Christian Darkin / Science Photo Library
Animals first evolved to live exclusively on land about 370 million years ago – but on dozens of occasions since then land animals have gone back to exploiting the seas. That might be because the shallow seas around continents are so full of food that they proved an irresistible lure.
Some of the most spectacular species now living in the sea have land-living ancestors. Whales are descended from animals similar to deer, while walruses and seals evolved from animals a bit like modern otters.
What’s more, many land-dwelling …