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).
Ophidia is a group of squamate reptiles including modern snakes and reptiles more closely related to snakes than to other living groups of lizards.
Lepidosauromorpha is a group of reptiles comprising all diapsids closer to lizards than to archosaurs. The only living sub-group is the Lepidosauria, which contains two subdivisions, Squamata, which contains lizards and snakes, and Rhynchocephalia, the only extant species of which is the tuatara.
Sarcosaurus is a genus of basal neotheropod dinosaur, roughly 3.5 metres (11 ft) long. It lived in what is now England and maybe Ireland and Scotland during the Hettangian-Sinemurian stages of the Early Jurassic, about 199-196 million years ago. Sarcosaurus is one of the earliest known Jurassic theropods, and one of only a handful of theropod genera from this time period. Along with Dracoraptor hanigani it is one of the two described neotheropods from the lowermost Jurassic of the United Kingdom.
Marmorerpeton is an extinct genus of prehistoric stem group-salamanders that lived in Britain during the Bathonian stage of the Middle Jurassic. They are among the oldest known salamanders. Two species were named when the genus was first described by Susan E. Evans et al. in 1988, M. freemani, and M. kermacki, from disarticulated remains found via screenwashing in the Forest Marble Formation of England. Due to the size of their osteocytic lacunae suggesting a large genome size and some morphological characters, like the presence of calcified cartilage in the medulla of its humerus, it was assumed that Marmorerpeton was neotenic. New partly articulated remains of Marmorerpeton representing a new species, M. wakei, were described in 2022 from the Kilmaluag Formation of the Isle of Skye, Scotland. These remains include a nearly complete skull, complete tail, partly articulated back bone, and several limb bones. These remains conclusively demonstrated that Marmorerpeton was neotenic, and was a member of the family Karauridae, with the other two members of the family, Karaurus and Kokartus which are known from the Middle-Late Jurassic of Central Asia. The teeth appear to have been weakly pedicellate.
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has a wide assortment of taxa represented in its fossil record, including dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish gray, or red. Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period.
Schillerosaurus was a genus of prehistoric lizard of the Late Jurassic Morrison Formation of Western North America, and is currently the only squamate genus known to be endemic to the Morrison Formation. Described based on a partial skeleton from Dinosaur National Monument by Susan Evans and Dan Chure in 1999 as Schilleria utahensis, its name was subsequently changed to Schillerosaurus due to the former name already being occupied by a modern-day arachnid subgenus.
Parviraptor is a genus of squamate containing one species, Parviraptor estesi, from the Late Jurassic (Tithonian) or Early Cretaceous (Berriasian) Purbeck Limestone Formation of Dorset, England. A second species, Parviraptor gilmorei, was described from the Late Jurassic Morrison Formation of Western North America; it was present in stratigraphic zone 4. However, the second species was subsequently transferred to a separate genus Diablophis. An indeterminate species is known from the Bathonian aged Kirtlington Mammal Bed.
Huehuecuetzpalli mixtecus is an extinct lizard from the Early Cretaceous Tlayúa Formation in Tepexi de Rodríguez, Central Mexico. Although it is not the oldest known lizard, Huehuecuetzpalli may be amongst the most basal members of Squamata, making it an important taxon in understanding the origins of squamates.
Marmoretta is an extinct genus of small lepidosauromorph reptile known from the Middle Jurassic (Bathonian) of Britain, as well as the Late Jurassic of Portugal. It contains a single species, Marmoretta oxoniensis.
Megachirella is an extinct genus of lepidosaur, possibly a stem-squamate that lived about 240 million years ago during the Middle Triassic and contains only one known species, Megachirella wachtleri. It is known from a partial skeleton discovered in the Dolomites of Northern Italy and was described in 2003.
Borealestes is a genus of docodontan from the Middle Jurassic of Britain, first discovered on the Isle of Skye near the village of Elgol. It was the earliest mammaliaform from the Mesozoic found and named in Scotland. A second species and was later found in other Middle Jurassic sites in England, but is now shown to be a different genus. A new species, B. cuillinensis was named in 2021, also from Skye.
Wareolestes rex is a mammaliaform from the Middle Jurassic (Bathonian) rocks of England and Scotland. It was originally known from isolated teeth from England, before a more complete jaw with teeth was found in the Kilmaluag Formation of Skye, Scotland.
Eichstaettisaurus is a genus of lizards from the Late Jurassic and Early Cretaceous of Germany, Spain, and Italy. With a flattened head, forward-oriented and partially symmetrical feet, and tall claws, Eichstaettisaurus bore many adaptations to a climbing lifestyle approaching those of geckoes. The type species, E. schroederi, is among the oldest and most complete members of the Squamata, being known by one specimen originating from the Tithonian-aged Solnhofen Limestone of Germany. A second species, E. gouldi, was described from another skeleton found in the Matese Mountains of Italy. Despite being very similar to E. schroederi, it lived much later, during the Albian stage. Fossils of both species show exceptional preservation due to deposition in low-oxygen marine environments.
Oculudentavis is an extinct genus of lizard of uncertain taxonomic placement, originally identified as an avialan dinosaur. It contains two known species, O. khaungraae and O. naga. Each species is known from one partial fossil specimen in Burmese amber, which differ in several proportions. Their skulls measure 1.4–1.7 centimetres (0.55–0.67 in) in length, indicating that Oculudentavis would have been comparable in size with the modern bee hummingbird if it were an avialan. Both specimens were retrieved from 99-million-year-old deposits of the Hukawng Basin in Kachin State, northern Myanmar. The type specimen of O. khaungraae is embroiled in controversy regarding its identity and the ethical issues surrounding the acquisition and study of Burmese amber. The original description advocating for an avialan identity was published in Nature, but has since then been retracted from the journal.
Ardeosauridae is an extinct family of lizards known from the Late Jurassic of Germany and North America and Early Cretaceous of Mongolia, with other potential species elsewhere from Europe and Asia over the same time period.
Taytalura is an extinct genus of lepidosauromorph reptile from the Late Triassic of Argentina. It contains a single species, Taytalura alcoberi, which is based on a well-preserved skull from the fossiliferous Ischigualasto Formation. As a lepidosauromorph, Taytalura is a distant relative of modern lepidosaurs such as sphenodontians and squamates. Taytalura did not belong to any group of modern lepidosaurs, since it bears unique features, such as unfused bones in the skull roof and teeth which all sit loosely in a deep groove without sockets. Regardless, Micro-CT scanning reveals features of the skull previously only seen in rhynchocephalians. This suggests that the ancestral condition of the skull in lepidosaurs was more similar to sphenodonts than to squamates.
Slavoia is an extinct genus of lizard from the Early Cretaceous of Mongolia, and Late Cretaceous of Kazakhstan and Mongolia.
Ceoptera is an extinct genus of darwinopteran pterosaur from the Middle Jurassic Kilmaluag Formation of Scotland. The genus contains a single species, C. evansae, known from a partial skeleton. It is the only pterosaur from Kilmaluag Formation. Ceoptera represents the second pterosaur named from Scotland, after Dearc in 2022.
