Evolution produced the same flightless bird species twice, with each occurrence separated by tens of thousands of years. The phenomena, called iterative evolution, helped bring the flightless rail species back from the dead.

According to a new study, the bird twice settled on an isolated atoll near the Seychelles called Aldabra, losing its ability to fly after a several thousand years on the island. After climate change and rising seas in the Indian Ocean wiped out the original colonizers, the bird returned several thousand years later -- after the seas subsided -- and once again became flightless.

Both bird species evolved from the same ancestor, the white-throated rail, a chicken-sized bird native to Madagascar. Paleontologists analyzed rail fossils from deposits from before and after the atoll was inundated by rising seas. Their analysis revealed changes to the wing and ankle bones linked with the adoption of a flightless existence.

Because Aldabra is without terrestrial predators, the rail was able to quickly forego flight without putting itself at risk. The flightless rail species is still living on Aldabra today.

"These unique fossils provide irrefutable evidence that a member of the rail family colonized the atoll, most likely from Madagascar, and became flightless independently on each occasion," Julian Hume, an avian paleontologist at the Natural History Museum in London, said in a news release. "Fossil evidence presented here is unique for rails, and epitomizes the ability of these birds to successfully colonize isolated islands and evolve flightlessness on multiple occasions."

Hume and his colleagues published their analysis of rail's iterative evolution this week in the Zoological Journal of the Linnean Society.

"We know of no other example in rails, or of birds in general, that demonstrates this phenomenon so evidently," said David Martill, an environmental scientist at the University of Portsmouth. "Only on Aldabra, which has the oldest palaeontological record of any oceanic island within the Indian Ocean region, is fossil evidence available that demonstrates the effects of changing sea levels on extinction and recolonization events."

Related Links
Darwin Today At TerraDaily.com

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