The Raft of the Lemurs

A new study reveals that Madagascar's animals arrived there by hitching rides on rafts

Located in the Indian Ocean about 300 miles from Africa's southeastern coast, Madagascar is an island nation whose main island, also called Madagascar, is the world's fourth largest-island. It is home to 5% of the world's plant and animal species, 90% of which are endemic to the island. Lemurs -- all 70 different kinds of them -- are found nowhere else.

Madagascar has been an island for some 120 million years. But animals did not start arriving there until much later -- about 55 million years after the island was born. For generations of scientists, it has been a mystery as to how this extremely isolated island was populated by such a diverse array of life.

One theory was that the animals arrived via a land bridge that has since disappeared from shifts in the Earth's tectonic plates. In 1915, scientists came up with an alternate theory: The animals arrived on rafts. Now a three-year study of ancient ocean currents is giving weight to this idea.

Professors Matthew Huber of Purdue University and Jason Ali of the University of Hong Kong, in a study to be published in the February 4 issue of the journal Nature, have found that "the prevailing flow of ocean currents between Africa and Madagascar millions of years ago would have made such a trip not only possible, but fast, too," according to a Purdue press release.

"Rafting would have involved animals being washed out to sea during storms, either on trees or large vegetation mats, and floating to the mini-continent, perhaps while in a state of seasonal torpor or hibernation."

"Huber and Ali's work supports a 1940 paper by George Gaylord Simpson, one of the most influential paleontologists and evolution theorists of the 20th century. Simpson introduced the concept of a "sweepstakes" process to explain the chance of raft colonization events taking place through vast stretches of geological time. Once the migrants arrived on the world’s fourth largest island, their descendants evolved into the distinctive, and sometimes bizarre forms seen today."

Additionally, Huber said that the Madagascar study was also a test case that demonstrated the ability of computer models to mimic the interactions of the ocean and the atmosphere in a greenhouse climate from the distant past.

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image: Black-and-white Ruffed Lemur (Varecia variegata) (credit: jo-h)