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Dromaeosauridae

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Dromaeosaurids, "raptors" or members of the family Dromaeosauridae ("running lizards") are theropod dinosaurs. They were mainly small, gracile carnivores that flourished in the Cretaceous period. In popular usage they are often called "raptors" after the Velociraptor (which was made famous by the film Jurassic Park) and their similarities to modern carnivorous birds who are also commonly called raptors.

Dromaeosaurids
Temporal range: Jurassic-Cretaceous
File:Amnh30.jpg
Model of Microraptor at
American Museum of Natural History, New York City
Fossil
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Sauropsida
Order:
Saurischia
Suborder:
Theropoda
Infraorder:
Coelurosauria
(unranked):
Deinonychosauria
Family:
Dromaeosauridae

Matthew & Brown, 1922
Genera

See text.

Dromaeosaurids have been found in North America, Europe, North Africa, Japan, China, Mongolia and Argentina. They first appeared in the Mid-Jurassic period (Bathonian stage, 167 million years ago) and survived until the end of the Cretaceous (Maastrichtian stage, 65.5 ma), existing for over 60 million years, up until the Cretaceous-Tertiary extinction event. Jurassic dromaeosaurs are known primarily from teeth (Metcalf et al., 1992).

Characteristics

Dromaeosaurs were small to medium-sized dinosaurs, ranging from about 2-20 feet in length. Like other theropods, they walked on their hind legs, however the large second toe claw was apparently held retracted, with the third and fourth toes bearing the weight of the animal. The second toe claw is curved and bladelike, and there is currently disagreement about its function. Some have argued that it served as a hook, but its sharp ventral edges and flattened shape suggest it may have been used as a slashing weapon, like the canines of saber-toothed cats. The long tail of dromaeosaurs had a flexible base, but most of its length was stiffened by bony tendons. It has been proposed that this tail was used as a stabilizer, in Microraptor gui the tail ends in a small, diamond-shaped fan of feathers which may have been used as an aerodynamic stabilizer and rudder. There is some evidence that some dromaeosaurids hunted in packs: Deinonychus fossils have been uncovered in small groups that seem to have been killed while attacking Tenontosaurus tilletti, a larger ornithischian dinosaur. Not all paleontologists find the evidence conclusive, however.

Relationship with birds

Main article: Feathered dinosaurs

Dromaeosaurids are theropods, and may be the sister taxon to Aves (birds), though there is mounting evidence (including the Thermopolis specimen of Archaeopteryx which preserves a retractable second toe claw) that they are true Avian birds (see below). Either way, Dromaeosauridae is a subgroup of Deinonychosauria, and includes such animals as Deinonychus, Dromaeosaurus, Velociraptor, Microraptor, Saurornitholestes, and Utahraptor. Dromaeosauridae is sometimes seen as synonymous to Deinonychosauria, when Troodontidae is placed in less derived maniraptorans.

Evidence from dromaeosaur skin impressions (in animals such as Microraptor, Cryptovolans and Sinornithosaurus) shows modern pennaceous feathers and fully formed remiges or "flight feathers", leading to the question of whether these animals were capable of powered flight. Modern feathers are a primitive trait of the maniraptora, and primitive dromaeosaurids and dromaeosaur relatives (like Jinfengopteryx, Pedopenna, and Archaeopteryx) show evidence of feathers. While it is extremely likely that all small dromaeosaurs had feathers, it is possible that the larger forms lost some or all of their insulatory covering (Prum & Brush, 2002).

True birds?

While dromaeosaurids have traditionally been considered non-avian dinosaurs, some researchers (such as Martin, Paul, and Czerkas) consider dromaeosaurids and other maniraptorans to be more derived than the first bird, Archaeopteryx, and therefore members of the clade/class Aves. While few published cladistic studies support this hypothesis (instead favoring a position as the closest relatives of Aves but not true members of that group), these researchers point to a number of skeletal features present in dromaeosaurs that are usually found only in flightless birds. The presence of advanced wing feathers, the possibility of flight in the most primitive dromaeosaurs (microraptorians and Rahonavis) (Czerkas, 2002), and the shoulder joints adapted for flapping in many species (such as Unenlagia) also lend support to the idea that dromaeosaurs were true birds (Paul, 2002).

Classification

The family Dromaeosauridae was first erected by Matthew and Brown (1922) for the new genus Dromaeosaurus, and was given a cladistic definition by Sereno (1998). Sereno defined it as the most inclusive clade containing Dromaeosaurus but not Troodon, Ornithomimus, or Passer. The subfamilies of Dromaeosauridae frequently shift in content based on new analysis, but typically consist of the following groups:

  • Dromaeosaurinae: Defined as all dromaeosaurs closer to Dromaeosaurus than to Velociraptor, Microraptor, Unenlagia, or Passer. This subfamily is usually found to consist of medium to giant-sized species, with generally box-shaped skulls (the other subfamilies generally have narrower snouts).
  • Velociraptorinae: Defined as all dromaeosaurs closer to Velociraptor than to Dromaeosaurus, Microraptor, Unenlagia, or Passer. Velociraptorinae has traditionally included Deinonychus and Saurornithoides, though most recent studies suggest those genera are closer to Dromaeosaurus, leaving only Velociraptor in this subfamily.
  • Microraptorinae: (aka Microraptoria) Defined as all dromaeosaurs closer to Microraptor than to Dromaeosaurus, Velociraptor, Unenlagia, or Passer. This subfamily includes many of the smallest dromaeosaurs, which show adaptations for living in trees. All known dromaeosaur skin impressions hail from this group, and all show an extensive covering of feathers and well-developed wings. Some species may have been capable of powered flight.
  • Unenlagiinae: Defined as all dromaeosaurs closer to Unenlagia than to Dromaeosaurus, Velociraptor, Microraptor, or Passer. This enigmatic group is the most poorly supported subfamily of dromaeosaurs, and it is possible that some or all of its members belong outside of Dromaeosauridae. The larger, ground-dwelling members like Buitreraptor and Unenlagia show strong flight adaptations, though they were probably too large to actually take off. One possible member of this group, Rahonavis, is very small, with well-developed wings that show evidence of quill knobs (the attatchment points for flight feathers), and it is very likely that it could fly.

Note: Some authors and cladistic studies, especially those that factor in the small flying species of dromaeosaurid, find the first bird Archaeopteryx to be an early member of Dromaeosauridae. If this is the case, since its family was named before the family Dromaeosauridae, ICZN rules state that its family name has priority. Therefore, when Archaeopteryx is included, the name "Dromaeosauridae" becomes invalid in favor of the name Archaeopterygidae. Paul (1986) was among the first to name dinosaurs such as Deinonychus and Velociraptor as archaeopterygids, rather than dromaeosaurids.

Species

A classification of the various species of dromaeosaurids, based on Sereno (2005), Senter (2004), and Makovicky (2005).

References

  • Czerkas, S.A., Zhang, D., Li, J., and Li, Y. (2002). "Flying Dromaeosaurs". In Czerkas, S.J. (ed.). Feathered Dinosaurs and the Origin of Flight: The Dinosaur Museum Journal 1. Blanding: The Dinosaur Museum. pp. 16–26. {{cite book}}: External link in |chapter= and |title= (help)CS1 maint: multiple names: authors list (link)
  • Colbert, E. and D. A. Russell (1969). "The small Cretaceous dinosaur Dromaeosaurus". American Museum Novitates. 2380: 1–49.
  • Hopson, J. A. (1980). "Relative brain size in dinosaurs: implications for dinosaurian endothermy". American Association for the Advancement of Science Symposium. 28: 287–310.
  • Qiang Ji, Mark A. Norell, Ke-Qin Gao, Shu-An Ji and Dong Ren (26 April 2001). "Distribution of integumentary structures in a feathered dinosaur". Nature. 410: 1084–1088. doi:10.1038/35074079.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: year (link)
  • Kirkland, J. I., R. Gaston; et al. (1993). "A large dromaeosaur (Theropoda) from the Lower Cretaceous of Eastern Utah". Hunteria. 2: 1–16. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
  • Makovicky, Apesteguía and Agnolín (2005). "The earliest dromaeosaurid theropod from South America". Nature. 437: 1007–1011.
  • Metcalf SJ, Vaughan RF, Benton MJ, Cole J, Simms MJ & Dartnall DL (1992). "A new Bathonian (Middle Jurassic) microvertebrate site, within the Chipping Norton Limestone Formation at Hornsleaslow Quarry, Gloucestershire". Proceedings of the Geologists’ Association. 103: 321–342.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Norell, Mark A. and P. J. Makovicky (2004). "Dromaeosauridae". In D. B. Weishampel, P. Dodson and H. Osmolska (ed.). The Dinosauria. Berkeley: University of California Press. pp. 196–209.
  • Ostrom, J. H. (1969). "Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana". Peabody Museum of Natural History Bulletin. 30: 1–165.
  • Paul, G.S. (2002). Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Baltimore: Johns Hopkins University Press.
  • Perle, A., M. Norell and J. Clark (1999). "A new maniraptoran theropod Achillobator giganticus (Dromaeosauridae) from the Upper Cretaceous of Burkhant, Mongolia". Contributions of the Department of Geology, National University of Mongolia, Ulaanbaatar. 101: 1–105.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Prum, R. & Brush A.H. (2002). "The evolutionary origin and diversification of feathers". The Quarterly Review of Biology. 77: 261–295.
  • Senter, P., R. Barsold, B.B. Britt and D.A. Burnham (2004). "Systematics and evolution of Dromaeosauridae (Dinosauria, Theropoda)". Bulletin of the Gunma Museum of Natural History. 8: 1–20.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Sereno, P. C. (2005). "The logical basis of phylogenetic taxonomy". Systematic Biology. 51: 1–25.
  • Xing Xu, Xiao-Lin Wang and Xiao-Chun Wu (16 September 1999). "A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China". Nature. 401: 262–266. doi:10.1038/45769. {{cite journal}}: Check date values in: |date= (help)
  • Xing Xu, Zhonghe Zhou, Xiaolin Wang, Xuewen Kuang, Fucheng Zhang and Xiangke Du (23 January 2003). "Four winged dinosaurs from China". Nature. 421: 335–340. doi:10.1038/nature01342.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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