Extinct bird species has evolved and come 'back from dead' after 136,000 years

last surviving flightless bird species in Indian Ocean, which h previously gone extinct, rose from de thanks to a rare process called 'iterative evolution', scientists say.

Researchers from University of Portsmouth in UK and Natural History Museum found that on two occasions, separated by tens of thousands of years, a rail species was able to successfully colonise an isolated atoll called Aldabra and subsequently became flightless on both occasions.

This is first time that iterative evolution -- repeated evolution of similar or parallel structures from same ancestor but at different times -- has been seen in rails and one of most significant in bird records.

last surviving colony of flightless rails is still found on island today, according to study published in Zoological Journal of Linnean Society.

white-throated rail is a chicken-sized bird, indigeus to Magascar in south-western Indian Ocean.

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y are persistent colonisers of isolated islands, who would have frequent population explosions and migrate in great numbers from Magascar.

Many of those that went rth or south drowned in expanse of ocean and those that went west landed in Africa, where predators ate m.

Of those that went east, some landed on many ocean islands such as Mauritius, Reunion and Aldabra, last-named is a ring-shaped coral atoll that formed around 400,000 years ago.

With absence of predators on atoll, and just like Dodo of Mauritius, rails evolved so that y lost ability to fly.

However, Aldabra disappeared when it was completely covered by sea during a major inundation event around 136,000 years ago, wiping out all fauna and flora including flightless rail.

researchers studied fossil evidence from 100,000 years ago when sea-levels fell during subsequent ice and atoll was recolonised by flightless rails.

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y compared bones of a fossilised rail from before inundation event with bones from a rail after inundation event.

researchers found that wing bone showed an vanced state of flightlessness and ankle bones showed distinct properties that it was evolving towards flightlessness.

This means that one species from Magascar gave rise to two different species of flightless rail on Aldabra in of a few thousand years.

"se unique fossils provide irrefutable evidence that a member of rail family colonised atoll, most likely from Magascar, and became flightless independently on each occasion," said Julian Hume from Natural History Museum.

"Fossil evidence presented here is unique for rails, and epitomises ability of se birds to successfully colonise isolated islands and evolve flightlessness on multiple occasions," Hume said.