STEVE BRUSATTE - The image of Velociraptor and other dromaeosaurids as pack hunters has permeated popular culture, thanks largely to Jurassic Park.
One of the most iconic scenes in the movie shows a pack of Velociraptors banding together to hunt human prey, using their keen senses and intelligence to track their quarry.
In the 20 years since Jurassic Park the image of pack-hunting dromaeosaurs has shown up often in television documentaries, books, and museum exhibits. That includes Walking with Dinosaurs.
In both the documentary TV series and the arena live show, the grizzly-bear-sized dromaeosaurid Utahraptor is portrayed as a vicious pack animal that would team up with its mates to take down much larger plant-eating dinosaurs.
But what is the evidence for this?
It turns out that it is quite weak. The idea that dromaeosaurids might have been pack hunters was advocated by one of the 20th century's most eminent palaeontologists, John Ostrom of Yale University.
Ostrom was the scientist who found a stunning skeleton of the dromaeosaurid Deinonychus in the 1960s, which showed convincingly that these dinosaurs were very bird-like in their anatomy, posture, and behaviour. A few decades later Ostrom described more fossils of Deinonychus, which he interpreted as showing pack-like behaviour.
These new fossils - the partial skeletons of four individuals - were found in the middle Cretaceous Cloverly Formation of Montana. The four Deinonychus fossils were found associated with the skeleton of a larger plant-eating dinosaur called Tenontosaurus.
Ostrom argued that the association of multiple Deinonychus individuals with a larger plant eater, and the presence of numerous shed teeth of Deinonychus at the site, meant that he was looking at a Cretaceous crime scene, where a pack of dromaeosaurids were killed in the act of taking down their prey.
He suggested that the large herbivore was able to kill off some members of the attacking pack, but later succumbed to its injuries, at which point it was consumed by the surviving members of the raptor pack.
Although this is a plausible scenario, it is only one interpretation. It could be that the fossils of the four Deinonychus individuals and the single Tenontosaurus were randomly washed together by a flood. Or maybe they were gathered together by another predator. Or maybe they just coincidentally were fossilised next to each other.
This was the argument advanced by another team of palaeontologists, Roach and Brinkman, in 2007. They suggested that it was more plausible that Deinonychus was not a pack hunter, because this behaviour is rare in living crocodiles and birds, the closest relatives of dinosaurs.
But this conclusion is also tenuous. Just because a particular type of behaviour is rare for living dinosaur cousins does not mean it was impossible for dinosaurs. After all, there are no modern day dinosaur relatives that approach the huge sizes of Brachiosaurus or Tyrannosaurus, so dinosaurs clearly did some unusual things compared to living creatures.
So, then, where does the debate about dromaeosaurid pack-hunting stand? Because the fossil evidence is so fragmentary the debate continues, and will probably do so until more convincing evidence of pack-hunting behaviour emerges in the fossil record (such as the skeletons of multiple dromaeosaurids preserved ‘in the act’ of ripping into their prey).
- Steve Brusatte is the resident palaeontologist at Walking with Dinosaurs.
- Illustration of Utahraptor by Emily Willoughby
- Photograph of landscape in eastern Ladakh by McKay Savage