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White-throated Rail - Dryolimnas cuvieri
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White-throated Rail - Dryolimnas cuvieri

[Image: thebirdthatc.jpg]
White-throated rail. Credit: Charles J Sharp [CC BY-SA 4.0]

Scientific classification
Kingdom:  Animalia
Phylum:  Chordata
Class:  Aves
Order:  Gruiformes
Family:  Rallidae
Genus:  Dryolimnas
Species:  Dryolimnas cuvieri (Pucheran, 1845)

The white-throated rail (Dryolimnas cuvieri) or Cuvier's rail is a species of bird in the family Rallidae. It is found in Comoros, Madagascar, Mayotte, and Seychelles. A flightless subspecies, Dryolimnas cuvieri aldabranus (Aldabra rail), inhabits Aldabra, while another, D. c. abbotti (Assumption rail), from Assumption went extinct in the early 20th century due to introduced predators.
It is now the last living member of the genus Dryolimnas and believed to be the last flightless bird in the Indian Ocean. Its natural habitats are subtropical or tropical moist lowland forest and subtropical or tropical mangrove forest.



The bird that came back from the dead

by University of Portsmouth

New research has shown that the last surviving flightless species of bird, a type of rail, in the Indian Ocean had previously gone extinct but rose from the dead thanks to a rare process called 'iterative evolution'.
The research, from the University of Portsmouth and Natural History Museum, found that on two occasions, separated by tens of thousands of years, a rail species was able to successfully colonise an isolated atoll called Aldabra and subsequently became flightless on both occasions. The last surviving colony of flightless rails is still found on the island today.
This is the first time that iterative evolution (the repeated evolution of similar or parallel structures from the same ancestor but at different times) has been seen in rails and one of the most significant in bird records.
The white-throated rail is a chicken-sized bird, indigenous to Madagascar in the south-western Indian Ocean. They are persistent colonisers of isolated islands, who would have frequent population explosions and migrate in great numbers from Madagascar. Many of those that went north or south drowned in the expanse of ocean and those that went west landed in Africa, where predators ate them. Of those that went east, some landed on the many ocean islands such as Mauritius, Reunion and Aldabra, the last-named is a ring-shaped coral atoll that formed around 400,000 years ago.
With the absence of predators on the atoll, and just like the Dodo of Mauritius, the rails evolved so that they lost the ability to fly. However, Aldabra disappeared when it was completely covered by the sea during a major inundation event around 136,000 years ago, wiping out all fauna and flora including the flightless rail.

[Image: 1-thebirdthatc.jpg]
Wing bones fossils of flighted (right) and flightless Dryolimnas rails. Credit: Dr Julian Hume.

The researchers studied fossil evidence from 100,000 years ago when the sea-levels fell during the subsequent ice age and the atoll was recolonised by flightless rails. The researchers compared the bones of a fossilised rail from before the inundation event with bones from a rail after the inundation event. They found that the wing bone showed an advanced state of flightlessness and the ankle bones showed distinct properties that it was evolving toward flightlessness.
This means that one species from Madagascar gave rise to two different species of flightless rail on Aldabra in the space of a few thousand years.
Lead researcher Dr. Julian Hume, avian paleontologist and Research Associate at the Natural History Museum, said: "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. 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."
Co-author Professor David Martill, from the School of Earth and Environmental Sciences at the University of Portsmouth, said: "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 region, is fossil evidence available that demonstrates the effects of changing sea levels on extinction and recolonisation events.
"Conditions were such on Aldabra, the most important being the absence of terrestrial predators and competing mammals, that a rail was able to evolve flightlessness independently on each occasion."

https://phys.org/news/2019-05-bird-dead.html



Journal Reference:
Julian P Hume et al, Repeated evolution of flightlessness in Dryolimnas rails (Aves: Rallidae) after extinction and recolonization on Aldabra, Zoological Journal of the Linnean Society(2019). DOI: 10.1093/zoolinnean/zlz018

Abstract
The Aldabra rail, Dryolimnas cuvieri subsp. aldabranus, endemic to the Aldabra Atoll, Seychelles, is the last surviving flightless bird in the Indian Ocean. Aldabra has undergone at least one major, total inundation event during an Upper Pleistocene (Tarantian age) sea-level high-stand, resulting in the loss of all terrestrial fauna. A flightless Dryolimnas has been identified from two temporally separated Aldabran fossil localities, deposited before and after the inundation event, providing irrefutable evidence that a member of Rallidae colonized the atoll, most likely from Madagascar, and became flightless independently on each occasion. Fossil evidence presented here is unique for Rallidae and epitomizes the ability of birds from this clade to successfully colonize isolated islands and evolve flightlessness on multiple occasions.

https://academic.oup.com/zoolinnean/adva...m=fulltext
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