Ornithomimiformes

Taxobox
name = Ornithomimiformes
fossil_range = Early - Late Cretaceous

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image_width = 250px
image_caption = "Gallimimus" skeleton, Experimentarium, Copenhagen.
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Theropoda
unranked_familia = Ornithomimiformes
unranked_familia_authority = Sereno, 2005
subdivision_ranks = Sub-clades
subdivision =
Alvarezsauridae
Ornithomimosauria

Ornithomimiformes is a clade of theropod dinosaurs. They contain the Ornithomimosauria and the Alvarezsauridae.

The paleontologist Paul Sereno, in 2005, conceived the concept Ornithomimiformes, defining them as all species closer to "Ornithomimus edmontonicus" than to "Passer domesticus". Because he had redefined Ornithomimosauria in a much narrower sense, a new term was made necessary within his preferred terminology to denote the clade containing the sistergroups Ornithomimosauria and Alvarezsauridae — previously the latter had been contained within the former.Sereno, P. C. (2005). [http://www.taxonsearch.org/Archive/stem-archosauria-1.0.php Stem Archosauria—TaxonSearch] [version 1.0, 2005 November 7] ]

The Ornithomimiformes are the probable sister clade of Maniraptora within the Maniraptoriformes.

History of classification

In the early 1990s, prominent paleontologists such as Thomas R. Holtz Jr. proposed a close relationship between theropods with an "arctometatarsalian" foot; that is, bipedal dinosaurs in which the upper foot bones were 'pinched' together, an adaptation for running. Holtz (1994) defined the clade Arctometatarsalia as "the first theropod to develop the arctometatarsalian pes and all of its descendants." This group included the Troodontidae, Tyrannosauroidea, and Ornithomimosauria. Holtz (1996, 2000) later refined this definition to the branch-based "Ornithomimus" and all theropods sharing a more recent common ancestor with "Ornithomimus" than with birds." Subsequently, the idea that all arctometatarsalian dinosaurs formed a natural group was abandoned by most paleontologists, including Holtz, as studies began to demonstrate that tyrannosaurids and troodontids were more closely related to other groups of coelurosaurs than they were to ornithomimosaurs. Since the strict definition of Arctometatarsalia was based on "Ornithomimus", it became redundant with the name Ornithomimosauria under broad definitions of that clade, and the name Arctometatarsalia was mostly abandoned.

Ornithomimiformes is identical in content to Holtz's Arctometatarsalia, as it has a very similar definition. While Ornithomimiformes is the newer group, Sereno rejected the idea that Arctometatarsalia should take precedence over Ornithomimiformes, because the meaning of the former name has been changed very radically by Holtz.

References