WASHINGTON (Reuters) - On a semiarid Patagonian landscape 85 million years ago, a formidable meat-eater called Tratayenia rosalesi reigned as the apex predator, part of an enigmatic dinosaur group that menaced South America and Australia for tens of millions of years.

The newly discovered predatory dinosaur, Tratayenia rosalesi, is shown in this handout illustration crossing a stream in what is now Patagonia, Argentina, roughly 85 million years ago. Andrew McAfee, Carnegie Museum of Natural History/Handout via REUTERS

Scientists on Wednesday described Tratayenia, a two-legged beast up to about 30 feet (9 meters) long, based on fossils unearthed in Argentina’s Neuquén province, adding another impressive dinosaur to the list of those that inhabited Patagonia during the Cretaceous Period.

It was a member of a group called megaraptorids that lived in the Southern Hemisphere from about 105 to 85 million years ago. The group was recognized by paleontologists only in the past few years, and all of its members -- including Tratayenia -- are known only from incomplete skeletons.

“Megaraptorids, although still mysterious, seem to have been a pretty badass bunch of predatory dinosaurs,” said paleontologist Matt Lamanna of the Carnegie Museum of Natural History in Pittsburgh.

“Using the remains of different species, including Tratayenia, we can make something like a ‘police composite’ of a megaraptorid skeleton,” Lamanna added. “Megaraptorids had long, low skulls that were crammed with lots of small but sharp and serrated teeth, bones that were riddled with air cavities, and powerful forelimbs that were tipped with absolutely ginormous, wickedly hooked claws on the innermost two fingers.”

For Tratayenia, the researchers found about half of the back vertebrae, all its hip vertebrae, some ribs and a fair bit of the pelvis, but none of the skull, limbs or tail.

Patagonia boasted some of the most impressive dinosaurs ever found, including the giant predator Giganotosaurus and the immense long-necked, four-legged plant-eaters Patagotitan, Argentinosaurus and Dreadnoughtus.

“Tratayenia was the largest-known predator about 85 million years ago in Patagonia and perhaps one of the last in its group,” said paleontologist Juan Porfiri of the National University of Comahue’s Museum of Natural Sciences in Argentina.

It lived in an ecosystem that included smaller carnivorous dinosaurs including Viavenator, large herbivores such as Traukutitan, snakes similar to boas, crocs, turtles and birds, Porfiri added.

The best known member of Tratayenia’s group is Megaraptor, which lived slightly earlier in Patagonia and wielded 16-inch (40-cm) claws.

“Megaraptorids certainly would have been terrifying to encounter in life: big, heavily armed and powerful, but also probably lighter on their feet than really giant meat-eaters such as Giganotosaurus or T. rex,” Lamanna said.

The research was published in the journal Cretaceous Research.