Scientists try to explain why 1000s of dinosaurs died in one mass grave

Deep in the lush forests of Alberta, Canada, lies a prehistoric scene that has befuddled scientists for decades. Pipestone Creek, grimly dubbed the “River of Death,” is home to a jaw-dropping mass grave where thousands of Pachyrhinosaurus bones lie packed in one place as if they had been cornered or had gathered there due to a threat that endangered them all.

This 72-million-year-old mystery, where a herd of these horned, Triceratops-like giants met their end, is finally getting some answers, thanks to a team led by Professor Emily Bamforth. Their work, featured in the BBC’s Walking With Dinosaurs series, is peeling back the layers of a catastrophic day frozen in time, according to a BBC report.

The bonebed, discovered in 1974 by a local teacher, Al Lakusta, stretches across a kilometre, with up to 300 bones per square meter in some spots. That’s 8,000 fossils collected so far, from tiny juveniles to hefty adults, all from a single species. 

They weighed about 2 tonnes

Five metres long and weighing two tonnes, these plant-eating beasts sported bony frills and a distinctive nasal bump. Bamforth’s team, wielding sledgehammers to crack through rock, uncovers hips, ribs, and toe bones, each a clue to a herd that roamed a warmer, greener Alberta during the Late Cretaceous. 

The sheer density—covering an area the size of a tennis court so far—makes this one of North America’s largest bonebeds.

So, scientists are trying to determine what killed the milennary giants. According to some of the theories scientists are contemplating, the evidence points to a flash flood of biblical proportions.

Picture a herd migrating north for summer, munching on delicious and nutritional vegetation, when a monstrous storm, possibly a hurricane, unleashed a torrent from the mountains, forcing them to concentrate in one area where they believed they could survive the vast water downpour.

Wiped out in one brutal event

Swirling sediment in the rocks and jumbled bones tell the story of fast-moving water that swept away everything—trees, boulders, and top-heavy dinosaurs that couldn’t swim. 

Bamforth says their sheer numbers and bulky builds left them no chance. It’s a snapshot of devastation, with the herd’s young and old wiped out in one brutal event.

Nearby, the Deadfall Hills offer more clues. No digging needed here—just a hike through dense forest and a wade across a river to find Edmontosaurus bones, like vertebrae and teeth, scattered along the shore. 

These 10-metre-long duck-billed dinosaurs shared the ecosystem, and their fossils help paint a picture of a vibrant, prehistoric world. 

At the Philip J. Currie Dinosaur Museum, where Bamforth and collection manager Jackson Sweder work, a massive Pachyrhinosaurus skull nicknamed “Big Sam” (missing one horn) reveals individual quirks, shedding light on how these creatures lived and grew.