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'Dromaeosauridae' is a family of bird-like theropod dinosaurs. They were mainly small, gracile carnivores that flourished in the Cretaceous Period. In informal usage they are often called "raptors" (after ''Velociraptor''), a term popularized by the film ''Jurassic Park''. The name Dromaeosauridae means 'running lizards', from Greek ''dromeus'' (''δρομευς'') meaning 'runner' and ''sauros'' (''σαυρος'') meaning 'lizard'.
Dromaeosaurids have been found in North America, Europe, North Africa, Japan, China, Mongolia, Madagascar 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 100 million years, up until the Cretaceous-Tertiary extinction event. Jurassic dromaeosaurs are known primarily from teeth.^[1]

Contents

Characteristics

Relationship with birds

Systematics

Taxonomy

Phylogeny

Paleobiology

Predatory behavior

Feathers

In popular culture

References

External links

Characteristics

Dromaeosaurids were small to medium-sized dinosaurs, ranging from about .5 meters in length (2 feet, in the case of ''Microraptor'') to over 6 m (20 ft, in ''Utahraptor'' and ''Achillobator''). Like other theropods, they walked on their hind legs. However, the large, curved second toe claw was apparently held retracted, with the third and fourth toes bearing the weight of the animal. The long tail of dromaeosaurids 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 ended in a small diamond-shaped fan of feathers which may have been used as an aerodynamic stabilizer and rudder.

Relationship with birds

Dromaeosaurids were members of the clade Maniraptora, and may be the sister taxon to Aves (birds), although there is mounting evidence that they are true birds themselves. Evidence from dromaeosaurid 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 active 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.
Whether dromaeosaurids were birds or non-avian dinosaurs depends on their position relative to ''Archaeopteryx'', on which most scientific definitions of "bird" are based. In phylogenetic nomenclature, all members of the clade Aves are dinosaurs, but since dromaeosaurids are found to be slightly less advanced than ''Archaeopteryx'' by most studies, they are exluded from Aves.Senter, Phil, Barsbold, R., Britt, Brooks B. & Burnham, David B. (2004). Systematics and evolution of Dromaeosauridae (Dinosauria, Theropoda). ''Bulletin of the Gunma Museum of Natural History'' 8: 1–20. However, some researchers (such as Alan Feduccia, Larry Martin, Gregory S. Paul,Paul, Gregory S. (1988). ''Predatory Dinosaurs of the World.'' New York: Simon and Schuster. 464 pp. and Stephen Czerkas^[2]) have considered dromaeosaurids to be more advanced than ''Archaeopteryx'', and therefore members of the clade (or class) Aves. Paul, for example, pointed out numerous features of the dromaeosaurid skeleton which he interpreted as evidence that the entire group had evolved from flying ancestors.Paul, Gregory S. (2002). ''Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds.'' Baltimore: Johns Hopkins University Press. 472 pp. Mackovicky and collegues also found that primitive dromaeosaurids, such as ''Microraptor'' and ''Rahonavis'', were more bird-like than advanced forms like ''Velociraptor'', indicating that the larger dromaeosaurids were secondarily flightless, like the modern ostrich. Additionally, the discovery in 2005 of the Thermopolis specimen of ''Archaeopteryx'', which preserved a dromaeosaurid-like hyperextendible second toe, may mean that ''Archaeopteryx'' itself is more primitive than the dromaeosaurids.Mayr, G., Pohl, B., and Peters, D.S. (2005). "A well-preserved ''Archaeopteryx'' specimen with theropod features." ''Science'', 310: 1483–1486. .

Systematics

Taxonomy

The authorship of the family Dromaeosauridae is credited to W.D. Matthew and Barnum Brown, who erected it as a subfamily (Dromaeosaurinae) of the now-defunct family Deinodontidae in 1922, containing only the new genus ''Dromaeosaurus''.^[3] Dromaeosauridae, along with Troodontidae, make up the infraorder Deinonychosauria.
The subfamilies of Dromaeosauridae frequently shift in content based on new analysis, but typically consist of the following groups. The most basal subfamily of dromaeosaurids is often found to be the Unenlagiinae.^[4] 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, although they were probably too large to 'take off'. One member of this group, ''Rahonavis'', is very small, with well-developed wings that show evidence of quill knobs (the attachment points for flight feathers) and it is very likely that it could fly. The next most primitive clade of dromaeosaurs is the Microraptoria. This group 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. Like the unenlagiines, some species may have been capable of active flight. The subfamily Velociraptorinae has traditionally included ''Velociraptor'', ''Deinonychus'', and ''Saurornitholestes'', and while the discovery of ''Tsaagan'' lent support to the this grouping, the inclusion of ''Saurornitholestes'' is still uncertain. The Dromaeosaurinae is usually found to consist of medium to giant-sized species, with generally box-shaped skulls (the other subfamilies generally have narrower snouts).
The following classification of the various genera of dromaeosaurids is based on studies by Sereno (2005), Senter (2004), Makovicky ''et al.'' (2005), Norell ''et al.'' (2006), and Turner ''et al.'' (2007).^[5][6][7] A basal dromaeosaurid and size evolution preceding avian flight, , Alan H., Turner, Science, 2007

★ 'Family Dromaeosauridae'

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★ ''Atrociraptor''

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★ ''Dromaeosauroides''

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★ ''Mahakala''

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★ ''Pyroraptor''

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★ ''Variraptor''

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★ 'Clade Microraptoria'

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★ ''Bambiraptor''

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★ ''Cryptovolans''

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★ ''Graciliraptor''

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★ ''Microraptor''

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★ ''Sinornithosaurus''

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★ 'Subfamily Dromaeosaurinae'

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★ ''Achillobator''

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★ ''Adasaurus''

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★ ''Dromaeosaurus''

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★ ''Utahraptor''

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★ 'Subfamily Unenlagiinae'^[8]

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★ ''Buitreraptor''

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★ ''Neuquenraptor''

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★ ''Rahonavis''

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★ ''Shanag''

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★ ''Unenlagia''

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★ 'Subfamily Velociraptorinae'^[9]

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★ ''Deinonychus''

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★ ''Saurornitholestes''

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★ ''Tsaagan''

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★ ''Velociraptor''

Phylogeny

Dromaeosauridae was first defined as a clade by Paul Sereno in 1998, as the most inclusive natural group containing ''Dromaeosaurus'' but not ''Troodon'', ''Ornithomimus'' or ''Passer''. The various "subfamilies" have also been re-defined as clades, usually defined as all species closer to the groups namesake than to ''Dromaeosaurus'' or any namesakes of other sub-clades (for example, Makovicky defined the clade Unenlagiinae as all dromaeosaurids closer to ''Unenlagia'' than to ''Velociraptor''). The Microraptoria is the only dromaeosaurid sub-clade not converted from a subfamily. Senter and collegues expressly coined the name without the subfamily suffix ''-inae'' to avoid perceived issues with erecting a traditional family-group taxon, should the group be found to lie outside dromaeosauridae proper. Sereno offered a revised definition of the sub-group containing ''Microraptor'' to ensure that it would fall within Dromaeosauridae, and erected the subfamily Microraptorinae, attributing it to Senter ''et al.'', though this usage has only appeared on his online TaxonSearch database and has not been formally published.
The cladogram below follows a 2007 analysis by Turner and collegues, with sub-clades labelled according to definitions by Sereno, 2005.

Paleobiology

Predatory behavior

There is currently disagreement about the function of the enlarged "sickle claw" on the second toe. When John Ostrom described it for ''Deinonychus'' in 1969, he interpreted the claw as a blade-like slashing weapon, much like the canines of some saber-toothed cats, used with powerful kicks to disembowel prey. This interpretation was commonly applied to all dromaeosaurids. However, Manning ''et al.'' argued that the claw instead served as a hook, reconstructing the keratinous sheath with an elliptical cross section, instead of the previously inferred inverted teardrop shape.^[10] In Manning's interpretation, the second toe claw would be used as a climbing aid when subduing bigger prey and also as stabbing weapon.
'Pack Hunting'

''Deinonychus'' fossils have been uncovered in small groups near the remains of the herbivore ''Tenontosaurus'', a larger ornithischian dinosaur. This had been interpreted as evidence that these dromaeosaurs hunted in coordinated packs like some modern mammals.^[11] However, not all paleontologists found the evidence conclusive, and subsequent studies suggest that the ''Deinonychus'' were more likely to have been engaged in disorganized mobbing behavior. Modern birds and crocodiles (the closest relatives of dromaeosaurs) display little cooperative hunting; instead, they are usually either solitary hunters, or are drawn to previously-killed carcasses, where conflict often occurs between individuals of the same species. For example, in situations where groups of komodo dragons are eating together, the largest individuals eat first and will attack smaller komodos that attempt to feed; if the smaller animal dies, it is cannibalized. When this information is applied to the sites containing putative pack-hunting behavior in dromaeosaurs, it appears consistent with a komodo- or crocodile-like feeding strategy. ''Deinonychus'' skeletal remains found at these sites are from subadults, with missing parts consistent with having been eaten by other ''Deinonychus'', evidence against the idea that the animals cooperated in the hunt.^[12] No evidence for any kind of social behavior has been reported for dromaeosaurs other than ''Deinonychus''.

Feathers

The first known dromaeosaur with definitive evidence of feathers was ''Sinornithosaurus'', reported from China by Xu ''et al.'' in 1999.^[13] Many other dromaeosaurid fossils have been found with feathers covering their bodies, some with fully-developed feathered wings. Some even show evidence of a second pair of wings on the hind legs, including ''Microraptor'' and ''Cryptovolans''.Xing, X., Zhou, Z., Wang, X., Kuang, X., Zhang, F., and Du, X. (2003). "Four-winged dinosaurs from China." ''Nature'', '421': 335–340. In light of this, it is most likely that even the large, ground-dwelling dromaeosaurids bore feathers, since even flightless birds today retain most of their plumage. While it is extremely likely that all dromaeosaurs had feathers, it is also possible that the larger forms lost some or all of their insulatory covering.^[14]

In popular culture

The ''Velociraptor'' from the movie ''Jurassic Park'' were actually much larger than the genus.

The dimensions of the supposed ''Velociraptor'' in the film Jurassic Park are much larger than the largest members of the genus. Robert Bakker recalled that Steven Spielberg had been disappointed with the dimensions of ''Velociraptor'' and so upsized it, adding that soon afterwards he named ''Utahraptor'' which was more the size depicted. Gregory S. Paul, in his book ''Predatory Dinosaurs of the World'', concluded that ''Deinonychus'' was a species of ''Velociraptor'' and rechristened the species ''Velociraptor antirrhopus'', a theory that has since been largely rejected.^[15][16] The Dinosauria, Norell, M.A., Makovicky, P.J., , , University of California Press, 2004, Michael Crichton continued to synonymize the two genera in his novels, on which the first two films were based. The depiction of the dromaeosaurid in the original ''Jurassic Park'' film, while accurate for its time, is now known to have been inaccurate in many respects, including the lack of feathers, though ''Jurassic Park III'' addressed this last oversight.

References

1. A new Bathonian (Middle Jurassic) microvertebrate site, within the Chipping Norton Limestone Formation at Hornsleaslow Quarry, Gloucestershire, Metcalf, S.J., Vaughan, R.F., Benton, M.J., Cole, J., Simms, M.J. and Dartnall, D.L., , , Proceedings of the Geologists’ Association, 1992
2. 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, 16-26.[1]
3. Matthew, W. D., and Brown, B. (1922) "The family Deinodontidae, with notice of a new genus from the Cretaceous of Alberta." ''Bulletin of the American Museum of Natural History'', '46': 367-385.
4. A small derived theropod from Öösh, Early Cretaceous, Baykhangor Mongolia, , A.S., Turner, American Museum Novitates, 2007
5. Sereno, P. C. 2005. Stem Archosauria—TaxonSearch [version 1.0, 2005 November 7]
6. Makovicky, Peter J., Apesteguía, Sebastián & Agnolín, Federico L. (2005). The earliest dromaeosaurid theropod from South America. ''Nature'', 437: 1007–1011.
7. Norell, M.A., Clark, J.M., Turner, A.H., Makovicky, P.J., Barsbold, R., and Rowe, T. (2006). "A new dromaeosaurid theropod from Ukhaa Tolgod (Omnogov, Mongolia)." ''American Museum Novitates'', '3545': 1-51.
8. Bonaparte, (1999).
9. Barsbold, R. (1983). "O ptich'ikh chertakh v stroyenii khishchnykh dinozavrov. ["Avian" features in the morphology of predatory dinosaurs]." ''Transactions of the Joint Soviet Mongolian Paleontological Expedition'' '24': 96-103. [Original article in Russian.] Translated by W. Robert Welsh, copy provided by Kenneth Carpenter and converted by Matthew Carrano. PDF fulltext
10.
11. Taphonomy and paleobiological implications of ''Tenontosaurus''-''Deinonychus'' associations, , W. D., Maxwell, Journal of Vertebrate Paleontology, 1995
12. A reevaluation of cooperative pack hunting and gregariousness in ''Deinonychus antirrhopus'' and other nonavian theropod dinosaurs, , B. T., Roach, Bulletin of the Peabody Museum of Natural History, 2007
13.
14. Prum, R., and Brush, A.H. (2002). "The evolutionary origin and diversification of feathers". ''The Quarterly Review of Biology'', '77': 261-295.
15. A theropod dinosaur from the Lower Cretaceous of southern France, , B.P., Pérez-Moreno, Dinosaurs and Other Fossil Reptiles of Europe, Second Georges Cuvier Symposium, Montbéliard; Revue de Paléobiologie, Volume spécial, 1994
16. New information on the anatomy and relationships of ''Dromaeosaurus albertensis'' (Dinosauria: Theropoda), , P. J., Currie, Journal of Vertebrate Paleontology, 1995 (abstract)

External links

★ Dromaeosauridae at DinoData.

★ The Dromaeosauridae: The Raptors!, from the University of California Berkeley Museum of Paleontology.

★ Dromaeosauridae, by Justin Tweet from ''Thescelosaurus''.

★ Dinosaurs - Complete and free online edition of the book "Dinosaurs" as written by W. D. Matthew (cited in this article with authorship of the family Dromaeosauridae), and former Curator of Vertebrate Paleontology at the American Museum of Natural History in New York; Originally published in 1915