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Speaker 1: Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,

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Speaker 1: Lauren bolg bomb here. If you've ever been whale watching,

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Speaker 1: visited a large aquarium, or even seen the skeleton of

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Speaker 1: a whale in a museum of natural history, you know

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Speaker 1: the majestic massiveness of these aquatic mammals. The largest mammal

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Speaker 1: to have ever lived on Earth in the history of

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Speaker 1: the planet is not some prehistoric monstrosity. It's actually the

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Speaker 1: blue whale, and is alive right now swimming around in

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Speaker 1: our oceans. Whales range in size from the massive blue whales,

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Speaker 1: which can grow to more than ninety feet that's twenty

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Speaker 1: seven in length, to the relatively tiny pigmy sperm whales,

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Speaker 1: which measure a measly ten feet or three meters in length.

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Speaker 1: But with all that ocean to swim around in, why

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Speaker 1: aren't whales even bigger. It's not like they have to

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Speaker 1: support their big bodies on legs and walk around. For

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Speaker 1: that matter, though, why aren't they smaller? Both answers have

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Speaker 1: to do with food and heat. At least, that's what

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Speaker 1: researchers at Stanford University found when they compiled the body

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Speaker 1: mass data for nearly four thousand living whales. And three

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Speaker 1: thousand fossilized species. Their analysis determined that aquatic mammals actually

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Speaker 1: face more size constraints than their counterparts on land. The

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Speaker 1: study authors determined that there are two main factors why

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Speaker 1: whales are big but not bigger, heat loss and metabolism.

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Speaker 1: Oceans can be pretty cold places to live, and whales,

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Speaker 1: while very intelligent, don't really have the aquatic equivalent to

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Speaker 1: thermal underwear. So because they're warm blooded mammals, they have

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Speaker 1: to be large enough to keep from losing too much

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Speaker 1: body heat to the surrounding water. Thermoregulation than it keeps

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Speaker 1: whales from being the size of, say dogs. Study co

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Speaker 1: author Jonathan Payne, a professor of geological sciences at Stanford's

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Speaker 1: School of Earth, Energy and Environmental Sciences, explained in a

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Speaker 1: press statement, when you're very small, you lose heat back

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Speaker 1: into the water so fast there's no way to eat

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Speaker 1: enough food to keep up. And speaking of eating, whales

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Speaker 1: have to do it a lot. Like all mammals, they

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Speaker 1: convert that food into energy for swimming, growing, and doing

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Speaker 1: other whale like things. That's the metabolic system at work.

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Speaker 1: But the researchers suggest that the metabolism of whales only

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Speaker 1: gets faster as they get bigger, and so they can

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Speaker 1: only get so large. Another study co author, Craig McLaine

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Speaker 1: of the Louisiana University's Marine Consortium, explained it this way. Basically,

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Speaker 1: animals are machines that require energy to operate. This need

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Speaker 1: for energy places hard limits on what animals can do

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Speaker 1: and how big they can be. So it boils down

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Speaker 1: to how much whales can eat versus their metabolic rate

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Speaker 1: that keeps whales from getting infinitely large. But how do

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Speaker 1: those massive blue whales get so massive? They have bailean

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Speaker 1: instead of teeth and strain their food a little shrimp

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Speaker 1: like creatures called krill instead of chewing it. Krill are

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Speaker 1: only a few centimeters long, but they really add up.

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Speaker 1: Every day a blue whale eats about eight thousand pounds.

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Speaker 1: That's over three thousand, six hundred kilos of krill. So

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Speaker 1: blue whales are not only the largest whales in the ocean,

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Speaker 1: they're also the most efficient eaters of all. Today's episode

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Speaker 1: was written by Kristen hall Geisler and produced by Tyler

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Speaker 1: Clang for iHeart Media and How Stuff Works. For more

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Speaker 1: on this and lots of other huge topics, visit our

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Speaker 1: home planet, How stuff Works dot com,