Marine mammals have evolved their whopping size for a reason—and it's not what we expected.
Land mammals can get plenty big, but to find the planet’s true giants, you'll have to take to the seas.
In a new study, scientists show why that is. Marine mammals "have to find a happy medium between getting enough food and producing enough body heat," says study leader William Gearty, an ecologist at Stanford University. (Read about a bus-size whale that's still a mystery to scientists.)
Previously, researchers believed that marine mammals could be so large because the buoyancy of water frees them from the constraints of gravity. Although this freedom may still be a factor, Gearty says that his results show that marine mammals need their heft to keep themselves warm in the often chilly oceans.
"These animals are big for very specific reasons. It’s not that they could be big, it’s that they must be big," he says.