With extra-long arms, Deinocheirus mirificus was one weird dinosaur


Just in time for Halloween, an international team of researchers has unearthed fossils from Mongolia with seemingly mismatched body parts: a beaked, humpbacked, ostrich-like dinosaur with incredibly long arms.

The Frankenstein’s dinosaur is named Deinocheirus mirificus, which translates to “unusual horrible hand” in a combination of Latin and Greek. The mysterious dinosaur’s true form had been largely unknown for almost 50 years. But two newly discovered specimens allowed scientists to reconstruct a nearly complete skeleton of the bizarre creature, described online in the journal Nature.

“This has been a mystery since literally as long as I’ve been around,” said Thomas Holtz Jr., a vertebrate paleontologist at the University of Maryland, College Park, who was not involved in the study. “There’s a bunch of features that no one had seen in combination before in any one dinosaur.”


Deinocheirus mirificus lived 70 million years ago during the late Cretaceous period and was omnivorous, dining on plants, small animals and even seafood (judging by the fish remains found in the belly of one of the two new fossils). It sported a bony “sail” on its back, akin to its distant cousin Spinosaurus.

Its toothless, duck-like bill might have helped it forage for food at the bottom of streams; unusual, hoof-like claws might have kept it from sinking into muddy ground. One of the specimens appears to have measured about 36 feet long and weighed about 14,000 pounds, according to scientists.

“It’s a big animal,” said study coauthor Philip J. Currie, a dinosaur paleontologist at the University of Alberta. “This is as big as T. rex.”

But aside from the extra-long arms, most of these details about Deinocheirus’ strange body were shrouded in mystery. That’s because when Deinocheirus was discovered in July 1965 in Mongolia, the fossil consisted only of a few ribs and vertebrae, shoulder girdles, and an enormous set of arms nearly 8 feet long.

Although the bones seemed to put the species among the theropods — a group of dinosaurs that includes Tyrannosaurus rex and the ancestors of modern birds — it had such a strange mix of traits that the fossil defied easy categorization.

Scientists theorized it was part of a group of superficially ostrich-like theropods called ornithomimosaurs — but early reconstructions varied wildly. Some likened the fossil to an Allosaurus (which looks something like a smaller T. rex) with long arms, and others said the animal might have used its generous forelimbs to hang from enormous trees like a giant sloth — even though such massive trees don’t exist in the fossil record, Holtz pointed out.

Very little else was known about these dinosaurs until two other skeletons were discovered more than 40 years later, one in 2006 and one in 2009. But parts of those two fossils had been poached and sold. The 2009 fossil was damaged and scarred; poachers had already collected the skull, hands and feet.


Luckily, Pascal Godefroit of the Royal Belgian Institute of Natural Sciences told his coauthors he’d seen some bones that fit that description of the 2009 fossil in Europe. The poached bones had apparently been sold to a buyer in Japan and then to another in Germany. The researchers tracked down the missing pieces from the specimen (including the skull, left hand and feet), and when certain bones were reunited, their joint surfaces matched exactly. Together, the fossils allowed the scientists to reconstruct a near complete skeleton.

The fact that Deinocheirus was likely omnivorous is unusual for theropods, which were typically carnivorous.

Its feet don’t make sense, either: Even though scientists have now officially placed the dinosaur among the ostrich-like ornithomimosaurs — where it’s the biggest of the bunch — its feet are short and stubby like the tyrannosaurids, rather than long and slender like the feet of many of its fellow ornithomimosaurs.

Some researchers think major divergences in the dinosaur family tree occurred early in the animals’ evolutionary history, Holtz said. But the discovery of Deinocheirus, with its chimeric mix of body parts, belies that idea, he said.

“Even late in the history of the dinosaurs, lineages were exploring new directions that they hadn’t done before,” Holtz pointed out.

Deinocheirus isn’t the only theropod with a strange mix of traits that wouldn’t have been predicted from looking at its close relatives. A recently unearthed Spinosaurus fossil shows that the mysterious species, discovered a century ago, had weirdly powerful arms and stubby legs that scientists now say make it the first known amphibious dinosaur.

There, too, the fossil’s separated bones had to be tracked down across continents, reunited and returned to their home country.

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