On a fateful day in the Early Cretaceous, a large, four-legged armoured dinosaur dropped dead on a beach in what is now modern day Alberta. The remains of this 5.49m-long beast drifted out to sea and eventually sank, where it became buried in a thick layer of mud. Over time, the dinosaur became petrified, its soft tissues replaced by hard minerals. And then, quite by chance -- some 110 million years later -- a Canadian mining operator stumbled upon what is now considered to be one of the finest fossils ever discovered.