A chicken-sized bird species that went extinct 136,000 years ago has come back to existence due to a rare evolutionary process. This last surviving flightless species of rail bird was found by researchers in the Indian Ocean. It has come back through a process called “iterative evolution”.
It was found by researchers from the University of Portsmouth in the UK and Natural History Museum that on two occasions the species was able to colonise an isolated atoll called Aldabra but separated by tens of thousands of years.
“Iterative evolution happens when the same or similar structures evolve out of the same common ancestor, but at different times – meaning that the animal actually comes about twice over, completely separately,” said the report. “This is the first time it has been seen in rails and one of the most significant ever seen in a bird of any kind.”
The study published in the Zoological Journal of the Linnean Society stated that the last surviving colony of flightless rails is still found on Aldabra. It is a white-throated, chicken-sized rail that is indigenous to Madagascar in the south-western Indian Ocean.
“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,” said Julian Hume, official at the Natural History Museum.
Some went east, some landed on the many ocean islands such as Mauritius, Reunion and Aldabra. The atoll disappeared when it was completely covered by the sea during a major inundation event around 136,000 years ago. This wiped out all fauna and flora including the flightless rail.
Comparing the bones of a fossilised rail from before the event showed the wing bone showed an advanced state of flightlessness and the ankle bones had distinct properties that it was evolving towards flightlessness.
This only means that one species from Madagascar actually gave rise to two different species of flightless rail on Aldabra in a span of a few thousand years.