The kiwi (Apteryx spp.), a national symbol of New Zealand, is most closely related to members of the family Aepyornithidae – enormous, flightless birds that lived on the island of Madagascar before the 17th century CE.
The elephant bird Aepyornis maximus, left, and a male and a juvenile of the Great spotted kiwi, Apteryx haastii. Credit: Delaware Museum of Natural History / John Gerrard Keulemans.
The kiwi of New Zealand, Madagascan elephant birds as well as the emu, ostrich and the extinct giant moa are part of a bird group called ratites.
In 1990, scientists suggested that the closest living relatives of the kiwi are the Australian ratites – the emu and cassowary.
However, a new analysis of DNA extracted from bones of two Madagascan elephant birds has revealed a close genetic connection with the kiwi, despite the striking differences in geography, morphology and ecology between the two.
“This result was about as unexpected as you could get. New Zealand and Madagascar were only ever distantly physically joined via Antarctica and Australia, so this result shows the ratites must have dispersed around the world by flight,” said Kieren Mitchell, a PhD candidate with the University of Adelaide’s Australian Center for Ancient DNA and the lead author of a paper published in the journal Science.
Mr Mitchell and his colleagues were able to use the elephant bird DNA to estimate when the ratite species had separated from each other.
“The evidence suggests flying ratite ancestors dispersed around the world right after the dinosaurs went extinct, before the mammals dramatically increased in size and became the dominant group. We think the ratites exploited that narrow window of opportunity to become large herbivores, but once mammals also got large, about 50 million years ago, no other bird could try that idea again unless they were on a mammal free island – like the Dodo,” said study senior author Prof Alan Cooper, also from the University of Adelaide’s Australian Center for Ancient DNA.
“We can now see why the evolutionary history of the ratites has been such a difficult problem. Many of them independently converged on very similar body plans, complicating analysis of their history,” said co-author Prof Mike Lee from the South Australian Museum and the University of Adelaide.
“We recently found fossils of small kiwi ancestors, which we suggested might have had the power of flight not too long ago,” added study co-author Dr Trevor Worthy of Flinders University.
“The genetic results back up this interpretation, and confirm that kiwis were flying when they arrived in New Zealand. It also explains why the kiwi remained small. By the time it arrived in New Zealand, the large herbivore role was already taken by the moa, forcing the kiwi to stay small, and become insectivorous and nocturnal.”
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Kieren J. Mitchell et al. 2014. Ancient DNA reveals elephant birds and kiwi are sister taxa and clarifies ratite bird evolution. Science, vol. 344, no. 6186, pp. 898-900; doi: 10.1126/science.1251981