Rather than being pack hunters, as they are usually portrayed, the dinosaur raptors probably fended for themselves, palaeontologists have concluded, based on changes to their teeth as they aged.
The Jurassic Park films may have been great for inspiring a generation of wannabe paleontologists, but they weren't so good at scientific accuracy. To be fair, their portrayal of raptors as hunting collectively aligned with the predominant view when the films were made – unlike many other plot features – but the advancement of knowledge looks set to change that.
"Raptorial dinosaurs often are shown as hunting in packs similar to wolves," said Dr Joseph Frederickson of the University of Wisconsin Oshkosh in a statement. "The evidence for this behavior, however, is not altogether convincing. Since we can't watch these dinosaurs hunt in person, we must use indirect methods to determine their behavior in life."
Frederickson noted that modern animals that hunt alone usually consume different prey as they grow up – when small they're incapable of catching the diet they will depend on as adults. Pack animals, once weaned, get to share in kills made by their older relatives.
On the basis that we are what we eat, the bones and teeth of animals contain an isotopic signature tied to their diet, and this varies far more for solitary feeders through life than those that share the family bounty. In Paleogeography, Paleoclimatology, Paleoecology Frederickson confirms Cretaceous crocodilians, like their modern counterparts, have isotopes indicating a changing diet as they grow capable of catching larger prey, then turns his attention to the raptor Deinonychus antirrhopus, a 3.4-meter-long (11-foot) carnivore that lived 110-120 million years ago.
"We also see the same pattern in the raptors, where the smallest teeth and the large teeth do not have the same average carbon isotope values, indicating they were eating different foods,” he said.
Frederickson noted pack hunting is rare among surviving avian dinosaurs. Many birds may gather where food is abundant, and sometimes one will benefit from this by capturing prey trying to evade another. Nevertheless, co-ordination to bring down large prey, or to herd smaller ones, is usually the domain of mammals.
Quite why birds don't usually hunt in packs is a mystery. After all, plenty live communally and the exceptional intelligence shown by some crows and parrots suggests lack of brains is not the obstacle. We also see many birds acting collectively to repel threats.
Unlike so many other dinosaur portrayals, the notion of pack hunting raptors doesn't just come from an author or scriptwriter's head. Yale palaeontologist John Ostrom proposed the idea in the 1960s to explain why Deinonychus fossils are often found around the bones of dinosaurs large enough to have been hard to tackle alone. The adult Deinonychus isotopes are consistent with eating large prey like this, however, suggesting that even alone they were fearsome hunters.