Natural rafts carried Madagascar's unique wildlife to its shores
January 20, 2010
The world's fourth largest island, Madagascar is home to some of world's most unique and bizarre wildlife, including more than 100 species of the much-loved lemur. But how did such animals reach the island, 300 miles from the African mainland? A new study published in Nature has uncovered the dramatic answer.
Using a computer simulation of ocean currents during that time, the researchers argue that the long migration would have been possible. The animals that reached the island would then have evolved in complete isolation over millions of years into the odd forms that survive today, such as the long-fingered aye-aye and the world's tiniest chameleon.
Today, currents between Africa and Madagascar flow south and southwest—not east—making such rafting trips impossible. However according to the complex computer simulation, currents flowed eastward between 20 to 60 million years ago, the pivotal period when researchers say terrestrial species arrived in Madagascar. In addition, these currents were fast enough to bring animals across the 300 miles before they would have perished from thirst. As well, Madagascar's fauna are all small-bodied and capable of long periods of dormancy, raising the chances of the success of their journey. The scientists argue that some of the animals may have been swept out into sea during hibernation, which would increase their chances of survival, since hibernating animals require little food or water.
The other theory of how Madagascar was populated entails a landbridge connecting Africa to Madagascar. However there is no physical evidence of such a landbridge and the land bridge hypothesis should mean that Madagascar would also contain large-bodied vertebrates, such as ancestors of giraffes, elephants, cats, and dogs. But, of course, there is no record of any such animals reaching the island.
"I was very excited to see this paper," says Anne Yoder director of the Duke University Lemur Center and a reviewer of the study. "Dispersal [byway of rafts] has been a hypothesis about a mechanism without any actual data. This takes it out of the realm of storytelling and makes it science."
Madagascar is second only to Australia in terms of its number of endemic, i.e. unique, species, but is thirteen times smaller than Australia.
Editor's note: the number of lemur species found in Madagascar has been updated from 70 to more than 100 and the text claiming the absence of hippos, which indeed were present on Madagascar until recent times, has been corrected. We apologize for the errors.
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