The riddle of the dino grave

About 72 million years ago, around 10,000 dinosaurs died instantly in a relatively small area in Alberta, Canada, and scientists are unsure why.

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Pipestone Creek, sometimes known as the "River of Death", is the final resting place of a herd of Pachyrhinosaurus. These large four-legged dinosaurs, which are related to Triceratops, could grow up to eight metres long and weighed up to four tonnes - bigger than a white rhino.