Fat and fuzzy, it was a dino!

- Size of feathered find pre-dating T-rex throws up big surprise

G.S. MUDUR

Artist's impression of the gigantic feathered dinosaur, Yutyrannus, walking with two of the smaller Beipiaosaurus, one-fortieth the size of the giant. Credit: Brian Choo

The fossilised skull (snout-shaped impression pointed to the right) of Yutyrannus embedded in a rock. Credit: Zang Hailong

Filament-like fossilised (embedded) feathers of Yutyrannus. Credit: Zang Hailong

New Delhi, April 4: Scientists today announced the discovery in China of fossils of the largest-known feathered dinosaur, a creature that resembledTyrannosaurus rex but had a fuzzy coat that has surprised the scientific community.

While small feathered dinosaurs have been known for about a decade, this previously unknown dinosaur provides the first direct evidence for a gigantic but flightless species with an extensive feathery covering, a team of Chinese and Canadian scientists said.

The dinosaur, Yutyrannus huali, recovered from a quarry in China's northeastern province of Liaoning, lived about 125 million years ago, an ancestor ofTyrannosaurus rex. The finding will be published in tomorrow's issue of the journal Nature.

"This is an unexpected discovery," said Xu Xing, professor of paleontology at the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing. "Most scientists expect really large dinosaurs to be featherless as overheating becomes a problem for large animals."

"That's why large modern-day animals such as elephants don't have feathers," Xing told The Telegraph.

But the fossil remains suggest that an adultYutyrannus could grow up to 9 metres in length and weigh about 1,400kg, and still have feathers.

Scientists say the discovery is consistent with the idea that birds evolved from dinosaurs. But the presence of feathers in a large and ancestral dinosaur raises a question whether the feathers were for insulation or sexual display or flight.

"These were fully terrestrial, like modern ostriches," said Sankar Chatterjee, a professor and curator of palaeontology at the Museum of Texas Tech University in the US, who is an authority on ancient flying reptiles called pterosaurs and the biomechanics of flight but was not associated with this discovery.

Scientists say it is possible that Yutyrannus lived during a period that was considerably colder than subsequent periods of what is dubbed the Cretaceous period — western Liaoning could have had average temperatures of about 10°C during the early Cretaceous compared to 18°C in the late Cretaceous.

"It may have needed this coat of feathers to keep warm," said Corwin Sullivan, an associate professor of palaeontology at the IVPP, Beijing, and a member of the discovery team. "It's possible other large dinosaurs will also turn out to be feathered — we'll have to wait for more evidence to emerge," Sullivan told The Telegraph.

Yutyrannus is about 40 times the size of Beipiaosaurus, which was until now the largest known feathered dinosaur, also reported from Liaoning province in China.

"The large size is the puzzle with this new feathered dinosaur — that's what makes this a big discovery," said Ashok Sahni, an Indian palaeontologist at Lucknow University.

Chatterjee said the specimens discovered are unlikely to settle the long-standing issue of the role of small filamentous feathers that had earlier been reported from dinosaurs in China.

"They (the feathers) had no aerodynamic function, but they could have been used for insulation as well as for species recognition and sexual display," Chatterjee said. "These small feathered dinosaurs were arboreal and lived in trees for safety. The feather coat would have provided them insulation as trees are colder than the ground."

But the feathers themselves evolved over time. "As these small dinosaurs began to jump, and learned first to parachute, then to glide and then to fly, feathers became enlarged and co-opted for flight," Chatterjee said.

The scientists said Yutyrannus was a dwarf in contrast to an adult Tyrannosaurus rexwhich they say grew up to 12 metres and could weigh up to 6,000kg.