By Andrew V. Ste. Marie
If a giant shark is called Jaws, then Deinocheirus could aptly be called Arms. For decades, little was known of this dinosaur but its enormous, terrifying, mysterious 8-foot long arms tipped with huge claws – arms so awe-inspiring that the dinosaur’s name means “Terrible Hand.”
These arms were discovered in 1965 during the Polish-Mongolian Palaeontological Expedition in the Gobi Desert of Mongolia. Along with a few ribs, vertebrae, and other scraps, the arms were all that was found of the skeleton. A later expedition to the same site found hundreds of bone fragments, but not much more from which to reconstruct the creature’s skeleton. What it did find was two Deinocheirus belly ribs with bite marks on them from a Tarbosaurus, a giant predatory dinosaur very similar to Tyrannosaurus rex. This gives us a clue as to why so little of the Deinocheirus skeleton was found.
So for nearly 50 years, this animal has been a mystery. What could it have been? Early on, it was imagined as a giant, Allosaurus-style predator. If its arms were the same size proportionate to its body as those of Allosaurus, we would have a gigantic theropod which would put Tyrannosaurus rex to shame!
Later analyses suggested a more mundane explanation. The arms bore similarities to the ornithomimids, the “ostrich mimic” theropods with long necks, toothless beaks, small skulls, and long arms. Their slight build suggests they were apt at running and they seem to have had little other defense against more aggressive theropods. For some time, their diet was unknown as well.
So it came to be somewhat accepted by the paleontological community that Deinocheirus was an ornithomimid. The question remained, however, of its exact size and form. Were its arms the same size, proportionately, as other ornithomimids? If so, Deinocheirus would be about forty feet long – the size of T. rex. Or was it a smaller animal with disproportionately long arms?
All of these questions promise to be answered soon, as two new skeletons of Deinocheirus have been discovered near the site of the original find. Between the two, we now have a mostly complete skeleton of Deinocheirus – missing only the end of the tail, the feet, some of the vertebrae, and the skull. One of the specimens has an arm even larger than the original Deinocheirus arms!
So what do these new remains reveal? They reveal that Deinocheirus was, indeed, an ornithomimid about the size of Tyrannosaurus rex. But it was not just any old ornithomimid! In addition to its immense size, it had another unique feature which no one had suspected – it had a sail or partial sail on its back, similar to some other theropod dinosaurs such as Spinosaurus and Concavenator. This very interesting feature adds to the thrill of finally discovering the identity of Deinocheirus. The skeletons also reveal that whereas most ornithomimosaurs seem to have been lightly-built creatures fit for running, Deinocheirus was a heavier-built animal which probably was not as much of a runner.
Additionally, one of the skeletons was discovered with over 1,100 gastroliths, or stomach stones. These are stones swallowed by plant-eating animals to help grind up vegetable material in the stomach to facilitate the digestion process. This find indicates that Deinocheirus, despite its terrifying arms, was a plant-eater.
This discovery, combined with the revelation that Deinocheirus had been scavenged by a Tarbosaurus, shows that, while certainly exciting and unique, it does not displace Tyrannosaurus rex from its long-held position as “tyrant lizard king.”
We eagerly await the publication of the description of the new Deinocheirus material, at which time we will be able to learn more about this long-standing paleontological mystery.
“It is the glory of God to conceal a thing: but the honour of kings is to search out a matter” (Proverbs 25:2).
Holy Bible, Authorized Version
Halszka Osmólska & Ewa Roniewicz, “Deinocheiridae, A New Family of Theropod Dinosaurs,” Palaeontologica Polonica 21:5-19
Phil R. Bell, Philip J. Currie, & Yuong-Nam Lee, “Tyrannosaur feeding traces on Deinocheirus (Theropoda:?Ornithomimosauria) remains from the Nemegt Formation (Late Cretaceous), Mongolia,” Cretaceous Research 37 (October 2012):186-190
Yuong-Nam Lee, Rinchen Barsbold, Philip Currie, Yoshitsugu Kobayashi, & Hang-Jae Lee, “New Specimens of Deinocheirus mirificus from the Late Cretaceous of Mongolia,” Journal of Vertebrate Paleontology October 2013 supplement, p. 161
 Or possibly a fleshy hump.
Originally published in The Witness (March 2014).