diapsid

Diapsids Fossil range: Carboniferous-Recent
the diapsid skull
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida (unranked) Eureptilia Subclass: Diapsida Osborn, 1903
Groups
See text

Diapsids ("two arches") are a group of tetrapod animals that developed two holes (temporal fenestra) in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all birds, crocodiles, lizards, snakes, tuatara, and possibly even turtles. While some lost either one hole (lizards), or both holes (snakes), or even have a much more restructured skull (modern birds), they are still classified as diapsids based on their ancestry. There are 14,600 species of diapsid existing in environments around the world today, including most flying and venomous vertebrates.

The ancestral openings are 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 (radius), compared to the upper arm bone (humerus). Extinct groups include the dinosaurs, pterosaurs, plesiosaurs, mosasaurs, and many more obscure lineages. The classification of most of the early groups is fluid and subject to change.

Taxonomy

Classification

• Subclass DIAPSIDA
  • Order Araeoscelidia
  • Order Avicephala
  • Order Younginiformes
  • Superorder Ichthyopterygia (ichthyosaurs)
  • Infraclass Lepidosauromorpha
    • Order Eolacertilia
    • Superorder Lepidosauria (tuatara, lizards, amphisbaenians and snakes)
    • Superorder Sauropterygia (plesiosaurs)
  • Infraclass Archosauromorpha
    • Order Aetosauria
    • Order Choristodera
    • Order Phytosauria
    • Order Prolacertiformes
    • Order Pterosauria (pterosaurs)
    • Order Rauisuchia
    • Order Rhynchosauria
    • Order Trilophosauria
    • Superorder Crocodylomorpha (crocodiles and extinct relatives)
    • Superorder Dinosauria (dinosaurs)

Phylogeny

Diapsida
|--Araeoscelida
|-?Sphodrosaurus
|-?Palacrodon
|-?Omphalosaurus
`--+--Avicephala
    `--Neodiapsida
          |--Apsisaurus
          `--Eosuchia
                 |-?Younginiformes
                 `--+-?Claudiosaurus
                       |-?Ichthyopterygia
                       `--Sauria
                              |-?Thalattosauriformes
                              |--Lepidosauromorpha
                              `--Archosauromorpha

See also

• Vertebrate paleontology
• Synapsida
• Anapsida

External links

• Diapsida. Michel Laurin and Jacques A. Gauthier. Tree of Life Web Project. June 22, 2000.

• Diapsida Cladogram at Mikko's Phylogeny Archive

Caption: Skull of false gharial (Tomistoma schlegeli)

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