The massive chunk of Cretaceous stone is a self-contained monument to an ancient death trap. Carefully pulled out of the ground near Moab by Utah state paleontologist Jim Kirkland and crew late in 2014, the mass has yielded the remains of at least nine Utahraptor of various ages — fuzzy, three-foot-long yearlings laid to rest alongside adults that stretched 16 feet from snout to feathery tail tip.
But how did so many carnivorous dinosaurs wind up in one place? At first, Kirkland said, he thought “we were looking at a small river channel,” or some other body of water where animals might have frequently fought or drowned. Yet all the dinosaur bones were encased in sandstone blobs that were distinct from the surrounding rock. Something else was going on. And now, working with Kutztown University paleontologist Edward Simpson and colleagues, Kirkland thinks he's found the answer: Quicksand is what snared, killed and buried these unfortunate dinosaurs.
Drawing from the behavior of modern quicksand traps in the vicinity of Lake Powell, which Kirkland said inspired the Utahraptor eureka moment, the researchers reconstructed what transpired in eastern Utah 125 million years ago. They’ve published their results in the journal PALAIOS.
It took another dinosaur entirely to crack the case. In addition to Utahraptor, Kirkland said, the trap has yielded bones of beaked, herbivorous dinosaurs called iguanodonts. At least one of these herbivores likely blundered into the quicksand, Kirkland said, where it got stuck and died.
“You do not sink in quicksand like the 'Tarzan' movies,” Kirkland said. The mix of water and sand looks solid until something — like a bulky dinosaur — steps on it, when it temporarily becomes a more liquid mix before solidifying again. This happens because the water and sand are balanced perfectly before being disturbed by the extra weight, which makes them mix and turns the disturbed area soupy. Once the sand and water have time to separate once more, the mixture goes solid again.
It’s unlikely that the iguanodont became totally submerged, but struggling would have caused it to sink to a level where the dinosaur would have become irrevocably stuck. And even if the dinosaur didn’t cry out and attract nearby predators, the postmortem smell of its carcass would have seemed like a clanging dinner bell to the Utahraptor. But alas, Utahraptor, the bell tolled for thee.
Whether or not the Utahraptor arrived at the quicksand buffet en masse or one by one is still unclear. Work on the immense chunk of rock has temporarily halted, awaiting an upcoming crowdfunding project to bring experienced fossil preparator Scott Madsen back on to pick away at the bones.
For now, though, Kirkland said that this is “the first published attribution of a predator death trap due to quicksand." Bad news for the dinosaurs, but a boon to paleontologists.