By Will Dunham

WASHINGTON (Reuters) - In a humid, tropical jungle in southern China eons ago, a remarkably bird-like dinosaur with wing-like arms, a toothless beak and a dome-shaped crest atop its head became trapped in mud, struggled in vain to escape and died.

Workmen blasting bedrock while building a school near the city of Ganzhou unearthed a beautifully preserved fossil of the roughly 6.5-foot-long (2-meter-long) dinosaur, nicknamed the "Mud Dragon," still in that contorted position, scientists said on Thursday.

The Cretaceous Period creature, called Tongtianlong limosus, lived 66 to 72 million years ago, at the twilight of the dinosaurs' more than 160-million-year reign on Earth. It was a member of a group called oviraptorosaurs, one of the closest relatives to birds, which evolved earlier from small, feathered dinosaurs.

Paleontologist Steve Brusatte of Scotland's University of Edinburgh, who worked on the study published in the journal Scientific Reports, said the fossil adds to the understanding of dinosaur evolution on the eve of destruction.

The discovery of Tongtianlong and five other oviraptorosaur species in southern China showed this group was still blossoming and diversifying during the last few million years before an asteroid struck Earth about 66 million years ago, wiping out the dinosaurs, Brusatte said.

"The fact there were so many of them is a testament to just how well the dinosaurs were doing right up until the end," Brusatte added.

The fossil preserved a tragic moment for posterity.

"Its neck is arched, its head sticking up, its arms out-stretched to the sides. It is a strange posture," Brusatte said.

The fact that the fossil was found in rock formed from mud and the skeleton is in pristine condition suggests the dinosaur got mired in mud, tried to get free, but died and was buried, Brusatte said. Its scientific name means "muddy dragon on the road to heaven," paying homage to how it perished.

Other previous dramatic fossil finds include Mongolia's famous "fighting dinosaurs," a Velociraptor and Protoceratops apparently locked in mortal combat when a sand dune collapsed on them.

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Tongtianlong was a two-legged omnivore, with a bony crest on its short, squat skull that was probably used for display purposes to attract mates and intimidate rivals. Its arms likely had quill-like feathers layered over each other like on a wing, though it could not fly.

"If you saw the 'Mud Dragon' alive, you probably would have said, 'That's a big, funny-looking bird,'" Brusatte said.

(Reporting by Will Dunham; Editing by Sandra Maler)