Madagascar’s unique animal population probably rafted there
January 1, 2010
How Madagascar got its unique collection of lemurs and other animals has puzzled naturalists for a century. Data from a Purdue professor’s three-year computer simulation appears to provide an answer: the animals floated there on natural log rafts blown to sea in storms.
The flow of the ocean currents between Africa and Madagascar 20 million to 60 million years ago would have made such a trip not only possible for the animals’ ancestors but fast, too, says Purdue earth, atmospheric, and planetary science Professor Matthew Huber.
To help understand today’s global warming and project the warming trend ‘s future impact, Huber models the climate, including ancient ocean currents, on an Earth that was much warmer millions of years ago, warm enough for crocodiles to live in an ice-free Arctic.
Huber had just completed a three-year simulation on ITaP supercomputers when a fellow researcher contacted him about a longstanding scientific mystery. Could currents between Africa and Madagascar, which flow away from the island mini continent today, have flowed toward it in the Eocene Epoch, when ancestors of the 70 kinds of lemurs and the other members of Madagascar’s animal population first began arriving?
Since the early 1900s, scientists have used seaborne immigration as an alternative theory to a land bridge, later erased by the shifting of the continents. Little geologic evidence exists for such a bridge. Rafting would have involved the creatures being washed out to sea during storms, either on trees or large vegetation mats, and floating to Madagascar.
Huber’s modeling revealed that:
- Currents flowed toward Madagascar in the Eocene because the island and Africa were 1,600 kilometers south in a different ocean current system.
- The currents flowed quickly during peak surges, fast enough to transport small animals alive (there are no large animals on Madagascar).
- The region was a hotspot, as it is today, for powerful tropical cyclones capable of washing trees and tree islands into the ocean regularly.
- The raft, or “dispersal,” hypothesis has always been the most plausible, says Anne Yoder, at the Duke University Lemur Center, who specializes in the evolutionary history of Madagascar. But Huber’s study puts hard data behind it.
“Dispersal has been a hypothesis about a mechanism without any actual data,” Yoder says. “This takes it out of the realm of storytelling and makes it science."