It seems implausible. However, genetic data are confirming it. What is the origin of Madagascar’s fauna? By all indications, the animals arrived… by crossing the sea on rafts of vegetation. How is this possible?
“It seems a far-fetched idea. Surviving drifting across the sea is even difficult for humans,” says Matthew Borths. He is a fossil curator at Duke University’s Lemur Center.
Genetic data
But when comparing genetic data of modern Malagasy with the fossil record of their African ancestors, everything changes. The research is in the journal Biological Reviews.
Reptiles, amphibians and mammals from continental Africa would have been stranded on giant rafts of vegetation. And they floated to Madagascar, where they evolved. There, 95% of the mammals and 98% of the reptiles are endemic to the country.
Vegetation could have contained fruits or other food sources, or trapped rain to keep animals alive. There are three main theories. One, the species were there before Madagascar broke up to become an island. Two, they rafted across from mainland Africa. Three, they crossed land bridges that may have existed at different periods.
But the fossil record from Madagascar between the time of the dinosaurs and about 2000 years ago is almost non-existent. So genes from 28 terrestrial vertebrates were compared with African relatives. It turned out that some Madagascan species have been there at least as long as the island.
Other rafts
But most of the rest of the reptiles, mammals, and amphibians, do not. They are descended from relatively small animals that rafted in from land. The models in the new study rule out the use of land bridges.
Nor is the use of rafts unique to Madagascar. Several animals made the much longer crossing from Africa to South America by raft. And these can be huge. He points to a video of a huge clump of vegetation floating down the Panama Canal, complete with upright trees. “A monkey could have been on that raft,” Borths says.
“The origin of Madagascar’s fauna is a product of the randomness of the island. And of the organisms that manage to find their place in this ecosystem.”
