A flightless bird that was driven to extinction more than 136,000 years ago has re-emerged in a stunning display of evolution.
Fossils on a Madagascan island suggest that the white-throated rail bird went extinct when the island it was living on was submerged beneath the ocean.
It is believed that as the island recovered, so did the island’s population of flightless birds.
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The white-throated rail bird (pictured) went extinct when its island home was submerged Fossil records show it died and then miraculously returned to the island
Researchers from the University of Portsmouth and London’s Natural History Museum said that rails conquered the island of Aldabra and eventually lost the ability to fly.
This ensured its demise when the land that it lived on was submerged beneath the waves during a bout of global warming.
The Aldabra atoll sunk beneath the waves, killing off all local flora and fauna including the rail, whose flightlessness would have rendered it unable to relocate.
When sea levels fell during the subsequent ice age, however, the atoll reemerged — as did flightless rails, seemingly unfettered by having been driven to extinction.
To find out how they returned, palaeontologists Julian Hume of the Natural History Museum and David Martill of the University of Portsmouth compared rail fossils from before the island sank with those from after, at around 100,000 years ago.
They found that the rails that lived on the island after it had emerged back out of the ocean had both wings that had developed into an advanced state of flightless and ankle bones that were evolving in the same direction.
This means that one parent species of rail originating from Madagascar spun off two distinct but similar species of flightless rail on the Aldabra atoll within the space of thousands of years.
‘These unique fossils provide irrefutable evidence that a member of the rail family colonised the [Aldabra] atoll, most likely from Madagascar, and became flightless independently on each occasion,’ said Dr Hume.
This process, where distinct species with similar or parallel adaptations develop from the same ancestor at different points in time, is known as ‘iterative evolution’.
‘We know of no other example in rails, or of birds in general, that demonstrates this phenomenon so evidently,’ said Professor Martill.
‘Only on Aldabra […] is fossil evidence available that demonstrates the effects of changing sea levels on extinction and recolonisation events,’ he added.
The white-throated rail is a chicken-sized bird, native to Madagascar, that lives in tropical or subtropical moist lowland and mangrove forests.
The white-throated rail (pictured) is a chicken-sized bird, native to Madagascar, that lives in tropical or subtropical moist lowland and mangrove forests
Aldabra atoll is a ring-shaped coral atoll which first grew up from the ocean around 400,000 years ago. The Aldabra rail is thought to be the last flightless bird living in the Indian Ocean
Rails are aggressive colonisers of isolated islands, who experience frequent population booms and migrate out from Madagascar in great numbers.
Those that migrate north or south typically end up drowning in the vast ocean, whereas those that headed west reach Africa to face heavy predation.
However, those that flew east could reach one of the many neighbouring islands, which include Mauritius — famously once home to another flightless bird, the dodo — Reunion and the Aldabra islands.
Aldabra atoll is a ring-shaped coral atoll which first grew up from the ocean around 400,000 years ago.
The Aldabra rail is commonly thought to be the last flightless bird living in the Indian Ocean.
Another rail species had once occupied Assumption Island, another member of the Aldabra Group.
However, these birds went extinct in the early 20th Century, not to return, after human settlers brought predators to the island.
The full findings of the study were published in the journal Zoological Journal of the Linnean Society.
Rails are aggressive colonisers of isolated islands, who experience frequent population booms and migrate out from Madagascar in great numbers
WHY DO SOME BIRDS THAT MIGRATE TO ISOLATED ISLANDS LOSE THE ABILITY TO FLY?
The extinct and flightless Dodo (pictured), was once native to the island of Mauritius
Birds that migrate to isolated, predator-free islands often evolve to lose their ability to fly.
The loss is often an evolutionary trade-off against other traits that are more beneficial in such environments.
Flightlessness can become a weakness, however, in instances where predators are subsequently introduced to the birds’ homes.
Being unable to fly away, these birds can easily be hunted to extinction.
There are over 60 flightless bird species living today.
These include emus, kiwis, penguins and the Aldabra rail.
One of the most famous flightless birds is the Dodo, which lived on the Indian Ocean island of Mauritius before it was hunted to extinction by humans.
In many cases, the development of flightlessness is accompanied by increasing body sizes.
The biggest flightless bird, the ostrich, can reach up to around 9 feet (2.7 metres) in height and weigh as much as 344 pounds (156 kilograms).
Flightlessness can also develop in selectively bred birds, such as the Broad Breasted White turkey.
Bred specifically to grow larger breast meat, this turkey has become too large for its wings to support in flight.