Chilesaurus diegosuarezi is named after the country where it was unearthed and Diego Suarez, the 7-year-old boy who spotted the first fossils. Scientists have unearthed fossils of a strange dinosaur in southern Chile that boasts such an unusual combination of traits that they are comparing it to a platypus, that oddball egg-laying, duckbilled mammal from Australia.

Named Chilesaurus diegosuarezi, it is a member of the same dinosaur group as Tyrannosaurus rex, theropods, which includes the largest land meat-eaters in Earth's history, but it ate only plants with a beak and leaf-shaped teeth, scientists said on Monday.

Most theropods were meat-eaters, although a few lineages preferred salad over steak. Chilesaurus diegosuarezi, whose name honours the country where it was unearthed and Diego Suarez,the seven-year-old boy who spotted the first fossils, is the first known Southern Hemisphere herbivorous theropod.

Its skull and neck resembled those of primitive long-necked dinosaurs, and its vertebrae those of primitive meat-eating theropods. It had robust arms, but just two blunt fingers on each hand. It was bipedal, but its wide, four-toed feet were unlike the slender, three-toed feet of most theropods. And it had a bird-like pelvis.

'One of the most bizarre dinosaurs ever found'

"Chilesaurus constitutes one of the most bizarre dinosaurs ever found," said paleontologist Fernando Novas of the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, calling the creature an evolutionary "jigsaw puzzle."

"The skeletal anatomy of Chilesaurus gathers characteristics of different dinosaur groups, like a floor is composed of mosaics of different shapes and colors. No other dinosaurs exhibit such a combination or mixture of features."

Chilesaurus lived in a region crisscrossed by rivers at the Jurassic Period's end, approximately 145 million years ago. It was relatively small, reaching up to 3.2 metres (10.5 feet) long, although most specimens found were more the size of a turkey.

It belongs to a previously unknown dinosaur lineage, University of Birmingham paleontologist Martín Ezcurra said.

"The most interesting (aspect) about Chilesaurus is the story that it tells about how evolution works," he said.

"'Convergent evolution' is a process in which two unrelated species or groups acquire similar characteristics from living in similar environments or having a similar behavior," like the wings of a bat and a bird, Ezcurra added.

"In the case of 'mosaic convergent evolution,' different parts of the body resemble those of other unrelated species, such as in the case of the platypus and Chilesaurus."

Four nearly complete skeletons and dozens of bones from other individuals were found, making Chilesaurus one of the best understood Jurassic Southern Hemisphere dinosaurs.

The research appears in the journal Nature.