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New research has shown that the last species of bird unable to fly and surviving, a type of rail of the Indian Ocean, had already been extinguished but that it has passed from death thanks to a rare process called "iterative evolution".
Research, from the University of Portsmouth and the Natural History Museum, revealed that on two occasions, separated by tens of thousands of years, a railway species had successfully colonized an isolated atoll called Aldabra, then to become unable to fly twice. The last colony of rails incapable of flying still exists on the island.
This is the first time that an iterative evolution (repeated evolution of similar or parallel structures from the same ancestor but at different times) has been found in the rails and one of the most significant in bird records.
The white-throat rail is a bird the size of a chicken, native to Madagascar in the southwest Indian Ocean. They are persistent colonizers of isolated islands, which would experience frequent population explosions and migrate in large numbers from Madagascar. Many of those who went north or south drowned in the expanse of the ocean and those who went to the west landed in Africa, where the predators ate them. Of those who have gone to the east, some have landed on many oceanic islands such as Mauritius, Reunion and Aldabra, the latter is a ring-shaped coral atoll that has formed there about 400,000 years ago.
With the absence of predators on the atoll, and just like the Maurice Dodo, the rails evolved so that they lost the ability to fly. However, Aldabra disappeared when it was completely covered by the sea during a major flood about 136,000 years ago, wiping out all the fauna and flora, including the leak-free rail.
The researchers studied traces of fossils dating back 100,000 years ago, when sea level had dropped during the next ice age and that the atoll had been recolonized by rails unable to steal. The researchers compared the bones of a fossilized rail from before the flood with those of a rail after flooding. They discovered that the wing bone exhibited an advanced state of loss of flight and that the ankle bones had distinct properties, namely that it was evolving towards a loss of flying ability .
This means that one species from Madagascar has given birth to two different species of rails unable to fly on Aldabra in the space of a few thousand years.
Dr. Julian Hume, Principal Investigator at the Avian Paleontologist and Associate Researcher at the Natural History Museum, said, "These unique fossils provide compelling evidence that a rail family member colonized the atoll, probably from Madagascar, and has become unable to fly at every opportunity.The fossil evidence presented here is unique with respect to rails, and embody the ability of these birds to successfully colonize isolated islands and avoid flying repeatedly. "
Professor David Martill, co-author of the School of Earth Sciences and Environment of the University of Portsmouth, said: "We know of no other example in the rails, nor in the case of birds in general, which demonstrates this phenomenon so clearly.Only Aldabra, which has the oldest paleontological record of all oceanic islands in the Indian Ocean region, offers fossil evidence demonstrating the effects sea level change on extinction and recolonization phenomena.
"The conditions were such at Aldabra, the most important being the absence of terrestrial predators and competing mammals, which allowed a rail to evolve autonomously in the face of theft on every occasion."
The study is published in the last issue of Zoological Journal of the Linnaean Society.
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Material provided by University of Portsmouth. Note: Content can be changed for style and length.
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