Squamates facts for kids

Quick facts for kids 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, 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:

• 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 iguanas and chameleons)
• Suborder Scleroglossa
  • Infraorder Gekkota (the geckos)
  • Infraorder Anguimorpha (the monitors, Gila monster, and slow-worms)
  • Infraorder Scincomorpha (skinks, whiptail lizards and common European lizards)
• Suborder Serpentes (the snakes)
  • Infraorder Alethinophidia (vipers, boas, cobras, etc.)
  • Infraorder Scolecophidia (blind snakes)
• Suborder Amphisbaenia

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, 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

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)
Blanidae	Mediterranean worm lizards	Mediterranean worm lizard (Blanus cinereus)
Cadeidae Vidal & Hedges, 2008	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 (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)
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	Enyalioides binzayedi
Iguanidae	Iguanas	Marine iguana (Amblyrhynchus cristatus)
Leiosauridae Frost et al., 2001	–	Darwin's iguana (Diplolaemus darwinii)	–
Liolaemidae Frost & Etheridge, 1989	Swifts	Shining tree iguana (Liolaemus nitidus)
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 (+ Dactyloidae)	Anoles	Carolina anole (Anolis carolinensis)
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		Ptychoglossus vallensis
Gymnophthalmidae Fitzinger, 1826	Spectacled lizards	Bachia bicolor
Lacertidae Oppel, 1811	Wall or true lizards	Ocellated lizard (Lacerta lepida)
Teiidae	Tegus or 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	Gila monsters	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	Spinytail 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	File snakes	Marine file snake (Acrochordus granulatus)
Aniliidae Stejneger, 1907	Coral pipe snakes	Burrowing false coral (Anilius scytale)
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)
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)
Cylindrophiidae Fitzinger, 1843	Asian pipe snakes	Red-tailed pipe snake (Cylindrophis ruffus)
Elapidae Boie, 1827	Cobras, coral snakes, mambas, kraits, sea snakes, sea kraits, Australian elapids	King cobra (Ophiophagus hannah)
Homalopsidae Bonaparte, 1845			–
Lamprophiidae Fitzinger, 1843		Bibron's burrowing asp (Atractaspis bibroni)
Loxocemidae Cope, 1861	Mexican burrowing snakes	Mexican burrowing snake (Loxocemus bicolor)
Pareatidae Romer, 1956			–
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	Vipers, pitvipers, rattlesnakes	European asp (Vipera aspis)
Xenodermatidae Fitzinger, 1826			–
Xenopeltidae Gray, 1849	Sunbeam snakes	Sunbeam snake (Xenopeltis unicolor)
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)
Typhlopidae Merrem, 1820	Blind snakes	European blind snake (Typhlops vermicularis)
Xenotyphlopidae Vidal et al., 2010		Xenotyphlops grandidieri	–

Images for kids

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  Trachylepis maculilabris skinks mating

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  The Japanese striped snake has been studied in sexual selection.

See also

In Spanish: Squamata para niños