Thousands of dinosaurs were buried here, killed in an instant on a day of utter devastation. Now, a group of palaeontologists have come to Pipestone Creek - appropriately nicknamed the "River of Death" - to help solve a 72-million-year-old enigma: how did they die?

Trying to work out exactly what happened here starts with the hefty strike of a sledgehammer. Brute force is needed to crack open the thick layer of rock that covers what Professor Emily Bamforth, who's leading the dig, describes as "palaeo gold". As her team begins the more delicate job of removing the layers of dirt and dust, a jumble of fossilised bones slowly begins to emerge.

"That big blob of bone right there is, we think, part of a hip," Prof Bamforth says, watched on by her dog Aster - whose job today is to bark if she spots any nearby bears. "Then here, we have all of these long, skinny bones. These are all ribs. And this is a neat one - it's part of a toe bone. This one here, we have no idea what it is - it's a great example of a Pipestone Creek mystery." BBC News has come to Pipestone Creek to witness the sheer scale of this prehistoric graveyard and see how researchers are piecing together the clues. Thousands of fossils have been collected from the site, and are constantly generating new discoveries.

The bones all belong to a dinosaur called Pachyrhinosaurus. The species, and Prof Bamforth's excavation, feature in a new landmark BBC series - Walking With Dinosaurs - which uses visual effects and science to bring this prehistoric world to life. These animals, which lived during the Late Cretaceous period, were a relative of the Triceratops. Measuring about five metres long and weighing two tonnes, the four-legged beasts had large heads, adorned with a distinctive bony frill and three horns. Their defining feature was a big bump on the nose called a boss. (BBC)