Squamates
| Scaled reptiles Temporal range: Early Jurassic – Present, 199–0 Ma |
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| Eastern blue-tongued lizard | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | Lepidosauria |
| Order: |
Squamata Oppel, 1811 |
| Subgroups | |
The order Squamata, or the scaled reptiles, are the largest recent order of reptiles, comprising all lizards and snakes. With over 10,000 species, it is also the second-largest order of extant vertebrates, after the perciform fish, and roughly equal in number to the Saurischia (one of the 2 major groups of dinosaurs). 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 neurocranium. 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 5.21 m (17.1 ft) green anaconda (Eunectes murinus) and the now-extinct mosasaurs, which reached lengths of 14 m (46 ft).
Among the other reptiles, squamates are most closely related to the tuatara, which strongly resembles lizards.
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. Fossils of the squamate sister group, the Rhynchocephalia, appear in the Early Triassic, meaning that the lineage leading to squamates must have existed as well. Modern squamates probably originated in the mid Jurassic, when fossil relatives of geckos and skinks and snakes appear; other groups, including iguanians and varanoids, first appear in the Cretaceous period. Also appearing in the Cretaceous are the polyglyphanodonts, a lizard group of uncertain affinities, and the mosasaurs, a group of predatory, marine lizards that grew to enormous sizes. At the end of the Cretaceous, squamates suffered a major extinction at the K-T boundary which wiped out polyglyphanodonts, mosasaurs, and a number of other groups.
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Wikipedia