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Diapsids ("two arches") are a group of reptile
Reptile

Reptiles, or members of the class Reptilia, are air-breathing, cold-blooded vertebrates that have skin covered in scale as opposed to hair or feathers....
s that developed two holes (temporal fenestra) in each side of their skull
Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
s, about 300 million years ago during the late Carboniferous
Carboniferous

The Carboniferous is a geologic period that extends from the end of the Devonian period, about 359.2 ? 2.5 annum , to the beginning of the Permian period, about 299.0 ? 0.8 Ma ...
 period. Living diapsids are extremely diverse, and include all crocodile
Crocodile

A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all members of the order Crocodilia: i.e....
s, lizard
Lizard

Lizards are a large and widespread group of squamate reptiles, with nearly 5,000 species, ranging across all continents except Antarctica as well as most oceanic island chains....
s, snake
Snake

Snakes are elongate legless carnivore reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears....
s, and tuatara
Tuatara

The tuatara is a reptile endemism to New Zealand which, though it resembles most lizards, is actually part of a distinct lineage, order Sphenodontia....
. Under modern classification systems, even bird
Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
s are considered diapsids, since they evolved from diapsid ancestors and are nested within the diapsid clade
Clade

A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.The term "monophyletic group" is used in this article in the conventional sense of "an a...
. While some diapsids have lost either one hole (lizards), or both holes (snakes), or even have a heavily restructured skull (modern birds), they are still classified
Scientific classification

Biological classification or scientific classification in biology, is a method by which biologists group and categorize species of organisms....
 as diapsids based on their ancestry.






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Diapsids ("two arches") are a group of reptile
Reptile

Reptiles, or members of the class Reptilia, are air-breathing, cold-blooded vertebrates that have skin covered in scale as opposed to hair or feathers....
s that developed two holes (temporal fenestra) in each side of their skull
Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
s, about 300 million years ago during the late Carboniferous
Carboniferous

The Carboniferous is a geologic period that extends from the end of the Devonian period, about 359.2 ? 2.5 annum , to the beginning of the Permian period, about 299.0 ? 0.8 Ma ...
 period. Living diapsids are extremely diverse, and include all crocodile
Crocodile

A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all members of the order Crocodilia: i.e....
s, lizard
Lizard

Lizards are a large and widespread group of squamate reptiles, with nearly 5,000 species, ranging across all continents except Antarctica as well as most oceanic island chains....
s, snake
Snake

Snakes are elongate legless carnivore reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears....
s, and tuatara
Tuatara

The tuatara is a reptile endemism to New Zealand which, though it resembles most lizards, is actually part of a distinct lineage, order Sphenodontia....
. Under modern classification systems, even bird
Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
s are considered diapsids, since they evolved from diapsid ancestors and are nested within the diapsid clade
Clade

A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.The term "monophyletic group" is used in this article in the conventional sense of "an a...
. While some diapsids have lost either one hole (lizards), or both holes (snakes), or even have a heavily restructured skull (modern birds), they are still classified
Scientific classification

Biological classification or scientific classification in biology, is a method by which biologists group and categorize species of organisms....
 as diapsids based on their ancestry. There are at least 7,925 species
Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring....
 of diapsid reptile existing in environments around the world today (over 14,600 when birds are included).

Characteristics

The name Diapsida means "two arches", and diapsids are traditionally classified based on their two ancestral skull openings (temporal fenestrae) posteriorly above and below the eye. This arrangement allows for the attachment of larger, stronger jaw muscles, and enables the jaw to open more widely. A more obscure ancestral characteristic is a relatively long lower arm bone (the radius
Radius (bone)

The radius is the bone of the forearm that extends from the lateral side of the Elbow-joint to the thumb side of the wrist. The radius is situated on the lateral side of the ulna, which exceeds it in length and size....
), compared to the upper arm bone (humerus
Humerus

The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow.Anatomically, it connects the scapula and the ulna, and consists of the following three sections:...
).

Systematics

Diapsids were originally classified as one of four subclasses of the class Reptilia, all of which were based on the number and arrangement of openings in the skull. The other three subclasses were Synapsida (one opening low on the skull, for the "mammal-like reptiles"), Anapsida (no skull opening, including turtles and their relatives), and Euryapsida
Euryapsida

Euryapsida is a polyphyletic group of reptiles that are distinguished by a single temporal fenestra, an opening behind the orbit , under which the post-orbital and squamosal bones articulate....
 (one opening high on the skull, including many prehistoric marine reptiles). With the advent of phylogenetic nomenclature
Phylogenetic nomenclature

Phylogenetic nomenclature or phylogenetic taxonomy is an alternative to Biological classification, applying definitions from cladistics ....
, this system of classification was heavily modified. The Synapsids today are often not considered true reptiles, while the Euryapsida was found to be an unnatural assemblage of diapsids that had lost one of their skull openings. Some studies have suggested that this is the case in turtles as well, and that turtles are actually heavily modified diapsids, which would leave only some prehistoric forms in the Anapsida. In phylogenetic systems, birds (descendants of traditional diapsid reptiles) are also considered to be members of this group.

Well known extinct diapsid groups include the dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s, pterosaur
Pterosaur

Pterosaurs were flying reptiles of the clade or Order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight....
s, plesiosaur
Plesiosaur

Plesiosaurs were carnivore aquatic reptiles. After their discovery, they were somewhat fancifully said to have resembled , although they had no shell....
s, mosasaur
Mosasaur

Mosasaurs were serpentine marine reptiles. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1778. These ferocious marine predators are now considered to be the closest relatives of snakes, due to cladistic analysis of symptomatic similarities in jaw and skull anatomies....
s, and many more obscure lineages. The classification of most of the early groups is fluid and subject to change.

Taxonomy

  • Subclass DIAPSIDA
    • Order Araeoscelidia
      Araeoscelidia

      Araeoscelidia or Araeoscelida is a clade of extinct diapsid reptiles superficially resembling lizards. It contains the genus Araeoscelis, Petrolacosaurus, the possibly aquatic Spinoaequalis, and less well-known genera such as Kadaliosaurus and Zarcasaurus....
    • Order Avicephala
      Avicephala

      Avicephala is an extinct clade of bizarre diapsid reptiles that lived during the Late Permian and Triassic periods. Many species had odd specialized grasping limbs and prehensile tails, adapted to arboreal lifestyles....
    • Order Thalattosaur
      Thalattosaur

      Thalattosaurs are a group of prehistoric marine reptiles which lived during the mid-late Triassic Period. Some species of thalattosaur grew to over 4 meters in length, including a long, flattened tail used in underwater propulsion....
      ia
    • Order Younginiformes
      Younginiformes

      Younginiformes is a replacement name for the taxon Eosuchia, proposed by Alfred Romer in 1947.The Eosuchia having become rather a dustbin for many probably distantly-related primitive diapsid reptiles ranging from the late Carboniferous to the Eocene, Romer proposed that this be replaced by Younginiformes, to include the Younginidae and a v...
    • Superorder Ichthyopterygia
      Ichthyopterygia

      Ichthyopterygia was a designation introduced by Sir Richard Owen in 1840 to designate the Jurassic Ichthyosaurs that were known at the time, but the term is now used more often for both true Ichthyosauria and their more primitive early and middle Triassic ancestors ....
       (ichthyosaur
      Ichthyosaur

      Ichthyosaurs were giant marine reptiles that resembled fish and dolphins. Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 245 million years ago and disappeared about 90 million years ago, about 25 million years before the dinosaurs became extinct....
      s)
    • Infraclass Lepidosauromorpha
      Lepidosauromorpha

      Lepidosauromorpha is a group of reptiles comprising all diapsids closer to lizards than to archosaurs . The only living sub-group is the Lepidosauria: extant lizards, snakes, and tuatara....
      • Order Eolacertilia
        Eolacertilia

        Eolacertilia is a group of extinction diapsid reptiles that may be the ancestors of Squamata. It is uncertain as to whether they are a natural group and it has been suggested that they form a "waste basket" taxon....
      • Superorder Lepidosauria
        Lepidosauria

        The Lepidosauria are reptiles with overlapping scales. They include the tuataras, lizards, snakes and amphisbaenians. Lepidosaurians are the most successful of modern reptiles....
         (tuatara
        Tuatara

        The tuatara is a reptile endemism to New Zealand which, though it resembles most lizards, is actually part of a distinct lineage, order Sphenodontia....
        , lizards, amphisbaenians and snake
        Snake

        Snakes are elongate legless carnivore reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears....
        s)
      • Superorder Sauropterygia
        Sauropterygia

        Sauropterygia is a group of very successful aquatic reptiles that flourished during the Mesozoic before they became extinct. They are united by a radical adaptation of their shoulder, designed to support powerful flipper strokes....
         (plesiosaurs and relatives)
    • Infraclass Archosauromorpha
      Archosauromorpha

      Archosauromorpha is an Infraclass of diapsid reptiles that first appeared during the late Permian and became more common during the Triassic. Included in this infraclass are the orders Rhynchosauria, Trilophosauridae, Prolacertiformes, Archosauriformes, and, tentatively, the Choristodera....
      • Order Aetosauria
      • Order Choristodera
        Choristodera

        Choristodera is an Order of semi-aquatic diapsid reptiles which ranged from the Middle Jurassic, or possibly Late Triassic, to at least the early Miocene....
      • Order Phytosauria
      • Order Prolacertiformes
        Prolacertiformes

        Prolacertiformes were an order of archosauromorpha reptiles that lived during the Permian and Triassic Periods. Many species seem to have been adapted for an arboreal lifestyle, including the "delta-winged glider" Sharovipteryx, while others, such as Tanystropheus, had extremely long, stiffened necks , and may have been at least part...
      • Order Pterosauria
      • Order Rauisuchia
        Rauisuchia

        Rauisuchia are a poorly known assemblage of predatory and mostly large Triassic archosaurs. Originally it was believed that they were related to Erythrosuchidae, but it is now known that they are Crurotarsi....
      • Order Rhynchosauria
      • Order Trilophosauria
      • Superorder Crocodylomorpha
        Crocodylomorpha

        The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now....
         (crocodile
        Crocodile

        A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all members of the order Crocodilia: i.e....
        s and extinct relatives)
      • Superorder Dinosaur
        Dinosaur

        Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
        ia


Phylogeny


Diapsida |--Araeoscelida |-?Sphodrosaurus |-?Palacrodon |-?Omphalosaurus
Omphalosaurus

Omphalosaurus is an extinct genus of marine reptile from the Early Triassic of Spitsbergen.Is has been considered an ichthyopterygian, however a study by Motani showed that it lacks the basal synapomorphy of Ichthyopterygia....
 `--+--Avicephala
Avicephala

Avicephala is an extinct clade of bizarre diapsid reptiles that lived during the Late Permian and Triassic periods. Many species had odd specialized grasping limbs and prehensile tails, adapted to arboreal lifestyles....
 `--Neodiapsida
Neodiapsida

Neodiapsida is a clade or major branch of the reptilian family tree, that includes all Diapsids apart from some early primitive types known as Araeoscelidia....
 |--Apsisaurus `--Eosuchia
Eosuchia

Eosuchians are an extinct Order of diapsid reptiles. Depending on which taxa are included the order may have ranged from the late Carboniferous to the Eocene but the consensus is that eosuchians are confined to the Permian and Triassic....
 |-?Younginiformes
Younginiformes

Younginiformes is a replacement name for the taxon Eosuchia, proposed by Alfred Romer in 1947.The Eosuchia having become rather a dustbin for many probably distantly-related primitive diapsid reptiles ranging from the late Carboniferous to the Eocene, Romer proposed that this be replaced by Younginiformes, to include the Younginidae and a v...
 `--+-?Claudiosaurus
Claudiosaurus

Claudiosaurus is an extinct genus of diapsid reptile from the Permian period. It was about 60 cm long.Claudiosaurus was one of the first members of the Neodiapsida, a group of diapsid containing most diapsids except the primitive Araeoscelidia....
 |-?Ichthyopterygia
Ichthyopterygia

Ichthyopterygia was a designation introduced by Sir Richard Owen in 1840 to designate the Jurassic Ichthyosaurs that were known at the time, but the term is now used more often for both true Ichthyosauria and their more primitive early and middle Triassic ancestors ....
 `--Sauria
Sauria

Sauria is a clade of reptiles that includes all living diapsids, as well as their common ancestor and all its extinct descendants. The ancestral saurian was probably a small lizard-like creature living in the Permian Period....
 |-?Thalattosauriformes |--Lepidosauromorpha
Lepidosauromorpha

Lepidosauromorpha is a group of reptiles comprising all diapsids closer to lizards than to archosaurs . The only living sub-group is the Lepidosauria: extant lizards, snakes, and tuatara....
 `--Archosauromorpha
Archosauromorpha

Archosauromorpha is an Infraclass of diapsid reptiles that first appeared during the late Permian and became more common during the Triassic. Included in this infraclass are the orders Rhynchosauria, Trilophosauridae, Prolacertiformes, Archosauriformes, and, tentatively, the Choristodera....


See also

  • Vertebrate paleontology
    Vertebrate paleontology

    Vertebrate paleontology seeks to discover the behavior, reproduction and appearance of extinct animals with vertebrae or a notochord, through the study of their fossilized remains....
  • Synapsid
    Synapsid

    Synapsids , also known as theropsids , are a class of animals that includes mammals and everything closer to mammals than to other living amniotes....
    a
  • Anapsid
    Anapsid

    An anapsid is an amniote whose skull does not have temporal fenestra near the Temple s.While "anapsid reptiles" or "anapsida" are traditionally spoken of as if they were a coherent group, it has been suggested that several groups of reptiles that had anapsid skulls may be only distantly related: scientists still debate the exact relationshi...
    a
  • Euryapsida
    Euryapsida

    Euryapsida is a polyphyletic group of reptiles that are distinguished by a single temporal fenestra, an opening behind the orbit , under which the post-orbital and squamosal bones articulate....


External links

  • . Michel Laurin and Jacques A. Gauthier. Tree of Life Web Project. June 22, 2000.
  • Cladogram at Mikko's Phylogeny Archive
    Mikko's Phylogeny Archive

    Mikko's Phylogeny Archive is an amateur paleontology website maintained by Mikko Haaramo, a student at the University of Helsinki's Department of Geology, Division of Geology and Palaeontology....