Recently, scientists from the University of Portsmouth and Natural History Museum have announced that a flightless bird that has become extinct around 136,000 years ago has managed to return. This event in nature is called iterative evolution. This type of evolution calls for a species from the same ancestor to be repeated along with different points of history.
The bird that resided on the Indian Ocean atoll of Aldabra, the white-throated rail, is a bird that is indigenous to Madagascar. Aldabra lost its flora and fauna when it was wiped out as the sea flooded the island.
The rails became flightless when 100,000 years ago, the sea levels fell due to the ice age. The island of Aldabra existed once again and the rails from Madagascar migrated to the island. The lack of predators has allowed the rails to evolve and become flightless, much like the same manner of evolution that the previous island rails exhibited.
In their study, the researchers probed on the fossils and found out that the wing bones were in an advanced state of flightlessness, while bones from the ankle of the rails showed signs that it was evolving toward flightlessness. The fossils studied included those that were from before the inundation event which they compared to the bird fossils from after the said change in sea levels.
The scientists pointed out that this means that one species from Madagascar has produced two subspecies of flightless birds in Aldabra.
Julian Hume, the lead researcher, stated that the fossils they found provided irrefutable evidence that a number of the rail species colonize the atoll. The fossil evidence presented in the study is unique for rails. It shows the ability of birds to successfully colonize isolated islands and evolve flights on multiple occasions.
David Martill, a co-author of the paper, stated that there are no other known examples of rails or birds that have exhibited iterative evolution. He added that only Aldabra can provide fossil evidence that demonstrates the effect of changing sea levels on extinction and recolonization events.
The island of Aldabra is known as the oldest paleontological record of any oceanic island found in the Indian Ocean region. The island is also known as the second largest coral atoll in the world.
The flightless white-throated rails that inhabit Aldabra are the last known living member of the Dryolimnas genus. These birds are also known as the last flightless birds of the Indian Ocean.
