In an extremely rare case of a species effectively evolving into existence twice, the Aldabra rail has re-evolved back into existence after having gone extinct 136,000 years ago, as a new study demonstrates.
Not only that, but the flightless bird has also reclaimed its home island in the Aldabra Atoll in the Indian Ocean.
The study, published in the peer-reviewed scientific journal Zoological Journal of the Linnean Society, shows that the rail’s home in the atoll has been submerged many times throughout history during events that wiped out all the species which inhabited it.
Nevertheless, the Aldabra rail has continued to return in a rare phenomenon which is known as iterative evolution, when the same ancestral lineage leads to the repeated evolution of a species at different points in time, producing parallel offshoot species which are almost identical to one another and can pop up many times in various eras and locations—even when past iterations have gone entirely extinct.
Such was the case with the Aldabra rail, having descended from a chicken-sized flying bird also known as the white-throated rail, that faced its demise approximately 136,000 years ago when the island was entirely inundated and submerged below sea level, wiping out all local fauna and flora.
As sea levels fell throughout tens of thousands of years, though, fossil evidence has shown that the species once again re-colonized it. That time, the bird lost the ability to fly because of the absence of predators that once populated the island.
Lead researcher and avian paleontologist Julian Hume at the Natural History Museum stated:
“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. 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.”
This is not the first case of iterative evolution, which has also been observed in animals such as ammonites, sea turtles, and sea cows. However, the two species of rail—the long-extinct iteration and the revived one—are the “most significant” case of iterative avian evolution ever found, the researchers concluded.
According to David Martill, co-author of the study and paleobiologist at the University of Portsmouth:
“We know of no other example in rails, or of birds in general, that demonstrates this phenomenon 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 recolonization events. Conditions were such on Aldabra, the most important being the absence of terrestrial predators and competing mammals, that a rail was able to evolve flightlessness independently on each occasion.”
With sea levels expected to rise in the coming years, the modern flightless Aldabra rail might not fare much better than its ancestors. Indeed, with the very real possibility of extinction threatening the existence of over one million plant and animal species, the odds are that the bird could face its demise yet again. However, based on this study, a third iteration of the rail could perhaps return long after a potential deluge subsides.
Reference: The Mind Unleashed
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