Back in July 1965, two gigantic fossilized dinosaur arms replete with menacing claws were unearthed in the remote southern Gobi desert of Mongolia.

Measuring 8 feet, the dino had the longest arms of any known bipedal creature in Earth's history.

Nearly everything else was missing however, leaving researchers confused about the nature of this beast with the long arms. Half a century later, the mystery has finally been solved, according to Reuters.

Scientists announced on Wednesday that two almost complete skeletons of the bizarre 70-million-year-old creature, Deinocheirus mirificus, show it had a combination of unorthodox traits, including the famous arms, never seen before in a single dinosaur.

At 36-feet-long and 6.4 tons, it was the largest known member of a group of bird-like dinosaurs called ornithomimosaurs ("ostrich mimics"), the researchers said, according to Reuters.

The dinosaur's back was toppled with long spines that supported a sail-like structure whose function remains enigmatic. It had fused tail vertebrae to support tail feathers.

Living in a river region, the Deinocheirus mirificus was an omnivore, living off fish and plants with a beaked, toothless snout that flared out to the sides like the herbivorous duckbilled dinosaurs. It also had broad feet with toes ending in squared-off hooves that could have helped it stand on wet ground.

Deinocheirus had wide hops and moved slowly but was capable of defending itself thanks to its sized and its three ripping claws on each hand. It was basically as big as Tyrannosaurus rex's cousin Tarbosaurus.

Scientists had long speculated about Deincheirus.  It was accurately recognized as a type of theropod, the dinosaur branch that includes the T.rex and the lineage that evolved into birds.

"Deinocheirus has remained one the most mysterious dinosaurs in the world. We found almost (complete) skeletons of Deinocheirus and know now how it looked, how big it was and what it ate," said paleontologist Yuong-Nam Lee, director of Geological Museum at the Korea Institute of Geoscience and Mineral Resources in Daejeon, South Korea, according to Reuters.

University of Maryland paleontologist Thomas Holtz, who wrote a commentary for the study in the journal Nature, said no one could have predicted its astonishing array of attributes.

"I've literally waited my whole life to see Deinocheirus finally unveiled," Holtz said, according to Reuters.

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