A new study by the University of Adelaide shed light on the origins of the iconic flightless bird from New Zealand, Kiwi.

According to a DNA analysis, the tiny Kiwi's closest relative is an extinct Madagascan elephant bird and not the Australian emu - as was previously believed. The giant bird measured 2-3 metre and weighed about 275 kg.

Researchers said that both these flightless birds used to fly once.

"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 of the Australian Centre for Ancient DNA or ACAD, in a statement.

Besides emu and ostrich, the category of giant flightless "ratite" birds also includes some of the world's largest birds like the extinct giant moa of New Zealand and elephant birds of Madagascar.

For the study, researchers analysed ancient DNA extractions from bones of two elephant birds. They observed similar genetic profiles between the two species, despite geographical, morphological and ecological differences between the two flightless birds.

With the help of a DNA extract, the researchers were also able to determine the period as to when the ratite species 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," said ACAD Director Professor Alan Cooper. "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."

The recent fossil analysis of small kiwi ancestors indicated that the bird had the ability to fly. The genetic results now support the hypothesis and confirm that kiwis were winged 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," said Trevor Worthy of Flinders University in Adelaide.

The finding is published in the journal Science.