Made in Madagascar. Exotic species such as the fossa may have evolved from a single family of African mongooses marooned on the island.

The Carnivores' Ark

John is a Science contributing correspondent.

Madagascar is home to some of the strangest carnivores on the planet--such as the fossa, a chimeric-looking mix of cat, dog, and bear features. So where did they come from? A genetic analysis may have solved the riddle: They all evolved from a single group that arrived by sea.

You might expect that Madagascar's fauna evolved from animals trapped on the island when it broke away from Africa 165 million years ago, or from India 88 million years ago. But this can be ruled out because they carry features that evolved on the mainland more recently. One popular alternative holds that African carnivores scurried across a land bridge that might have connected Madagascar to Africa between 26 million and 45 million years ago. Another suggests that the weird diversity of Malagasy meat-eaters derives from a single colonization by sea, a seemingly unlikely event because the prevailing winds blow away from Madagascar toward African shores.

Such riddles are usually solved with the help of fossils, but Madagascar has a notoriously poor record for the critical period of 2 million to 65 million years ago. So biologist Anne Yoder of Yale University and colleagues turned to the DNA record instead. They sequenced several genes shared by living Malagasy, African, and Indian carnivores, as well as other mammals.

Though Malagasy carnivores look strikingly different, their DNA reveals a tight-knit family, all descending from a mongoose-like animal that arrived from Africa between 18 million and 24 million years ago, the team reports in the 13 February issue of Nature. A likely explanation for this heritage, says Yoder, is a powerful storm that might have blown a tree trunk containing a family of these animals from Africa to Madagascar. Their survival on this roughly 500-kilometer journey could have been aided by a state of semi-hibernation, an ability which is retained by some of the carnivores on Madagascar today. Upon arriving, they would have found themselves in a carnivore's paradise, teeming with lemurs that would have been "pretty naive about terrestrial predators."

The evidence is compelling, says David Krause, a paleontologist at the State University of New York, Stony Brook. The origin of Madagascar's diverse biota "constitutes one of the greatest unsolved mysteries of natural history." Krause adds that the final verdict won't come until researchers unearth fossils of Madagascar's earliest carnivores.

Related sites
The World Wildlife Fund's Madagascar page
The Missouri Botanical Garden photo-essay of Madagascar

Posted in Evolution