Deinocheirus mirificus: A Fossil Goose Chase

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

A reconstruction of what Deinocheirus mirificus may have looked like. Artwork by Julio Lacerda. Available at: https://twitter.com/JuliotheArtist/status/1222290257644859392.

1965. The Gobi Desert. A joint Polish and Mongolian team of palaeontologists are digging in the Upper Cretaceous sandstones of the Negmet Basin. It is here that they discover some of the strangest looking fossils found in the region. A pair of giant arms, 2.4m in length, along with some rib fragments, are uncovered by Prof. Zofia Kielan-Jaworowska. The arms are taken away and studied, and given the name Deinocheirus mirificus by Halszka Osmólska and Ewa Roniewicz in 1970. It would take another 44 years before a whole specimen was brought together and described by science. 

The first step towards the unification of a complete Deinocheirus was another discovery of more of the creature in 2006 and 2009, by a joint Korean and Mongolian team. Their digging resulted in the discoveries of two animals, who together formed a nearly complete skeleton. However, the parts that were missing were the feet and the head. These were thought to have been poached from the site for sale on the black market, a problem that plagues global fossils, as they are sequestered into private collections and away from science. 

Jump forward to 2011, and fossil collector François Escuillié (director of the Eldonia fossil dealership in Gannat, France) notices something interesting in a private collection. He contacts the palaeontologist Pascal Godefroit, who worked at the Belgian Institute of Natural Sciences in Brussels. Pascal goes to see the fossils – the head and feet of an unknown dinosaur. The skull measures 1m in length and is accompanied by foot bones, with all but one of the toe bones present. Pascal recognises the possible importance of the fossil and soon afterwards it is acquired by François, who donates it to the Institute, and then both François and Pascal pass it onto the Mongolian government. It is then described by an international team of palaeontologists led by Yuong-Nam Lee in 2014, and revealed to be an incredibly odd looking dinosaur.

A skeletal reconstruction of Deinocheirus mirificus showing it’s anatomical features. Image by Scott Hartman. Available at: https://www.skeletaldrawing.com/theropods/deinocheirus.

Deinocheirus turned out to be an ornithomimosaur, which roughly means ‘ostrich dinosaur’. Nearly all other ornithomimosaurs are small to medium in size and well adapted for running, as their name implies. Deinocheirus, on the other hand, went for size over speed. At approximately 11m long and nearly 6.5 tonnes, Deinocheirus is the largest ornithomimosaur ever known. 

The local large predator was Tarbosaurus, a relative of the infamous Tyrannosaurus rex. Bite marks have been found on gastralia (the belly ribs) of Deinocheirus, which can be linked to Tarbosaurus. However, we do not know if these marks are from active predation, or from scavenging, especially as Deinocheirus and Tarbosaurus are roughly the same size. This would have made Deinocheirus a tough challenge to take down for any hungry tyrannosaurs.  

Deinocheirus was an omnivore, even though its beak is very similar to those of hadrosaurs. It lived in floodplain environments, and so had a wide range of plants available to eat. Some fossil evidence even suggests they may have eaten fish. The claws at the end of its hands are much like the claws of a generalist therizinosaur Alxasaurus, which lends further evidence to this interpretation. Deinocheirus’ feet are also adapted to its swampy home. Each toe has a comma shaped claw at the end of it, and it has been suggested that these were to prevent the animal from sinking into deep mud. The feet themselves are also quite large, which means that Deinocheirus could have spread its weight more evenly, which would further help prevent it from sinking. 

Deinocheirus is a wonderfully bizarre dinosaur, with an equally bizarre story of discovery. It is the third group of theropods that were herbivorous and evolved to massive sizes by the end of the Cretaceous, alongside therizinosaurs and oviraptorids. We have much more to learn about this magnificent species, and hopefully it won’t take as long as it did to reconstruct it.

Image References
[1] A reconstruction of what Deinocheirus mirificus may have looked like. Artwork by Julio Lacerda. Available at: https://twitter.com/JuliotheArtist/status/1222290257644859392
[2] A skeletal reconstruction of Deinocheirus mirificus showing it’s anatomical features. Image by Scott Hartman. Available at: https://www.skeletaldrawing.com/theropods/deinocheirus

Information References and Further Sources
[1] Hecht, J. (2014). ‘Stolen Dinosaur Head Reveals Weird Hybrid Species’, New Scientist, 2969. Accessed 3rd February 2020. Click Here.
[2] Holtz, T. (2014). ‘Mystery of Horrible Hands Solved’, Nature, 515, pp. 203-205. Accessed 3rd February 2020. Click Here.
[3] Kobayashi, Y., and Barsbold, R. (2006). ‘Ornithomimids of the Negmet Formation of Mongolia’, Journal of the Palaeontological Society of Korea, 22 (1), pp. 195-207. Accessed 3rd February 2020. Click Here.
[4] Lee, Y., Barsbold, R., Currie, P., Kobayashi, Y., Lee, HJ., Godefroit, P., Escuillé, F., and Chinzorig, T. (2014). ‘Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus’, Nature, 515, pp. 257-260.  Accessed 3rd February 2020. Click Here.
[5] Osmólska, H., and Roniewicz, E. (1969) ‘Deinocheirdae, A New Family of Theropod Dinosaurs’, Palaeontologia Polonica, 21, pp. 5-19. Accessed 3rd February 2020. Click Here.