KEY POINTS:
It weighed more than a tonne, walked on two legs and was armed with dagger-like claws and a giant, fearsome beak. It is also the latest addition to the growing menagerie of large, flesh-eating dinosaurs.
Scientists who discovered fossils of the creature, called gigantoraptor, at a site in China said they were surprised by its size and similarity to modern-day birds - it was even covered in feathers.
Gigantoraptor was at least twice the height of a man at the shoulder and grew more than 8m long.
At 1400kg, it was about 35 times heavier than any of the feathered dinosaurs known by science.
In fact, it might have been even bigger, because the specimen unearthed from the Sunitezuoqi region of Inner Mongolia was not fully grown when it perished tens of millions of years ago, scientists said.
Gigantoraptor was the stuff of nightmares.
Although it could not fly, it had short forelimbs ending in large clawed "hands".
The head, which sat on an ostrich-like neck, resembled that of a bird with a powerful snapping beak instead of a toothed jaw.
The dinosaur lived in the Late Cretaceous period, around 70 million years ago, at the same time that tyrannosaurus rex, one of the largest land carnivores, terrorised what is now the continent of North America.
Gigantoraptor is about 300 times as heavy as primitive feathered peers already known to science.
Previously, the largest known feathered animal was the 500kg Stirton's thunder bird, (dromornis stirtoni) which lived in Australia and was a third as big.
Most theories suggest that carnivorous dinosaurs became smaller as they grew more bird-like. However, gigantoraptor, which evolved towards the end of the dinosaurs' reign on Earth, proved this was not always the case.
A team led by Dr Xing Xu, from the Chinese Academy of Sciences in Beijing, described the find in the latest Nature.
The partial skeleton showed in the first official scientific description of gigantoraptor included pieces of the beak, vertebrae, limb bones, right shoulder blade and pelvis.
Because of its bird-like features, scientists have placed gigantoraptor in the family of oviraptorosuarids, a group of small, feathered dinosaurs which rarely weighed more than 40kg.
The scientists wrote: "As an oviraptorosaurian, gigantoraptor is remarkable in its gigantic size."
Bone structure patterns suggested that the dinosaur had an unusually fast growth rate, which may help explain how it got so big.
"It also had a number of bird-like features which were absent from its smaller, feathered relatives.
Most experts now believe that modern birds evolved from a branch of small, feathered dinosaurs whose feathers may have evolved originally for thermal protection but later became useful for gliding flight and then powered flight.
Some of the largest avian carnivores lived when the dinosaurs died off about 65 million years ago.
These so-called "terror birds" had giant, curved beaks roughly 45cm long and similar in shape to those of gigantoraptor.
Terror birds also had massive skulls which sometimes grew as big as those of a horse. The birds crushed their prey in their powerful beaks.
Terror birds were the biggest birds the world has ever seen and stood more than 3m tall. They were flightless, lived in what is now South America and were one of the top predators of their time.
- INDEPENDENT
