Andrew Griffin - Bird that went extinct 136,000 years ago comes ‘back from the dead’ after evolving again
A bird that previously
went extinct rose from the dead after it evolved all over again, scientists
have found. The last surviving
flightless species of bird in the Indian Ocean, a type of rail, has actually
been around before, the research found. It came back through a process called
"iterative evolution",
which saw it emerge twice over, the researchers found.
It means that on two
separate occasions – tens of thousands of years apart – a species of rail was
able to colonise an atoll called Aldabra. In both cases it eventually
became flightless, and those birds from the latter
time can still be found on the island now. Iterative evolution
happens when the same or similar structures evolve out of the same common
ancestor, but at different times – meaning that the animal actually comes about
twice over, completely separately.
The white-throated rail has made a surprising return. (Charles J Sharp)
This is the first time
it has been seen in rails, and one of the most significant ever seen in a bird
of any kind. White-throated rails
are roughly the size of a chicken. They come from Madagascar, but
repeatedly colonise other isolated islands, growing in number and then heading
out of the island where they began.
Many of those that
left to go north or south either died or were eaten. But some of the ones that
headed eastwards went to live on the other ocean islands in the area, which
includes Aldabra.
Aldabra does not
have predators, and so the rails gradually lost the ability to fly. But then
the island completely disappeared when it was covered by the sea, and the rail
was wiped out, along with everything else on the island.
But after that event,
some 100,000 years ago, the sea levels fell again and the atoll was once
again taken over by flightless rails. By comparing the bones of those after and
the ones before, researchers found that the evolution happened twice over a few
thousand years ago. "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," said lead researcher Dr Julian Hume, avian paleontologist
and Research Associate at the Natural History Museum.
"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."
