Whales are the biggest
animals of all time. Heavier than elephants, wooly
mammoths, and even dinosaurs. But they weren't always
the titans of the sea. Let's rewind the clock
around 50 million years. No, you won't find any whales here. You have to go ashore. Meet Pakicetus, the very first whale. Life on earth spent millions
of years clawing its way out of the oceans. But whales took all that effort
and threw it out the window. From 50 - 40 million years ago, they traded in their
four legs for flippers. In fact, some whales today still have leftover bones of hind legs. Once submerged, their weight under gravity no longer mattered. So they could theoretically
grow to enormous proportions. And they did. Today, a blue whale is
10,000 times more massive than the Pakicetus was. But this transformation wasn't as gradual as you might think. In fact over the next
37 million years or so, whales grew increasingly diverse, but their size remained small. For example, one of the first whales with baleen instead of
teeth was only 18 feet long, making them easy prey for
predators, like giant sharks. It wasn't until around
three million years ago that an ice age tipped the
scales in the whales' favor. Ocean temperatures and currents shifted, sparking concentrated swarms of plankton, and plankton-seeking krill. It was an all-you-can-eat
buffet for the baleen whales, who grew larger as a result. And the larger they became,
the farther they could travel in search of more food to grow even more. You can probably see where this is going. Three million years later,
humpbacks, for example, have one of the longest
migrations of any mammal on earth traveling over 5,000 miles each year. As a result, modern whales are
the largest they've ever been in history. Take the biggest of the
bunch, the blue whale. It weighs more than a Boeing 757, has a belly button the size of a plate. And its network of blood vessels, if you laid them out in a line, could stretch from Pluto
to the sun and back, over two and a half times. In fact, the largest
blue whales are so huge that scientists think they
may have hit a physical limit. When they open their wide mouths to feed, they engulf enough water to
fill a large living room. So it can take as long as 10
seconds to close them again. Scientists estimate once
a whale is 110 feet long, it can't close its mouth fast
enough before prey escapes. So it's possible we're living
amongst the largest animal that will ever exist. Lucky for us, they mostly just eat krill. This was made in large
part thanks to Nick Pyenson and the information in his
new book, "Spying on Whales."
