10 Facts About Deinocheirus, the "Terrible Hand" Dinosaur

01
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How Much Do You Know About Deinocheirus?

deinocheirus
Wikimedia Commons

For years, Deinocheirus was one of the most mysterious dinosaurs in the Mesozoic bestiary--until the recent discovery of two new fossil specimens allowed paleontologists to finally unlock its secrets. On the following slides, you'll discover 10 fascinating Deinocheirus facts.

02
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Deinocheirus Was Once Known by its Huge Arms and Hands

deinocheirus
Wikimedia Commons

In 1965, researchers in Mongolia made an amazing fossil discovery--a pair of arms, complete with three-fingered hands and intact shoulder girdles, measuring almost eight feet long. A few years of intensive study determined that these limbs belonged to a new type of theropod (meat-eating) dinosaur), which was finally named Deinocheirus ("terrrible hand") in 1970. But as tantalizing as these fossils were, they were far from conclusive, and much about Deinocheirus remained a mystery.

03
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Two New Deinocheirus Specimens Were Discovered in 2013

deinocheirus
Wikimedia Commons

Almost 50 years after the discovery of its type fossil, two new Deinocheirus specimens were unearthed in Mongolia--though one of them could only be pieced together after various missing bones (including the skull) were recovered from poachers. The announcement of this discovery at the 2013 meeting of the Society of Vertebrate Paleontology caused an uproar, a bit like a crowd of Star Wars enthusiasts learning about the existence of a previously unknown, 1977-vintage Darth Vader figurine.

04
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For Decades, Deinocheirus Was the World's Most Mysterious Dinosaur

deinocheirus
Luis Rey

What did people think of Deinocheirus between the discovery of its type fossil in 1965 and the discovery of additional fossil specimens in 2013? If you check any popular dinosaur book from that stretch of time, you're likely to see the words "mysterious," "terrifying," and "bizarre." Even more amusing are the illustrations; paleo-artists tend to let their imaginations run riot when they're reconstructing a dinosaur that's known only by its gigantic arms and hands!

05
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Deinocheirus Has Been Classified as a "Bird Mimic" Dinosaur

ornithomimus
Ornithomimus, a classic "bird mimic" dinosaur. Nobu Tamura

So exactly what kind of dinosaur was Deinocheirus? The discovery of those 2013 specimens sealed the deal: Deinocheirus was an ornithomimid, or "bird mimic," of late Cretaceous Asia, albeit one very different from classic ornithomimids like Ornithomimus and Gallimimus. These latter "bird mimics" were sufficiently small and fleet to motor across the North American and Eurasian plains at speeds of up to 30 miles per hour; the enormous Deinocheirus couldn't even begin to match that pace.

06
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A Full-Grown Deinocheirus Could Weigh up to Seven Tons

deinocheirus
Wikimedia Commons

When paleontologists were finally able to assess Deinocheirus in its entirety, they could see that the rest of this dinosaur lived up to the promise of its enormous hands and arms. A full-grown Deinocheirus measured anywhere from 35 to 40 feet from head to tail and weighed as much as seven to ten tons. Not only does this make Deinocheirus the largest identified "bird mimic" dinosaur, but it also puts it in the same weight class as distantly related theropods like Tyrannosaurus Rex!

07
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Deinocheirus Was Probably a Vegetarian

deinocheirus
Luis Rey

As huge as it was, and as terrifying as it looked, we have every reason to believe that Deinocheirus wasn't a devoted carnivore. As a rule, ornithomimids were mostly vegetarians (though they may have supplemented their diets with small servings of meat); Deinocheirus probably used its enormous clawed fingers to rope in plants, though it wasn't adverse to swallowing the occasional fish, as evidenced by the discovery of fossilized fish scales in association with one specimen.

08
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Deinocheirus Had an Unusually Small Brain

deinocheirus
Sergio Perez

Most of the ornithomimids of the Mesozoic Era had a relatively large encephalization quotient (EQ): that is, their brains were slightly larger than you would expect in relation to the rest of their bodies. Not so for Deinocheirus, whose EQ was more in the range of what you would find for a sauropod dinosaur like Diplodocus or Brachiosaurus. This is unusual for a late Cretaceous theropod, and may reflect a lack of both social behavior and the inclination to actively hunt prey.

09
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One Deinocheirus Specimen Contains Over 1,000 Gastroliths

gastroliths
Wikimedia Commons

It's not unusual for plant-eating dinosaurs to have deliberately eaten gastroliths, small stones that helped to mash up the tough vegetable matter in their stomachs. One of the newly identified Deinocheirus specimens was found to contain well over 1,000 gastroliths in its swollen gut, yet another strand of evidence pointing to its mostly vegetarian diet. (Fortunately, Deinocheirus didn't have any teeth, so it wouldn't need any dental work after accidentally chomping a large rock.)

10
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Deinocheirus May Have Been Preyed on by Tarbosaurus

tarbosaurus
Tarbosaurus. Wikimedia Commons

Deinocheirus shared its central Asian habitat with a wide variety of dinosaurs, the most notable being Tarbosaurus, a comparably sized (about five tons) tyrannosaur. While it's unlikely that a single Tarbosaurus would deliberately take on a full-grown Deinocheirus, a pack of two or three might have had more success, and in any case this predator would have concentrated its efforts on sick, aged or juvenile Deinocheirus individuals that put up less of a fight.

11
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Superficially, Deinocheirus Looked a Lot Like Therizinosaurus

therizinosaurus
Therizinosaurus. Wikimedia Commons

One of the most remarkable things about Deinocheirus is its similarity to another bizarre theropod of late Cretaceous central Asia, Therizinosaurus, which was also endowed with unusually long arms capped by terrifyingly long-clawed hands. The two families of theropods to which these dinosaurs belonged (ornithomimids and therizinosaurs) were closely related, and in any case, it's not inconceivable that Deinocheirus and Therizinosaurus arrived at the same general body plan via the process of convergent evolution.