The Lepidosauria is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata also includes lizards and snakes. Squamata contains over 9,000 species, making it by far the most species-rich and diverse order of non-avian reptiles in the present day. Rhynchocephalia was a formerly widespread and diverse group of reptiles in the Mesozoic Era. However, it is represented by only one living species: the tuatara, a superficially lizard-like reptile native to New Zealand.
Squamata is the largest order of reptiles, comprising lizards and snakes. With over 12,162 species, it is also the second-largest order of extant (living) vertebrates, after the perciform fish. Squamates are distinguished by their skins, which bear horny scales or shields, and must periodically engage in molting. 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 widely to accommodate comparatively large prey. Squamates are the most variably sized living reptiles, ranging from the 16 mm (0.63 in) dwarf gecko to the 6.5 m (21 ft) reticulated python. The now-extinct mosasaurs reached lengths over 14 m (46 ft).
Hoplocercidae are a family of lizards native to the tropical forests, woodlands and savanna-like habitats of Central and South America. Alternatively they are recognized as a subfamily, Hoplocercinae. 20 species in two genera are described.
Leiosauridae is a family of iguanian lizards containing six genera and 34 species. The family is endemic to Central America and South America.
The Iguanidae is a family of lizards composed of the iguanas, chuckwallas, and their prehistoric relatives, including the widespread green iguana.
Dibamidae or blind skinks is a family of lizards characterized by their elongated cylindrical body and an apparent lack of limbs. Female dibamids are entirely limbless and the males retain small flap-like hind limbs, which they use to grip their partner during mating. They have a rigidly fused skull, lack pterygoid teeth and external ears. Their eyes are greatly reduced, and covered with a scale.
Toxicofera is a proposed clade of scaled reptiles (squamates) that includes the Serpentes (snakes), Anguimorpha and Iguania. Toxicofera contains about 4,600 species of extant Squamata. It encompasses all venomous reptile species, as well as numerous related non-venomous species. There is little morphological evidence to support this grouping; however, it has been recovered by all molecular analyses as of 2012.
Iguania is an infraorder of squamate reptiles that includes iguanas, chameleons, agamids, and New World lizards like anoles and phrynosomatids. Using morphological features as a guide to evolutionary relationships, the Iguania are believed to form the sister group to the remainder of the Squamata, which comprise nearly 11,000 named species, roughly 2000 of which are iguanians. However, molecular information has placed Iguania well within the Squamata as sister taxa to the Anguimorpha and closely related to snakes. The order has been under debate and revisions after being classified by Charles Lewis Camp in 1923 due to difficulties finding adequate synapomorphic morphological characteristics. Most iguanians are arboreal but there are several terrestrial groups. They usually have primitive fleshy, non-prehensile tongues, although the tongue is highly modified in chameleons. Today they are scattered occurring in Madagascar, the Fiji and Friendly Islands and Western Hemisphere.
Aigialosauridae is a family of Late Cretaceous semiaquatic pythonomorph lizards closely related to the mosasaurs. Regarded by some paleontologists as a distinct monophyletic group and by others as an adaptive grade within the basal mosasauroids, recent molecular and morphological data suggests that they are the oldest known members of the lineage leading to the mosasaurs.
The Anguimorpha is a suborder of squamates. The group was named by Fürbringer in 1900 to include all autarchoglossans closer to Varanus and Anguis than Scincus. These lizards, along with iguanians and snakes, constitute the proposed "venom clade" Toxicofera of all venomous reptiles.
Iguana is a genus of herbivorous lizards that are native to tropical areas of Mexico, Central America, South America, and the Caribbean. The genus was first described by Austrian naturalist J.N. Laurenti in 1768. Two species are placed in the genus: The green iguana, which is widespread throughout its range and a popular pet; and the Lesser Antillean iguana, which is native to the Lesser Antilles. Genetic analysis indicates that the green iguana may comprise a complex of multiple species, some of which have been recently described, but the Reptile Database considers all of these as subspecies of the green iguana.
Platynota is a polyphyletic group of anguimorph lizards and thus belongs to the order Squamata of the class Reptilia. Since it was named in 1839, it has included several groups, including monitor lizards, snakes, mosasaurs, and helodermatids. Its taxonomic use still varies, as it is sometimes considered equivalent to the group Varanoidea and other times viewed as a distinct group. It is phylogenetically defined as a clade containing Varanidae. It also includes many extinct species.
Aigialosaurus is an extinct genus of Late Cretaceous marine or semiaquatic lizard classified as part of the family Aigialosauridae within the Mosasauroidea. Exclusively found in deposits of Cenomanian age near Hvar, Croatia, the genus contains one valid species, A. dalmaticus. According to recent molecular and morphological data, Aigialosaurus is the oldest known member of the lineage leading to large Cretaceous marine reptiles called mosasaurs, a group most closely related to snakes among living squamates. It was a relatively small reptile with a complete specimen measuring 65 cm (2.13 ft) long.
Monstersauria is a clade of anguimorph lizards, defined as all taxa more closely related to Heloderma than Varanus. It includes Heloderma, as well as several extinct genera, such as Estesia, Primaderma and Gobiderma, but this group was found to be polyphyletic in the most recent and complete squamate phylogenetic analysis by Reeder et al. (2015).
The Polychrotidae family of iguanian lizards contains the living genus Polychrus and the extinct genus Afairiguana. The family Polychrotidae was once thought to encompass all anoles, including those in the genus Anolis. Studies of the evolutionary relationships of anoles based on molecular information has shown that Polychrus is not closely related to Anolis, but instead closer to Hoplocercidae. It is therefore not part of Dactyloidae and instead is treated as the family, Polychrotidae.
Acrodonta are a subclade of iguanian squamates consisting almost entirely of Old World taxa. Extant representation include the families Chamaeleonidae (chameleons) and Agamidae, with at least over 500 species described. A fossil genus, Gueragama, was found in Brazil, making it the only known American representative of the group.
Neoanguimorpha is a clade of anguimorphs comprising Monstersauria and Diploglossa. Morphological studies in the past had classified helodermatids with the varanoids in the clade Platynota, while the Chinese crocodile lizard was classified as a xenosaurid. However molecular work found no support in these groupings and instead has found the helodermatids more related to Diploglossa, while the Chinese crocodile lizard and varanoids to form the clade Paleoanguimorpha.
Paleoanguimorpha is a clade of anguimorphs comprising Shinisauria and Goannasauria. Morphological studies in the past also classified helodermatids and pythonomorphs with the varanoids in the clade Platynota, while the Chinese crocodile lizard was classified as a xenosaurid. Current molecular work finds no support in these groupings and instead has found the helodermatids more related to Diploglossa in the sister clade Neoanguimorpha, while the Chinese crocodile lizard is the closet living relative to varanoids. Pythonomorphs represented by snakes today are not closely related to varanoids and are instead a sister lineage to Anguimorpha and Iguania in the clade Toxicofera.
Diploglossa is a clade of neoanguimorphs represented by the families Xenosauridae, Diploglossidae, Anniellidae and Anguidae, the latter three placed in the superfamily Anguioidea. In the past the Chinese crocodile lizard was classified as a xenosaurid; current molecular work has shown evidence the species related to varanoids in the clade Paleoanguimorpha.
The Arretosauridae are an extinct family of iguanian lizards from the Paleogene of east-central Asia.
