Biology

Extinct bird resurrected as evolution starts over again

Extinct bird resurrected as ev...
The white-throated rail twice colonized the island of Aldabra and twice evolved to become flightless
The white-throated rail twice colonized the island of Aldabra and twice evolved to become flightless
View 1 Image
The white-throated rail twice colonized the island of Aldabra and twice evolved to become flightless
1/1
The white-throated rail twice colonized the island of Aldabra and twice evolved to become flightless

Evolution is an amazing process, helping life adapt to new environments and conditions – and now scientists have uncovered a rare occasion where it got a second chance. About 136,000 years ago, a flightless bird on an island in the Indian Ocean was wiped out, only to re-evolve itself back into existence tens of thousands of years later.

Species are shaped by environmental pressures, which can make evolution a predictable process at times. It's not entirely surprising that sometimes after a species dies off, a new species with some very similar characteristics might arise in the same location later on. After all, evolution is basically following a recipe – if you put similar ingredients through the same process, the end result should be similar the second time around. This reoccurrence is known as iterative evolution.

According to a new study, that's essentially what happened on the island of Aldabra, a ring-shaped coral atoll just north of Madagascar. The fossil record shows that sometime after the island formed 400,000 years ago, the white-throated rail – a bird native to Madagascar – colonized Aldabra. Since there were no natural predators, the birds soon evolved to become flightless.

But about 136,000 years ago, sea levels rose and the island was completely submerged. Since evolution needs time to work its magic, life on Aldabra – including the flightless rails – was wiped out.

Thankfully, the story doesn't end there. Around 100,000 years ago, the island re-emerged when sea levels dropped due to an ice age. White-throated rails migrated there from Madagascar and once again, evolved to become flightless – a textbook example of iterative evolution, and one of the strongest cases ever seen in birds.

The team discovered this process was at work by studying rail bones from before and after the inundation event. The wing bones demonstrated an advanced state of flightlessness, and bones from the ankles showed signs of being clearly on their way towards flightlessness.

"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," says Julian Hume, lead researcher on the study. "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."

The research was published in the Zoological Journal of the Linnean Society.

Source: University of Portsmouth

8 comments
Tacky-on
The big question is what is the evolutionary advantage to flightlessness to a creature with no hands. Why would flightless birds have more offspring than ones that can fly? Do female Rails think male rails who fly are showing toxic aviation and only breed with males that walk most of the time?
Nahor
@Tacky-on Flying requires a lot of energy, the advantage of flightlessness is energy conservation. Flightless birds don't need to find as much food (and probably as chicks to, because the metabolism will be lower overall). And that also means more energy available for other uses (fight diseases, reproduce, ...). And the question can be reversed: what is the advantage of flight if they are no predators to flee from, food is abundant (no need to travel long distances) and climate is stable all year long (no need to migrate)?
McDesign
Lots of tradeoffs for flight - high, fast metabolism; weak lightweight bone structure.
ljaques
This begs the question "How many extinct species =remain= extinct?" As the Earth moves from Ice Age to OhMyGodWereAllGonnaDieHot to Ice Age, what is the percentage of species ad-libbing (OK, "evolving") like this in warmth-tolerating bodied form? Those questions ought to give the Climate Alarmists nightmares.
Nik
An imprint of a cartwheel was found in a coalmine, also a shoe-print, complete with stitching around the edges, was found in a piece of coal. So, its just possible that evolution produced two legged hominids many millions of years ago, which died out, and later re-emerged, as the hominid group of which only homo sapiens survives today....for the time being.
Wildfly
So the bird was not extinct. It was just absent from the island. And what is the evidence that the return to the island was via flight?
Expanded Viewpoint
Evidently, Wildfly, you missed something in the article. The White Throated Rail MIGRATED from Madagascar, meaning that it moved to the tiny island when it reappeared from the ocean. Migration means to move from one place to another, and these birds would have done so by flying, as there were no Uber or Lyft drivers back then. Then, once the new flocks of birds were living in an area with no predators stalking them, they gradually lost their wings, just like their predecessors did. Get it? The genetic lines attain and maintain those qualities of the organism which best suit it for survival, and it drops off those things which are no longer needed. Like our appendix and tail. Have you ever wondered why there are four vertebrae, which are fused into the coccyx? Why do we have claws on our toes? What purpose do they serve modern Man? Why is it that men and bears and other animals share so many common traits in their skeletons? Randy
Thorneel
Sounds like adaptation to me!