Once upon a time, before India knew Asia, when alligators sunned themselves on shores north of the Arctic Circle, a small, timid, dog-like creature tentatively waded into a river. Fifty million years passed. The continents wandered and crashed, and the ocean reconfigured itself.
Now, where there were once Arctic alligators, there was ice. As for the creature who once dipped its toes into the tepid river, it now swam the frigid seas. The intervening age had transformed it into the largest animal in the history of life on Earth.
“There’s a famous paleontologist who’s dead by now, George Gaylord Simpson, and he once described whales as, ‘On the whole, the most peculiar and aberrant of mammals,’” says Felix Marx, a whale paleontologist and Marie Skłodowska-Curie Fellow at Monash University in Melbourne, Australia. “And I think that’s really true, because, I mean, they’re mammals, so they have to face all of the challenges that a normal mammal does. They’re adapted to living on land: they’re [warm-blooded], they have fur, they breathe air, they give birth to live young and they have to suckle those live young. And then you try and do all of that in the sea, and of course, almost everything is stacked against you. Like, the milk is floating away, heat is draining from your body, your fur isn’t really that useful, there’s no air to breathe—like, everything is against you. And yet, within a relatively short period of time they’ve managed to tackle all of that, and they managed to achieve feats like diving down several kilometers and staying down for—I don’t know—an hour at a time, and doing some of the weirdest, biggest feeding events in all of the animal kingdom.”