Dinosaur victim of mistaken identity: it was a veggie, not a fearsome killer

A bus-sized dinosaur portrayed as a killer based on fearsome claws unearthed 49 years ago was really a toothless, gentle plodder, palaeontologists reported after new fossil evidence.

Rather than tearing prey limb from limb with talons that gave birth to its name, meaning "horrible hand", Deinocheirus mirificus was a peaceable giant that fed on plants and small fish, palaeontologists said.

It probably used its magnificent 2.4-metre arms for digging and gathering vegetation, they reported in the journal Nature.

And the reptile likely supplemented its diet by scooping up little fish with a duck-like bill as it roamed a lush river habitat 70 million years ago in what is now the Gobi desert in Mongolia.

"For 50 years Deinocheirus has remained one of the most mysterious dinosaurs," the study's authors wrote.

Its incomplete profile was long based solely on a pair of massive arms with fearsome claws, a handful of ribs and some shoulder bones found in 1965. But from new fossil finds, a near-complete picture now exists of this largest known member of a group of ostrich-like dinosaurs called ornithomimosaurs.