Dromaeosauridae

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Dromaeosaurids
Fossil range: Jurassic - Cretaceous
Model of Microraptor at theAmerican Museum of Natural History
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Infraorder: Deinonychosauria
Family: Dromaeosauridae
Matthew & Brown, 1922
Genera

See text.

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, Argentina, and Antarctica.[1] 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. The presence of dromaeosaurs as early as the mid-Jurassic has been confirmed by the discovery of isolated fossil teeth, though no dromaeosaurid body fossils have been found from this period.[2]

Contents

[edit] Characteristics

Dromaeosaurids were small to medium-sized dinosaurs, ranging from about .5 meters in length (2 ft, in the case of Microraptor) to over 6 m (20 ft, in Utahraptor and Achillobator).[3][4] Like other theropods, they walked on their hind legs. However, whereas other theropods walked with three toes contacting the ground, dromaeosaurids apparently held the second toe off the ground in a hyperextended position, with only the third and fourth toes bearing the weight of the animal.[5] The "retracted" second toe bore an unusually large, curved sickle-shaped claw (see "Predatory behavior" below). Dromaeosaurids had long tails with a flexible base, but most of the tail length was stiffened by bony, rod-like extensions of the vertebrae, as well as bony tendons in some species.[6] It has been proposed that this tail was used as a stabilizer while running or in the air;[6] 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 during gliding flight.[7]

[edit] Relationship with birds

Comparison of the forelimbs of Deinonychus (left) and Archaeopteryx (right), one of many skeletal similarities between avians and dromaeosaurids.
Comparison of the forelimbs of Deinonychus (left) and Archaeopteryx (right), one of many skeletal similarities between avians and dromaeosaurids.
For more details on this topic, see Origin of birds and Feathered dinosaurs.

Dromaeosaurids were members of the clade Maniraptora, and a consensus among most modern paleontologists is that they, along with their close relatives the troodontids (which together form the clade Deinonychosauria) are the sister taxon to Aves (birds), and therefore the closest non-avian relatives of birds.[8]

Evidence from dromaeosaurid skin impressions (in animals such as Microraptor, Cryptovolans and Sinornithosaurus) and quill knobs (the anchor points for large wing feathers, seen in Rahonavis and Velociraptor[9]) show that dromaeosaurids had modern pennaceous feathers, leading to the question of whether the smaller, larger-winged species were capable of aerodynamic behaviors like pouncing, parachuting, gliding, or even powered flight. Such advanced feathers are not unique to birds and dromaeosaurs; they may be a primitive trait of the Maniraptora, and are known from diverse maniraptoran taxa (like Caudipteryx, Jinfengopteryx, Pedopenna and Archaeopteryx).

Some researchers have suggested that rather than being the closest non-avian relatives of birds, dromaeosaurids may have been members of the clade Aves (if defined as all animals more closely related to modern birds than to Archaeopteryx). This minority of researchers researchers (such as Alan Feduccia, Larry Martin, Gregory S. Paul,[10] and Stephen Czerkas[11]) have considered dromaeosaurids to be more advanced than Archaeopteryx, and therefore members of the clade (or class) Aves.

[edit] Possible loss of flight

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Whether or not dromaeosaurids were true birds or the closest relatives of birds, a number of paleontologists have suggested that dromaeosaurids may have descended from ancestors that were capable of some form of powered or gliding flight. Gregory S. 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.[12] Makovicky and colleagues also found that primitive dromaeosaurids, such as Microraptor and Rahonavis[verification needed], were more bird-like than advanced forms like Velociraptor, indicating that the larger dromaeosaurids were secondarily flightless, like the modern ostrich.[13] 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[14][verification needed]

[edit] Systematics

[edit] 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.[15] 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. A number of dromaeosaurids have not been assigned to any particular subfamily, often because they are too poorly preserved to be placed confidantly in phylogenetic analysis (see section Phylogeny below), or because they are basal relative to the primary subdivisions of Dromaeosauridae (Mahakala, for example, is the most primitive known dromaeosaurid and falls outside any named sub-group). The most basal subfamily of dromaeosaurids is often found to be the Unenlagiinae.[16] 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).

Mahakala, a basal dromaeosaurid.
Mahakala, a basal dromaeosaurid.
Utahraptor, a dromaeosaurine.
Utahraptor, a dromaeosaurine.
Unenlagia, an unenlagiine.
Unenlagia, an unenlagiine.
Velociraptor, a velociraptorine.
Velociraptor, a velociraptorine.

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).[17][8][13][18][19]

[edit] 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 colleagues 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.[8] 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.[17]

The cladogram below follows a 2007 analysis by Turner and colleagues, with sub-clades labelled according to definitions by Sereno, 2005.[9]

Dromaeosauridae

Mahakala

unnamed
Unenlagiinae

Shanag


Buitreraptor

unnamed

Rahonavis


Unenlagia



Microraptorinae

Microraptor


Graciliraptor



Sinornithosaurus


unnamed
Velociraptorinae

Tsaagan

unnamed

Saurornitholestes

unnamed

Deinonychus


Velociraptor




Dromaeosaurinae

Adasaurus


Dromaeosaurus

unnamed

Achillobator


Utahraptor






[edit] Paleobiology

[edit] Predatory behavior

Model of the "sickle claw" of Utahraptor.
Model of the "sickle claw" of Utahraptor.

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.[23] In Manning's interpretation, the second toe claw would be used as a climbing aid when subduing bigger prey and also as stabbing weapon.

[edit] 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.[24] 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.[25]

In 2007, scientists described the first known extensive dromaeosaur trackway, in Shandong, China. In addition to confirming the hypothesis that the sickle-claw was held retracted off the ground, the trackway (made by a large, Achillobator-sized species) showed evidence of six individuals of about equal size moving together along a shoreline. The individuals were spaced about one meter apart, and retained the same direction of travel, walking at a fairly slow pace. The authors of the paper describing these footprints interpreted the trackways as evidence that some species of dromaeosaurs lived in groups. While the trackways clearly do not represent hunting behavior, the idea that groups of dromaeosaurs may have hunted together could not be ruled out.[5]

[edit] Feathers

Fossil of Microraptor gui with feather impressions.
Fossil of Microraptor gui with feather impressions.

The first known dromaeosaur with definitive evidence of feathers was Sinornithosaurus, reported from China by Xu et al. in 1999.[26] 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.[27] While direct feather impressions are only possible in fine-grained sediments, some fossils found in coarser rocks show evidence of feathers by the presence of quill knobs, the attachment points for wing feathers possessed by some birds. The dromaeosaurids Rahonavis and Velociraptor have both been found with quill knobs, showing that these forms had feathers despite no impressions having been found. In light of this, it is most likely that even the larger ground-dwelling dromaeosaurids bore feathers, since even flightless birds today retain most of their plumage, and relatively large dromaeosaurids, like Velociraptor, are known to have retained pennaceous feathers.[12][9] Though some scientists had suggested that the larger dromaeosaurids lost some or all of their insulatory covering, the discovery of feathers in Velociraptor specimens has been used as evidence that all members of the family retained feathers.[28][9]

[edit] In popular culture

See also: Biological issues in Jurassic Park

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.[29] 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,[10] a theory that has since been largely rejected.[30][31][32] 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.

[edit] References

  1. ^ Case, J.A., Martin, J.E., and Reguero, M. (2007). "A dromaeosaur from the Maastrichtian of James Ross Island and the Late Cretaceous Antarctic dinosaur fauna." Pp. 1-4 in Cooper, A., Raymond, C., and Team, I.E. (eds.), Antarctica: a Keystone in a Changing World -- Online Proceedings for the Tenth International Symposium on Antarctic Earth Sciences, U.S. Geological Survey Open-File Report 2007-1047, SRP 083. U.S. Geological Survey, Washington, D.C.
  2. ^ Metcalf, S.J., Vaughan, R.F., Benton, M.J., Cole, J., Simms, M.J. and Dartnall, D.L. (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. 
  3. ^ Hwang, S.H., Norell, M.A., Ji, Q., and Gao, K. (2002). "New Specimens of Microraptor zhaoianus (Theropoda: Dromaeosauridae) from Northeastern China." American Museum Novitates, 3381: 44pp.[1]
  4. ^ Perle, A., Norell, M.A., and Clark, J. (1999). "A new maniraptoran theropod - Achillobator giganticus (Dromaeosauridae) - from the Upper Cretaceous of Burkhant, Mongolia." Contributions of the Mongolian-American Paleontological Project, 101: 1–105.
  5. ^ a b Li, Rihui; Lockley, M.G., Makovicky, P.J., Matsukawa, M., Norell, M.A., Harris, J.D. and Liu, M. (2007). "Behavioral and faunal implications of Early Cretaceous deinonychosaur trackways from China". 
  6. ^ a b Norell, Mark A.; & Makovicky, Peter J. (1999). "Important features of the dromaeosaurid skeleton II: information from newly collected specimens of Velociraptor mongoliensis". American Museum Novitates 3282: 1–45. 
  7. ^ Chatterjee, S., and Templin, R.J. (2007). "Biplane wing planform and flight performance of the feathered dinosaur Microraptor gui." Proceedings of the National Academy of Sciences, 104(5): 1576-1580. [2]
  8. ^ a b c d 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.
  9. ^ a b c d Turner, A.H., Makovicky, P.J., and Norell, M.A. (2007). "Feather quill knobs in the dinosaur Velociraptor." Science, 317(5845): 1721.
  10. ^ a b Paul, Gregory S. (1988). Predatory Dinosaurs of the World. New York: Simon and Schuster. 464 pp.
  11. ^ 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.[3]
  12. ^ a b 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.
  13. ^ a b Makovicky, Peter J., Apesteguía, Sebastián & Agnolín, Federico L. (2005). The earliest dromaeosaurid theropod from South America. Nature, 437: 1007–1011. doi:10.1038/nature03996
  14. ^ Mayr, G., Pohl, B., and Peters, D.S. (2005). "A well-preserved Archaeopteryx specimen with theropod features." Science, 310: 1483–1486. doi:10.1126/science.1120331.
  15. ^ a b 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.
  16. ^ Turner, A.S.; Hwang, S.H.; and Norell, M.A. (2007). "A small derived theropod from Öösh, Early Cretaceous, Baykhangor Mongolia". American Museum Novitates 3557: 1-27. Retrieved on 2007-03-29. 
  17. ^ a b Sereno, P. C. 2005. Stem Archosauria—TaxonSearch [version 1.0, 2005 November 7]
  18. ^ 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.
  19. ^ Turner, Alan H.; Pol, Diego; Clarke, Julia A.; Erickson, Gregory M.; and Norell, Mark (2007). "A basal dromaeosaurid and size evolution preceding avian flight" (pdf). Science 317: 1378-1381. doi:10.1126/science.1144066. 
  20. ^ Novas and Agnolin, (2004). "Unquillosaurus ceibalii Powell, a giant maniraptoran (Dinosauria, Theropoda) from the Late Cretaceous of Argentina." Rev. Mus. Argentino Cienc. Nat., n.s. 6(1): 61-66.
  21. ^ Bonaparte, (1999).
  22. ^ 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
  23. ^ Manning, P.L., Payne, D., Pennicott, J., Barrett, P.M., and Ennos, R.A. (2005). "Dinosaur killer claws or climbing crampons?". Biology Letters 2: 110-112. doi:10.1098/rsbl.2005.0395. 
  24. ^ Maxwell, W. D.; Ostrom, J.H. (1995). "Taphonomy and paleobiological implications of Tenontosaurus-Deinonychus associations". Journal of Vertebrate Paleontology 15 (4): 707-712. 
  25. ^ Roach, B. T.; D. L. Brinkman (2007). "A reevaluation of cooperative pack hunting and gregariousness in Deinonychus antirrhopus and other nonavian theropod dinosaurs". Bulletin of the Peabody Museum of Natural History 48 (1): 103–138. 
  26. ^ Xu, X., Wang, X.-L., and Wu, X.-C. (1999). "A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China". Nature 401: 262–266. doi:10.1038/45769. 
  27. ^ Xing, X., Zhou, Z., Wang, X., Kuang, X., Zhang, F., and Du, X. (2003). "Four-winged dinosaurs from China." Nature, 421: 335–340.
  28. ^ Prum, R., and Brush, A.H. (2002). "The evolutionary origin and diversification of feathers". The Quarterly Review of Biology, 77: 261-295.
  29. ^ Bakker, Robert T. (1995). Raptor Red. New York: Bantam Books, pg. 4. ISBN 0-553-57561-9. 
  30. ^ Pérez-Moreno, B.P.; J. L. Sanz, J. Sudre and B. Sigé (1994). "A theropod dinosaur from the Lower Cretaceous of southern France". Dinosaurs and Other Fossil Reptiles of Europe, Second Georges Cuvier Symposium, Montbéliard; Revue de Paléobiologie, Volume spécial 7: 173-188. 
  31. ^ Currie, P. J. (1995). "New information on the anatomy and relationships of Dromaeosaurus albertensis (Dinosauria: Theropoda)". Journal of Vertebrate Paleontology 15 (3): 576-591.  (abstract)
  32. ^ Norell, M.A., Makovicky, P.J. (2004). "Dromaeosauridae", in Weishampel, D.B., Dodson, P., Osmólska, H.: The Dinosauria, 2nd edition, Berkeley: University of California Press, 196-210. ISBN 0-520-24209-2. 

[edit] 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
  • Dromaeosauridae, Dinosaur-world reference with in-depth description and pictures of many dromaeosauridae dinosaurs
 Dinosaurs Portal
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