A bird once extinct returned from the dead in a process of unusual evolution.

Image: Charles J Sharp [CC BY-SA 4.0 ]

Approximately 136,000 years ago, a bird that did not fly became extinct.

The bird resided in the atoll of the Indian Ocean of Aldabra, whose flora and fauna disappeared when the island was completely flooded by the sea.

Now, scientists at the University of Portsmouth and the Museum of Natural History say that the bird managed to return from death.

It is thanks to a rare event called iterative evolution, in which the process of evolution of the same ancestor is repeated throughout different points of history.

In this case, the white-throated rail, an indigenous bird of Madagascar, had evolved to become flightless on separate occasions separated by a few thousand years.

About 100,000 years ago, sea levels dropped due to an ice age, allowing the island of Aldabra to re-exist. The rails, which migrated to other islands, including Mauritius and Reunion, also landed in Aldabra.

Aldabra, then free of predators, allowed the railroad to evolve into a flight due to the lack of threats on the island. You can still find the last colony of surviving rails on the island today.

The researchers in the study, who published their findings in the Zoological magazine of the Lininese society, studied the fossils of the rail before and after the flood event. They found that the wing bones were in an advanced state of absence of flight, while the bones of the ankle showed signs that it was evolving towards the absence of flight.

"These unique fossils provide irrefutable evidence that a member of the railroad family colonized the atoll, probably from Madagascar, and became an independent flight attendant on each occasion," said lead researcher Julian Hume in a statement.

"The fossil evidence presented here is unique to the rails, and represents the ability of these birds to successfully colonize isolated islands and evolve without flight on multiple occasions."

David Martill, coauthor of the study, said that they do not know any other example of rails or birds in general, that have shown the phenomenon of iterative evolution. Sabretooths, with its impressive teeth, has benefited from this process throughout history.

"Aldabra alone, which has the oldest paleontological record of any oceanic island within the Indian Ocean region, is available fossil evidence that demonstrates the effects of sea level change on extinction and recolonization events," he added.

"The conditions were such in Aldabra, the most important being the absence of land predators and mammals in competition, that a rail could evolve independently on each occasion."