An illustration of Murusraptor barrosaensis . (Jan Sovak/University of Alberta)

Paleontologists name a new dinosaur species about every two weeks. That’s a hell of a pace, and from that statistic alone, it might seem that researchers are soon going to rocket past Peak Dinosaur. The truth of the matter, however, is that fossil hunters have truly only scratched the surface of prehistoric dinosaur diversity, a point driven home by this week’s announcement of a new carnivorous enigma from South America.

The new dinosaur, described in the journal PLOS ONE by paleontologists Rodolfo Coria and Philip Currie, is named Murusraptor barrosaensis. The dinosaur’s name is a tribute to how it was found. During an expedition to Sierra Barrosa in northwestern Patagonia, Coria says, team member Sergio Saldivia spotted dinosaur bones jutting from the 80 million-year-old stone. Because the disarticulated pieces were found in a canyon wall, Coria and Currie combined the Latin words for "wall" (murus) and "thief" (raptor) to coin Murusraptor.

Coria knew right away that this was something special. “We knew since the beginning that it was a new species because no theropods were known from this particular geological formation,” Coria said. And once the dinosaur was cleaned up back at the lab, it turned out to be something of a Cretaceous head-scratcher.

If you’re going to belong to a fierce-sounding family, you could do worse than the megaraptors. This is the group of dinosaurs that Coria and Currie determined Murusraptor belonged to — mid-sized carnivores, some of which bore terrifyingly large claws. But then things get a little bit tricky.

No one can quite agree on who the closest relatives of the megaraptors are. Some experts suggest that they’re most closely related to the allosaurs — huge carnivores with teeth suited to slicing flesh — while others have proposed a closer kinship with the famous tyrannosaurs.

Megaraptors cluster together in their own special group, but the lineage from which they sprang is still shrouded. Unfortunately, Murusraptor alone won’t solve the mystery. Murusraptor and all the other known megaraptors lived around the same time, Coria said, when the group had already differentiated itself from its closest relatives. The dinosaurs that connect these slashers to their ancestral stock have yet to be found.

“Murusraptor provides a new glimpse to the megaraptor diversity in the Late Cretaceous,” Coria said, “but in order to clarify their phylogeny, we need to find more primitive forms.”

This isn’t bad news. If anything, it means there are even more dinosaurs out there. With a targeted search of older rocks (and a dollop of luck), paleontologists will eventually find the creatures that help resolve the identity of these puzzling dinosaurs. Murusraptor is another glimpse of what’s still out there awaiting discovery. All in all, it’s not just another megaraptor in the wall.

Brian Switek is a freelance science writer and the author of "My Beloved Brontosaurus." For more, read his Scientific American blog and follow him on Twitter or Instagram

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