One of the little mysteries of biogeography is how did mammals get to Madagascar?
Madagascar is an island. It is ~300 miles from Africa.
160 million years ago Madagascar was part of Gondwanaland, but it and India broke away from the supercontinent and went traveling north. Then 80 million years ago Madagascar and India broke apart, with India continuing north (eventually to bash into Asia) while Madagascar dawdled around Africa.
It has had no land contact with the rest of the world for ~160 million years.
The trouble is that placental mammals didn’t evolve until 125 million years ago. Long after Madagascar and India were adrift. But Madagascar is covered with modern mammals, and while these mammals tend to differ at the family level they clearly belong to modern orders (Primates, Carnivores, Insectivores, Rodents, Chiroptera, …).
Parallel evolution would not have done that.
The ancestors of the Malgache mammals were not on board when Madagascar broke away form Gondwanaland. How did they get there?
OK, bats could be blown across the Mozambique channel fairly easily, but most mammals on the island are not bats.
I’ve heard three explanations:
- A cyclone hit Africa and knocked a tree into a river where it got blown across to Madagascar. And there happened to be ancestral lemurs (or rats, weasels, geckos, or what have you) in the tree.
- During an ice age the water level was very low and the Mozambique channel dried up and animals could walk across.
- Maybe it was easier to make the crossing 90 million years ago, and some animal did, evolved into the original primate, and then was carried by India to Asia whence they populated the rest of the world.
All these have problems.
- A tree from Africa would never reach Madagascar. Ocean currents would carry it to South Africa and not toward Madagascar.
- The Mozambique channel is too deep to be dried up by an ice age.
- India rammed into Asia somewhere around 45 million years ago, but the earliest primate fossil is from 55 million years ago (and was not found in Madagascar or India)
But a recent study by a climatologist points out that ocean currents would be different 50 million years ago, because the continents were in different places, and that his research indicates that at that time the currents might indeed carry an animal from Africa to Madagascar.
Now most mammals in Madagascar are little guys. Or could have evolved from small arborial ancestors, and might well have been up a tree when a storm struck.
But not all. How on earth did the hippopotamus get there?