You might know raptors as the fast, nimble dinosaurs whose killer sickle-shaped claws made Jurassic Park's infamous kitchen scene so enjoyably terrifying. You might also know that Spielberg's creations were waaay bigger than the real thing. But now, thanks to a discovery made in the fossil graveyards of North America, a new member has joined the raptor ranks – and it's big enough to live up to the Jurassic Park dream.

A North American research team led by Robert DePalma has unearthed a new species of giant raptor from the Hell Creek Formation of Harding County in South Dakota, a region that got its name because it's, well, hot as hell and devoid of almost any life. Known from a partial skeleton, the new find – Dakotaraptor steini – is one of the largest ‘raptors’ (also known as dromaeosaurids) ever discovered.

 Dakotaraptor steini life restoration by Emily Willoughby.
Size Comparison 2015 11 03
Image: DePalma et al., 2015

At around five metres from snout to tail, Dakotaraptor would still have appeared tiny alongside the 12-metre-long Tyrannosaurus rex, which lived at around the same time. But compared to its own kind, including the turkey-sized Velociraptor, Dakotaraptor ranked among the biggest – and most dangerous.

For a start, the dino boasted claws that would have put Velociraptor to shame. At 24cm (9.5 inches) along the outer curve, they're among the largest of any raptor claws known. While the function of this distinctive raptor feature remains a mystery, some speculate that the fearsome weapons were used for disembowelling prey, or perhaps clinging on to other animals like climbing crampons!

The presence of 'quill knobs' is clear evidence that this predator would have had feathers on its arms. Image: Robert DePalma

Claws aside, perhaps the coolest thing about the Dakotaraptor find is the row of "quill knobs" on the surface of its ulna (one of the lower arm bones). In living birds, these knobs are reinforced and show where feather quills would have attached for support. While Dakotaraptor would have been unable to fly due to its size, these knobs are clear evidence that the predator would have had feathers on its arms. Evidence of bristle-like "protofeathers" has been found on other large dinosaurs, but Dakotaraptor is the largest dinosaur with true wings discovered to date.

But why the feathers if you don't fly? “Either it evolved from an ancestor that could fly but had lost the ability ..., like an ostrich, or dinosaurs evolved big quill-pen feathers for another reason, such as display or egg brooding,” explains Steve Brusatte, a dinosaur researcher at the University of Edinburgh, who was not part of the Dakotaraptor research.

Dakotaraptor hunted with the help of some supersized claws. Image: DePalma et al., 2015

But what we really want to know about these dinosaurs is how they hunted, right? Raptors are sometimes portrayed as pack hunters, similar to modern wolves, and there's even track evidence of some moving together and feeding on the same animal. “I think there is at least moderate evidence that some raptors were pack hunters, but it's not a slam-dunk that all of them were, or that they normally hunted this way,” cautions Brusatte.

Certainly, the discovery of Dakotaraptor raises questions about where this supersized predator would have fitted in the food chain. Did T. rex rule every carnivorous niche, out-competing any other large predators? Or could a fully grown Dakotaraptor (about the same size as a younger T. rex) have been a challenger? The two might have avoided competition with each other by adopting different hunting styles: younger T. rex had long legs built for pursuing prey over longer distances, while the more lightweight Dakotaraptor was the perfect killing machine for ambushing and grappling with its prey.

“Dakotaraptor very well may have been filling a similar niche as a pre-teen T. rex. [And] that's a chilling thought...,” says Brusatte.