Lepidosauromorpha (in

PhyloCode The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the ...

known as ''Pan-Lepidosauria'') is a group of

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchoce ...

s comprising all

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ...

s closer to

lizard Lizards are a widespread group of Squamata, squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbae ...

s than to

archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian ...

s (which include

crocodile Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant me ...

s and

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s). The only living sub-group is the

Lepidosauria The Lepidosauria (, from Greek meaning ''scaled lizards'') 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 ...

, which contains two subdivisions,

Squamata Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species, i ...

, which contains

lizards Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia althou ...

and

snakes Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints ...

, and

Rhynchocephalia Rhynchocephalia (; ) is an order of lizard-like reptiles that includes only one living species, the tuatara (''Sphenodon punctatus'') of New Zealand. Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a diverse gr ...

, the only extant species of which is the

tuatara Tuatara (''Sphenodon punctatus'') are reptiles endemic to New Zealand. Despite their close resemblance to lizards, they are part of a distinct lineage, the order Rhynchocephalia. The name ''tuatara'' is derived from the Māori language an ...

. Lepidosauromorphs are distinguishable from archosauromorphs (reptiles closer to archosaurs) by their primitive sprawling gait (allowing for the same sinusoidal trunk and tail movement seen in fish), the sliding "joint" between the coracoids and the sternum (for a longer stride), and their pleurodont dentition. In contrast, Archosauromorphs possess a

parasagittal The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divid ...

gait, a reduction in their dermal girdle, a reduction and/or loss of the sternum, and a more thecodont dentition. Living lepidosauromorphs have retained an ectothermic (" cold blooded") metabolism, unlike the ancestral condition in archosauromorphs. While some putative stem-lepidosauromorphs like '' Palaeagama'' are known from the Late

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

, the oldest definitive lepidosauromorphs, ''

Sophineta ''Sophineta'' is an extinct genus of basal lepidosauromorph reptile known from the Early Triassic (late Olenekian age) of Małopolska Province, southern Poland. It contains a single species, ''Sophineta cracoviensis''. Discovery ''Sophineta' ...

'' and ''

Paliguana ''Paliguana'' is an extinct genus of lizard-like lepidosauromorph reptile from the earliest Triassic Katberg Formation (Beaufort Group) in the upper ''Lystrosaurus'' Assemblage Zone of South Africa South Africa, officially the Republic ...

'', are known from the Early

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

. ''

Taytalura ''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 late Carnian Ischigualasto Formation. Alt ...

'' from the early Late

of Argentina is the most complete fossil of an early lepidosauromorph and is one of the few fossils robustly inferred as an early evolving lepidosauromorph. The

Kuehneosauridae Kuehneosauridae is an extinct family of small, lizard-like gliding diapsids known from the Triassic period of Europe and North America. They are distinguished from other diapsids by their 'wings' formed by elongated ribs. These allowed the anima ...

, a family of reptiles with elongated ribs which allowed them to glide akin to living gliding lizards have been historically typically considered early lepidosauromorphs. However, several recent studies have been found them in other positions within Sauria, including Archosauromorpha. Almost all non-lepidosaurian lepidosauromorphs became extinct by the end of the Triassic, the with the latest non lepidosaur-lepidosauromorphs being ''

Marmoretta ''Marmoretta'' is an extinct genus of small lepidosauromorph reptile known from the Middle Jurassic (late Bathonian age) of Oxfordshire, England and Skye, Scotland. It contains a single species, ''Marmoretta oxoniensis''. Etymology ''Marmoret ...

'' from the Middle Jurassic of Britain and an indeterminate form from the Middle Jurassic Moskvoretskaya Formation of Russia, which appear to be closely related to '' Fraxinisaura'' from the Middle Triassic of Germany. Other studies have recovered ''Marmoretta'' as a stem-squamate.

References

Tetrapod unranked clades Early Triassic reptiles Extant Early Triassic first appearances Olenekian first appearances {{Reptile-stub

See also

References