrates, after the perciform fish. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making possible movement of the upper jaw relative to the neurocranium. This is particularly visible in snakes, which are able to open their mouths very wide to accommodate comparatively large prey. Squamata is the most variably sized order of reptiles, ranging from the 16 mm (0.63 in) dwarf gecko (Sphaerodactylus ariasae) to the 5.21 m (17.1 ft) green anaconda (Eunectes murinus) and the now-extinct mosasaurs, which reached lengths over 14 m (46 ft).

Among other reptiles, squamates are most closely related to the tuatara, which superficially resembles lizards.

Evolution
Slavoia darevskii, a fossil squamate

Squamates are a monophyletic sister group to the rhynchocephalians, members of the order Rhynchocephalia. The only surviving member of the Rhynchocephalia is the tuatara. Squamata and Rhynchocephalia form the subclass Lepidosauria, which is the sister group to the Archosauria, the clade that contains crocodiles and birds, and their extinct relatives. Fossils of rhynchocephalians first appear in the Early Triassic, meaning that the lineage leading to squamates must have also existed at the time.[4] Scientists believe crown group squamates probably originated in the Early Jurassic based on the fossil record.[4] The first fossils of geckos, skinks, and snakes appear in the Middle Jurassic.[5] Other groups like iguanians and varanoids appeared in the Cretaceous. Polyglyphanodontia, an extinct clade of lizards, and mosasaurs, a group of predatory marine lizards that grew to enormous sizes, also appeared in the Cretaceous.[6] Squamates suffered a mass extinction at the Cretaceous–Paleogene (K–PG) boundary, which wiped out polyglyphanodontians, mosasaurs, and many other distinct lineages.[7]

The relationships of squamates is debatable. Although many of the groups originally recognized on the basis of morphology are still accepted, understanding of their relationships to each other has changed radically as a result of studying their genomes. Iguanians were long thought to be the earliest crown group squamates based on morphological data,[6] but genetic data suggest that geckoes are the earliest crown group squamates.[8] Iguanians are now united with snakes and anguimorphs in a clade called Toxicofera. Genetic data also suggest that the various limbless groups - snakes, amphisbaenians, and dibamids - are unrelated, and instead arose independently from lizards.

A study in 2018 found that Megachirella, an extinct genus of lepidosaurs that lived about 240 million years ago during the Middle Triassic, was a stem-squamate, making it the oldest known squamate. The phylogenetic analysis was conducted by performing high-resolution microfocus X-ray computed tomography (micro-CT) scans on the fossil specimen of Megachirella to gather detailed data about its anatomy. These data were then compared with a phylogenetic dataset combining the morphological and molecular data of 129 extant and extinct reptilian taxa. The comparison revealed Megachirella had certain features that are unique to squamates. The study also found that geckos are the earliest crown group squamates, not iguanians.[9][10]
Reproduction
See also: Sexual selection in scaled reptiles
Trachylepis maculilabris skinks mating

The male members of the group Squamata have hemipenes, which are usually held inverted within their bodies, and are everted for reproduction via erectile tissue like that in the mammalian penis.[11] Only one is used at a time, and some evidence indicates that males alternate use between copulations. The hemipenis has a variety of shapes, depending on the 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 that seals as the erectile tissue expands. This is also the only reptile group in which both viviparous and ovoviviparous species are found, as well as the usual oviparous reptiles. Some species, such as the Komodo dragon, can reproduce asexually through parthenogenesis.[12]
The Japanese striped snake has been studied in sexual selection.

Studies have been conducted on how sexual selection manifests itself in snakes and lizards. Snakes use a variety of tactics in acquiring mates.[13][dubious – discuss] Ritual combat between males for the females with which they want to mate includes topping, a behavior exhibited by most viperids, in which one male twists around the vertically elevated fore body of his opponent and forcing it downward. Neck biting commonly occurs while the snakes are entwined.[14]
Facultative parthenogenesis
The effects of central fusion and terminal fusion on heterozygosity

Parthenogenesis is a natural form of reproduction in which the growth and development of embryos occur without fertilization. Agkistrodon contortrix (copperhead snake) and Agkistrodon piscivorus (cottonmouth snake) can reproduce by facultative parthenogenesis; they are capable of switching from a sexual mode of reproduction to an asexual mode.[15] The type of parthenogenesis that likely occurs is automixis with terminal fusion (see figure), a process in which two terminal products from the same meiosis fuse to form a diploid zygote. This process leads to genome-wide homozygosity, expression of deleterious recessive alleles, and often to developmental abnormalities. Both captive-born and wild-born A. contortrix and A. piscivorus appear to be capable of this form of parthenogenesis.[15]

Reproduction in squamate reptiles is ordinarily sexual, with males having a ZZ pair of sex-determining chromosomes, and females a ZW pair. However, the Colombian rainbow boa, Epicrates maurus, can also reproduce by facultative parthenogenesis, resulting in production of WW female progeny.[16] The WW females are likely produced by terminal automixis.
Inbreeding avoidance

When female sand lizards mate with two or more males, sperm competition within the female's reproductive tract may occur. Active selection of sperm by females appears to occur in a manner that enhances female fitness.[17] On the basis of this selective process, the sperm of males that are more distantly related to the female are preferentially used for fertilization, rather than the sperm of close relatives.[17] This preference may enhance the fitness of progeny by reducing inbreeding depression.
Evolution of venom
Main article: Evolution of snake venom
See also: Venom

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 clades Caenophidia, Anguimorpha, and Iguania, and has been shown to have evolved a single time along these lineages before the three groups diverged, because all lineages share nine common toxins.[18] The fossil record shows the divergence between anguimorphs, iguanians, and advanced snakes dates back roughly 200 million years ago (Mya) to the Late Triassic/Early Jurassic,[18] but the only good fossil evidence is from the Middle Jurassic.[1]

Snake 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.[19] Previous literature hypothesized that venoms were modifications of salivary or pancreatic proteins,[20] but different toxins have been found to have been recruited from numerous different protein bodies and are as diverse as their functions.[21]

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,[22] which leads to a diversification of toxins that allows the ambush predators the ability to attack a wide range of prey.[23] The rapid evolution and diversification is thought to be the result of a predator–prey evolutionary arms race, where both are adapting to counter the other.[24]
Humans and squamates
Bites and fatalities
See also: Snakebite
Map showing the global distribution of venomous snakebites

An estimated 125,000 people a year die from venomous snake bites.[25] In the US alone, more than 8,000 venomous snake bites are reported each year, but only one in 50 million people (five or six fatalities per year in the USA) will die from venomous snake bites.[26][27]

Lizard bites, unlike venomous snake bites, are usually 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 that 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.[28] The Gila monster and beaded lizards of North and Central America are venomous, but not deadly to humans.
Conservation

Though they survived the Cretaceous–Paleogene extinction event, many squamate species are now endangered due to habitat loss, hunting and poaching, illegal wildlife trading, alien species being introduced to their habitats (which puts native creatures at risk through competition, disease, and predation), and other anthropogenic causes. Because of this, some squamate species have recently become extinct, with Africa having the most extinct species. Breeding programs and wildlife parks, though, are trying to save many endangered reptiles from extinction. Zoos, private hobbyists, and breeders help educate people about the importance of snakes and lizards.
Classification and phylogeny
Desert iguana from Amboy Crater, Mojave Desert, California

Historically, the order Squamata has been divided into three suborders:

Lacertilia, the lizards
Serpentes, the snakes (see also Ophidia)
Amphisbaenia, the worm lizards

Of these, the lizards form a paraphyletic group,[29] since "lizards" excludes the subclades of snakes and amphisbaenians. Studies of squamate relationships using molecular biology have found several distinct lineages, though the specific details of their interrelationships vary from one study to the next. One example of a modern classification of the squamates is[2][30]

Squamata

Dibamia Dibamidae   Bifurcata Gekkota Pygopodomorpha   Diplodactylidae Underwood 1954       Pygopodidae Boulenger 1884     Carphodactylidae       Gekkomorpha   Eublepharidae   Gekkonoidea   Sphaerodactylidae Underwood 1954       Phyllodactylidae     Gekkonidae           Unidentata Scinciformata Scincomorpha Scincidae   Cordylomorpha   Xantusiidae       Gerrhosauridae     Cordylidae         Episquamata Laterata Teiformata   Gymnophthalmidae Merrem 1820     Teiidae Gray 1827     Lacertibaenia Lacertiformata Lacertidae   Amphisbaenia   Rhineuridae Vanzolini 1951       Bipedidae Taylor 1951         Blanidae Kearney & Stuart 2004     Cadeidae Vidal & Hedges 2008         Trogonophidae Gray 1865     Amphisbaenidae Gray 1865               Toxicofera   Anguimorpha Paleoanguimorpha Shinisauria Shinisauridae Ahl 1930 sensu Conrad 2006   Varanoidea   Lanthanotidae     Varanidae       Neoanguimorpha Helodermatoidea Helodermatidae Gray 1837     Xenosauroidea Xenosauridae   Anguioidea   Diploglossidae       Anniellidae     Anguidae Gray 1825             Iguania Acrodonta   Chamaeleonidae     Agamidae Gray 1827     Pleurodonta   Leiocephalidae       Iguanidae         Hoplocercidae Frost & Etheridge 1989       Crotaphytidae     Corytophanidae           Tropiduridae         Phrynosomatidae       Dactyloidae     Polychrotidae           Liolaemidae       Leiosauridae     Opluridae                     Serpentes Scolecophidia   Leptotyphlopidae Stejneger 1892       Gerrhopilidae Vidal et al. 2010       Xenotyphlopidae Vidal et al. 2010     Typhlopidae Merrem 1820             Anomalepididae   Alethinophidia Amerophidia   Aniliidae     Tropidophiidae Brongersma 1951     Afrophidia Booidea     Uropeltidae       Anomochilidae     Cylindrophiidae             Xenopeltidae Bonaparte 1845       Loxocemidae     Pythonidae Fitzinger 1826           Boidae       Xenophidiidae     Bolyeriidae Hoffstetter 1946           Caenophidia   Acrochordidae Bonaparte 1831       Xenodermidae   Colubroidea   Pareidae       Viperidae   Proteroglypha   Homalopsidae       Colubridae       Lamprophiidae     Elapidae

 

All recent molecular studies[18] suggest that several groups form a venom clade, which encompasses a majority (nearly 60%) of squamate species. Named Toxicofera, it combines the groups Serpentes (snakes), Iguania (agamids, chameleons, iguanids, etc.), and Anguimorpha (monitor lizards, Gila monster, glass lizards, etc.).[18]
List of extant families

The over 10,900 extant squamates are divided into 60 families.
Amphisbaenia

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)
Blanidae	Mediterranean worm lizards	Mediterranean worm lizard (Blanus cinereus)
Cadeidae Vidal & Hedges, 2008[31]	Cuban worm lizards	Cadea blanoides
Rhineuridae Vanzolini, 1951	North American worm lizards	North American worm lizard (Rhineura floridana)
Trogonophidae Gray, 1865	Palearctic worm lizards	Checkerboard worm lizard (Trogonophis wiegmanni)
Gekkota (geckos, incl. Dibamia)
Family	Common names	Example species	Example photo
Carphodactylidae Kluge, 1967	Southern padless geckos	Thick-tailed gecko (Underwoodisaurus milii)
Dibamidae Boulenger, 1884	Blind lizards	Dibamus nicobaricum
Diplodactylidae Underwood, 1954	Australasian geckos	Golden-tailed gecko (Strophurus taenicauda)
Eublepharidae Boulenger, 1883	Eyelid geckos	Common leopard gecko (Eublepharis macularius)
Gekkonidae Gray, 1825	Geckos	Madagascar giant day gecko (Phelsuma grandis)
Phyllodactylidae Gamble et al., 2008	Geckos	Moorish gecko (Tarentola mauritanica)
Pygopodidae Boulenger, 1884	Flap-footed lizards	Burton's snake lizard (Lialis burtonis)
Sphaerodactylidae Underwood, 1954	Geckos	Fantastic least gecko (Sphaerodactylus fantasticus)
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)
Dactyloidae Fitzinger, 1843	Anoles	Carolina anole (Anolis carolinensis)
Hoplocercidae Frost & Etheridge, 1989	Wood lizards or clubtails	Enyalioides binzayedi
Iguanidae	Iguanas	Marine iguana (Amblyrhynchus cristatus)
Leiocephalidae Frost & Etheridge, 1989	Curly-tailed lizards	Hispaniolan masked curly-tailed lizard (Leiocephalus personatus)
Leiosauridae Frost et al., 2001	Leiosaurid lizards	Enyalius bilineatus
Liolaemidae Frost & Etheridge, 1989	Swifts	Shining tree iguana (Liolaemus nitidus)
Opluridae Frost & Etheridge, 1989	Malagasy iguanas	Chalarodon madagascariensis
Phrynosomatidae Frost & Etheridge, 1989	Earless, spiny, tree, side-blotched and horned lizards	Greater earless lizard (Cophosaurus texanus)
Polychrotidae Frost & Etheridge, 1989	Bush anoles	Brazilian bush anole (Polychrus acutirostris)
Tropiduridae Frost & Etheridge, 1989	Neotropical ground lizards	Microlophus peruvianus
Lacertoidea (excl. Amphisbaenia)
Family	Common Names	Example Species	Example Photo
Alopoglossidae Goicoechea, Frost, De la Riva, Pellegrino, Sites Jr., Rodrigues, & Padial, 2016	Alopoglossid lizards	Alopoglossus vallensis
Gymnophthalmidae Fitzinger, 1826	Spectacled lizards	Bachia bicolor
Lacertidae Oppel, 1811	Wall lizards	Ocellated lizard (Lacerta lepida)
Teiidae	Tegus and whiptails	Gold tegu (Tupinambis teguixin)
Neoanguimorpha
Family	Common names	Example species	Example photo
Anguidae Oppel, 1811	Glass lizards, alligator lizards and slowworms	Slowworm (Anguis fragilis)
Anniellidae Gray, 1852	American legless lizards	California legless lizard (Anniella pulchra)
Helodermatidae	Beaded lizards	Gila monster (Heloderma suspectum)
Xenosauridae Cope, 1866	Knob-scaled lizards	Mexican knob-scaled lizard (Xenosaurus grandis)
Paleoanguimorpha or Varanoidea
Family	Common names	Example species	Example photo
Lanthanotidae	Earless monitor	Earless monitor (Lanthanotus borneensis)
Shinisauridae	Chinese crocodile lizard	Chinese crocodile lizard (Shinisaurus crocodilurus)
Varanidae	Monitor lizards	Perentie (Varanus giganteus)
Scincoidea
Family	Common Names	Example Species	Example Photo
Cordylidae	Girdled lizards	Girdle-tailed lizard (Cordylus warreni)
Gerrhosauridae	Plated lizards	Sudan plated lizard (Gerrhosaurus major)
Scincidae Oppel, 1811	Skinks	Western blue-tongued skink (Tiliqua occipitalis)
Xantusiidae	Night lizards	Granite night lizard (Xantusia henshawi)
Alethinophidia
Family	Common names	Example species	Example photo
Acrochordidae Bonaparte, 1831[32]	File snakes	Marine file snake (Acrochordus granulatus)
Aniliidae Stejneger, 1907[33]	Coral pipe snakes	Burrowing false coral (Anilius scytale)
Anomochilidae Cundall, Wallach and Rossman, 1993.[34]	Dwarf pipe snakes	Leonard's pipe snake, (Anomochilus leonardi)
Boidae Gray, 1825[32] (incl. Calabariidae)	Boas	Amazon tree boa (Corallus hortulanus)
Bolyeriidae Hoffstetter, 1946	Round Island boas	Round Island burrowing boa (Bolyeria multocarinata)
Colubridae Oppel, 1811[32] sensu lato (incl. Dipsadidae, Natricidae, Pseudoxenodontidae)	Colubrids	Grass snake (Natrix natrix)
Cylindrophiidae Fitzinger, 1843	Asian pipe snakes	Red-tailed pipe snake (Cylindrophis ruffus)
Elapidae Boie, 1827[32]	Cobras, coral snakes, mambas, kraits, sea snakes, sea kraits, Australian elapids	King cobra (Ophiophagus hannah)
Homalopsidae Bonaparte, 1845	Indo-Australian water snakes, mudsnakes, bockadams	New Guinea bockadam (Cerberus rynchops)
Lamprophiidae Fitzinger, 1843[35]	Lamprophiid snakes	Bibron's burrowing asp (Atractaspis bibroni)
Loxocemidae Cope, 1861	Mexican burrowing snakes	Mexican burrowing snake (Loxocemus bicolor)
Pareidae Romer, 1956	Pareid snakes	Perrotet's mountain snake (Xylophis perroteti)
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[32]	Vipers, pitvipers, rattlesnakes	European asp (Vipera aspis)
Xenodermidae Fitzinger, 1826	Odd-scaled snakes and relatives	Khase earth snake (Stoliczkia khasiensis)
Xenopeltidae Gray, 1849	Sunbeam snakes	Sunbeam snake (Xenopeltis unicolor)
Scolecophidia (incl. Anomalepidae)
Family	Common names	Example species	Example photo
Anomalepidae Taylor, 1939[32]	Dawn blind snakes	Dawn blind snake (Liotyphlops beui)
Gerrhopilidae Vidal et al., 2010[31]	Indo-Malayan blindsnakes	Andaman worm snake (Gerrhopilus andamanensis)	–
Leptotyphlopidae Stejneger, 1892[32]	Slender blind snakes	Texas blind snake (Leptotyphlops dulcis)
Typhlopidae Merrem, 1820[36]	Blind snakes	European blind snake (Typhlops vermicularis)
Xenotyphlopidae Vidal et al., 2010[31]	Malagasy blind snakes	Xenotyphlops grandidieri	–

–

References

Hutchinson, M. N.; Skinner, A.; Lee, M. S. Y. (2012). "Tikiguania and the antiquity of squamate reptiles (lizards and snakes)". Biology Letters. 8 (4): 665–669. doi:10.1098/rsbl.2011.1216. PMC 3391445. PMID 22279152.
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Further reading

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 978-0-394-50824-5.
Capula, Massimo; Behler (1989). Simon & Schuster's Guide to Reptiles and Amphibians of the World. New York: Simon & Schuster. ISBN 978-0-671-69098-4.
Cogger, Harold; Zweifel, Richard (1992). Reptiles & Amphibians. Sydney: Weldon Owen. ISBN 978-0-8317-2786-4.
Conant, Roger; Collins, Joseph (1991). A Field Guide to Reptiles and Amphibians Eastern/Central North America. Boston, Massachusetts: Houghton Mifflin Company. ISBN 978-0-395-58389-0.
Ditmars, Raymond L (1933). Reptiles of the World: The Crocodilians, Lizards, Snakes, Turtles and Tortoises of the Eastern and Western Hemispheres. New York: Macmillan. p. 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 (4): 513–551. doi:10.1017/S1464793103006134. PMID 14700390. S2CID 4845536.
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). Ithaca, 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. Lecture Notes in Earth Sciences. Vol. 132. pp. 27–44. doi:10.1007/978-3-642-10311-7_2. ISBN 978-3-642-10310-0.
Freiberg, Dr. Marcos; Walls, Jerry (1984). The World of Venomous Animals. New Jersey: TFH Publications. ISBN 978-0-87666-567-1.
Gibbons, J. Whitfield; Gibbons, Whit (1983). Their Blood Runs Cold: Adventures With Reptiles and Amphibians. Alabama: University of Alabama Press. pp. 164. ISBN 978-0-8173-0135-4.
McDiarmid, RW; Campbell, JA; Touré, T (1999). Snake Species of the World: A Taxonomic and Geographic Reference. Vol. 1. Herpetologists' League. p. 511. ISBN 978-1-893777-00-2.
Mehrtens, John (1987). Living Snakes of the World in Color. New York: Sterling. ISBN 978-0-8069-6461-4.
Rosenfeld, Arthur (1989). Exotic Pets. New York: Simon & Schuster. p. 293. ISBN 978-0-671-47654-0.