Of all the dinosaurs to have ever lived, Centrosaurus had some of the worst luck. Hundreds of these horned dinosaurs have been found buried together in massive bonebeds strewn through Alberta, Canada’s Dinosaur Provincial Park. These dense dinosaur graveyards seem to be the remnants of great herds – possibly numbering in the thousands – that drowned when intense storms roared up the nearby coast and inundated the floodplains these dinosaurs called home. And this raises a Cretaceous quandary. Why are Dinosaur Provincial Park’s ceratopsids found in such great numbers while other dinosaurs are not?
Social behavior may hold part of the answer. The geologic context of the Centrosaurus bonebeds indicates that all the horned dinosaurs died practically simultaneously. This, along with their sheer numbers, hints at herding behavior. Much like reindeer or wildebeest today – which sometimes die in great numbers in local floods – the dinosaurs might have been trying to cross a river or other body of water when catastrophe struck.
Yet dinosaur social life doesn’t give us the entire story. The shovel-beaked hadrosaurs are commonly found in Dinosaur Provincial Park, yet they are rarely found in bonebeds like the horned dinosaurs. To investigate this mystery, Royal Tyrrell Museum palaeontologist Donald Henderson simulated some waterlogged dinosaurs.
Given that we’re 75 million years too late to watch Centrosaurus and its neighbours swim, Henderson created virtual 3D models of four Dinosaur Provincial Park species. For the horned dinosaurs he picked Centrosaurus and Chasmosaurus, and for the hadrosaurs he modelled Lambeosaurus and Gryposaurus. After adjusting the models to account for the densities of the living animals – for example, lungs filled with air and heavier heads for the horned dinosaurs – Henderson dunked them in a digital pool to see whether they would sink or swim.
The hadrosaurs performed just fine. Even with their lungs half full of air, Henderson found, the dinosaurs would have been able to keep their mouths and noses above the surface of the water. This is partly due to their thick, muscular tails. Their back halves were heavy enough that their heads and necks tipped up while floating at the surface.
Centrosaurus and Chasmosaurus were another story. The muscle and bone of their large skulls tipped the dinosaurs forward, dunking their heads beneath. Worse still, their noses and mouths were oriented downwards, making it almost impossible for them to raise their heads above the surface. They could only do a dead dinosaur float, their skulls hopelessly beneath the water.
While hadrosaurs were adapted to life on land, swimming wasn’t a problem for them. In the wake of a storm, Henderson suspects, they could have survived for hours or even days until the water level dropped. But the same events would kill most any horned dinosaur whose feet couldn’t touch the bottom, and there are multiple, as-yet-undescribed horned dinosaur bonebeds that hint Centrosaurus weren’t the only dinosaurs to suffer such a fate. Of course, the misfortune of some dinosaurs was a boon to others. Shed tyrannosaur teeth found in horned dinosaur bonebeds show that these terrible drownings offered the first all-you-can-eat buffets to Cretaceous carnivores.
Henderson, D. 2014. Duck Soup: The floating fates of hadrosaurs and ceratopsians at Dinosaur Provincial Park, in Eberth, D. and Evans, D. (eds). Hadrosaurs. Bloomington: Indiana University Press. pp. 459-466