Recently, scientists at the University of Portsmouth in England discovered fossils of a bird species from more than 100,000 years ago. These fossils were found on the Aldabra Atoll, a small, island-like landform in the Indian Ocean. The atoll was formed when coral grew to the surface, creating a triangular shape with a large lagoon in the center of the island. Due to its distance from the mainland and its small size, the atoll is largely untouched by most animals (including humans), allowing the few organisms who arrive there to evolve quicker than their land dwelling relatives.
The fossils that researchers examined originated from a chicken-sized rail, one that had evolved wing bones unable to support flight but ankle bones that were strong enough to hold the bird’s weight throughout its entire lifespan. This evidence suggests that the rail was flightless, spending its days running around the coral rocks and sandy beaches of the atoll.
Sadly, the flightless rails were soon deemed extinct, as mass flooding events occurring 136,000 years ago wiped out all life on the island, submerging the atoll completely undersea. All terrestrial life was killed during this disaster. Around 40,000 years later, during the next ice age, the island resurfaced. Plants and animals from the mainland returned, and among them, a group of white-throated rails were blown in.
The rails lived in seclusion from the rest of their population on Aldabra, and eventually, they began to evolve to adapt to their new environment. How did they adapt? The same way as the extinct rails. Their wings began to shrink, and their ankles lengthened and flattened. Eventually, they became so similar they were almost the same species. The flightless birds had managed to evolve twice from the same common ancestor, nearly 100,000 years apart!
However, scientists will never be able to truly ascertain that the two rails are exactly the same, as the definition of a species pertains to their ability to interbreed, and it is impossible to breed a dead fossil with a living bird. Also, the plumage of the birds could be completely different, but researchers will never know the feathers of the extinct species as fossil records cannot preserve soft materials like feathers. The closest humans can get to viewing soft tissues is by seeing their imprint in mud, which then hardens to rock. Unfortunately, no such soft mud exists in the atoll, which is mostly composed of coral-based limestone. Nevertheless, the evolution of a flightless rail on the island of Aldabra from the same common ancestor happening twice is still an amazing coincidence.
Global sea levels are rising, and the extinction rate of species is reaching what some call the “sixth great extinction.” It is tempting to believe that this process will act as a safeguard and allow species harmed by human caused extinction to re-enter the world, helping to keep the earth alive. Alas, evolution does not always work that way, and this situation is an interesting combination of many coincidences that have little chance of happening on a mass scale. Regardless, despite not being able to save the world, this little bird shows how a unique set of circumstances can make anything—even coming back from extinction—possible.
