The fossilised remains of a bizarre, bird-like dinosaur, nicknamed the "chicken from hell" by scientists, have been unearthed in the US.

The 66-million-year-old feathered beast would have resembled a beefed-up emu with a long neck, a metre-long tail and a tall crest on its head. At the end of its forelimbs were long, sharp claws. The creature stood 1.5 metres high at the hip and reached more than three metres from beak to tail. Researchers believe it lived on ancient floodplains and fed on plants, small animals and possibly eggs. An adult weighed up to 300kg.

Researchers dug the remains from mudstone in the Hell Creek formation in North and South Dakota, where fossil hunters have previously excavated bones from Tyrannosaurus rex and triceratops. Over the past decade they have recovered three partial skeletons of the animal but until now had not recognised it as a new genus and species of a mysterious family of dinosaurs called Caenagnathidae. The fossils are being kept at the Carnegie Museum of Natural History in Pittsburgh.

Scientists working on the remains coined the "chicken from hell" monicker, which later influenced their choice of its more formal name, Anzu wyliei. Anzu is the name of a giant bird-like demon from ancient mythology. Wyliei comes from Wylie J Tuttle, the son of a donor who helps to fund research at the museum.

The animal belongs to a group called the oviraptorosaurs, which are mostly known from fossils found in central and east Asia but the remains provide the first detailed picture of the North American oviraptorosaurs.

"For almost a hundred years, the presence of oviraptorosaurs in North America was only known from a few bits of skeleton, and the details of their appearance and biology remained a mystery," said Hans-Dieter Sues, curator of vertebrate palaeontology at the Smithsonian National Museum of Natural History. "With the discovery of A. wyliei, we finally have the fossil evidence to show what this species looked like and how it is related to other dinosaurs."

Anzu had the build of a fast runner and with substantial claws at the tips of its forelimbs was well-equipped to fight. A close inspection of the fossils revealed that two showed signs of skirmishes. One had a healed broken rib. Another had an arthritic toe that was probably caused by a tendon being ripped off the bone. The fossils are described in the journal Plos One.

An artist's impression of A. wyliei. Illustration: Bob Walters

"Whether these injuries were the result of combat between two individuals or an attack by a larger predator remains a mystery," said Emma Schachner, a palaeontologist at the University of Utah.

Anzu is not the largest of the oviraptorosaurs found to date. The aptly named Gigantoraptor discovered in Inner Mongolia in 2005 grew to around eight metres long and weighed more than a tonne. "We're finding that the caenagnathids were an amazingly diverse bunch of dinosaurs," said Matthew Lamanna at the Carnegie Museum of Natural History.

"Whereas some were turkey-sized, others like Anzu and Gigantoraptor, were the kind of thing you definitely wouldn't want to meet in a dark alley."

"We jokingly call this thing the 'chicken from hell' and I think that's pretty appropriate," Lamanna added.

"These fossils are some of the most interesting new dinosaurs to come out of North America over the past decade," said Stephen Brusatte, a vertebrate palaeontologist at the University of Edinburgh.

"Oviraptorosaurs are one of the most bizarre groups of dinosaurs to ever live. This new dinosaur, Anzu, looks like something that was placed in the Cretaceous by a Hollywood monster movie director. Looking at these animals, it's hard to believe they were real. They had big crests on their skulls, a beak, no teeth, and a very bird-like skeleton."

Brusatte added that the new fossils provided a glimpse of what the skeleton of the North American oviraptorosaurus was like, and showed that they were highly unusual. "Anzu would have lived alongside T. rex, and believe it or not, T. rex was a close cousin. But Anzu was an entirely different type of dinosaur: a fast-running, ecological generalist that didn't quite fit the usual moulds of meat-eating or plant-eating dinosaur."