Nicknamed the "chicken from hell," a newly identified species of feathered dinosaur as tall as a human roamed North America at least 66 million years ago, paleontologists announced Wednesday.
With a hen-like crest on its head, lanky legs like an ostrich, sharp claws on its forelimbs and jaws built for crushing eggs and prey, the Anzu wyliei weighed a hefty 200-300kg.
The long-tailed creature is the largest known member of the legendary "egg-thief" dinosaurs, known as Oviraptorosaurs, which are closely related to birds, said the study in the journal PLOS ONE.
"We jokingly call this thing the 'chicken from hell,' and I think that's pretty appropriate," said lead author Matt Lamanna of the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania.
A collection of fossilized bones from three separate dinosaurs provided the first nearly complete glimpse of the 11.5-foot-long (3.5 metre) beast that stood five feet (1.5 metres) high at the hip.
"It would be scary, as well as absurd, to encounter," said co-author Emma Schachner, a biology postdoctoral fellow at the University of Utah.
The dinosaur was named after Anzu, a bird-demon from Mesopotamian mythology, and Wylie, the grandson of a museum trustee.
- Related to Asian cousins -
The skeletal pieces were found over a decade ago in the Hell Creek rock formation in North and South Dakota, where many other fossils have been found, including those of T. rex and Triceratops.
The Anzu specimens are dated to between 66 and 68 million years old, very close to the end of the dinosaur era some 65 million years ago when an asteroid is believed to have wiped them out.
The fossils reveal new details about a category of Oviraptorosaurs called caenagnathids, which were first discovered a century ago and came in a variety of sizes, from as small as a turkey to - in the case of Gigantoraptor - as heavy as 1.5 tonnes.
Philip Currie, a paleontologist and professor at the University of Alberta described the latest findings as "critical" and "anatomically, a fantastic specimen."
Anzu wyliei appears similar in some ways to its cousins, the Oviraptorids, which have been found in Mongolia and China.
There are differences, too. The jaws from the Mongolian fossils are short and deep, while the North American specimens have longer jaws that are still very bird-like.
Anzu's legs appear to have been longer, too, said Currie, who was not involved in the study.
"So these were - unlike the ones from Mongolia - animals that were capable of running much faster," he told AFP.
- Egg thief, or not? -
The first Oviraptor fossil was described in 1924 and was named the "egg thief" because it was found on top of a nest of eggs, and paleontologists assumed it was eating them.
In the 1990s, the same type of fossil egg was found with a baby Oviraptor inside, suggesting that the earlier examples were not raiding nests but were parents, protecting their own eggs.
Currie said he still believes, however, that other dinos' eggs were a part of Anzu's diet, based on the shape of its jaws, which had a hollow that was sized just right for an egg and protrusions on the roof for crushing it.
Since dinosaurs only laid eggs at certain times, Anzu wyliei - which was distantly related to the T. rex - likely ate other creatures, too.
"They are also well-adapted for nipping the heads off mammals and birds and things like that," Currie said.
The latest findings portray a creature double the size of those found in older rock beds, a trend also seen in T. rex and Triceratops, which by the end of the dinosaur age were also the largest of their kind.
"Dinosaur diversity was going down, and at the same time we ended up with more specialized animals in a lot of ways, and they ended up being the biggest animals in each of their lineages," said Currie.