Across the waters

Japanese tsunami debris has been arriving on the northwest coast of the United States, carrying exotic Asian marine species along for the ride. Earth magazine takes the opportunity to tell a broader story about long-distance dispersal by rafting: “Setting sail on unknown seas: The past, present and future of species rafting”. The evolution of primates included at least two major rafting dispersals, into South America and onto Madagascar:

Perhaps the most famous example of rafting is the colonization of the island of Madagascar across 400 kilometers of open water from Africa. Madagascar appears to have been an island for at least 120 million years. Genetic studies suggest that animals began arriving about 60 million years ago. Geologic evidence for land bridges or island chains during this window has never been found, leaving rafting as the most likely explanation.
The rafting hypothesis has been well explored; its really been a process of elimination, says Ann Yoder, an evolutionary anthropologist at the Duke Lemur Center in Durham, N.C. Its kind of crazy to imagine lemurs clinging to vegetation and rafting across the Mozambique Channel, she says. But time and time again, it really seems to be the best fit for the data.

It’s the kind of stuff that inspired long-dead theories of sunken continents – in this case, Lemuria.

Many people have discussed shorter-distance rafting among present and past Mediterranean islands to explain the dispersal of Miocene primates, most notably Oreopithecus. By the time hominins show up and begin dispersing to islands (first Flores, more than a million years ago), rafting was probably deliberate.