The Ornithomimosauria, ornithomimosaurs ("bird-mimic lizards") or ostrich dinosaurs are theropod dinosaurs which bore a superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia (now Asia, Europe and North America), as well as Africa and possibly Australia. The group first appeared in the Early Cretaceous and persisted until the Late Cretaceous. Primitive members of the group include Nqwebasaurus, Pelecanimimus, Shenzhousaurus, Hexing and Deinocheirus, the arms of which reached 2.4 m (8 feet) in length. More advanced species, members of the family Ornithomimidae, include Gallimimus, Struthiomimus, and Ornithomimus. Some paleontologists, like Paul Sereno, consider the enigmatic alvarezsaurids to be close relatives of the ornithomimosaurs and place them together in the superfamily Ornithomimoidea (see classification below).
|Cast of an ornithomimid (Struthiomimus altus) skeleton, Royal Tyrrell Museum|
The skulls of ornithomimosaurs were small, with large eyes, above relatively long and slender necks. The most basal members of the taxon (such as Pelecanimimus and Harpymimus) had a jaw with small teeth, while the later and more derived species had a toothless beak.
The fore limbs ("arms") were long and slender and bore powerful claws. The hind limbs were long and powerful, with a long foot and short, strong toes terminating in hooflike claws. Ornithomimosaurs were probably among the fastest of all dinosaurs. Like other coelurosaurs, the ornithomimosaurian hide was feathered rather than scaly.
Ornithomimosaurs probably acquired most of their calories from plants. Many ornithomimosaurs, including primitive species, have been found with numerous gastroliths in their stomachs, characteristic of herbivores. Henry Fairfield Osborn suggested that the long, sloth-like "arms" of ornithomimosaurs may have been used to pull down branches on which to feed, an idea supported by further study of their strange, hook-like hands. The sheer abundance of ornithomimids — they are the most common small dinosaurs in North America — is consistent with the idea that they were plant eaters, as herbivores usually outnumber carnivores in an ecosystem. However, they may have been omnivores that ate both plants and small animal prey.
Comparisons between the scleral rings of two ornithomimosaur genera (Garudimimus and Ornithomimus) and modern birds and reptiles indicate that they may have been cathemeral, active throughout the day at short intervals.
Unambiguous evidence of feathers is known from Ornithomimus/Dromiceiomimus, of which there are multiple specimens preserving feather traces. Deinocheirus and Pelecanimimus have been speculated to be feathered as well, the former due to the presence of a pygostyle, and the later due to possible impressions (otherwise taken to be collagen fibers).
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.
Ornithomimosauria has variously been used for the branch-based group of all dinosaurs closer to Ornithomimus than to birds, and in more restrictive senses. The more exclusive sense began to grow in popularity when the possibility arose that alvarezsaurids might fall under Ornithomimosauria if an inclusive definition were adopted. Another clade, Ornithomimiformes, was defined by Sereno (2005) as (Ornithomimus velox > Passer domesticus) and replaces the more inclusive use of Ornithomimosauria when alvarezsaurids or some other group are found to be closer relatives of ornithomimosaurs than maniraptorans, with Ornithomimosauria redefined to include dinosaurs closer to Ornithomimus than to alvarezsaurids. Gregory S. Paul has proposed that Ornithomimosauria might be a group of primitive, flightless birds, more advanced than Deinonychosauria and Oviraptorosauria.
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.
Aepyornithomimus (meaning "Aepyornis mimic") is a genus of ornithomimid theropod dinosaur from the Late Cretaceous Djadokhta Formation in Mongolia. It lived in the Campanian, around 80 million years ago, when the area is thought to have been a desert. The type and only species is A. tugrikinensis.Alvarezsauridae
Alvarezsauridae is a group of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, a consensus of recent work suggests that they evolved from an early branch of maniraptoran theropods. Alvarezsaurids were highly specialized. They had tiny but stout forelimbs, with compact, bird-like hands. Their skeletons suggest that they had massive breast and arm muscles, possibly adapted for digging or tearing. They had long, tube-shaped snouts filled with tiny teeth. They may have been adapted to prey on colonial insects such as termites.
Alvarezsaurus, the namesake member of the group, was named for the historian Gregorio ÁlvarezArchaeornithomimus
Archaeornithomimus (meaning "ancient bird mimic") is a genus of ornithomimosaurian theropod dinosaur from the Late Cretaceous of China, 70 million years ago.Beishanlong
Beishanlong is a genus of giant ornithomimosaurian theropod dinosaur from the Early Cretaceous of China.Coelurosauria
Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrannosaurs, ornithomimosaurs, and maniraptorans; Maniraptora includes birds, the only dinosaur group alive today.Most feathered dinosaurs discovered so far have been coelurosaurs. Philip J. Currie considers it likely and probable that all coelurosaurs were feathered. In the past, Coelurosauria was used to refer to all small theropods, but this classification has since been abolished.Dromiceiomimus
Dromiceiomimus is a genus of ornithomimid theropod from the Late Cretaceous (early Maastrichtian) of Alberta, Canada.Evolution of dinosaurs
This article gives an outline and examples of dinosaur evolution. For a detailed list of interrelationships see Dinosaur classification.
Dinosaurs evolved within a single lineage of archosaurs 243-233 Ma (million years ago) from the Anisian to the Carnian ages, the latter part of the middle Triassic. Dinosauria is a well-supported clade, present in 98% of bootstraps. It is diagnosed by many features including loss of the postfrontal on the skull and an elongate deltopectoral crest on the humerus.In March 2017, scientists reported a new way of classifying the dinosaur family tree, based on newer and more evidence than available earlier. According to the new classification, the original dinosaurs, arising 200 million years ago, were small, two-footed omnivorous animals with large grasping hands. Descendants (for the non-avian dinosaurs) lasted until 66 million years ago.Garudimimus
Garudimimus ("Garuda mimic") is a basal ornithomimosaurian theropod dinosaur from the Upper Cretaceous of Mongolia.Harpymimus
Harpymimus is a basal ornithomimosaurian theropod dinosaur from the Early Cretaceous Period of what is now Mongolia. Unlike later, more derived ornithomimosaurs, Harpymimus still possessed teeth, although they appear to have been restricted to the dentary of the lower jaw.Kinnareemimus
Kinnareemimus is a genus of ornithomimosaurian theropod dinosaur from Thailand. It is known only from incomplete remains including vertebrae, partial pubic bones, metatarsals, and an incomplete fibula. The third metatarsal exhibits a distinctive lateral "pinching", known as the "arctometarsalian" condition, variations of which are found in ornithomimosaurs, tyrannosauroids, troodontids, and caenagnathids. Its remains were collected from the Early Cretaceous Sao Khua Formation, dating to the Valanginian to Hauterivian stage, at Phu Wiang, Khon Kaen Province. Its early occurrence makes it among the earliest (if not the earliest) ornithomimosaur known, depending on the age of the formation. Buffetaut et al. suggest the fossils of Kinnareemimus may indicate an Asian origin for advanced ornithomimosaurs.The genus was first described by Eric Buffetaut, Varavudh Suteethorn and Haiyan Tong in 2009 and the type and only species is K. khonkaenensis. It was named in honor of Kinnaree, "graceful beings of Thai mythology, with the body of a woman and the legs of a bird, said to inhabit the depths of the legendary Himmapan Forest, by allusion to the bird-like feet of this dinosaur". The name "Kinnareemimus" was first mentioned in a 1999 paper by Sasithorn Kamsupha, and (as "Ginnareemimus") in a publication by Ryuichi Kaneko in 2000.Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea are also often included. Together with the next closest sister group, the Ornithomimosauria, Maniraptora comprises the more inclusive clade Maniraptoriformes. Maniraptorans first appear in the fossil record during the Jurassic Period (see Eshanosaurus), and are regarded as surviving today as living birds.Maniraptoriformes
Maniraptoriformes is a clade of dinosaurs with pennaceous feathers and wings that contains ornithomimosaurs and maniraptors. This group was named by Thomas Holtz, who defined it as "the most recent common ancestor of Ornithomimus and birds, and all descendants of that common ancestor."Nqwebasaurus
Nqwebasaurus (IPA: [ᵑǃʷɛbaˈsɔɹəs]; anglicized as or ) is a basal coelurosaur and is the basal-most member of the coelurosaurian clade Ornithomimosauria from the Early Cretaceous of South Africa. The name Nqwebasaurus is derived from the Xhosa word "Nqweba" which is the local name for the Kirkwood district, and "thwazi" is ancient Xhosa for lightning. Currently it is the only known coelurosaur discovered in Africa and shows that basal coelurosaurian dinosaurs inhabited Gondwana 50 million years earlier than previously thought. The type specimen of Nqwebasaurus was discovered by William J. de Klerk who is affiliated with the Albany Museum in Grahamstown. It is the only fossil of its species found to date and was found in the Kirkwood Formation of the Uitenhage Group. Nqwebasaurus has the unofficial nickname "Kirky", due to being found in the Kirkwood.Ornithomimidae
Ornithomimidae (meaning "bird-mimics") is a group of theropod dinosaurs which bore a superficial resemblance to modern ostriches. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia (now Asia and North America), though they have also been reported from the Wonthaggi Formation of Australia. The group first appeared in the Early Cretaceous.Ornithomimus
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.Pelecanimimus
Pelecanimimus (meaning "pelican mimic") is a genus of basal ("primitive") ornithomimosaurian theropod dinosaur from the Early Cretaceous of Spain. It is notable for possessing more teeth than any other member of the Ornithomimosauria (or any other theropod), most of which were toothless.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 North America. Ornithomimids were long-legged, bipedal, ostrich-like dinosaurs with toothless beaks. The type species, Struthiomimus altus, is one of the more common small dinosaurs found in Dinosaur Provincial Park; its abundance suggests that these animals were herbivores or omnivores rather than pure carnivores.Timeline of ornithomimosaur research
This timeline of ornithomimosaur research is a chronological listing of events in the history of paleontology focused on the ornithomimosaurs, a group of bird-like theropods popularly known as the ostrich dinosaurs. Although fragmentary, probable, ornithomimosaur fossils had been described as far back as the 1860s, the first ornithomimosaur to be recognized as belonging to a new family distinct from other theropods was Ornithomimus velox, described by Othniel Charles Marsh in 1890. Thus the ornithomimid ornithomimosaurs were one of the first major Mesozoic theropod groups to be recognized in the fossil record. The description of a second ornithomimosaur genus did not happen until nearly 30 years later, when Henry Fairfield Osborn described Struthiomimus in 1917. Later in the 20th century, significant ornithomimosaur discoveries began occurring in Asia. The first was a bonebed of "Ornithomimus" (now Archaeornithomimus) asiaticus found at Iren Debasu. More Asian discoveries took place even later in the 20th century, including the disembodied arms of Deinocheirus mirificus and the new genus Gallimimus bullatus. The formal naming of the Ornithomimosauria itself was performed by Rinchen Barsbold in 1976.Early research into ornithomimosaur evolution was based on comparative anatomy. In 1972, Dale Russell argued that the Jurassic Elaphrosaurus of Africa was an ancestral relative of ornithomimids. The descriptions of Garudimimus and Harpymimus in the 1980s revealed the existence of primitive ornithomimosaurs outside of the Ornithomimidae proper. Subsequent research and discoveries during the 1990s refined science's knowledge of ornithomimosaur evolution. In 1994, Pelecanimimus polyodon was described from Europe, the first known ornithomimosaur from that continent and apparently a very evolutionarily primitive taxon. From the late 1990s into the early 21st century cladistic evidence mounted against Russell's hypothesis that ornithomimosaurs were descended from a close relative of Elaphrosaurus, and favored an ancestry close to Pelecanimimus. Paleontologists found that within the theropod family tree, ornithomimosaurs were primitive coelurosaurs closely related to, but outside of, the maniraptorans.The juxtaposition of apparent evolutionary affinities to carnivorous dinosaurs with the possession of toothless beaks has led to controversy among paleontologists trying to reconstruct the diet of ornithomimosaurs. Osborn hypothesized in 1917 that ornithomimosaurs may have eaten plants, social insects, or aquatic invertebrates. In the 1970s paleontologists Russell, Halszka Osmolska, and her colleagues considered ornithomimosaurs carnivores that may have fed on insects, small vertebrates, or eggs. In the early to mid 1980s, however Russell and Elizabeth Nicholls began advocating a reinterpretation of ornithomimosaurs as herbivores. With the 1999 report of gastroliths in the new genus Sinornithomimus, came further support for reinterpreting ornithomimosaurs as herbivores or filter feeders rather than carnivores. In 2001, Mark Norell reported a comb-like structure in the beak of Gallimimus that may have been used for filter feeding, bringing renewed credibility to one of Osborn's 1917 hypotheses. If this interpretation of the evidence is correct, Gallimimus would be the largest terrestrial filter feeder in history.Timimus
Timimus is a genus of small coelurosaurian theropod dinosaur from the Early Cretaceous of Australia. It was originally identified as an ornithomimosaur, but now it is thought to be a different kind of theropod, possibly a tyrannosauroid.