How blue whales became giants of the sea

Blue whales are the most massive animals to exist in the history of animals. Dreadnoughtus and those other thundering, 60-tonne dinosaurs? Bantamweights next to one of today's 100-tonne Balaenoptera musculus.

"We truly live in an age of giants," said Nicholas D. Pyenson, an expert in the paleobiology of marine mammals at the Smithsonian's National Museum of Natural History. Blue whales, he said, can grow as long as three city buses parked end to end. Living blue whales would be even bigger, too, if it weren't for the sailors who killed most of the 33m, 110-tonne specimens 100 years ago.

Yet evolutionarily speaking, whales are recent leviathans. After the largest dinosaurs died off, land mammals bulked up, leading to elephant-size rhinoceroses, sloths and armadillos about 35 million years ago. The ancestors of today's giant whales, meanwhile, stayed curiously small.

"It is only since around the beginning of the so-called ice ages that whales have not just evolved to be huge, but titanic in size," Erich M.G.

 

Fitzgerald, a vertebrate paleontologist at Museum Victoria in Australia, said in an email. "Most baleen whales that ever lived were little fellows compared to their modern descendants."

 a mystery.

"It's such an obvious question," he said. "If you're an evolutionary biologist or a paleobiologist, you want to know how it came to be that way."

Relying on the extensive collection of fossil whale skulls at the Smithsonian, Pyenson and his colleagues tracked the evolution of baleen whale size. (Baleen whales lack teeth, instead using the moustache-like bristles that hang in their mouths to scoop up krill, fish and other tiny sea creatures.) 

From the skull sizes, the scientists could estimate the body lengths of about 60 species of modern and extinct whales.

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