Open Paleo

Deinonychus

Ostrom, 1969 dy-NON-ih-kuhs /daɪˈnɒnɪkəs/

From Ancient Greek deinos (δεινός, 'terrible') + onyx/onuchos (ὄνυξ/ὄνυχος, 'claw'), meaning 'terrible claw', referring to the enlarged sickle-shaped claw on the second toe.

113.2–93.9 million years ago Albian–Cenomanian, Early Cretaceous–Late Cretaceous
Early Cretaceous and Late Cretaceous stages

Deinonychus is a genus of dromaeosaurid theropod dinosaur with one described species, Deinonychus antirrhopus. This species could grow up to 3.4 meters (11 ft) long and lived during the Early and Late Cretaceous Period, about 115-93.9 million years ago. Fossils have been recovered from the U.S. states of Montana, Utah, Wyoming, and Oklahoma, in rocks of the Cloverly Formation and Antlers Formation.

Under dispute

The subfamily placement of Deinonychus is genuinely unresolved. It has been recovered as a velociraptorine (Turner and colleagues, 2012; Napoli and colleagues, 2021; Powers and colleagues, 2020), as a dromaeosaurine (DePalma and colleagues, 2015; the placement Jones (2026) adopts), and in a distinct clade with Utahraptor and Achillobator outside both subfamilies (Hartman and colleagues, 2019; Jasinski and colleagues, 2020). It is placed at Eudromaeosauria incertae sedis pending resolution.

Diagnosis

  1. Pes functionally didactyl (digits III and IV), with digit II bearing a very large, trenchant, strongly recurved ungual; distal end of metatarsal II deeply grooved; metatarsal III not greatly compressed proximally
  2. Manus with three very long digits (phalangeal formula 2-3-4), digits IV and V lost; metacarpal I short and irregular, metacarpal III long, slender, and divergent; carpus of radiale and ulnare only, the radiale with a well-defined asymmetrical proximal ginglymus
  3. Skull with large, sub-circular to oval orbits and three antorbital fenestrae; supraorbital rugosities on the postorbital and lacrimal; quadratojugal very small and T-shaped, apparently not contacting the squamosal; nasals long, narrow, and unfused
  4. Presacral vertebrae with small but deep pleurocoels; caudal vertebrae behind the eighth or ninth bearing extremely long rod-like prezygapophyseal processes (up to ~10 segments) and correspondingly elongated paired chevron rods, stiffening the tail
  5. Ischium with a triangular obturator process; pubis short and greatly expanded into a subcircular, scoop-shaped element with a distinct obturator foramen
  6. Dentition of about four sub-incisiform premaxillary teeth, ~15 maxillary, and ~16 sub-isodont dentary teeth, with posterior serration denticles nearly twice the size of the anterior denticles

Species

Deinonychus antirrhopus Ostrom, 1969

Type species

From Ancient Greek 'antirrhopus' (ἀντίρροπος) meaning 'counterbalancing', referring to the stiffened tail that served as a balancing mechanism during locomotion and predatory strikes.

Holotype
YPM 5205 , Yale Peabody Museum of Natural History
Material
Complete left pes and incomplete right pes.
Horizon
upper Himes Member, Cloverly Formation, Albian–Cenomanian, Early Cretaceous–Late Cretaceous , 113.2–93.9 million years ago
Locality
YPM 64-75, Montana, United States

Synonyms of the genus

Name Type Reason
Daptosaurus junior subjective Informal name used by Barnum Brown for material from southern Montana; the specimen was later formally described as Deinonychus.
Megadontosaurus nomen nudum Informal name; never met ICZN requirements for formal publication and is treated as referable to Deinonychus. Per Olshevsky's Dinosaur Genera List.

Notable specimens

  • AMNH 3015

    American Museum of Natural History Found 1931 by Barnum Brown reproductive

    The original and most complete Deinonychus specimen, found in 1931 near Billings, Montana. Fossilized eggshells in its matrix, in close contact with the gastralia, were identified as the first dromaeosaurid egg, suggesting the animal brooded its eggs.

    Makovicky & Grellet-Tinner (2000)

  • MCZ 4371

    Museum of Comparative Zoology, Harvard University Found 1974 by Steven Orzack complementary

    A referred skeleton excavated in Montana in 1974, preserving well-preserved femora, pubes, a sacrum, better ilia, and pes and metatarsus elements that were missing or poorly known from earlier material, prompting Ostrom to revise the skeletal restoration of Deinonychus.

    Ostrom (1976)

References

  1. Ostrom, J. H. (1969). A new theropod dinosaur from the Lower Cretaceous of Montana. Postilla 128: 1-17. ostrom1969a
  2. Ostrom, J. H. (1970). Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana. Bulletin of the Peabody Museum of Natural History 35: 1-234.

    Names the holotype's type locality YPM 64-75 in Carbon County and equates its horizon, Unit VII, with the upper part of the Himes Member.

    ostrom1970a
  3. Ostrom, J. H. (1969). Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana. Bulletin of the Peabody Museum of Natural History 30: 1-165.

    Comprehensive osteological monograph of Deinonychus antirrhopus providing the formal diagnosis; refers the genus to the Dromaeosauridae.

    ostrom1969b
  4. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Source of the appearance features.

    jones2026c
  5. Makovicky, P. J.; Grellet-Tinner, G. (2000). Association between a specimen of Deinonychus antirrhopus and theropod eggshell. First international symposium on dinosaur eggs and babies, Isona i Conca Dellà, Catalonia, Spain, 23-26 September 1999 123-128. makovicky2000a
  6. Ostrom, J. H. (1976). On a new specimen of the Lower Cretaceous theropod dinosaur Deinonychus antirrhopus. Breviora 439: 1-21. ostrom1976a
  7. Turner, A. H.; Makovicky, P. J.; Norell, M. A. (2012). A Review of Dromaeosaurid Systematics and Paravian Phylogeny. Bulletin of the American Museum of Natural History 371: 1-206. doi:10.1206/748.1

    Recovered Deinonychus as a velociraptorine in its dromaeosaurid systematics review.

    turner2012a
  8. Napoli, J. G.; Ruebenstahl, A. A.; Bhullar, B. A. S.; Turner, A. H.; Norell, M. A. (2021). A New Dromaeosaurid (Dinosauria: Coelurosauria) from Khulsan, Central Mongolia. American Museum Novitates 2021(3982). American Museum of Natural History (BioOne sponsored). doi:10.1206/3982.1

    New dromaeosaurid description's phylogeny recovered Deinonychus as a velociraptorine.

    napoli2021a
  9. DePalma, R. A.; Burnham, D. A.; Martin, L. D.; Larson, P. L.; Bakker, R. T. (2015). The first giant raptor (Theropoda: Dromaeosauridae) from the Hell Creek Formation. The University of Kansas Paleontological Contributions 14: 1-16. University of Kansas. doi:10.17161/paleo.1808.18764

    Giant raptor description's phylogenetic analysis recovered Deinonychus as a dromaeosaurine.

    depalma2015a
  10. Hartman, S.; Mortimer, M.; Wahl, W. R.; Lomax, D. R.; Lippincott, J.; Lovelace, D. M. (2019). A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight. PeerJ 7: e7247. PeerJ. doi:10.7717/peerj.7247

    New paravian's phylogeny placed Deinonychus with Utahraptor and Achillobator outside both dromaeosaurid subfamilies.

    hartman2019a
  11. Jasinski, S. E.; Sullivan, R. M.; Dodson, P. (2020). New Dromaeosaurid Dinosaur (Theropoda, Dromaeosauridae) from New Mexico and Biodiversity of Dromaeosaurids at the end of the Cretaceous. Scientific Reports 10(1). Springer Science and Business Media LLC. doi:10.1038/s41598-020-61480-7

    New Mexico dromaeosaurid description supported placing Deinonychus outside velociraptorine/dromaeosaurine subfamilies.

    jasinski2020a
  12. Powers, M. J.; Sullivan, C.; Currie, P. J. (2020). Re-examining ratio based premaxillary and maxillary characters in Eudromaeosauria (Dinosauria: Theropoda): Divergent trends in snout morphology between Asian and North American taxa. Palaeogeography, Palaeoclimatology, Palaeoecology 547: 109704. doi:10.1016/j.palaeo.2020.109704

    Supported dromaeosaurine placement of Deinonychus via snout morphology character analysis

    powers2020a