Rafting

We'll talk more about Madagascar in the next class but if you are interested in biology it is hard not to be interested in just why Madagascar has such a high number of endemic species.

The simplest explanation would be that after Gondwana broke apart and Madagascar separated from Africa 120 million years ago the isolation led to evolution and allopatric speciation. The problem though is that lemurs and some other groups had not yet evolved on the African continent 120 million years ago. We think much of Madagascar's animal population began arriving much later, sometime after 65 million years ago - and subsequently speciated from these original colonists. This raises the very interesting question of how they got there. Did they cross a causeway or land bridge that now no longer exists, did they swim or 'raft' on vegetation?

A paper in Science earlier this year provides evidence supporting the rafting hypothesis: Mammalian biodiversity on Madagascar controlled by ocean currents
There's a nice editorial summary too: Biogeography: Washed up in Madagascar

How, when and from where did Madagascar's unique mammalian fauna originate? The idea that the ancestors of that fauna rafted from Africa finds support in innovative simulations of ancient ocean currents.

Which explains why there are no elephants on Madagascar. A rat on a bunch of sticks and vegetation swept out to sea surviving for a few days is not hard to believe. Even a lemur ancestor on a tree swept downriver and out to sea in a storm. But an elephant? It's an amusing image but simply not likely.


As an aside it is perhaps an indication of one of the problems of conservation that a Google Image search on one of the most photogenic and unique places on earth brings up page after page of pictures of an animated movie.