Ornithomimus (/ˌɔːrnɪθəˈmaɪməs, -θoʊ-/;[2] "bird mimic") is a genus of ornithomimid dinosaurs from the Late Cretaceous Period of what is now North America. Ornithomimus was a swift bipedal theropod which fossil evidence indicates was covered in feathers, equipped with a small toothless beak that may indicate an omnivorous diet. It is usually classified into two species: the type species, Ornithomimus velox, and a referred species, Ornithomimus edmontonicus. O. velox was named in 1890 by Othniel Charles Marsh on the basis of a foot and partial hand from the late Maastrichtian-age Denver Formation of Colorado, United States. Another seventeen species have been named since, though most of them have subsequently been assigned to new genera or shown to be not directly related to Ornithomimus velox. The best material of species still considered part of the genus has been found in Alberta, Canada, representing the species O. edmontonicus, known from several skeletons from the early Maastrichtian Horseshoe Canyon Formation. Additional species and specimens from other formations are sometimes classified as Ornithomimus, such as Ornithomimus samueli (alternately classified in the genera Dromiceiomimus or Struthiomimus) from the earlier, Campanian-age Dinosaur Park Formation of Alberta.
The history of Ornithomimus classification, and the classification of ornithomimids in general, has been complicated. The type species, Ornithomimus velox, was first named by O.C. Marsh in 1890, based on syntypes YPM 542 and YPM 548, a partial hindlimb and forelimb found on 30 June 1889 by George Lyman Cannon in the Denver Formation of Colorado. The generic name means "bird mimic", derived from Greek ὄρνις, ornis, "bird", and μῖμος, mimos, "mimic", in reference to the bird-like foot. The specific name means "swift" in Latin.[3] Simultaneously, Marsh named two other species: Ornithomimus tenuis, based on specimen USNM 5814, and Ornithomimus grandis. Both consist of fragmentary fossils found by John Bell Hatcher in Montana of which it is today understood they represent tyrannosauroid material. At first Marsh assumed Ornithomimus was an ornithopod but this changed when Hatcher found specimen USNM 4736, a partial ornithomimid skeleton, in Wyoming, which Marsh named Ornithomimus sedens in 1892. On that occasion also Ornithomimus minutus was created based on specimen YPM 1049, a metatarsus,[4] since recognized as belonging to the Alvarezsauridae.[5]
A sixth species, Ornithomimus altus, was named in 1902 by Lawrence Lambe, based on specimen CMN 930, hindlimbs found in 1901 in Alberta,[6] but this was in 1916 renamed to a separate genus, Struthiomimus, by Henry Fairfield Osborn.[7] In 1920 Charles Whitney Gilmore named Ornithomimus affinis for Dryosaurus grandis Lull 1911,[8] based on indeterminate material. In 1930 Loris Russell renamed Struthiomimus brevetertius Parks 1926 and Struthiomimus samueli Parks 1928 into Ornithomimus brevitertius and Ornithomimus samueli.[9] The same year Oliver Perry Hay renamed Aublysodon mirandus Leidy 1868 into Ornithomimus mirandus,[10] today seen as a nomen dubium. In 1933 William Arthur Parks created a Ornithomimus elegans,[11] today seen as either belonging to Chirostenotes or Elmisaurus. That same year, Gilmore named Ornithomimus asiaticus for material found in Inner Mongolia.[12]
Also in 1933, Charles Mortram Sternberg named the species Ornithomimus edmontonicus for a nearly complete skeleton from the Horseshoe Canyon Formation of Alberta, specimen CMN 8632.[13]