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 and small fish. Instead of being spread throughout the ocean, lots of krill started being packed into a small area. Bigger whales were simply more efficient at eating the dense pockets of krill, and they beat out their smaller cousins.