Reconstruction of Deinocheirus mirificus.
Yuong-Nam Lee (KIGAM)
New fossils for an incredibly long-armed dinosaur nicknamed "Horrible
Hands" reveal that it had a prominent hunchback, ate both plants and
animals, and had features that prevented it from sinking into wet
ground.The discoveries, presented in the latest issue of the journal Nature, unravel a nearly 50-year-old mystery concerning the dinosaur, Deinocheirus mirificus. Fossils for the dinosaur's 8-foot-long arms were found in 1965, but little else, leaving paleontologists with a lot of unanswered questions concerning "Horrible Hands."
With two almost complete skeletons now pieced together, most of the mysteries have been resolved, yet the dinosaur has lost none of its shock value.
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Lee is director of the Geological Museum at the Korea Institute of Geoscience and Mineral Resources. He and his colleagues came to the conclusions after studying the newly found fossils.
The fossils were originally located at the Nemegt Formation in Mongolia. Poachers not associated with the research team found some of the parts that wound up in private hands before being repatriated to Mongolia, making the recent study possible.
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"Horrible Hands" turns out not to have been so horrible. Because its arms are the longest on record for any two-legged animal, paleontologists suspected that the dinosaur could have been a ferocious predator on par with meat-loving hunters like T. rex and Allosaurus.The dinosaur, however, lacked an important feature that would have completed such an imagined picture: teeth.
Toothless Deinocheirus instead sported a beak. Stomach remains suggest that the dinosaur died with a belly full of fish and probably plants too. Gastroliths (small swallowed stones) helped to pulverize all of the edibles grabbed by the dinosaur's beak and claws.
Deinocheirus mirificus recreation.
Michael Skrepnick
"Long forearms with giant claws may have been used for digging and
gathering herbaceous plants in riverside and lakeside environments," Lee
said, adding that he and his colleagues doubt that the dinosaur swam.Instead, they believe it frequently stood on very wet substrates, which can be like quicksand for animals. To support such a lifestyle, the dinosaur evolved sink-repellent squared-off toes that functioned similar to snowshoes.
"The tips of the pedal unguals (toe bones) are wide and flattened," he explained. "Much less downward force per unit area causes the blunt unguals not to sink in deeper on substrates. Some fossils show that theropod (two-legged carnivorous) dinosaurs died after becoming mired in mud."
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As for the dinosaur's prominent hump, he and his team believe it was primarily for display. The intricate system of ligaments within it also likely helped to support the dinosaur's abdomen from the hips and hind limbs "in a manner similar to an asymmetrical cable-stayed bridge.""The new finds help close a chapter on a mystery," said vertebrate paleontologist Thomas Holtz, Jr., of both the University of Maryland and the National Museum of Natural History. "We've known about Deinocheirus as long as I've been alive. Basically every book on dinosaurs featured these enormous theropod arms with the statement, 'Some day we may know what the whole dinosaur looks like.' Well, now we do."
Holtz, who authored a "News & Views" Nature article concerning the dinosaur, said that, in addition to fish and plants, this ostrich-type dinosaur would have eaten "small land animals," but the word "small" is relative in this case. Holtz explained that "to a 6-ton animal with a yard-long skull, something the size of a dog would qualify as a 'small land animal.'"
He added that the dinosaur "is one of the largest and tallest of the theropod dinosaurs, the group that includes Tyrannosaurus, Velociraptor, and modern birds, among many others. It is less massive than T. rex and shorter than Spinosaurus, but otherwise is among the biggest of them all."
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