After nearly 50 years of searching for skeletal parts of a mysterious dinosaur, enough pieces have been found to reconstruct an almost complete fossil -- and it's a truly unusual creature, paleontologists say.

Bones of its 8-foot long arms -- the longest forelimbs ever discovered of a two-legged creature -- were found in 1965, but there was little other evidence of the shape or form of the dinosaur scientists dubbed "Horrible Hands."

However, two partial skeletons discovered in 2006 and 2009 have allowed the true nature of Deinocheirus mirificus to be determined, a study published in the journal Nature reported.

Paleontologists have placed the creature in the dinosaur group ornithomimosaurs, vaguely resembling modern ostriches.

Living in what is now Mongolia around 70 million years ago, Deinocheirus had a "hump" or sail-like fin on its back formed by its spine, a large duck-bill-like snout devoid of teeth, and unusually large, flat feet that may have allowed it to forage in soft, swampy ground without sinking it, scientists say.

"Long forearms with giant claws may have been used for digging and gathering herbaceous plants in riverside and lakeside environments," says study lead author Yuong-Nam Lee, Director of the Geological Museum at the Korea Institute of Geoscience and Mineral Resources.

However, Lee says, he and his research colleagues doubt the animal was capable of swimming.

The toothless bill suggests a herbivore, but fossilized fish found in stomach contents are evidence Deinocheirus was omnivorous, they say.

The unusual features of the now complete fossil should remind scientists not to jump to conclusions based on incomplete examples of any creature, the study authors said.

"The discovery of the original specimen almost half a century ago suggested that this was an unusual dinosaur, but did not prepare us for how distinctive Deinocheirus is -- a true cautionary tale in predicting body forms from partial skeletons, even for animals in which the relationships are known," they wrote.

Still, scientists say, it is gratifying to have a glimpse at last of the true form of a creature that had been a mystery for so long.

"The new finds help close a chapter on a mystery," said vertebrate paleontologist Thomas Holtz, Jr., of 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,'" he said. "Well, now we do."