Ornithomimus Tenuis

''Ornithomimus'' (; "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.

History of discovery

First species named

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. 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, since recognized as belonging to the Alvarezsauridae.Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2010 Appendix.
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A sixth species, ''Ornithomimus altus'', was named in 1902 by Lawrence Lambe, based on specimen CMN 930, hindlimbs found in 1901 in Alberta, but this was in 1916 renamed to a separate genus, '' Struthiomimus'', by Henry Fairfield Osborn. In 1920 Charles Whitney Gilmore named ''Ornithomimus affinis'' for ''Dryosaurus grandis'' Lull 1911, based on indeterminate material. In 1930 Loris Russell renamed ''Struthiomimus brevetertius'' Parks 1926 and ''Struthiomimus samueli'' Parks 1928 into ''Ornithomimus brevitertius'' and ''Ornithomimus samueli''. The same year Oliver Perry Hay renamed ''Aublysodon mirandus'' Leidy 1868 into ''Ornithomimus mirandus'', today seen as a ''nomen dubium''. In 1933 William Arthur Parks created a ''Ornithomimus elegans'', today seen as either belonging to '' Chirostenotes'' or '' Elmisaurus''. That same year, Gilmore named ''Ornithomimus asiaticus'' for material found in Inner Mongolia.

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.

Reclassification by Dale Russell

At first it had been common to name each newly discovered ornithomimid as a species of ''Ornithomimus''. In the sixties, this tendency was still strong as is shown by the fact that Oskar Kuhn renamed ''Megalosaurus lonzeensis'' Dollo 1903 from Belgium into ''Ornithomimus lonzeensis'' (today understood to be an abelisauroid claw), and Dale Russell in 1967 renamed ''Struthiomimus currellii'' Parks 1933 and ''Struthiomimus ingens'' Parks 1933 into ''Ornithomimus currellii'' and ''Ornithomimus ingens''. At the same time it was usual that workers referred to the entire ornithomimid material as simply "Struthiomimus". To solve this confusion by scientifically testing the separation between ''Ornithomimus'' and ''Struthiomimus'', in 1972 Dale Russell published a morphometric study showing that statistical differences in some proportions could be used to distinguish the two. He concluded that ''Struthiomimus'' and ''Ornithomimus'' were valid genera. In the latter Russell recognised two species: the type species ''Ornithomimus velox'' and ''Ornithomimus edmontonicus'' even though he had trouble reliably distinguishing it from ''O. velox''. ''Struthiomimus currellii'' he considered a younger synonym of ''Ornithomimus edmontonicus''. However, Russell also interpreted the data as indicating that many specimens could not be referred to either ''Ornithomimus'' or ''Struthiomimus''. Therefore, he created two new genera. The first was '' Archaeornithomimus'' to which ''Ornithomimus asiaticus'' and ''Ornithomimus affinis'' were assigned, becoming an ''Archaeornithomimus asiaticus'' and an ''Archaeornithomimus affinis''. The second genus was ''Dromiceiomimus'', meaning "Emu mimic" from the old generic name for the emu, ''Dromiceius''. Russell assigned several former ''Ornithomimus'' species named during the 20th century, including ''O. brevitertius'' and ''O. ingens'', to the new genus as ''Dromiceiomimus brevitertius''. He renamed ''Ornithomimus samueli'' into a second ''Dromiceiomimus'' species: ''Dromiceiomimus samueli''.Russell, D. (1972). "Ostrich dinosaurs from the Late Cretaceous of western Canada." ''Canadian Journal of Earth Sciences'', 9: 375-402.

Misassigned to ''Ornithomimus''

Two tibiae from the Navesink Formation of New Jersey were named '' Coelosaurus antiquus'' ("antique hollow lizard") by Joseph Leidy in 1865. The tibiae were first attributed to ''Ornithomimus'' in 1979 by Donald Baird and John R. Horner as ''Ornithomimus antiquus''. Normally, this would have made ''Ornithomimus'' a junior synonym of ''Coelosaurus'', but Baird and Horner discovered that the name "Coelosaurus" was preoccupied by a dubious taxon based on a single vertebra, named ''Coelosaurus'' by an anonymous author now known to be Richard Owen in 1854. Baird referred several other specimens from New Jersey and Maryland to ''O. antiquus''. Beginning in 1997, Robert M. Sullivan regarded ''O. velox'' and ''O. edmontonicus'' as junior synonyms of ''O. antiquus''. Like Russell, he considered the former two species indistinguishable from each other, and noted that they both shared distinctive features with ''O. antiquus''.Sullivan, (1997). "A juvenile ''Ornithomimus antiquus'' (Dinosauria: Theropoda: Ornithomimosauria), from the Upper Cretaceous Kirtland Formation (De-na-zin Member), San Juan Basin, New Mexico." ''New Mexico Geological Society Guidebook, 48th Field Conference, Mesozoic Geology and Paleontology of the Four Corners Region''. 249-254. However, David Weishampel (2004) considered "C." ''antiquus'' to be indeterminate among ornithomimosaurs, and therefore a ''nomen dubium''.Weishampel, D.B.(2004).
Another Look at the Dinosaurs of the East Coast of North America. En (Colectivo Arqueológico-Paleontológico Salense, Ed.).
" ''Actas de las III Jornadas sobre Dinosaurios y su Entorno.'' 129-168. Salas de los Infantes, Burgos, España. An SVP 2012 abstract agreed with Weishampel by noting that ''Coelosaurus'' differs from ''Gallimimus'' and ''Ornithomimus'' in the features of the tibiae.

In 1988 Gregory S. Paul classified the species in genera '' Archaeornithomimus'', '' Struthiomimus'', ''Dromiceiomimus'' and ''Gallimimus'' in genus ''Ornithomimus''. This has found no acceptance among other workers and presently the name is not used by Paul himself.

Present interpretations

Even after Russell's study, various researchers have found reasons to lump some or all of these species back into ''Ornithomimus'' in various combinations. In 2004, Peter Makovicky, Yoshitsugu Kobayashi