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Mysteries of Madagascar's wildlife solved

Over 80% of the plants and over 90% of animals that live in Madagascar are found nowhere else on the planet.

The big Malagasy mystery is how did all these species get there? Now, a new study published in the journal Nature has provided strong evidence backing a theory that the ancient ancestors of Madagascar’s mammals drifted hundreds of kilometres across from mainland Africa, clinging to rafts of floating vegetation. And that includes the most famous of Malagasy inhabitants: the lemurs, a type of primate – like humans – but unlike any other primates in the world.

Using computer climate models to reconstruct ancient ocean currents, Jason Ali from the University of Hong Kong and Mathew Huber from Perdue University in the US, have shown that at around the time lemurs are thought to have arrived in Madagascar (60 million years ago), there were surface ocean currents flowing from northern Mozambique eastwards towards Madagascar; to ay the currents flow in the opposite direction, a change that took place as gradually Madagascar drifted northwards to its present location.

Ali and Huber found that for 3 or 4 weeks every century, the eastward currents were strong enough to propel a log from Mozambique to Madagascar in around a month. A small mammal, including the ancestors of the lemurs, could feasibly have clung on and survived for that long.

That may seem rather unlikely, but genetic studies suggest that it took fewer than a dozen colonisation events to bring all the mammalian ancestors to Madagascar, including carnivores, rodents and a crazy group of animals called tenrecs. And over the course of tens of millions of years, that certainly becomes possible.

This new evidence goes against another theory that Madagascar’s animals walked there across an ancient land bridge. This alternative theory doesn’t explain why other African animals, including many large-bodied groups like antelopes, elephants and apes, didn’t also make it across to Madagascar.

As well as helping us understand how Madagascar’s amazing wildlife evolved, but it also goes to show how much biology can tell us about the geology of the earth.

24th Jan 2010

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