Schlagwort-Archive: Seychelles

The rail that (not) existed two times

During the last few days the online newspapers were trying to outdo each other with silly headlines, headlines like … :   

The bird that came back from the dead” or: “Extinct species of bird came back from the dead, scientists find” or, the worst of them all: “Scientists discover bird that came back from the dead – A species which became extinct 136,000 years ago in a rare flood on an Indian Ocean atoll has now re-emerged in the same place“  

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What is wrong with that?  

Well, a lot, but let’s just start with the statement that their isn’t any species that really goes extinct and then comes back, also not a rail species!  

We actually deal with two distinct species here, or let’s rather say, with two distinct taxa, since they may not be species but subspecies.  

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May I introduce the White-throated Rail (Dryolimnas cuvieri (Pucheran)), a very beautiful rail species that is endemic to the island of Madagascar and that apparently has also colonized the island of Mayotte northeast of Madagascar.    

Photo: Bernard Dupont  

(under creative commons license (2.0)) 
http://creativecommons.org/licenses/by-sa/2.0 

This species obviously is the source of several other flightless species and subspecies that are known to have existed on many of the islands around Madagascar, such forms are known from the islands of Mauritius and Réunion west of Madagascar and others from some of the atolls that belong to the Seychelles north of Madagascar, including the Aldabra atoll.  

And the Aldabra atoll in fact is the only place where such a flightless form (subspecies or species if you want) still survives until today, this is the Aldabra Rail (Dryolimnas (cuvieri ssp.) aldabranus (Günther)).  

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Long time ago, some White-throated Rails for which reason ever, took a flight to the atoll to find it uninhabited (by rails) and decided to stay there … over time the rails that were born on this predator-free island stopped using their wings and their descendants again finally became completely flightless.  

But then the Aldabra atoll just disappeared due to total inundation in the middle Pleistocene, about 340000 years before present, leading to the extinction of all endemic animals and plants, including this ‘First’ Aldabra Rails.  

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Then again, around 100000 years before present, the sea-level begun to sink and the Aldabra atoll reemerged.  

Again, some White-throated Rails left their home island of Madagascar and took a flight to the north to find a new home on the now rail-free Aldabra atoll, and the story took the same direction as thousands of years before, and the final result are the recent endemic, flightless Aldabra Rails that one can see when visiting the atoll.  

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So, the Aldabra atoll was inhabited by two distinct lineages of flightless rails at two different times in history, respectively prehistory, that, despite both descenting from one and the same ancestor species, still represent two completely distinct forms, whether they are referred to as subspecies or as species.  

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References:  

[1] Julian P. Hume; David Martill: Repeated evolution of flightlessness in dryolimnas rails (Aves: Rallidae) after extinction and recolonization on Aldabra. Zoolocigal Journal of the linnean Society 20: 1-7. 2019  

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edited: 10.05.2019