What Caused the Dinosaur Stampede?

I have often been accused of being a fossil killjoy. I regularly disappoint paleontology fans who prefer to see prehistory as a constant battle of all against all. But them’s the breaks—as we understand the fossil record better, sometimes prehistory turns out to be less blood-spattered than we thought.

One of the most recently revised cases involved the approximately 100-million-year-old Lark Quarry in Australia. This place, an immense tracksite, is said to preserve the signs of a seldom-seen dinosaur stampede. The old story went something like this. A huge aggregation of small, bipedal dinosaurs were hanging out along the shore of an ancient lake. The small dinosaurs had no idea they were being watched by hungry eyes. Without warning, a huge carnivorous dinosaur burst from its cover in a nearby stand of trees. Little dinosaurs scattered everywhere, leaving behind evidence of a dinosaur stampede.

There is no doubt that a huge gaggle of little dinosaurs scurried away over the damp Cretaceous lake shore. What has come into question is the identity of the dinosaur that triggered the stampede. The dramatic predator vs. prey story was based on large, three-toed footprints found at the same site. These were previously attributed to a large theropod dinosaur akin to Allosaurus—the recently-discovered Australovenator seemed to be a good candidate—but a recent reanalysis by paleontologists Anthony Romilio and Steven Salisbury found that the imprints don’t actually match the foot anatomy of big predatory dinosaurs. Instead, the relatively blunt-toed tracks correspond to the feet of a herbivorous, iguanodontian dinosaur, something akin to Australia’s own Muttaburrasaurus.

This sort of revision has happened before. Many large, three-toed tracks attributed to tyrannosaurs and other predatory dinosaurs have later been found to belong to hadrosaurs and other herbivorous dinosaurs within a group called ornithopods. Rather than running for their lives, the little dinosaurs who left their footprints at the Lark Quarry site may have been yellow-bellied chickenosaurs that got spooked when a big herbivore got too close or surprised them. And even that scenario assumes that the big tracks and little tracks represent a single event. Something triggered the dinosaur stampede, but there is no solid evidence that a ravenous, sharp-toothed dinosaur was to blame.

Nevertheless, a new documentary about the Lark Quarry site created by the Australian Broadcasting Corporation has played up the drama of the traditional story. I have not been able to see the program yet—the show is only available to Australian viewers thus far—but the promotional trailer certainly emphasizes the role of a mysterious, carnivorous dinosaur. Maybe this is a bait-and-switch—build up the mystery, but then tell viewers that a wandering herbivore was really responsible. Then again, maybe the old story is just too hard to resist. Prime-time dinosaur documentaries are made of flesh-tearing predators, not bumbling ornithopods. Personally, I think a comedic angle—little dinosaurs tripping over themselves as Boots Randolph’s rendition of “Yakety Sax” played in the background—would be just as fitting as the dramatic, terror-laden one, but dinosaur documentary tradition is hard to break.

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.