''Ornithomimus'' (; "bird mimic") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

ornithomimid Ornithomimidae (meaning "bird-mimics") is a family of theropod dinosaurs which bore a superficial resemblance to modern ostriches. Ornithomimids were fast, omnivorous or herbivorous dinosaurs known mainly from the Late Cretaceous Period of Lauras ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s from the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

Period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

of what is now

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

. ''Ornithomimus'' was a swift bipedal

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

which fossil evidence indicates was covered in

feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premie ...

s, equipped with a small toothless beak that may indicate an

omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...

diet. It is usually classified into two species: the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...

, ''Ornithomimus velox'', and a referred species, ''Ornithomimus edmontonicus''. ''O. velox'' was named in 1890 by

Othniel Charles Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...

on the basis of a foot and partial hand from the late

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the inte ...

-age Denver Formation of

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

. 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 Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest T ...

, Canada, representing the species ''O. edmontonicus'', known from several skeletons from the early Maastrichtian

Horseshoe Canyon Formation The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller. The Horseshoe Canyon Formation is part of th ...

. Additional species and specimens from other formations are sometimes classified as ''Ornithomimus'', such as ''Ornithomimus samueli'' (alternately classified in the genera '' Dromiceiomimus'' or ''

Struthiomimus ''Struthiomimus'' (meaning "ostrich mimic", from the Greek στρούθειος/''stroutheios'' meaning "of the ostrich" and μῖμος/''mimos'' meaning "mimic" or "imitator") is a genus of ornithomimid dinosaurs from the late Cretaceous of No ...

'') from the earlier,

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...

-age

Dinosaur Park Formation The Dinosaur Park Formation is the uppermost member of the Belly River Group (also known as the Judith River Group), a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 76. ...

of Alberta.

History of discovery

First species named

The history of ''Ornithomimus'' classification, and the classification of ornithomimids in general, has been complicated. The

, ''Ornithomimus velox'', was first named by

O.C. Marsh Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among h ...

in 1890, based on

syntype In biological nomenclature, a syntype is any one of two or more biological types that is listed in a description of a taxon where no holotype was designated. Precise definitions of this and related terms for types have been established as part of ...

s YPM 542 and YPM 548, a partial hindlimb and forelimb found on 30 June 1889 by

George Lyman Cannon George may refer to: People * George (given name) * George (surname) * George (singer), American-Canadian singer George Nozuka, known by the mononym George * George Washington, First President of the United States * George W. Bush, 43rd Presid ...

in the Denver Formation of

. 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 Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

. 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 John Bell Hatcher (October 11, 1861 – July 3, 1904) was an American paleontologist and fossil hunter known as the "king of collectors" and best known for discovering ''Torosaurus'' and ''Triceratops'', two genera of dinosaurs described by O ...

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

of which it is today understood they represent tyrannosauroid material. At first Marsh assumed ''Ornithomimus'' was an

ornithopod Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous w ...

but this changed when Hatcher found specimen USNM 4736, a partial ornithomimid skeleton, in

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to t ...

, which Marsh named '' Ornithomimus sedens'' in 1892. On that occasion also '' Ornithomimus minutus'' was created based on specimen YPM 1049, a

metatarsus The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...

, since recognized as belonging to the

Alvarezsauridae Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...

.Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2010 Appendix.
/ref> A sixth species, ''Ornithomimus altus'', was named in 1902 by

Lawrence Lambe Lawrence Morris Lambe (August 27, 1863 – March 12, 1919) was a Canadian geologist, palaeontologist, and ecologist from the Geological Survey of Canada (GSC). His published work, describing the diverse and plentiful dinosaur discoveries from th ...

, based on specimen CMN 930, hindlimbs found in 1901 in

, but this was in 1916 renamed to a separate genus, ''

'', by

Henry Fairfield Osborn Henry Fairfield Osborn, Sr. (August 8, 1857 – November 6, 1935) was an American paleontologist, geologist and eugenics advocate. He was the president of the American Museum of Natural History for 25 years and a cofounder of the American Euge ...

. In 1920

Charles Whitney Gilmore Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the N ...

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 Oliver Perry Hay (May 22, 1846 – November 2, 1930) was an American herpetologist, ichthyologist, and paleontologist. Hay was born in Jefferson County, Indiana, to Robert and Margaret Hay. In 1870, Hay graduated with a bachelor of arts from Eu ...

renamed ''Aublysodon mirandus'' Leidy 1868 into ''Ornithomimus mirandus'', today seen as a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...

''. In 1933 William Arthur Parks created a ''Ornithomimus elegans'', today seen as either belonging to ''

Chirostenotes ''Chirostenotes'' ( ; named from Greek 'narrow-handed') is a genus of oviraptorosaurian dinosaur from the late Cretaceous (about 76.5 million years ago) of Alberta, Canada. The type species is ''Chirostenotes pergracilis''. History of discover ...

'' or ''

Elmisaurus ''Elmisaurus'' (meaning "foot sole lizard") is an extinct genus of caenagnathid dinosaur from the Late Cretaceous Nemegt Formation of Mongolia. It was a theropod belonging to the Oviraptorosauria. Discovery In 1970, a paleontological Polish-M ...

''. That same year, Gilmore named ''Ornithomimus asiaticus'' for material found in

Inner Mongolia Inner Mongolia, officially the Inner Mongolia Autonomous Region, is an autonomous region of the People's Republic of China. Its border includes most of the length of China's border with the country of Mongolia. Inner Mongolia also accounts for a ...

. Also in 1933,

Charles Mortram Sternberg Charles Mortram Sternberg (1885–1981) was an American-Canadian fossil collector and paleontologist, son of Charles Hazelius Sternberg. Late in his career, he collected and described '' Pachyrhinosaurus'', '' Brachylophosaurus'', '' Parksosaur ...

named the species ''Ornithomimus edmontonicus'' for a nearly complete skeleton from the

, 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 Oskar Kuhn (7 March 1908, Munich – 1990) was a German palaeontologist. Life and career Kuhn was educated in Dinkelsbühl and Bamberg and then studied natural science, specialising in geology and paleontology, at the University of Munich, f ...

renamed ''Megalosaurus lonzeensis'' Dollo 1903 from

Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to ...

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 Morphometrics (from Greek μορϕή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are c ...

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 ''Archaeornithomimus'' (meaning "ancient bird mimic") is a genus of ornithomimosaurian theropod dinosaur that lived in Asia during the Late Cretaceous period, around 96 million years ago in the Iren Dabasu Formation. Discovery and naming In 19 ...

'' 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

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it conn ...

e from the

Navesink Formation The Navesink Formation is a 66 to 70 mya greensand glauconitic marl and sand geological formation in New Jersey. It is known for its Cretaceous period fossil shell beds and dinosaur bones. Description The Navesink Formation, named after Navesi ...

New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delawa ...

were named '' Coelosaurus antiquus'' ("antique hollow lizard") by

Joseph Leidy Joseph Mellick Leidy (September 9, 1823 – April 30, 1891) was an American paleontologist, parasitologist and anatomist. Leidy was professor of anatomy at the University of Pennsylvania, later was a professor of natural history at Swarthmore ...

in 1865. The tibiae were first attributed to ''Ornithomimus'' in 1979 by

Donald Baird Donald is a masculine given name derived from the Gaelic name ''Dòmhnall''.. This comes from the Proto-Celtic *''Dumno-ualos'' ("world-ruler" or "world-wielder"). The final -''d'' in ''Donald'' is partly derived from a misinterpretation of the ...

and

John R. Horner John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Second E ...

as ''Ornithomimus antiquus''. Normally, this would have made ''Ornithomimus'' a

junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linn ...

of ''Coelosaurus'', but Baird and Horner discovered that the name "Coelosaurus" was preoccupied by a

dubious Doubt is a mental state in which the mind remains suspended between two or more contradictory propositions, unable to be certain of any of them. Doubt on an emotional level is indecision between belief and disbelief. It may involve uncertainty ...

taxon based on a single vertebra, named ''Coelosaurus'' by an anonymous author now known to be

Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Ow ...

in 1854. Baird referred several other specimens from New Jersey and

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean t ...

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 Professor David Bruce Weishampel (born November 16, 1952) is an American palaeontologist in the Center for Functional Anatomy and Evolution at Johns Hopkins University School of Medicine. Weishampel received his Ph.D. in Geology from the Universi ...

(2004) considered "C." ''antiquus'' to be indeterminate among ornithomimosaurs, and therefore a ''

''.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 Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...

classified the species in genera ''

'', ''

'', '' Dromiceiomimus'' and ''

Gallimimus ''Gallimimus'' ( ) is a genus of Theropoda, theropod dinosaur that lived in what is now Mongolia during the Late Cretaceous Period (geology), period, about seventy mya (unit), million years ago (mya). Several fossils in various stages of growth ...

'' 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 and

Phil Currie Philip John Currie (born March 13, 1949) is a Canadian palaeontologist and museum curator who helped found the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta and is now a professor at the University of Alberta in Edmonton. In the ...

studied Russell's 1972 proportional statistics to re-analyze ornithomimid relationships in light of new specimens. They concluded that there was no justification to separate ''Dromiceiomimus'' from ''Ornithomimus'', sinking ''Dromiceiomimus'' as a synonym of ''O. edmontonicus''.Makovicky, Kobayashi and Currie (2004). "Ornithomimosauria." In Weishampel, Dodson and Osmolska (eds.), ''The Dinosauria Second Edition''. University of California Press. 861 pp. However, they did not include the type species of ''Ornithomimus'', ''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 The Society of Vertebrate Paleontology (SVP) is a professional organization that was founded in the United States in 1940 to advance the science of vertebrate paleontology around the world. Mission and Activities SVP has about 2,300 members inte ...

annual meeting,Kobayashi, Makovicky and Currie (2006). "Ornithomimids (Theropoda: Dinosauria) from the Late Cretaceous of Alberta, Canada." ''Journal of Vertebrate Paleontology'', 26(3): 86A. and 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

which have 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

, two other species are presently considered to be possibly valid, both from the late Maastrichtian. '' O. sedens'' was named by Marsh in 1892 from partial remains found in the

Lance Formation The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the late ...

, only one 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 a species of ''Ornithomimus''. Although it has since been referred to mainly as ''Struthiomimus sedens'', based on complete specimens from

(as well as some fragments from Alberta and

Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...

), these yet have to be described and compared to the ''O. sedens'' holotype.Longrich, N. (2008). "A new, large ornithomimid from the Cretaceous Dinosaur Park Formation of Alberta, Canada: Implications for the study of dissociated dinosaur remains." ''Palaeontology'', 51(4): 983-997. 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 The Ferris Formation is a Late Cretaceous (~66 Ma) to Paleocene (66-63 Ma), fluvial-deltaic geological formation in southern Wyoming. It contains a variety of trace and body fossils, preserved in sandy fluvial channel deposits and overbank units. ...

.Lillegraven and Eberle (1999). "Vertebrate faunal changes through Lancian and Puercan time in southern Wyoming." ''Journal of Paleontology'', 73(4): 691-710. One specimen attributed to ''O. velox'' (MNA P1 1762A) from the

Kaiparowits Formation The Kaiparowits Formation is a sedimentary rock formation found in the Kaiparowits Plateau in Grand Staircase–Escalante National Monument, in the southern part of Utah in the western United States. It is over 2800 feet (850 m) thick, and is ...

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

, was described in 1985.DeCourten and Russell, D. (1985). "A specimen of ''Ornithomimus velox'' (Theropoda, Ornithomimidae) from the terminal Cretaceous Kaiparowits Formation of southern Utah." ''Journal of Paleontology'', 59(5): 1091-1099. 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''.Zanno, L.E., Weirsma, J.P., Loewen, M.A., Sampson, S.D. and Getty, M.A. (2010)
A preliminary report on the theropod dinosaur fauna of the late Campanian Kaiparowits Formation, Grand Staircase-Escalante National Monument, Utah.
''Learning from the Land Symposium: Geology and Paleontology''. Washington, DC: Bureau of Land Management. 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.Claessens, L. & Mark A. Loewen, M.A. (2015). A redescription of ''Ornithomimus velox'' Marsh, 1890 (Dinosauria, Theropoda). ''Journal of Vertebrate Paleontology'' (advance online publication).

Description

Like other ornithomimids, species of ''Ornithomimus'' are characterized by feet with three weight-bearing toes, long slender arms, and long necks with birdlike, elongated, toothless, beaked skulls. They were

biped Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

al and superficially resembled an

ostrich Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There ...

. They would have been swift runners. They had very long limbs, hollow bones, and large brains and eyes. The brains of ornithomimids in general were large for non-avialan dinosaurs, but this may not necessarily be a sign of greater intelligence; some paleontologists think that the enlarged portions of the brain were dedicated to

kinesthetic Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense". Proprioception is mediated by proprioceptors, mechanosensory neurons ...

coordination. The bones of the hands are remarkably sloth-like in appearance, which led

to suggest that they were used to hook branches during feeding. ''Ornithomimus'' differ from other ornithomimids, such as ''

'', in having shorter torsos, long slender forearms, very slender, straight hand and foot claws and in having hand bones (metacarpals) and fingers of similar lengths.Makovicky, P.J., Kobayashi, Y., and Currie, P.J. (2004). "Ornithomimosauria." In Weishampel, D.B., Dodson, P., & Osmólska, H. (eds.), ''The Dinosauria (second edition)''. University of California Press, Berkeley: 137-150. OrnithomimusSizeComparison

The two ''Ornithomimus'' species today seen as possibly valid differ in size. In 2010

estimated the length of ''O. edmontonicus'' at , its weight at . One of its specimens, CMN 12228, preserves a

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates ...

(thigh bone) long. ''O. velox'', the

of ''Ornithomimus'', is based on material of a smaller animal. Whereas the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

of ''O. edmontonicus'', CMN 8632, preserves a second

metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...

eighty-four millimetres long, the same element with ''O. velox'' measures only fifty-three millimetres.

Feathers and skin

''Ornithomimus'', like many dinosaurs, was long thought to have been scaly. However, beginning in 1995, several specimens of ''Ornithomimus'' have been found preserving evidence of

s. In 1995, 2008 and 2009, three ''Ornithomimus edmontonicus'' specimens with evidence of feathers were found; two adults with carbonized traces on the lower arm, indicating the former presence of

pennaceous feather The pennaceous feather is a type of feather present in most modern birds and in some other species of maniraptoriform dinosaurs. Description A pennaceous feather has a stalk or quill. Its basal part, called a ''calamus'', is embedded in the skin ...

shafts, and a juvenile with impressions of feathers, which were up to five centimetres in length, in the form of hair-like filaments covering the rump, legs and neck was also discovered. The fact that the feather imprints were found in

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

, previously thought to not be able to support such impressions, raised the possibility of finding similar structures with more careful preparation of future specimens. A study describing the fossils in 2012 concluded that ''O. edmontonicus'' was covered in plumaceous feathers at all growth stages, and that only adults had pennaceous wing-like structures, suggesting that wings may have evolved for mating displays. In 2014, Christian Foth and others argued that the evidence was insufficient to conclude that the forelimb feathers of ''Ornithomimus'' were necessarily pennaceous, citing the fact that the monofilamentous wing feathers in cassowaries would likely leave similar traces. A fourth feathered specimen of ''Ornithomimus'', this time from the lower portion of the

, was described in October, 2015 by Aaron van der Reest, Alex Wolfe, and Phil Currie. It was the first ''Ornithomimus'' specimen to preserve the feathers along the tail. The feathers, though crushed and distorted, bore numerous similarities with those of the modern

, both in their structure and distribution on the body. Skin impressions were also preserved in the 2015 specimen, which indicated that from mid-thigh to the feet, there was bare skin devoid of scales, and that a flap of skin connect the upper thigh to the torso. This latter structure is similar to that found in modern birds, including ostriches, but was positioned higher above the knee in ''Ornithomimus'' than in birds.

Classification

In 1890 Marsh assigned ''Ornithomimus'' to the

Ornithomimosauria Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia (now Asia, Europe and Nor ...

, a classification that is still common. Modern

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

studies indicate a derived position in the ornithomimids; these however have only included ''O. edmontonicus'' in their analyses. The relationships between ''O. edmontonicus'', ''O. velox'' and ''O. sedens'' have not been published. The following cladogram is based on Xu ''et al.'', 2011:

Paleobiology

The diet of ''Ornithomimus'' is still debated. As theropods, ornithomimids might have been carnivorous but their body shape would also have been suited for a partly or largely herbivorous lifestyle. Suggested food includes insects, crustaceans, fruit, leaves, branches, eggs, and the meat of lizards and small mammals."Dromiceiomimus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. ''The Age of Dinosaurs''. Publications International, LTD. p. 140. . ''Ornithomimus'' had legs that seem clearly suited for rapid locomotion, with the

about 20% longer than the

. The large eye sockets suggest a keen visual sense, and also suggest the possibility that they were nocturnal. In a 2001 study conducted by Bruce Rothschild and other paleontologists, 178 foot bones referred to ''Ornithomimus'' were examined for signs of

stress fracture A stress fracture is a fatigue-induced bone fracture caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated injury from repeated submaximal loading, such as running or ...

, but none were found.Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.