Deinonychus antirrhopus: More Than A “Six Foot Turkey”

Article by: J. D. Dixon
Edited by: Adam Manning, Harry T. Jones, and Jack Wood

Deinonychus antirrhopus illustration by Jack Wood

Name: Deinonychus antirrhopus
Name Meaning: Terrible Claw
Age: Early Cretaceous (Aptian – Albian)
Diet: Carnivore
Size: 1m tall approx. and 3-4m in length approx.
Weight: 70-100 kg
Location: North America

The initial discovery of Deinonychus antirrhopus was less of a purposeful find and more of a happy accident. Remains were unearthed in 1931 by Barnum Brown, who named the animal “Daptosaurus”. However, since Brown never formally described this find, this name has never been accepted. It was only when John Ostrom uncovered numerous skeletal samples in Montana, along with restudying Brown’s material, that the species was first described in 1969. Deinonychus has been discovered primarily in the Cloverly Formation of Montana and Wyoming, but some samples of a juvenile individual have originated from the Antlers Formation of Oklahoma. This meant the genus had a rather wide geographic distribution across North America.

The second digit on the hind legs of dinosaurs in the family Dromaeosauridae is highly specialised, equipped with a sickle-shaped claw. This digit was likely held in a retracted position during walking or running. The distinctive claw shape of this family is indicative of active predation, however, there are a number of hypotheses relating to its genuine use. Deinonychus may have gripped prey with its jaws and arms, while kicking at the prey animal’s stomach, using its second digit to slash and disembowel. The claw is also said to have potentially been used as a crampon, in order to climb and maintain position on large prey animals. Finds yielding bones of the large ornithopod Tenontosaurus tilletti and of Deinonychus antirrhopus in close proximity seem to indicate this may have been the case, as the former is much larger than the latter.

Nevertheless, newer research suggests that the sickle-claw may have been used as a means to pin smaller prey to the ground. When comparing Deinonychus morphology with the morphology and behaviours of modern predatory birds in the family Accipitridae, it was concluded that the claw would have been used to grasp prey while the predator’s bodyweight pinned its victim to the floor. These dromaeosaurids also had specialised limb adaptations which meant their grip strength was improved at the expense of their speed, making it more likely that they hunted in this manner. The jaws of Deinonychus simply lacked the strength to kill animals outright. Instead, it is thought that while prey was pinned down, Deinonychus’ head rotated and its jaws were used to dismember the animal, rather than using the sickle-claw. Deinonychus may have literally eaten its prey while it was still alive and struggling.

A Deinonychus skull replica on display in the Lapworth Museum of Geology. Image by J. D. Dixon.

There are conflicting lines of thought regarding the sociality of Deinonychus. The genus is sometimes interpreted as cooperative hunters, using teamwork to attack and kill prey. Evidence, such as closely spaced trackways and multiple individuals found near a prey animal, suggests high-level social interactions between hunters. Likewise, it seems sensible that the genus would have hunted as a coordinated group, especially if it were pursuing Tenontosaurus, given the sheer size of this dinosaur compared to Deinonychus. Yet, some research suggests that Deinonychus were actually solitary hunters, or at most only foraged in loose associations, rather than living in tight packs. These associations may be akin to the swarming of piranhas, and so members of the hunting party may have even been hostile to each other in order to gain more of the kill.

Many people are familiar with dromaeosaurs through the genus Velociraptor, the animal popularised in modern culture due to its appearance in the climax of the 1993 film ‘Jurassic Park’. However, the dinosaurs which appear in both the book and the film are not Velociraptors at all. Deinonychus and Velociraptor were categorised as belonging solely to the genus Velociraptor by palaeoartist and researcher Gregory S. Paul, who made this decision due to the morphological similarities between the two genera. Michael J. Crichton, the author of ‘Jurassic Park’, is said to have met with John Ostrom to gain insight into the physical proficiencies of Deinonychus, even crediting Ostrom in the acknowledgements of his famous book. However, due to his familiarity with Paul’s work, who is also credited in the novel, Crichton kept the name Velociraptor for writing purposes. Allegedly, Crichton also thought the name Velociraptor to be much more dramatic, but the creatures he describes in his book and the creatures which later appeared in the film adaptation were, in fact, based on Deinonychus.

In conclusion, this fearsome predator was exceptionally well adapted. Its mode of life and behaviours may continue to be debated, but regardless of this, it certainly would have been a formidable threat to nearly anything in its territory.

Image References
[1] Deinonychus antirrhopus illustration by Jack Wood
[2] A Deinonychus skull replica on display in the Lapworth Museum of Geology. Image by J. D. Dixon.

Information References and Further Sources
[1] Bivens, G. (2018). ‘Deinonychus Skeletals’. Accessed 22nd June 2019. Click Here.
[2] Black, R. (2008). ‘You say “Velociraptor”, I say “Deinonychus”’, Smithsonian Magazine. Accessed 21st May 2019. Click Here.
[3] Brinkman, D. L., Cifelli, R. L., and Czaplewski, N. J. (1998). ‘First Occurrence of Deinonychus antirrhopus (Dinosauria: Theropoda) from the Antlers Formation (Lower Cretaceous: Aptian-Albian) of Oklahoma’, Oklahoma Geological Survey Bulletin, 146. Accessed 22nd June 2019. Click Here.
[4] Crichton, M. J. (2015) Jurassic Park. First edition published in 1991. This edition was published in 2015 by Arrow Books.
[5] Cummings, M. (2015). ‘Yale’s legacy in ‘Jurassic World’’, YaleNews. Accessed 21st May 2019. Click Here.
[6] Dowswell, P., Malam, J., Mason, P., and Parker, S. (2005). The Ultimate Book of Dinosaurs. Bath: Parragon Books. pp. 92-95.
[7] Fowler, D. W., Freedman, E. A., Scannella, J. B., and Kambic, R. E. (2011). ‘The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds’, PLOS ONE, 6 (12). DOI: Accessed 22nd June 2019. Click Here.
[8] Jurassic Park. (1993). Steven Spielberg (director). DVD. Universal Studios and Amblin Entertainment, Inc.
[9] Li, R., Lockley, M. G., Makovicky, P. J., Matsukawa, M., Norell, M A., Harris, J. D., and Liu, M. (2008). ‘Behavioral and faunal implications of Early Cretaceous deinonychosaur trackways from China’, Naturwissenschaften, 95 (3), pp. 185-191. DOI: Accessed 22nd June 2019. Click Here.
[10] Manning, P. L., Payne, D., Pennicott, J., Barrett, P. M., and Ennos, R. A. (2005). ‘Dinosaur killer claws or climbing crampons?’, Biology Letters, 2 (1). DOI: Accessed 22nd June 2019. Click Here.
[11] Maxwell, W. D., and Ostrom, J. H. (1995). ‘Taphonomy and paleobiological implications of Tenontosaurus-Deinonychus associations’, Journal of Vertebrate Paleontology, 15 (4), pp. 707-712. DOI: Accessed 22nd June 2019. Click Here.
[12] Norell, M. A., and Makovicky, P. J. (2004). ‘Dromaeosauridae’, in Weishampel, D. B., Dodson, P., and Osmólska, H (2nd ed.) The Dinosauria. University of California Press. pp. 198.
[13] Roach, B. T., and Brinkman, D. L. (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), pp. 103-138. DOI:[103:AROCPH]2.0.CO;2. Accessed 22nd June 2019. Click Here.