The Lepidosauria is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species, making it by far the most species-rich and diverse order of 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, snakes, and amphisbaenians, which are collectively known as squamates or scaled reptiles. With over 10,900 species, it is also the second-largest order of extant (living) vertebrates, after the perciform fish. Members of the order are distinguished by their skins, which bear horny scales or shields. 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 wide to accommodate comparatively large prey. Squamata is the most variably sized order of reptiles, ranging from the 16 mm (0.63 in) dwarf gecko to the 5.21 m (17.1 ft) green anaconda and the now-extinct mosasaurs, which 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 three genera are described.
The Iguanidae are a family of lizards composed of iguanas and related species which includes species such as the green iguana, the Lesser Antillean iguana and the marine 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, and comprise nearly 13,000 named species. 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 Iguanias are arboreal but there are several terrestrial groups. They usually have primitive fleshy, non-prehensile tongues, although the tongue is highly modified in chameleons. The group has a fossil record that extends back to the Early Jurassic. Today they are scattered occurring in Madagascar, the Fiji and Friendly Islands and Western Hemisphere
Autarchoglossa is a clade of squamates that includes skinks, anguimorphs, snakes, and relatives. Autarchoglossa is supported as a monophyletic grouping by morphological features in living and extinct lizards and snakes. Some phylogenetic analyses based on molecular features such as DNA sequences in living squamates do not support Autarchoglossa.
Sineoamphisbaena is an extinct genus of squamate of uncertain phylogenetic placement. Its fossils are known from the Late Cretaceous deposits in Inner Mongolia, China. Wu et al. (1993), Wu et al. (1996) and Gao (1997) proposed and argued that it was the oldest known amphisbaenian; this, however, was challenged by other authors, such as Kearney (2003) and Conrad (2008), who instead assigned Sineoamphisbaena to the group of squamates variously known as Macrocephalosauridae, Polyglyphanodontidae or Polyglyphanodontia.
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 in 1768 by Austrian naturalist Josephus Nicolaus Laurenti in his book Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena. 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.
Polyglyphanodontia, also known as the Borioteiioidea, is an extinct clade of lizards from the Cretaceous that includes around a dozen genera. Polyglyphanodontians were the dominant group of lizards in North America and Asia during the Late Cretaceous. Most polyglyphanodontians are Late Cretaceous in age, though the oldest one, Kuwajimalla kagaensis, is known from the Early Cretaceous Kuwajima Formation (Japan). Early Cretaceous South American taxon Tijubina, and possibly also Olindalacerta, might also fall within Polyglyphanodontia or be closely allied to the group, but if so, they would be two of only three Gondwanan examples of an otherwise Laurasian clade. They produced a remarkable range of forms. Chamopsiids, including Chamops, were characterized by large, blunt, crushing teeth, and were most likely omnivores. Macrocephalosaurus, from the Gobi Desert, was a specialized herbivore; it grew to roughly a meter long and had multicusped, leaf-shaped teeth like those of modern iguanas. Polyglyphanodon, from the Maastrichtian of Utah, was another herbivore, but its teeth formed a series of transverse blades, similar to those of Trilophosaurus. Peneteius had remarkable, multicusped teeth, similar to those of mammals. The polyglyphanodontids first appear in the latter part of the Early Cretaceous in North America, and became extinct during the Cretaceous-Paleogene extinction event. Polyglyphanodontians closely resembled the teiid lizards, and purported teiid lizards from the Late Cretaceous appear to be polyglyphanodontians. The only species known to have survived the Cretaceous was Chamops, which survived until the very early Ypresian.
Gekkonomorpha is a clade of lizards that includes geckos and their closest relatives. Although it was first named in 1900, Gekkonomorpha was not widely used as a formal taxon until it was given a phylogenetic definition in the 1990s. Under this definition, Gekkonomorpha is a stem-based taxon containing the node-based taxon Gekkota, the group that includes the last common ancestor of all living geckos and its descendants. The extent of Gekkonomorpha beyond gekkotans differs between studies. For example, Lee (1998) defined Gekkonomorpha in such a way that it included not only Gekkota but the legless amphisbaenian and dibamid lizards as well. The phylogenetic analysis of Conrad (2008), which did not support a close relationship between geckos and legless lizards, used Gekkonomorpha in a much more restrictive sense so that it included only Gekkota and a few extinct lizards more closely related to Gekkota than to any other living group of lizards. Some of the most recent phylogenetic analyses suggest that the extinct lizards Gobekko and Parviraptor may be stem gekkotans, although other analyses find that Gobekko may instead be within Gekkota and Parviraptor outside Gekkonomorpha.
Shinisauria is a clade or evolutionary grouping of anguimorph lizards that includes the living Chinese crocodile lizard Shinisaurus and several of its closest extinct relatives. Shinisauria was named in 2008 as a stem-based taxon to include all anguimorphs more closely related to Shinisaurus than to any other lizard. Several recent phylogenetic analyses of lizard evolutionary relationships place Shinisauria in a basal position within the clade Platynota, which also includes monitor lizards, helodermatids, and the extinct mosasaurs. Shinisaurians were once thought to be closely related to the genus Xenosaurus, but they are now considered distant relatives within Anguimorpha. The fossil record of shinisaurians extends back to the Early Cretaceous with Dalinghosaurus, which is from the Aptian aged Yixian Formation of China. Two other extinct shinisaurians are currently known: Bahndwivici from the Eocene of Wyoming and Merkurosaurus from the Late Oligocene of Germany and the Early Miocene of the Czech Republic. An indeterminate shinisaurian is known from an isolated tail found in the Eocene aged Messel pit in Germany.
Scincogekkonomorpha is a clade of lizards that includes scleroglossans and all lizards more closely related to scleroglossans than to iguanians. These "stem" scleroglossans include extinct lizards from the Late Jurassic and Early Cretaceous such as Bavarisaurus, Eichstaettisaurus, Liushusaurus, and Scandensia. Scincogekkonomorpha was named in 1961 and is now occasionally used as a stem-based taxon in contrast to the node-based taxon Scleroglossa. According to phylogenies based on morphological characteristics, Scincogekkonomorpha is the sister taxon of Iguania and together they make up crown group Squamata, the smallest clade including all living snakes and lizards.
Myrmecodaptria is an extinct genus of scleroglossan lizard from the Late Cretaceous Djadokhta Formation in Ukhaa Tolgod, Mongolia. The type and only species, Myrmecodaptria microphagosa, was named in 2000 by paleontologists Gao Keqin and Mark Norell. Myrmecodaptria is known from a single holotype skull and lower jaws. It is distinguished from all other lizards by its extremely elongated skull. The eyes are placed close to the snout, which is short and rounded. The top of the skull is covered in bony knobs called osteoderms. The parietal bone at the back of the skull is elongated and about as long as the frontal bones, which are the usually the longest bones along the top of the skull in lizards. The squamosal bone at the back of the skull reaches forward to connect with the jugal bone behind the eye, forming a thin arch between the temporal fenestrae. Myrmecodaptria also has fewer and more widely spaced teeth in its jaws than do most other lizards.
Chamaeleontiformes is a hypothesized clade of iguanian lizards defined as all taxa sharing a more recent common ancestor with Chamaeleo chamaeleon than with Hoplocercus spinosus, Polychrus marmoratus, or Iguana iguana. It was named by paleontologist Jack Conrad in 2008 to describe a clade recovered in his phylogenetic analysis that included the extinct genus Isodontosaurus, the extinct family Priscagamidae, and the living clade Acrodonta, which includes agamids and chameleons. It is a stem-based taxon and one of two major clades within Iguania, the other being Pleurodonta. Below is a cladogram from Daza et al. (2012) showing this phylogeny:
Bharatagama is an extinct genus of lepidosaur from the Early Jurassic of India. It is has been suggested to be one of the oldest known lizards and the oldest known iguanian. The type and only species is Bharatagama rebbanensis, named in 2002. Over one hundred fossils of Bharatagama have been found in the Kota Formation, which outcrops in the Pranhita–Godavari Basin and dates back to about 190 million years ago (Ma). Despite its abundance, Bharatagama is known only from isolated jaw bones mixed together in microvertebrate assemblages with equally fragmentary remains of fish, sphenodontians, dinosaurs, crocodylomorphs, and mammals. These fossils represent all stages of development, from hatchlings to adults. The total length of the skull in adult specimens is estimated to have been about 15 millimetres (0.59 in). Later analysis suggested that the taxon might be a member of Rhynchocephalia.
Norellius is an extinct genus of scleroglossan lizard from the Early Cretaceous Öösh Formation of Mongolia. It is known from a well-preserved skull that was collected by an American Museum of Natural History expedition to Mongolia in 1923 and cataloged as AMNH FR 21444. After its initial cataloging, the specimen was not mentioned again in the scientific literature until 2004, when it was recognized as belonging to a potential early relative of modern groups of squamates such as gekkotans, amphisbaenians, dibamids, and snakes. AMNH FR 21444 was more fully described in a 2006 study that used high-resolution computed tomography to examine the skull and its braincase, and was described as a new genus and species, Norellius nyctisaurops, in 2015. The genus name honors paleontologist Mark Norell. The 2006 study incorporated the specimen into a phylogenetic analysis and found it to be a basal member of an evolutionary grouping called Gekkonomorpha, a stem-based taxon that includes living geckos and legless lizards (pygopodids) and all taxa more closely related to them than to any other living lizard. Norellius lies outside the node-based taxon Gekkota, a more strictly-defined subgroup of Gekkonomorpha that includes geckos, pygopodids, and all descendants of their most recent common ancestor. Therefore, while Norellius is more closely related to geckos and pygopodids than it is to any other living group of lizards, it branched off before the most recent common ancestor of these two groups. Below is a cladogram showing the position of Norellius according to this phylogeny:
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.
