This Bird Went Extinct and Then Evolved Into Existence Again
"We know of no other example in rails, or of birds in general, that demonstrates this phenomenon so evidently.”
The white-throated rail. Image: Charles J Sharp
The Aldabra white-throated rail, a flightless bird that lives on its namesake atoll in the Indian Ocean, doesn’t look like anything special at first glance. But the small bird has big bragging rights, because it has effectively evolved into existence twice after first going extinct some 136,000 years ago.
According to a study published Wednesday in the Zoological Journal of the Linnean Society, the rail is an example of a rarely observed phenomenon called iterative evolution, in which the same ancestral lineage produces parallel offshoot species at different points in time. This means that near-identical species can pop up multiple times in different eras and locations, even if past iterations have gone extinct.
Fossils of the flightless bird were found both before and after Albadra was submerged by an “inundation event” that occurred around 136,000 years ago, said study authors Julian Hume, an avian paleontologist at Natural History Museum in London, and David Martill, a paleobiologist at the University of Portsmouth.
Those rising sea levels wiped out the first iteration of the flightless rail, which was descended from flying forebears that originated in the Seychelles Islands and Madagascar. Amazingly, the same parent species appears to have recolonized the atoll once it emerged from under the waves tens of thousands of years later.
The fossils indicate that the new rail was evolving toward flightlessness again at the time, as the absence of predators on Aldabra rendered the ability obsolete. Around 100,000 years ago, the evolutionary process had already effectively produced the same bird that went extinct tens of thousands of years earlier.
Iterative evolution has been observed in many animals, such as sea cows, ammonites, and sea turtles. But the two rail species, on either side of the deluge, represent an unprecedented case study of avian iterative evolution, the authors concluded.
"We know of no other example in rails, or of birds in general, that demonstrates this phenomenon so evidently,” Martill said in a statement. “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.”
Sea levels are now rising once more, thanks in part to human-driven climate change, so modern Aldabra rails might face the same fate as their extinct sister species. Even if that grim future awaits them, perhaps a third incarnation of the rail will eventually reappear on the far-flung atoll.
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