Madagascar is famous for its strange endemic animals, including the black-and-white ruffed lemur, pictured here.
Credit: Wikimedia
PARIS: Madagascar's magnificent menagerie of mammals arrived tens of millions of years ago on natural rafts carried by storms and currents, and not across land bridges as some scientists contend.
A study published in the British journal Nature, uses new data about ancient ocean currents to revive an old hypothesis that Madagascan animals first arrived by sea.
Evolutionary biologists agree, based on evidence from molecular DNA, that the island's major fauna made their way from continental Africa in four stages.
A first wave of lemur-like animals appeared between 60 and 50 million years ago. Then, some 42 to 25 million years ago, they were followed by tenrecs - insect-eating relatives of hedgehogs, shrews and opossums.
"Sweepstakes hypothesis"
Carnivores arrived just after that, and then rodents. But just how these fauna - many of them today threatened with extinction - got there has been sharply debated.
The so-called "sweepstakes hypothesis," first laid out some 70 years ago, speculated that the forebear of today's Madagascar mammals came via driftwood 'rafts' across the 430-kilometre-wide Mozambique Channel.
The theory is consistent with a relatively small number of mammalian families, suggesting rare opportunities for migration.
All of the species that landed during the 40-million year period in question were also semi-aquatic. In other words, being able to swim at least a little bit might have been a required skill for the perilous voyage.
Land bridge from Africa unlikely
There has always been a problem with this notion: the currents swirling in the channel and the surrounding Indian Ocean would make it virtually impossible for a floating Noah's Ark of vegetation to reach Madagascar's shores.
A competing theory of land bridges argues that portions of the Davie Ridge running on the sea floor along the channel separating Madagascar and Africa may have been partially exposed.
This would have creating a causeway linking the two bodies of land. But the bridge hypothesis, in turn, raises questions. If animals could simply walk to Madagascar, why did so few species do so?
