The island of Madagascar, located off the east coast of Africa, is host to a bizarre menagerie of animals, many of which are found nowhere else.
Biologists believe these creatures arrived on the island millions of years ago from Africa — but no one has determined how they got there. Now, scientists are proposing that they floated there.
Madagascar has some 70 kinds of tree-dwelling lemurs, from the 1-ounce pygmy mouse lemur to the eerily vocal indri lemur, a creature that looks part monkey and part teddy bear, and sounds like an air horn.
Hitchin' A Ride On A Tree Branch
Lemurs, chameleons, a mongoose-like mammal called a fossa — these strange creatures look like something Noah's ark left behind.
Scientists believe they got to Madagascar from Africa millions of years ago and evolved in their own peculiar way. But how did they cross 300 miles of ocean?
Seventy years ago, eminent biologist George Gaylord Simpson noticed that the mammals in Madagascar are small. So their ancestors, similarly small, could have rafted over as refugees on floating mats of vegetation or tree limbs.
"But there was a big problem with the idea," says Matthew Huber, an Earth scientist at Purdue University. "The ocean currents go the other way."
So a tree dislodged from Africa's eastern coast would flow down toward Antarctica or up toward North Africa, but not east to Madagascar.
This was such a puzzle that some biologists concluded that the sea level must have been lower at some point, and the animals walked over.
Huber doesn't buy this theory. The undersea geology, he says, isn't right for that. Even if it were, larger animals like lions and elephants would have crossed over to Madagascar, too. But those hefty creatures are nowhere to be found on the island.
A Change Of Currents
So Huber and a scientific colleague at the University of Hong Kong, Jason Ali, wondered if the ocean currents were different millions of years ago. Huber built a computer model that simulated the Earth — oceans, continents, even vegetation — as it would have been 60 million years ago. Given the conditions then, he believes their hunch was correct.
"As far as Madagascar is concerned, the currents go the other way," he said. "They go from Africa towards Madagascar in the past. And the reason is actually pretty straightforward — the location of the continents were different."
Africa and Madagascar sat about a thousand miles farther south back then. So, Huber writes in the journal Nature, the lemurs and chameleons and fossa could have floated to Madagascar.
"I totally agree that it's far-fetched," says Huber. "I mean, what you are requiring is that some little lemur or, really, family of lemurs were holding onto a large tree, probably during a hurricane, and got swept down into a river and out to sea." But genetic studies of animals now in Madagascar suggest that there only needed to be four successful migrations over 50 million years to have populated the island with these unusual animals.
But it wouldn't have been much fun, or easy — as in a Hollywood movie. The currents would have only been right for the trip a few times each century. And the trip would've taken about three weeks. So you had to be a very lucky lemur to get to Madagascar.
Huber says he normally uses his computer models to simulate ancient climates to help understand our current climate. He says now he's intrigued about trying to figure out how other animal migrations might have occurred over large bodies of water.
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