Tyrannosaurus rex had an odd-looking vegetarian cousin with a tiny head, long neck and stubby fingers, say scientists.
Chilesaurus diegosuarezi had a bird-like beak with leaf-shaped teeth, evidence that it feasted on plants, but with hind leg features similar to theropod dinosaurs, the group into which it was slotted with notorious killers like T. rex, Velociraptor and the horned Carnotaurus.
The dinosaur -- nicknamed 'The Platypus -- is described today in the journal Nature .
"Chilesaurus constitutes one of the most bizarre dinosaurs ever found," says study co-author Fernando Novas of Argentina's Natural History Museum in Buenos Aires.
"At the beginning, I was convinced that we had collected three different dinosaurs, but when the most complete skeleton was prepared, it (became) evident that all the elements pertained to a single dinosaur species."
The bizarre dinosaur was named after the South American country where its fossilised remains were found, and the seven-year old boy, Diego Suarez, who discovered the first bones in 2004 while exploring the Andes mountains with his geologist parents.
About a dozen Chilesaurus specimens have since been dug up.
Theropods like T. rex tended to have relatively short necks, big heads and strong, muscled hind legs much bigger than their arms, vicious claws and jaws brimming with razor-sharp teeth.
But Chilesaurus cuts an altogether less threatening figure.
'Jigsaw puzzle' dinosaur
"The proportionally small skull of Chilesaurus, with the presence of a horn beak at the tip of the snout and... leaf-shaped teeth, reveal that Chilesaurus was a strict plant eater," says Novas."Its forearms were robust, but the hands were provided with just two blunt fingers."
Most skeletons discovered so far were the size of a turkey, but isolated bones have revealed that Chilesaurus could grow to about three metres in length.
Novas and his team have taken to comparing Chilesaurus to a platypus, which with its duck-like bill, beaver-like tail and otter-like feet.
"We are puzzled by the weird anatomy of Chilesaurus, which recalls different dinosaurian groups," says Novas.
Its pelvis is reminiscent of ornithischian dinosaurs with beaks, like Stegosaurus, and its wide, four-toed hind feet are similar to those of the massive, 'lizard-footed' sauropods like Brontosaurus.
Yet the research team believe Chilesaurus represents a new type of theropod -- "an evolutionary jigsaw puzzle that will generate debate among palaeontologists," says Novas.
Until now, herbivorous theropods were known only in close dinosaur relatives of modern-day birds, but the discovery of Chilesaurus shows that a meat-free diet was acquired much earlier than thought, say the scientists.
Chilesaurus lived at the end of the Jurassic period, some 145 million years ago -- long before T.rex which ruled the plate at the end of the Cretaceous era some 70-65 million years ago.
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