The last surviving flightless species of rails beat extinction by evolving flightlessness on two separate occasions in the exact same place 10,000 years apart.
It's an impressive feat possible through a phenomenon known as "iterative evolution," which refers to the repeated evolution of the same structures from a single ancestor at different times.
According to new research published in the Zoological Journal of the Linnean Society, a rail species migrated to the Aldabra coral atoll, went extinct, and thousands of years later, evolved itself back into existence. In fact, the last surviving colony of flightless rails still lives on the island to this day.
Migrating Rails Become Flightless In Aldabra
The white-throated rail in Madagascar have long been colonizers of isolated islands, migrating in huge numbers out of the country. Those who went north or south drowned in the long stretch of ocean, while those that went west to Africa got eaten by predators. The rails that went east likely made it to the many islands in the region, including Mauritius, Reunion, and Aldabra.
Aldabra, a coral atoll that formed 400,000 years ago, had no terrestrial predators, so the rails that made its way there eventually evolved and lost their ability to fly.
Then, a major inundation event about 136,000 years ago submerged Aldabra underwater and wiped out all existing life in the atoll—including the flightless rails that only existed there.
Flightless Rails Come Back From The Dead
During an ice age 100,000 years ago, the sea levels dropped and the island of Aldabra reemerged from the ocean. Eventually, rails recolonized the atoll.
In the new study, researchers analyze fossils of rails before and after the inundation event to compare the evolution of the rails. The team found changes in the wing and ankle bones, showing properties linked to flightlessness.
According to the researchers, this means that the white-throated rail from Madagascar gave birth to two different species of flightless rail in Aldabra in occasions 10,000 years apart.
"These unique fossils provide irrefutable evidence that a member of the rail family colonised the atoll, most likely from Madagascar, and became flightless independently on each occasion," Dr. Julian Hume, lead researcher and avian paleontologist and Research Associate at the Natural History Museum, said in a statement. "Fossil evidence presented here is unique for rails, and epitomises the ability of these birds to successfully colonise isolated islands and evolve flightlessness on multiple occasions."
Coauthor David Martill of the University of Portsmouth, said that the scientists know no other example demonstrating iterative evolution so evidently.
"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 recolonisation events," he continued, adding that conditions on the atoll were so ideal for flightlessness that the birds evolved this trait independently on two known occasions.
