Ornithomimus
Ornithomimus is a genus of ornithomimid theropod dinosaurs from the Campanian and Maastrichtian ages of the Late Cretaceous in western North America. Ornithomimus was a swift, bipedal dinosaur which was covered in feathers and 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 Denver Formation of Colorado. Other seventeen species have been named since then, though almost all of them have been subsequently assigned to new genera or shown not to be directly related to O. velox. The best material of species still considered part of the genus has been found in Alberta, representing the species O. edmontonicus, known from several skeletons from the Horseshoe Canyon Formation. Additional species and specimens from other formations are sometimes classified in the genus, such as Ornithomimus samueli from the earlier Dinosaur Park Formation.
History of discovery
First species named
The history of Ornithomimus classification and the classification of ornithomimids in general has been very complicated. The type species, Ornithomimus velox, was first named by O.C. Marsh in 1890 and is based on syntypes YPM 542 and YPM 548, found by George Lyman Cannon in the Denver Formation of Colorado on June 30, 1889. The generic name means "bird mimic", derived from Greek words ὄρνις, "bird", and μῖμος, "mimic", in reference to the bird-like foot. The specific name means "swift" in Latin. Simultaneously, Marsh named two other species: Ornithomimus tenuis and Ornithomimus grandis. Both consist of fragmentary fossils found by John Bell Hatcher in Montana, which is today understood as tyrannosauroid material. At first, Marsh assumed Ornithomimus was an ornithopod, but this changed when Hatcher and A. E. Sullins found the specimen USNM 4736, a partial ornithomimid skeleton, in 1891 from the Lance Formation of Wyoming. Marsh named it Ornithomimus sedens in 1892, though the specimen remained unnumbered and not figured until Charles Whitney Gilmore's 1920 re-description. Marsh also named Ornithomimus minutus was also created based on the specimen YPM 1049 in 1892, but it has since been recognized as belonging to an alvarezsaurid.A sixth species, Ornithomimus altus, was named in 1902 by Lawrence Lambe and was based on specimen CMN 930, but this was renamed to a separate genus in 1916: Struthiomimus, by Henry Fairfield Osborn. In 1920, Gilmore named Ornithomimus affinis for Dryosaurus grandis, based on indeterminate material. In 1930, Loris Russell renamed Struthiomimus brevetertius and Struthiomimus samueli into Ornithomimus brevitertius, Ornithomimus mirifica and Ornithomimus samueli, respectively. The very same year, Oliver Perry Hay renamed Aublysodon mirandus into Ornithomimus mirandus, which is today seen as a nomen dubium. In 1933, William Arthur Parks created the species Ornithomimus elegans, which is today seen as either 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.
Reclassification by Dale Russell
At first, it had been common practice to name each newly discovered ornithomimid as a species of Ornithomimus. In the sixties, this tendency was still very strong, as is shown by the fact that Oskar Kuhn renamed Megalosaurus lonzeensis from Belgium into Ornithomimus lonzeensis and Dale Russell in 1967 renamed Struthiomimus currellii and Struthiomimus ingens into Ornithomimus currellii and Ornithomimus ingens, respectively. 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, Dale Russell in 1972 published a morphometric study. It showed that statistical differences in some proportions could be used to distinguish the two and he concluded that Struthiomimus and Ornithomimus were valid genera. In the latter, Russell recognised two species: the type species Ornithomimus velox and Ornithomimus edmontonicus. He considered Struthiomimus currellii to be 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 one was Archaeornithomimus. ''Ornithomimus asiaticus and Ornithomimus affinis were reassigned to this new genus, becoming Archaeornithomimus asiaticus and Archaeornithomimus affinis. The second one was Dromiceiomimus, meaning "Emu mimic". This comes 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 this new genus as Dromiceiomimus brevitertius. He also renamed Ornithomimus samueli into a second Dromiceiomimus species: Dromiceiomimus samueli''.Misassigned to ''Ornithomimus''
Two tibiae from the Navesink Formation of New Jersey were named Coelosaurus antiquus 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, which was based on a single vertebra. It was originally 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. However, David Weishampel considered "C." antiquus to be indeterminate among ornithomimosaurs, resulting in it being a nomen dubium. 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 various species of Archaeornithomimus, Struthiomimus, Dromiceiomimus, and Gallimimus to the genus Ornithomimus. This has found no acceptance among other workers and the name is not presently 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, and Phil Currie studied Russell's 1972 proportional statistics to re-analyze ornithomimid relationships in light of newly discovered specimens. They concluded that there was no justification to separate Dromiceiomimus from Ornithomimus, sinking Dromiceiomimus as a synonym of O. edmontonicus. However, they did not include the type species O. velox in this analysis. The same team further supported the synonymy between Dromiceiomimus and O. edmontonicus in a 2006 lecture at the Society of Vertebrate Paleontology annual meeting. Their opinion has been followed by most later authors. Makovicky's team also considered Dromiceiomimus samueli to be a junior synonym of O. edmontonicus, though Longrich later suggested it may belong to a distinct, unnamed species from the Dinosaur Park Formation which has yet to be described. Longrich called the species Ornithomimus samueli in a faunal list for the Dinosaur Park Formation.Apart from O. edmontonicus dating to the early Maastrichtian, two other species are presently considered to be possibly valid and are also from the late Maastrichtian. O. sedens was named by Marsh in 1892 from partial remains found in the Lance Formation of Wyoming a year after the description of O. velox. Dale Russell, in his 1972 revision of ornithomimids, could not determine which genus it actually belonged to, though he speculated that it may be intermediate between Struthiomimus and Dromiceiomimus. In 1985, he considered it to be a species of Ornithomimus. Although it has since been referred to mainly as Struthiomimus sedens, these have yet to be described and compared to the O. sedens holotype.
The other is the original type species: O. velox, at first known from very limited remains. Additional specimens referred to O. velox have been described from the Denver Formation and from the Ferris Formation of Wyoming. One specimen attributed to O. velox from the Kaiparowits Formation of Utah was described in 1985. Re-evaluation of this specimen by Lindsay Zanno and colleagues in 2010, however, cast doubt on its assignment to O. velox and possibly even to Ornithomimus. This conclusion was supported by a 2015 re-description of O. velox, which found that only the holotype specimen was confidently referable to that species. The authors of this study tentatively referred to the Kaiparowits specimen as Ornithomimus sp., along with all of the specimens from the Dinosaur Park Formation.