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Squamata facts for kids

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Scaled reptiles
Brown tree snake and Green anole
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Lepidosauria
Order: Squamata
Oppel, 1811
Suborders

see text

black: range of Squamata

Squamata ("scaled reptiles") is the order of reptiles which includes lizards and snakes.

Their skins have overlapping horny scales. They also have movable quadrate bones, which make 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.) Dwarf gecko (Sphaerodactylus ariasae) to the 8 m (26 ft.) Green Anaconda (Eunectes murinus).

This is the only living reptile group which has both viviparous and ovoviviparous species, as well as the usual oviparous (egg-laying) reptiles.

The Squamata does not include the Tuataras from New Zealand. They are a sister group to the squamates. The Crocodilia are much more distantly related.

Evolution

Slavoia darevskii
Slavoia darevskii, a fossil squamate

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 living 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. Because snakes have a faster molecular clock than other squamates, and there are few early snake and snake ancestor fossils, it is difficult to resolve the relationship between snakes and other squamate groups.

Evolution of venom

Recent research suggests that the evolutionary origin of venom lies deep in the squamate phylogeny. 60% of squamates are venomous Toxicofera.

Venom in the families Caenophidia, Anguimorpha, and Iguania evolved once, then the three families diverged. All three lineages share nine common toxins. The fossil record shows that the divergence between anguimorphs, iguanians, and advanced snakes dates back roughly 200 MYA to the Upper Triassic/Lower Jurassic.

Snake venom evolved by the duplication of a gene encoding for a normal regulatory or bioactivity protein. Then the copy was expressed in the venom gland.

Different toxins have been recruited from different proteins and are diverse as the functions themselves.

Natural selection has driven the diversification of the toxins to counter the defences of the prey. Venom genes form large multigene families, and evolve by protein evolution. This leads to a diversification of toxins that let sit-and-wait predators attack a wide range of prey.

The rapid evolution and diversification is the result of a prey/predator evolutionary arms race where each adapts to counter the other.

Taxonomy

Classically, the order is divided into three suborders:

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:

Classification and phylogeny

DesertIguana031611
Desert iguana from Amboy Crater, Mojave Desert, California

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

Of these, the lizards form a paraphyletic group, 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

Squamata
Dibamia

Dibamidae


Bifurcata
Gekkota
Pygopodomorpha

Diplodactylidae Underwood 1954Hoplodactylus pomarii white background.jpg




Pygopodidae Boulenger 1884The zoology of the voyage of the H.M.S. Erebus and Terror (Lialis burtonis).jpg



Carphodactylidae




Gekkomorpha

Eublepharidae


Gekkonoidea

Sphaerodactylidae Underwood 1954




Phyllodactylidae Phyllodactylus gerrhopygus 1847 - white background.jpg



Gekkonidae






Unidentata
Scinciformata
Scincomorpha

ScincidaeBilder-Atlas zur wissenschaftlich-populären Naturgeschichte der Wirbelthiere (Plate (24)) Tribolonotus novaeguineae.jpg


Cordylomorpha

Xantusiidae




GerrhosauridaeGerrhosaurus ocellatus flipped.jpg



CordylidaeIllustrations of the zoology of South Africa (Smaug giganteus).jpg





Episquamata
Laterata
Teiformata

Gymnophthalmidae Merrem 1820PZSL1851PlateReptilia06 Cercosaura ocellata.png



Teiidae Gray 1827Bilder-Atlas zur wissenschaftlich-populären Naturgeschichte der Wirbelthiere (Tupinambis teguixin).jpg



Lacertibaenia
Lacertiformata

Lacertidae Brockhaus' Konversations-Lexikon (1892) (Lacerta agilis).jpg


Amphisbaenia

Rhineuridae Vanzolini 1951




Bipedidae Taylor 1951Bilder-Atlas zur wissenschaftlich-populären Naturgeschichte der Wirbelthiere (Bipes canaliculatus).jpg





Blanidae Kearney & Stuart 2004Blanus cinereus flipped.jpg



Cadeidae Vidal & Hedges 2008





Trogonophidae Gray 1865



Amphisbaenidae Gray 1865Amphisbaena microcephalum 1847 - white background.jpg








Toxicofera

Anguimorpha
Paleoanguimorpha
Shinisauria

Shinisauridae Ahl 1930 sensu Conrad 2006


Varanoidea

Lanthanotidae



VaranidaeZoology of Egypt (1898) (Varanus griseus).png




Neoanguimorpha
Helodermatoidea

Helodermatidae Gray 1837Gila monster ncd 2012 white background.jpg



Xenosauroidea

Xenosauridae


Anguioidea

Diploglossidae




Anniellidae



Anguidae Gray 1825







Iguania
Acrodonta

ChamaeleonidaeZoology of Egypt (1898) (Chamaeleo calyptratus).jpg



Agamidae Gray 1827Haeckel Lacertilia (Chlamydosaurus kingii).jpg



Pleurodonta

Leiocephalidae




IguanidaeStamps of Germany (Berlin) 1977, Cyclura cornuta.jpg





Hoplocercidae Frost & Etheridge 1989




Crotaphytidae



Corytophanidae






Tropiduridae





Phrynosomatidae




Dactyloidae



Polychrotidae






Liolaemidae




Leiosauridae



Opluridae











Serpentes
Scolecophidia

Leptotyphlopidae Stejneger 1892Epictia tenella 1847 -white background.jpg




Gerrhopilidae Vidal et al. 2010




Xenotyphlopidae Vidal et al. 2010



Typhlopidae Merrem 1820Typhlops vermicularis3 white background.jpg







Anomalepididae


Alethinophidia
Amerophidia

Aniliidae



Tropidophiidae Brongersma 1951



Afrophidia
Booidea


UropeltidaeUropeltis ceylanica (2) flipped.jpg




Anomochilidae



CylindrophiidaeCylind resplendens Wagler white background.JPG







Xenopeltidae Bonaparte 1845




Loxocemidae



Pythonidae Fitzinger 1826Python natalensis Smith 1840 white background.jpg






BoidaeBoa Iconographia Zoologica white background.tif




Xenophidiidae



Bolyeriidae Hoffstetter 1946






Caenophidia

Acrochordidae Bonaparte 1831




Xenodermidae


Colubroidea

Pareidae




ViperidaeOur reptiles and batrachians; a plain and easy account of the lizards, snakes, newts, toads, frogs and tortoises indigenous to Great Britain (1893) (Vipera berus).jpg


Proteroglypha

Homalopsidae




ColubridaeXenochrophis piscator 1 Hardwicke white background.jpg




Lamprophiidae



ElapidaeBilder-Atlas zur wissenschaftlich-populären Naturgeschichte der Wirbelthiere (Naja naja).jpg



















List of extant families

The over 10,000 extant squamates are divided into 58 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) Bipes biporus.jpg
Blanidae Mediterranean worm lizards Mediterranean worm lizard (Blanus cinereus) Culebra Ciega - panoramio.jpg
Cadeidae
Vidal & Hedges, 2008
Cuban worm lizards Cadea blanoides
Rhineuridae
Vanzolini, 1951
North American worm lizards North American worm lizard (Rhineura floridana) Amphisbaenia 1.jpg
Trogonophidae
Gray, 1865
Palearctic worm lizards Checkerboard worm lizard (Trogonophis wiegmanni)
Gekkota (incl. Dibamia)
Family Common names Example species Example photo
Dibamidae
Boulenger, 1884
Blind lizards Dibamus nicobaricum
Gekkonidae
Gray, 1825 (paraphyletic)
Geckos Thick-tailed gecko (Underwoodisaurus milii) Underwoodisaurus milii.jpg
Pygopodidae
Boulenger, 1884
Legless lizards Burton's snake lizard (Lialis burtonis) Lialis burtonis.jpg
Iguania
Family Common names Example species Example photo
Agamidae
Spix, 1825
Agamas Eastern bearded dragon (Pogona barbata) Bearded dragon04.jpg
Chamaeleonidae
Gray, 1825
Chameleons Veiled chameleon (Chamaeleo calyptratus) Chamaelio calyptratus.jpg
Corytophanidae
Frost & Etheridge, 1989
Casquehead lizards Plumed basilisk (Basiliscus plumifrons) Plumedbasiliskcele4 edit.jpg
Crotaphytidae
Frost & Etheridge, 1989
Collared and leopard lizards Common collared lizard (Crotaphytus collaris) Collared lizard in Zion National Park.jpg
Hoplocercidae
Frost & Etheridge, 1989
Wood lizards or clubtails Enyalioides binzayedi Holotype of Enyalioides binzayedi - ZooKeys-277-069-g007-top.jpg
Iguanidae Iguanas Marine iguana (Amblyrhynchus cristatus) Marineiguana03.jpg
Leiosauridae
Frost et al., 2001
Darwin's iguana (Diplolaemus darwinii)
Liolaemidae
Frost & Etheridge, 1989
Swifts Shining tree iguana (Liolaemus nitidus) Atacama lizard1.jpg
Opluridae
Frost & Etheridge, 1989
Madagascan iguanas Chalarodon (Chalarodon madagascariensis) Chalarodon madagascariensis male.jpg
Phrynosomatidae
Frost & Etheridge, 1989
Earless, spiny, tree, side-blotched and horned lizards Greater earless lizard (Cophosaurus texanus) Reptile tx usa.jpg
Polychrotidae
Frost & Etheridge, 1989 (+ Dactyloidae)
Anoles Carolina anole (Anolis carolinensis) Anolis carolinensis.jpg
Tropiduridae
Frost & Etheridge, 1989
Neotropical ground lizards (Microlophus peruvianus) Mperuvianus.jpg
Lacertoidea (excl. Amphisbaenia)
Family Common Names Example Species Example Photo
Alopoglossidae
Goicoechea, Frost, De la Riva, Pellegrino, Sites Jr., Rodrigues, & Padial, 2016
Ptychoglossus vallensis Ptychoglossus vallensis.jpg
Gymnophthalmidae
Fitzinger, 1826
Spectacled lizards Bachia bicolor Bachia bicolor.jpg
Lacertidae
Oppel, 1811
Wall or true lizards Ocellated lizard (Lacerta lepida) Perleidechse-20.jpg
Teiidae Tegus or whiptails Gold tegu (Tupinambis teguixin) Goldteju Tupinambis teguixin.jpg
Neoanguimorpha
Family Common names Example species Example photo
Anguidae
Oppel, 1811
Glass lizards, alligator lizards and slowworms Slowworm (Anguis fragilis) Anguidae.jpg
Anniellidae
Gray, 1852
American legless lizards California legless lizard (Anniella pulchra) Anniella pulchra.jpg
Helodermatidae Gila monsters Gila monster (Heloderma suspectum) Gila.monster.arp.jpg
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) Real Lanthanotus borneensis.jpg
Shinisauridae Chinese crocodile lizard Chinese crocodile lizard (Shinisaurus crocodilurus) Chin-krokodilschwanzechse-01.jpg
Varanidae Monitor lizards Perentie (Varanus giganteus) Perentie Lizard Perth Zoo SMC Spet 2005.jpg
Scincoidea
Family Common Names Example Species Example Photo
Cordylidae Spinytail lizards Girdle-tailed lizard (Cordylus warreni) Cordylus breyeri1.jpg
Gerrhosauridae Plated lizards Sudan plated lizard (Gerrhosaurus major) Gerrhosaurus major.jpg
Scincidae
Oppel, 1811
Skinks Western blue-tongued skink (Tiliqua occipitalis) Tiliqua occipitalis.jpg
Xantusiidae Night lizards Granite night lizard (Xantusia henshawi) Xantusia henshawi.jpg
Alethinophidia
Family Common names Example species Example photo
Acrochordidae
Bonaparte, 1831
File snakes Marine file snake (Acrochordus granulatus) Wart snake 1.jpg
Aniliidae
Stejneger, 1907
Coral pipe snakes Burrowing false coral (Anilius scytale) False Coral Snake (Anilius scytale) close-up (13929278050).jpg
Anomochilidae
Cundall, Wallach and Rossman, 1993.
Dwarf pipe snakes Leonard's pipe snake, (Anomochilus leonardi)
Boidae
Gray, 1825 (incl. Calabariidae)
Boas Amazon tree boa (Corallus hortulanus) Corallushortulanus.png
Bolyeriidae
Hoffstetter, 1946
Round Island boas Round Island burrowing boa (Bolyeria multocarinata)
Colubridae
Oppel, 1811 sensu lato (incl. Dipsadidae, Natricidae, Pseudoxenodontidae)
Colubrids Grass snake (Natrix natrix) Natrix natrix (Marek Szczepanek).jpg
Cylindrophiidae
Fitzinger, 1843
Asian pipe snakes Red-tailed pipe snake (Cylindrophis ruffus) Cylindrophis rufus.jpg
Elapidae
Boie, 1827
Cobras, coral snakes, mambas, kraits, sea snakes, sea kraits, Australian elapids King cobra (Ophiophagus hannah) Ophiophagus hannah2.jpg
Homalopsidae
Bonaparte, 1845
Lamprophiidae
Fitzinger, 1843
Bibron's burrowing asp (Atractaspis bibroni)
Loxocemidae
Cope, 1861
Mexican burrowing snakes Mexican burrowing snake (Loxocemus bicolor) Loxocemus bicolor.jpg
Pareatidae
Romer, 1956
Pythonidae
Fitzinger, 1826
Pythons Ball python (Python regius) Ball python lucy.JPG
Tropidophiidae
Brongersma, 1951
Dwarf boas Northern eyelash boa (Trachyboa boulengeri)
Uropeltidae
Müller, 1832
Shield-tailed snakes, short-tailed snakes Cuvier's shieldtail (Uropeltis ceylanica) Silybura shortii.jpg
Viperidae
Oppel, 1811
Vipers, pitvipers, rattlesnakes European asp (Vipera aspis)
Xenodermatidae
Fitzinger, 1826
Xenopeltidae
Gray, 1849
Sunbeam snakes Sunbeam snake (Xenopeltis unicolor) XenopeltisUnicolorRooij.jpg
Scolecophidia (incl. Anomalepidae)
Family Common names Example species Example photo
Anomalepidae
Taylor, 1939
Dawn blind snakes Dawn blind snake (Liotyphlops beui)
Gerrhopilidae
Vidal et al., 2010
Leptotyphlopidae
Stejneger, 1892
Slender blind snakes Texas blind snake (Leptotyphlops dulcis) Leptotyphlops dulcis.jpg
Typhlopidae
Merrem, 1820
Blind snakes European blind snake (Typhlops vermicularis) Typhlops vermicularis.jpg
Xenotyphlopidae
Vidal et al., 2010
Xenotyphlops grandidieri
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