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 means "scaled reptiles." This amazing group of reptiles includes all lizards and snakes you know!

These animals have special skins covered in overlapping, tough scales. They also have unique bones in their jaws called quadrate bones. These bones let them move their upper jaw separately from their skull. This is super helpful for snakes, allowing them to open their mouths incredibly wide to swallow prey much bigger than their heads!

Squamates come in all sizes, from tiny to huge. The smallest is the Dwarf gecko, which is only about 16 millimeters (0.63 inches) long. The largest is the Green Anaconda, which can grow up to 8 meters (26 feet) long!

This group is special because it's the only living reptile group that has different ways of giving birth. Some squamates lay eggs (this is called oviparous). Others give birth to live young (this is called viviparous). And some keep their eggs inside their bodies until they hatch, then give birth to live young (this is called ovoviviparous).

It's important to know that Tuataras from New Zealand are not part of the Squamata group. They are a close relative, but not the same. Crocodiles are much more distantly related.

How Squamates Evolved

Slavoia darevskii, an ancient squamate fossil.

Squamates are a monophyletic group, meaning they all came from one common ancestor. They are closely related to the tuatara. Together, squamates and tuataras are related to crocodiles and birds, which are living archosaurs.

The oldest squamate fossils we've found are from the early Jurassic period. However, some scientific studies using mitochondrial DNA suggest they might have first appeared even earlier, in the late Permian period. Scientists are still working to fully understand how all the different squamate groups are related to each other. The relationship of snakes to other groups is especially tricky to figure out.

For a long time, scientists thought that Iguanid lizards branched off from other squamates very early in their history. But newer studies, looking at DNA from both mitochondria and the cell's nucleus, don't support this idea. Snakes have a "faster molecular clock" than other squamates, meaning their DNA changes more quickly. Also, there aren't many early snake fossils. These things make it hard to know exactly how snakes are related to other squamate groups.

How Venom Evolved

Recent research shows that venom in squamates started very early in their evolutionary history. In fact, about 60% of all squamates are venomous Toxicofera.

Scientists believe that venom in certain families like Caenophidia (advanced snakes), Anguimorpha (like monitor lizards), and Iguania (like iguanas) evolved just once. Then, these three groups branched off from each other. All three groups share nine similar toxins. Fossils show that these groups separated about 200 million years ago, during the Upper Triassic and Lower Jurassic periods.

Snake venom developed when a normal gene, which usually makes a helpful protein, got duplicated. One copy kept its original job, but the other copy started making a new protein in the venom gland. Over time, this new protein changed and became a toxin.

Different toxins have come from different proteins, and they have many different jobs. Natural selection has caused these toxins to become very diverse. This helps sit-and-wait predators (animals that wait for prey) to hunt many different kinds of animals. Venom genes often form large groups of similar genes, and they evolve quickly. This leads to many different toxins, which helps predators catch a wide variety of prey.

This fast evolution and diversification is like an evolutionary arms race between predators and prey. Each side adapts to counter the other's defenses.

Squamate Families

Classically, squamates were divided into three main groups:

• Lacertilia: the lizards
• Serpentes: the snakes
• Amphisbaenia: the worm lizards

However, the "lizards" group is not a true monophyletic group because it leaves out snakes and worm lizards, even though they evolved from lizards. In newer classifications, the name Sauria is used for reptiles and birds in general. Squamates are now divided differently, into groups like:

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

Classification and Relationships

Desert iguana from Amboy Crater, Mojave Desert, California

Historically, the order Squamata was divided into three suborders:

• Lacertilia, which are the lizards
• Serpentes, which are the snakes (also known as Ophidia)
• Amphisbaenia, which are the worm lizards

However, the group called "lizards" is not a complete group because it doesn't include snakes and worm lizards, even though they came from lizard ancestors. Modern studies using molecular biology (looking at DNA) have found many different family lines within squamates. The exact details of how these groups are related can vary between studies.

Here is an example of how scientists classify squamates today:

List of Squamate Families

There are over 10,000 different kinds of squamates alive today, divided into 58 families. Here are some of them:

Amphisbaenia (Worm Lizards)
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 (Geckos, including 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 (Iguanas and Chameleons)
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 (True Lizards, excluding Worm Lizards)
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 (New Anguimorphs)
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 (Old Anguimorphs)
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 (Skinks and Plated Lizards)
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 (Advanced Snakes)
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 (Blind Snakes, including 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: Escamosos para niños