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Whales are the largest animals to ever live on Earth. But did you know they haven't always been so big? Now scientists think they know when whales got so enormous and why. NPR's Madeline Sofia reports.
MADELINE SOFIA, BYLINE: Blue whales are really big. They can be as long as a basketball court and weigh around 300,000 pounds. That's like 16 T. rexes.
JEREMY GOLDBOGEN: We're totally living in a time of giants unlike no other time in Earth's history.
SOFIA: That's Jeremy Goldbogen, a whale researcher from Stanford University. Giant whales need to eat a lot. To do that, they've evolved a secret weapon, a filter called baleen that they use to sweep up thousands of pounds of krill and fish. It allows whales to pack on the pounds. But baleen was around way before whales started getting huge.
GOLDBOGEN: Baleen evolved about 20 million years ago, and we didn't see the evolution in gigantism until very recently, about 3 to 5 million years ago.
SOFIA: So if it wasn't just baleen, how did whales get so big? Goldbogen's group looked back to see what was happening in the ancient oceans at the time to see if there were any clues into what caused the massive growth spurt. Goldbogen suggests it was all about the food.
GOLDBOGEN: Turns out from paleo-oceanographic studies that the oceans started to get really, really intense in terms of upwelling.
SOFIA: Upwelling occurs when wind pushes water on the surface of the ocean away from the shore, causing water rich in nutrients from the deep to rush up to the surface. Around the same time, the Earth's climate was changing, causing nutrients to pour into coastal waters. The researchers think this combination led to floating patches of dense food. And which whales got the most food? The ones with the biggest mouths.
GOLDBOGEN: As animals are getting bigger, they're getting much more efficient. So for every gulp, they're getting tremendous amounts of energy.
SOFIA: Some species got 10 times bigger in just a few million years. And sure, a few million years doesn't sound quick, but that's just a small fraction of the time they've been on Earth. The scientists write in the journal Royal Society B that the gigantic whales simply beat out their smaller cousins for food, leading to the die-off of the smaller baleen whales. And Goldbogen thinks whales might not be done just yet.
GOLDBOGEN: What's cool about that is that it begs the question, are whales still getting bigger?
SOFIA: Fast-forward a couple million years in the future, and today's whales might seem like smaller whales. Madeline Sofia, NPR News.
(SOUNDBITE OF MICHAEL JACKSON'S "WILL YOU BE THERE (THEME FROM 'FREE WILLY')")