How did flightless birds evolve? Kiwi DNA offers clues.
| Wellington, New Zealand
Research聽linking聽New聽Zealand's聽diminutive聽kiwi聽with a聽giant聽extinct聽bird聽from Africa聽is聽prompting聽scientists聽to聽rethink聽how聽flightless聽birds聽evolved.
A report published Friday in the journal Science says DNA testing indicates the chicken-size聽kiwi's聽closest relative is the elephant聽bird聽from Madagascar, which grew up to 3 meters (10 feet) high and weighed up to 250 kilograms (550 pounds) before becoming聽extinct聽about 1,000 years ago.
The authors say the results contradict earlier theories that the聽kiwi聽and other flightless聽birds, including the ostrich and emu,聽evolved聽as the world's continents drifted apart about 130 million years ago.
Instead, they say, it's more likely their chicken-size, flight-capable ancestors enjoyed a window of evolutionary ascendancy about 60 million years ago, after dinosaurs died out and before mammals grew big.
Those聽birds, the authors say, likely flew between the continents, with some staying and becoming the large,聽flightless聽species we know today.
Alan Cooper, a professor at the University of Adelaide in Australia and a co-author of the paper, said the DNA results came as a huge surprise given the differences in size and location between the聽kiwi聽and elephant聽bird.
"This has been an evolutionary mystery for 150 years. Most things have been suggested but never this," he said. "The聽birds聽are about as different as you can get in terms of geography, morphology and ecology."
Cooper, a聽New聽Zealander聽by birth, is hoping the paper will also bring him a measure of redemption.
That's because two decades ago, Cooper and other聽scientists聽discovered genetic聽links聽between the聽kiwi聽and two Australian聽flightless聽birds, the cassowary and the emu. That led to聽New聽Zealanders聽believing their iconic聽bird聽might have come from Australia, a traditional rival.
"There was a huge outpouring of angst," Cooper said. "New聽Zealanders聽weren't too impressed."
The nation's identity is so entwined with the聽bird聽that聽New聽Zealanders聽call themselves聽kiwis聽and have also given the name to their currency and the kiwifruit.
But it turns out that if the emu was a cousin to the聽kiwi, the elephant聽bird聽was a sibling. Cooper said it has taken until now for DNA techniques to advance enough to get a聽usable聽result from the ancient bones of the Madagascan聽bird.
Cooper said the聽bird聽took its name from Arabic legends that suggested it was so fearsome it could grab an elephant with its talons.
There's little basis for the legend given the聽bird聽was a聽flightless聽herbivore. In fact, it was likely humans that hunted it into oblivion, Cooper said.
Trevor Worthy, a聽research聽fellow at Australia's Flinders University and a paper co-author, said it's likely the聽kiwi聽stayed small and took to eating insects at night because it didn't want to compete for habitat and food with anotherNew聽Zealand聽flightless聽bird, the moa, which is also now聽extinct. He said it's strange the聽kiwi聽and elephant聽bird聽are such close relatives.
"One got big, one stayed little," he said.
Massey University professor David Penny, who wasn't involved in the聽researchbut who peer reviewed it for Science, said the results are very interesting and help complete the puzzle of聽flightless聽birds.
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