Ornithodira

Taxobox
name = Ornithodirans
fossil_range = Middle Triassic - Recent


image_width = 250px
image_caption =
regnum = Animalia
phylum = Chordata
classis = Sauropsida
subclassis = Diapsida
infraclassis = Archosauromorpha
unranked_ordo = Archosauria
unranked_familia = Ornithodira
unranked_familia_authority = Gauthier, 1986
subdivision_ranks = Clades
subdivision =
* Dinosauromorpha
* Pterosauromorpha

Ornithodira is a clade within the larger group Archosauria.

In 1986 Jacques Gauthier coined the name for a node clade, containing the last common ancestor of the dinosaurs and the pterosaurs and all of its descendants. In 1991 Paul Sereno was the first to give a formal definition, that explicitly included "Scleromochlus" and thus potentially was a larger group than Ornithodira "sensu Gauthier". In 1999 Michael Benton concluded that "Scleromochlus" was indeed outside of Ornithodira "sensu Gauthier"; that year he defined a stem clade Avemetatarsalia for all Archosauria "sensu Gauthier" (Benton's own Avesuchia) that were closer to dinosaurs than to Crocodylia. In 2004 Benton gave a formal definition of Ornithodira "sensu Gauthier". In 2005 Sereno stated the opinion that Ornithodira was not a useful concept, whereas Avemetatarsalia was.

Members of Ornithodira are characterized by an upright gait and an S-curved neck, hence the name "Ornithodira" ("bird necks"). It is by definition strictly divided into two subclades: Dinosauromorpha and Pterosauromorpha.

Dinosauromorpha contains more basal forms like "Lagerpeton" and "Marasuchus" and as more derived forms the dinosaurs, to a subgroup of which, the theropods, according to most modern scientists the birds belong. The Ornithodira are therefore still extant.

Pterosauromorpha contains Pterosauria, which are the famous flying reptiles, and as far as is known the first vertebrates capable of true flight. Most researchers think pterosaurians had neither an S-curved neck, nor an upright gait: the clade Ornithodira is defined on basis of ancestry, not characters — and it is always possible later descendants show a change in characters.

Phylogeny

Cladogram after Ezcurra (2006):

Ornithodira
--Pterosauromorpha

`--Pterosauria `--Dinosauromorpha
--"Lagerpeton" `--Dinosauriformes
--"Marasuchus" `--+--"Pseudolagosuchus" `--+--"Silesaurus" `--+--"Eucoelophysis" `--Dinosauria
--Saurischia
|--Herrerasauridae
`--Eusaurischia
|--Theropoda
`--Sauropodomorpha `--Ornithischia