I remember the first time I saw the Deinocheirus arms at the American Museum of Natural History.
Tipped with viciously curling claws, the arms clearly belonged to a theropod, a dinosaur suborder that includes the giant predators Allosaurus and Tyrannosaurus rex. But where all T. rex arms were puny and average Allosaur arms were a little over two feet long, Deinocheirus mirificus featured monstrous, eight-foot-long forelimbs — and that’s all we had to go on. There were no other bones to clue us in as to what D. mirificus was all about.
The arms were captivating enough on their own, but the absent body presented an irresistible mystery. Standing before the oversized glass case to the right of the dinosaur hall’s entrance, I stared and imagined. Surely with those arms, Deinocheirus must have been a fearsome predator. (In fact, so thought famed Polish paleontologist Halszka Osmólska, who first described the dinosaur in a 1970 paper and noted that the arms would be useful “in tearing dead or weakly agile prey asunder.”)
As it turns out, nope.
In recent years, paleontologists have generally agreed that Deinocheirus was probably an herbivore. And not just any herbivore, but an ornithomimosaur. While most theropods were predators with an assembly of sharp teeth and wicked claws, members of the theropod subgroup Ornithomimosauria generally had toothless beaks and many have been discovered with gastroliths (stones swallowed to aid digestion, typically by herbivores to grind up tough plant matter). The family’s name itself means “ostrich mimic reptile” — hardly the stuff of nightmares, and seemingly not the stuff of 8-foot-long, claw-tipped arms either. In fact, it was generally agreed that Deinocheirus would be an aberration as an ornithomimosaur — as one point of comparison, one of the largest definite ornithomimosaurs, Gallimimus, had differently-proportioned arms only about three feet long (and not nearly as imposing as those of Deinocheirus).
Now a recent presentation at the annual meeting of the Society for Vertebrate Paleontology apparently has confirmed that Deinocheirus was an ornithomimosaur. It seems that paleontologists returned to the Nemegt formation in Mongolia (where the original specimen was found) in 2006 and 2009 and discovered two near-complete Deinocheirus specimens indicating beyond doubt that those giant, claw-handed arms belonged to a giant, bizarre ornithomimosaur. (Though explanatory details were presented at the meeting, the rest of us will have to wait until a paper is published for these and other materials unavailable in the presentation’s abstract.) Giant is plain enough, but why bizarre? Deinocheirus possessed “anterodorsally oriented distal dorsal neural spines (7-8 times taller than centrum height) with basal webbing)” — which is to say, the skeletal undergirding for a sail or hump on its back.
Neural spines aside, what were those huge arms and claws for? Based on what’s available to the public, the answer to this question still seems unclear. A leading dinosaur text (Weishampel’s The Dinosauria) calls Deinocheirus‘s claws “raptorial.” Perhaps the presenters’ eventual paper will hazard a guess as to what use a massive herbivore had for these wicked-looking claws.
Despite hugely expanding our knowledge of the paleontological oddity Deinocheirus and promising to deliver even more, the presenters did provide one cause for unhappiness. According to a report by Brian Switek, when paleontological teams uncovered the new Deinocheirus specimens, the skulls of both had already been poached. In light of recent controversy over the smuggling of dinosaur bones from Mongolia to private auction-houses in the United States (which came to a head in a dramatic auction-room scene and led to the prosecution and guilty plea of smuggler Eric Prokopi), the loss of two Deinocheirus heads stands out as yet another instance of the plundering of Mongolia’s natural heritage to the loss of that country, the scientific community, and the public, with gains to only a few. To my cautious relief, Switek also reports that at least one skull might have been found:
“We still have no skull material,” [University of Edinburgh paleontologist Stephen] Brusatte says, “although there are rumors of a skull being privately collected, looted from Mongolia, and sold on the black market to a legitimate museum in Europe.”
So questions have been answered but mysteries remain, and those eight-foot arms are as impressive as ever — even if they did belong to an odd, herbivorous ornithomimid.
Osmólska, H. and E. Roniewicz (1970). “Deinocheiridae, a new family of theropod dinosaurs.” Palaeontologica Polonica 21:5-19. [Link]
Lee, Y., Barsbold, R., Currie, P., Kobayashi, Y., Lee, H. (2013). “New Specimens of Deinocheirus mirificus from the Late Cretaceous of Mongolia.” Journal of Vertebrate Paleontology, Program and Abstracts 162.
Middleton, Kevin M. (2000). “Theropod forelimb design and evolution.” Zoological Journal of the Linnean Society 128 (2): 149–187. [Link]
Weishampel, D., P. Dodson & H. Osmólska, eds. (2007). The Dinosauria: Second Edition.