Utahraptor ostrommaysorum update2

Restoration of Utahraptor

Utahraptor ("Utah thief") is a dromaeosaurid dinosaur from the early Cretaceous of Utah. It is one of the largest known dromaeosaurs to have existed.


The largest described specimens of Utahraptor, although incomplete, are estimated to have measured 7 meters in length and around 500 kilograms in weight.[1] Like other dromaeosaurids, it had a long, curving claw on the second toe. In Utahraptor, one such claw measures 22 centimeters long, and is estimated to have measured 24 centimeters long in life with a keratin sheath.[1]

Although no direct fossil evidence currently shows this, it is assumed that Utahraptor possessed feathers through phylogenetic bracketing.[2]


Utahraptor was a dromaeosaurine, along with genera such as Velociraptor. Specifically, it is thought to be most closely related to Dromaeosaurus and Achillobator.[3] There is one known species, U. ostrommaysorum.

The following cladogram is based on a 2012 analysis by Senter et al., showing the position of Utahraptor within the Dromaeosauridae:[4]













Microraptor sp.

Microraptor gui

Microraptor zhaoianus

















Fragmentary remains of Utahraptor were first discovered in 1975 but did not receive much attention. More significant fossils (including the distinctive dromaeosaurid sickle claw) were discovered in 1991 at the Cedar Mountain Formation in Utah by James Kirkland, Robert Gaston, and colleagues. They described the fossils in 1993 as Utahraptor ostrommaysi, after paleontologist John Ostrom and and Chris Mays of Dinamation International.[1] The species name was amended to the gramatically correct ostrommaysorum in 2000.[5]

Originally, it had been intended to name the species Utahraptor spielbergi after film director Steven Spielberg, who directed the 1993 dinosaur film Jurassic Park, in exchange for funding paleontological research. The deal fell through when the amount of financial assistance could not be agreed upon.[6] Coincidentally, the numerous individuals of Velociraptor featured in the film are much closer in size to Utahraptor than the genus they were based upon.[7]


Utahraptor lived in the 124 million-year-old[8] Cedar Mountain Formation now located in eastern Utah. Known dinosaur fauna from the area includes Brontomerus, Gastonia, Falcarius, and Tenontosaurus, all of which may have occasionally been prey of Utahraptor.

In popular cultureEdit

Due to its large size and dromaeosaurid affinity, Utahraptor has been featured several times in popular culture. It was most notably featured in the 1999 program Walking with Dinosaurs[9], although they were depicted as featherless and inhabitants of Europe.[10]

Robert Bakker's novel Raptor Red tells the story of a female Utahraptor that lives in ancient Utah.[11]


  1. 1.0 1.1 1.2 Kirkland, J.I.; Burge, D.; Gaston, R. (1993). "A large dromaeosaur [Theropoda] from the Lower Cretaceous of Utah". Hunteria 2 (10): 1–16.
  2. Prum, R.; Brush, A.H. (2002). "The evolutionary origin and diversification of feathers". The Quarterly Review of Biology 77 (3): 261–295. doi:10.1086/341993. PMID 12365352.
  3. Turner, Alan H.; Pol, D., Clarke, J.A., Erickson, G.M. and Norell, M. (2007). "A basal dromaeosaurid and size evolution preceding avian flight". Science 317 (5843): 1378–1381. doi:10.1126/science.1144066. PMID 17823350.
  4. Senter P., Kirkland J.I., DeBlieux D.D., Madsen S., Toth N. (2012). "New Dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous of Utah, and the Evolution of the Dromaeosaurid Tail". PLoS ONE 7 (5): e36790. Bibcode:2012PLoSO...7E6790S. doi:10.1371/journal.pone.0036790. PMC 3352940. PMID 22615813.
  5. Olshevsky, G., 2000, An annotated checklist of dinosaur species by continent. Mesozoic Meanderings 3: 1-157
  6. Brooke Adams, 1993, "Director Loses Utahraptor Name Game", Deseret News, 15 June 1993
  7. "What Do We Really Know About Utahraptor? | Dinosaur Tracking". doi:10.1080/02724634.2001.10010852. Retrieved January 24, 2013.
  8. McDonald AT, Kirkland JI, DeBlieux DD, Madsen SK, Cavin J et al. (2010). "New Basal Iguanodonts from the Cedar Mountain Formation of Utah and the Evolution of Thumb-Spiked Dinosaurs". In Farke, Andrew Allen. PLoS ONE 5 (11): e14075. doi:10.1371/journal.pone.0014075. PMC 2989904. PMID 21124919.
  9. "Unnatural history? Deconstructing the Walking with Dinosaurs phenomenon." Media Culture & Society, 25(3): 315-332. doi:10.1177/0163443703025003002
  10. Haines, T. (2000). Walking with Dinosaurs: A Natural History. London: BBC Publishing.
  11. Bakker, Robert (September 1996). Raptor Red (paperback ed.). Bantam Books. p. 4. ISBN 0-553-57561-9.