Weekend Economists Down Under May 23-26, 2014

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11. Kiwi DNA spurs scientists to rethink the evolution of birds

They could also estimate how long ago the two lineages shared a common ancestor by counting up the mutations that have accumulated in the kiwi and elephant bird DNA. They estimate that the ancestral bird lived 50 million years ago.

That date poses a serious problem to the idea that ratites have been flightless since the days of Gondwana. By 50 million years ago, Madagascar and New Zealand were already separated by an ocean. “You can’t get from Madagascar to New Zealand without flying,” Cooper said. “There isn’t any other way.”

These findings have led Cooper and his colleagues to propose a new hypothesis for how ratites evolved. Rather than being flightless, their ancestor was a partridge-like bird that could travel by air. Between 65 million and 50 million years ago, early ratites flew across much of the world.

It was a lucky time for them. The large plant-eating dinosaurs had become extinct, and it would take millions of years before large plant-eating mammals would take their place. In at least six instances, Cooper argues, ratites evolved, losing their wings and becoming plant-eating birds.

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