Named by
O.C. Marsh in 1890, the family
Ornithomimidae was originally classified as a group of "megalosaurs" (a "
wastebasket taxon" containing any medium to large sized theropod dinosaurs), but as more theropod diversity was uncovered, their true relationships to other theropods started to resolve, and they were moved to the
Coelurosauria. Recognizing the distinctiveness of ornithomimids compared to other dinosaurs,
Rinchen Barsbold placed ornithomimids within their own
infraorder, Ornithomimosauria, in 1976. The contents of Ornithomimidae and Ornithomimosauria varied from author to author as
cladistic definitions began to appear for the groups in the 1990s. 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. The
paleontologist Paul Sereno, in 2005, proposed the clade "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. However, this concept only appeared on Sereno's Web site and has not yet been officially published as a valid name. "Ornithomimiformes" was 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, because the meaning of the former name has been changed very radically by Holtz. The cladogram below follows an analysis by Yuong-Nam Lee, Rinchen Barsbold, Philip J. Currie, Yoshitsugu Kobayashi, Hang-Jae Lee, Pascal Godefroit, François Escuillié & Tsogtbaatar Chinzorig. The analysis was published in 2014, and includes many ornithomimosaurian taxa. }} The cladogram below follows the phylogenetic analysis by Scott Hartman and colleagues in 2019, which has included a vast majority of species and uncertain specimens, resulting in a novel phylogenetic arrangement. Below is a cladogram by Serrano-Brañas et al., 2020, showing an analysis more in line with previous assumptions about ornithomimosaur classification. }} ==Palaeobiology==