The Giants exhibition at the National Museum of Scotland displays some of the megafauna that once inhabited the Earth. Here, I highlight two marine species: Livyatan, an ancient sperm whale, and Megalodon, the biggest shark that ever lived.

In March 1997, Moby, a 40 ft sperm whale, stranded near my hometown on the Forth. But why did he strand and why do whales strand in general?