"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" said Lead researcher Dr. Julian Hume.
According to a new report, the rise from the extermination
of a flightless bird species in the Indian Ocean was potential due to one of the rare evolutionary process called 'Iterative Evolution'. A chicken-sized bird, the
white-throated rail aboriginal to Madagascar in the south-western Indian Ocean
is at the moment found in the isolated island of Aldabra.
Fossil evidence that is now available proposes that
the bird lived on the island around thousands of years ago. In the nonappearance
of predators and just like the Dodo of Mauritius, the rails changed. They lost
the skill to fly and they could not even fly to higher ground. They became almost
inexistent as the island was swamped.
The last surviving colony of flightless rails used
to migrate in great numbers from Madagascar. This is the first time that
iterative evolution has been seen in rails and is one of the most significant
in bird records.
Many of those that went north or south sunk in the stretch
of the ocean and those that went west landed in Africa are eaten by the predators.
Conversely, Aldabra became extinct when it was totally
covered by the sea during a major blizzard event around 136,000 years ago. It
wiped out all fauna and flora including the flightless rail. Investigators
studied fossil evidence from 100,000 years ago when sea-levels went down during
the succeeding Ice Age and the islet was re-colonized by flightless rails. They
equated the bones of a fossilized rail from before the inundation event and
after the inundation event.
They found out that the wing bone displayed the advanced state of flightlessness and the ankle bones exhibited discrete
properties that it was embryonic toward flightlessness.
Co-author Professor David Martill stated that,
"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 the region, is fossil evidence available that demonstrates the effects of changing
sea levels on extinction and re-colonization events."