How the biggest animal on Earth got so big

A blue whale, the largest animal on the planet, engulfs krill off the coast of California. (Photo courtesy Silverback Films/BBC/Proceedings of the Royal Society B)
Whales are the largest animals on the planet, but they haven’t always been giants. Fossil records show that ancient whales were much smaller than the currently living behemoths.
So when did whales get so big, and how?
A new study suggests it might be due to changes in climate that affected the food that some whales eat: krill an