Just how did all the exotic mammals of Madagascar, like its unique collection of lemurs, originally reach the African island? Did they float there from the African mainland, or did nature provide a land bridge? The question has vexed biologists because both explanations have their problems. But a new study in Nature proposes an answer to the main problem posed by the floating-across-the-channel idea, suggesting that it is the most likely explanation.

Because of the narrow range of biology on Madagascar, most biologists favored the floating rafts hypothesis. But there has always been a problem with this notion: the currents swirling in the channel and the surrounding Indian Ocean would make it virtually impossible for a floating Noah’s Ark of vegetation to reach Madagascar’s shores [AFP]. Were those currents always this way, though? No, says a team led by Matthew Huber.

Huber and his colleagues employed the computer modeling techniques used in modern climate studies to predict backwards. 50 million years ago Africa and Madagascar sat about 1,000 miles (1,600 kilometers) south of their current positions due to continental drift…. By plugging data about the ocean and atmosphere of ancient Earth into modern climate models, Huber and Ali found that ocean currents around the two land masses once flowed eastward, toward Madagascar, after all [National Geographic].

Madagascar’s four groups of land mammals would’ve arrived on the island between 60 and 20 million years ago. The peculiar set of creatures that arrived had always suggested that migration opportunities probably were scarce—otherwise (as with a land bridge) a greater mammalian variety probably would’ve arrived. The rafting hypothesis also matches the reality that none of the mainland Africa’s very large mammals made it to Madagascar. As you can see in the illustrative yet strange image above, you just can’t fit an elephant or hippo in a dinghy… or a natural raft.

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Image: Nature