Temporal range: Pennsylvanian-Present, 302–0Ma
Diapsids ("two arches") are a group of amniote tetrapods that developed two holes (temporal fenestra) in each side of their skulls about 300 million years ago during the late Carboniferous period. The diapsids are extremely diverse, and include all crocodiles, lizards, snakes, tuatara, birds and non-avian dinosaurs. Although some diapsids have lost either one hole (lizards), or both holes (snakes), or have a heavily restructured skull (modern birds), they are still classified as diapsids based on their ancestry. At least 7,925 species of diapsid reptiles exist in environments around the world today (nearly 18,000 when birds are included).
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) compared to the upper arm bone (humerus).
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 (one opening high on the skull, including many prehistoric marine reptiles). With the advent of phylogenetic nomenclature, this system of classification was heavily modified. Today, the synapsids are often not considered true reptiles, while Euryapsida were found to be an unnatural assemblage of diapsids that had lost one of their skull openings. Some studies have suggested that this is also the case in turtles, and that they 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 pterosaurs, plesiosaurs, and mosasaurs; many more obscure lineages once existed. The classification of most of the early groups is fluid and subject to change.
- Subclass DIAPSIDA
- Avicephala (polyphyletic)
- Younginiformes (paraphyletic)
- (unranked) Sauria
- Infraclass Lepidosauromorpha
- Order Eolacertilia
- Superorder Lepidosauria (tuatara, lizards, amphisbaenians and snakes)
- Superorder Sauropterygia (plesiosaurs and relatives, possibly including turtles)
- Testudines (?)
- Infraclass Lepidosauromorpha
Diapsids of uncertain placement (incertae sedis)
Below is a cladogram showing the relations of the major groups of diapsids.
- "Those diverse diapsids".
- Constanze Bickelmann, Johannes Müller and Robert R. Reisz (2009). "The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of younginiform reptiles". Canadian Journal of Earth Sciences 49 (9): 651–661. doi:10.1139/E09-038.
- Robert R. Reisz, Sean P. Modesto and Diane M. Scott (2011). "A new Early Permian reptile and its significance in early diapsid evolution". Proceedings of the Royal Society B 278 (1725): 3731–7. doi:10.1098/rspb.2011.0439. PMC 3203498. PMID 21525061.
|Wikispecies has information related to: Diapsid|
- Diapsida. Michel Laurin and Jacques A. Gauthier. Tree of Life Web Project. June 22, 2000.
- Diapsida Cladogram at Mikko's Phylogeny Archive