U.S. paleontologists have discovered a new raptor dinosaur that lived in western North America during the Cretaceous period, about 66 million years ago.

This is an artist’s impression of Anzu wyliei. Image credit: Mark Klingler / Carnegie Museum of Natural History.

The new fossil creature that resembled a cross between a modern emu and a reptile was described from three specimens that collectively preserve almost the entire skeleton, giving paleontologists an opportunity to study the anatomy and evolutionary relationships of a mysterious group of theropod dinosaurs known as caenagnathids.

The specimens were excavated from the uppermost level of the Hell Creek rock formation in North and South Dakota – a formation known for abundant fossils of Tyrannosaurus rex and Triceratops.

“Two of the specimens display evidence of pathology. One appears to have a broken and healed rib, and the other has evidence of some sort of trauma to a toe,” said Dr Emma Schachner from the University of Utah, who is a co-author of the paper published in the open-access journal PLoS ONE.

At 3.3 m (11 feet) long and 1.5 m (5 feet) tall at the hip, the dinosaur would have resembled a gigantic flightless bird, more than a typical theropod dinosaur such as Tyrannosaurus rex. It weighed an estimated 200 to 300 kg (440 to 660 pounds). Its jaws were tipped with a toothless beak, and its head sported a tall, rounded crest similar to that of a cassowary.

“It was a giant raptor, but with a chicken-like head and presumably feathers. The animal stood about 11 feet tall, so it would be scary as well as absurd to encounter,” Dr Schachner said.

Craniomandibular skeleton of Anzu wyliei. Image credit: Matthew C. Lamanna et al.

The beaked dinosaur has been scientifically named Anzu wyliei. The genus name is after a bird-like demon in Mesopotamian mythology, and the specific name is after a boy named Wylie, the dinosaur-loving grandson of a Carnegie Museums of Pittsburgh trustee.

With large sharp claws, Anzu wyliei was an omnivore, eating vegetation, small animals and perhaps eggs while living on a wet floodplain. The dinosaur apparently got into some scrapes.

“I am really excited about this discovery because Anzu wyliei is the largest oviraptorosaur found in North America,” Dr Schachner said.

“Oviraptorosaurs are a group of dinosaurs that are closely related to birds and often have strange, cassowary-like crests on their heads.”

They are widely known because the first fossil skeleton, described in 1924, was found atop a nest of dinosaur eggs, suggesting that the creature had died in the act of raiding the nest. This thinking prevailed until the 1990s, when the same type of egg was found with a baby oviraptorid inside, demonstrating that, rather than a nest plunderer, Oviraptor was a caring parent that perished while protecting its eggs.

More than a dozen oviraptorid species have been discovered, all in Mongolia and China, and many are known from beautifully-preserved, complete or nearly complete skeletons.

Additionally, beginning in the 1990s, several small, primitive relatives of oviraptorids were unearthed in much older, about 125 million-year-old rocks in northeastern China. Many of these are also represented by complete skulls or skeletons, some of which preserve fossilized feathers.

Postcranial skeleton of Anzu wyliei. Image credit: Matthew C. Lamanna et al.

Paleontologists have established that caenagnathids, oviraptorids, and these more archaic Chinese species are closely related to one another, and have united them as the theropod group Oviraptorosauria.

The occurrence of oviraptorosaurs in both Asia and North America was not a surprise to paleontologists, because these continents were frequently connected during the Mesozoic Era, allowing dinosaurs and other land animals to roam between them.

However, because their fossils were so incomplete, caenagnathids remained the most poorly known members of Oviraptorosauria, and indeed, one of the least understood of all major dinosaur groups.

“For almost a hundred years, the presence of oviraptosaurs in North America was only known from a few bits of skeleton, and the details of their appearance and biology remained a mystery,” explained study co-author Dr Hans-Dieter Sues from the Smithsonian Institution’s National Museum of Natural History in Washington.

“With the discovery of Anzu wyliei, we finally have the fossil evidence to show what this species looked like and how it is related to other dinosaurs.”

Source: sci.news