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Baleen whales such as this humpback whale (Megaptera novaeangliae) evolved large body sizes as their food supplies changed millions of years ago. Tony Wu/NPL

Evolution

Why baleen whales grew so big

Shifting winds and food supplies favoured the evolution of huge whales three million years ago.

Blue whales (Balaenoptera musculus) and other baleen whales are known for their size, but their ancestors weren’t so gargantuan. Graham Slater at the University of Chicago in Illinois and his colleagues modelled the evolution of whales using data on body length for both living and extinct whales. They conclude that baleen whales more than ten metres long diversified about three million years ago, at around the time when shifting winds started to draw colder water brimming with prey up from the deep ocean.

Larger whales were probably more efficient at moving between and rapidly feeding on dense but isolated patches of prey than their smaller counterparts, the authors suggest.