Ornithomimosauria

Filozoa

Ornithomimosaurs Temporal range: Early - Late Cretaceous, 130–65.5 Ma PreЄ Є O S D C P T J K Pg N
Cast of a Struthiomimus altus skeleton, Royal Tyrrell Museum
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Node:	Maniraptoriformes Barsbold, 1976
Infraorder:	†Ornithomimosauria Marsh, 1890
Families
Deinocheiridae Garudimimidae Harpymimidae Ornithomimidae
Synonyms
Arctometatarsalia Holtz, 1994

The Ornithomimosauria, ornithomimosaurs ("bird-mimic lizards") or ostrich dinosaurs^[1] were 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). The group first appeared in the Early Cretaceous and persisted until the Late Cretaceous. Primitive members of the group include Pelecanimimus, Shenzhousaurus, Harpymimus and probably the huge Deinocheirus, the arms of which reached 2.4 m (8 feet) in length. More advanced species, members of the family Ornithomimidae, include Gallimimus, Archaeornithomimus, Anserimimus, 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). An ornithomimid caudal vertebra has been discovered which has tooth drag marks attributed to Saurornitholestes.^[2]

Description

The skulls of ornithomimosaurs were small, with large eyes, above relatively long and slender necks. Some primitive species (such as Pelecanimimus and Harpymimus) had teeth, but most had toothless beaks.

Struthiomimus sedens forelimb, showing claws (OUMNH)

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 many other coelurosaurs, the ornithomimosaurian hide was probably feathered rather than scaly.

Diet

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.^[3] 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.

The feeding habits of ornithomimids have been controversial.

In 2001 Norell et al. reported a specimen of Gallimimus (IGM 100/1133) and one of Ornithomimus (RTMP 95.110.1). These two fossil skulls had soft tissue preservation, and both had keratinous beaks with vertical grooves extending ventrally from the bony upper mandible. These structures are reminiscent of the lamellae seen in ducks, in which they function to strain small edible items like plants, forams, mollusks, and ostracods from the water. The authors further noted that ornithomimids were abundant in mesic environments, and rarer in more arid environments, suggesting that they may have depended on waterborne sources of food, possibly filter feeding. They noted that primitive ornithomimids had well developed teeth, while derived forms were edentulous and probably could not feed on large animals.^[4]

One later paper questioned the conclusions of Norell et al. Barrett (2005) noted that vertical ridges are seen on the inner surface of the beaks of strictly herbivorous turtles, and also the hadrosaurid Edmontosaurus. Barrett also offered calculations, estimating how much energy could be derived from filter feeding and the probable energy needs of an animal as big as Gallimimus. He concluded that herbivory was more likely. ^[5]

Daily activity patterns

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.^[6]

Classification

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 distinctivness 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.^[7]

"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.^[7]

Taxonomy

Restoration of Beishanlong grandis

• Infraorder Ornithomimosauria
  • Pelecanimimus (central Spain)
  • Shenzhousaurus (northeastern China)
  • Kinnareemimus (Thailand)
  • Beishanlong (northeastern China)
  • Family Deinocheiridae
    • Deinocheirus (Mongolia)
  • Family Garudimimidae
    • Garudimimus (Mongolia)
  • Family Harpymimidae
    • Harpymimus (Mongolia)
  • Superfamily Ornithomimoidea
    • Family Ornithomimidae
      • Anserimimus (Mongolia)
      • Archaeornithomimus (China)
      • Gallimimus (Mongolia)
      • Ornithomimus (Alberta, Colorado, New Jersey, Utah, Wyoming)
      • Qiupalong (eastern China)
      • Sinornithomimus (Inner Mongolia)
      • Struthiomimus (Montana and Alberta)
• ?Timimus, from the early Cretaceous (a femur from Dinosaur Cove in Victoria in southeastern Australia), is possibly an ornithomimosaurian.

Phylogeny

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.^[8]

The cladogram presented here follows the one recovered by Turner, Clarke, Ericson and Norell, 2007.^[9] Clade names follow definitions provided by Sereno, 2005.^[10]

Ornithomimosauria	Pelecanimimus unnamed Archaeornithomimus Shenzhousaurus unnamed Harpymimus unnamed Garudimimus Ornithomimidae Struthiomimus Gallimimus unnamed Ornithomimus Anserimimus

Cladogram after Xu et al., 2011:^[11]

Ornithomimidae	Archaeornithomimus unnamed Sinornithomimus unnamed Anserimimus Gallimimus unnamed Qiupalong unnamed Struthiomimus Ornithomimus

Paleopathology

Main article: Paleopathology

An ornithomimid caudal vertebra has been discovered that has tooth drag marks attributed to Saurornitholestes.^[2] A specimen from an unidentified ornithomimid shows a pathologic toe bone whose far end is "mushroomed" compared to those of healthy specimens.^[12]

Reproduction

Neonate sized ornithomimid fossils have been documented in the scientific literature.^[13]

Footnotes

1. ^ British Museum (Natural History): Ostrich Dinosaurs
2. ^ ^{a b} "Introduction," Jacobsen (2001). Page 59.
3. ^ Nicholls and Russell (1985).
4. ^ Norell, et al. (2001).
5. ^ Barrett (2005).
6. ^ Schmitz and Motani (2011)
7. ^ ^{a b} Sereno, P. C. (2005). Stem Archosauria—TaxonSearch [version 1.0, 2005 November 7]
8. ^ Paul, G.S. (2002). Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Baltimore: Johns Hopkins University Press. 
9. ^ Turner, et al. (2007).
10. ^ Stem Archosauria—TaxonSearch Sereno (2005).
11. ^ Xu, et al. (2011).
12. ^ "Ornithomimidae," in Molnar (2001). Pg. 343.
13. ^ "Abstract," Tanke and Brett-Surman (2001). Page 207.

References

• Barrett, P. M. (2005). "The diet of ostrich dinosaurs (Theropoda: Ornithomimosauria)." Palaeontology, 48: 347-358.
• British Museum (Natural History): Ostrich Dinosaurs
• Jacobsen, A.R. 2001. Tooth-marked small theropod bone: An extremely rare trace. p. 58-63. In: Mesozioc Vertebrate Life. Ed.s Tanke, D. H., Carpenter, K., Skrepnick, M. W. Indiana University Press.
• Li Xu, Yoshitsugu Kobayashi, Junchang Lü, Yuong-Nam Lee, Yongqing Liu, Kohei Tanaka, Xingliao Zhang, Songhai Jia and Jiming Zhang (2011). "A new ornithomimid dinosaur with North American affinities from the Late Cretaceous Qiupa Formation in Henan Province of China". Cretaceous Research 32 (2): 213–222. doi:10.1016/j.cretres.2010.12.004. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WD3-51PH16S-4&_user=10&_coverDate=04%2F30%2F2011&_rdoc=12&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info(%23toc%236755%232011%23999679997%232878787%23FLA%23display%23Volume)&_cdi=6755&_sort=d&_docanchor=&view=c&_ct=15&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=e205c413625dff6a4bfa0d6b9e9d22b1&searchtype=a. 
• Molnar, R. E., 2001, Theropod paleopathology: a literature survey: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 337-363.
• Nicholls, E. L., and Russell, A. P. (1985). "Structure and function of the pectoral girdle and forelimb of Struthiomimus altus (Theropoda: Ornithomimidae)." Palaeontology, 28: 643-677.
• Norell, M. A., Makovicky, P., and Currie, P. J. (2001). "The beaks of ostrich dinosaurs." Nature, 412: 873-874.
• Schmitz, L. and Motani, R. (2011). "Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology". Science in press. doi:10.1126/science.1200043. PMID 21493820. 
• Sereno, P. C. 2005. Stem Archosauria—TaxonSearch [version 1.0, 2005 November 7]
• Tanke, D.H. and Brett-Surman, M.K. 2001. Evidence of Hatchling and Nestling-Size Hadrosaurs (Reptilia:Ornithischia) from Dinosaur Provincial Park (Dinosaur Park Formation: Campanian), Alberta, Canada. pp. 206-218. In: Mesozoic Vertebrate Life—New Research Inspired by the Paleontology of Philip J. Currie. Edited by D.H. Tanke and K. Carpenter. Indiana University Press: Bloomington. xviii + 577 pp.
• Turner, A.H., Pol, D., Clarke, J.A., Erickson, G.M., and Norell, M. (2007). "Supporting online material for: A basal dromaeosaurid and size evolution preceding avian flight". Science, 317: 1378-1381. doi:10.1126/science.1144066 (supplement)

External links

• Khalaf-von Jaffa, Norman Ali Bassam Ali Taher (2006). Ornithomimid Dinosaur Tracks from Beit Zeit, West of Jerusalem, Palestine. Gazelle: The Palestinian Biological Bulletin. Number 56, August 2006. pp. 1–7.

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