Flightless birds’ history upset by ancient DNA

Ancestors of kiwis and elephant birds didn’t just drift with the continents

RELATIVELY ODD  Ancient DNA has revealed an unusual pair of closest relatives: New Zealand’s flightless, roughly chicken-sized kiwi species (skeleton of adult Apteryx australis shown) and Madagascar’s huge elephant bird (egg of Aepyornis maximus shown). 

Kyle Davis and Paul Scofield/Canterbury Museum

Madagascar’s elephant birds — which weighed as much as three or four people and went extinct several hundred years ago — turn out to be the closest known relatives of New Zealand’s chicken-sized kiwi.

This genealogical surprise is “a slap in the face” to a long-standing idea of how many flightless birds evolved, says evolutionary biologist Alan Cooper  of the University of Adelaide in Australia.  Realizing that continents moved around, biologists in the 1970s debated whether ostriches, kiwis and the rest of the flightless wonders called ratites arose when flightless common ancestors drifted apart by riding along on land masses that fragmented and separated.

In 1992 Cooper raised some doubts about the continent-riding idea when he and his colleagues extracted ancient DNA from bones of New Zealand’s hefty flightless moa, now extinct. As fellow travelers, moas and kiwis should have been close relatives. But they weren’t.

BIG BIRD One of Madagascar’s now-extinct flightless elephant birds, which stood over 2 meters tall and weighed 250 kilograms, strolls through the island’s spiny forest in an artist’s reconstruction. Brian Choo

Kiwis were more closely related to Australia’s cassowaries and emus. “Hugely embarrassing,” Cooper says, for the national bird of New Zealand.

Now he and his colleagues have extracted DNA from the two genera of elephant birds and found that they were even more closely related to kiwis than the Australian birds were. Their homes weren’t near each other as continent fragments, so mere drifting doesn’t explain the close relationship. Distant ancestors must still have done some flying, he and his colleagues conclude in the May 23 Science

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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