Orange is the new black, 50 is the new 40 and “Re-evolved” is the new extinct. At least, that’s the case with the Aldabra white-throated rail – a flightless bird that went extinct 136,000 years ago but has followed the same evolutionary path and reappeared just a little while later. Is there hope for the dodo?
“Aldabra has undergone at least one major, total inundation event during an Upper Pleistocene (Tarantian age) sea-level high-stand, resulting in the loss of all terrestrial fauna. A flightless Dryolimnas has been identified from two temporally separated Aldabran fossil localities, deposited before and after the inundation event, providing irrefutable evidence that a member of Rallidae colonized the atoll, most likely from Madagascar, and became flightless independently on each occasion.”
According to a new study published in the Zoological Journal of the Linnean Society, fossils show that the white-throated rail (Dryolimnas cuvieri) existed solely on the Aldabra atoll, the world’s second-largest coral atoll. The fossils indicate that it was once capable of flight, which is how it got to the atoll from the Seychelles Islands and Madagascar. Those ancestors eventually evolved out of their need for flight due to a lack of predators. Unfortunately, the one other thing a non-flying, non-swimming bird on an island can’t escape is water. About 136,000 years ago, sea levels began rising during a global warming near the end of the Pleistocene period and caused an “inundation event” – aka ‘flood’ – which drowned the Aldabra white-throated rails into extinction.
Or did it?
Study authors Julian Hume, an avian paleontologist at Natural History Museum in London, and David Martill, a paleobiologist at the University of Portsmouth, found fossil evidence on the island which show that just 20,000 years later, the same evolutionary ancestor – which still existed on the Seychelles Islands and Madagascar – flew to the now dry atoll once again, stayed once again and evolved into the same flightless Aldabra white-throated rail once again. While this phenomenon, called “iterative evolution,” has been seen before in aquatic creatures (sea cows, ammonites and sea turtles), this is the first time for a bird, as Martill explained in the press release:
“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 recolonisation 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.”
Could this be good news for other extinct flightless birds, like the dodo, or extinct birds in general? Unfortunately, it’s not even good news for the Aldabra white-throated rail. That nemesis of flightless birds – flooding – may be returning soon to the atoll courtesy of climate change. If they go extinct again, there’s a possibility that they could iteratively evolve once again since its flighted rail ancestors still exist on other isolated islands. Sadly, that’s no longer the case for the dodo.
A better solution would be to stop eating, hunting, developing and climate-changing other species into extinction before we humans need an “iterative evolution” ourselves.