Posted by: paulgarner | January 21, 2010

Hitching a ride to Madagascar

In the light of Wise and Croxton‘s proposal that rafting on floating vegetation played a major role in post-Flood biogeographic dispersal, this advance Nature publication caught my eye. In 1940, George Gaylord Simpson proposed that the ancestors of the present-day mammals of Madagascar had rafted to the island from the African mainland. But there was a problem with his idea: the observed ocean currents didn’t fit the theory. Others argued that the mammals got there across a long-vanished land bridge – but that didn’t explain why only smaller mammals (e.g. lemurs, tenrecs, rodents) apparently made the journey.

New modelling work reported by Ali and Huber (2010) may have solved the problem. Their study suggests that during the Palaeogene (when the mammals in question were arriving) the ocean currents would have been in just the right position to allow rafting from the mainland. That’s because Africa and Madagascar were 15 degrees further south and the Mozambique Channel separating them was in a different ocean gyre than today. As plate tectonics moved Africa and Madagascar northwards, the current system evolved towards its present configuration and the delivery of species eventually stopped. So Ali and Huber conclude that Simpson was probably right all along.

Neat study.

References

Ali J. R. and Huber M. 2010. Mammalian biodiversity on Madagascar controlled by ocean currents. Nature advance online publication, 20 January 2010. doi:10.1038/nature08706.

Wise K. P. and Croxton M. 2003. Rafting: a post-Flood biogeographic dispersal mechanism, in: Ivey R. L., Jr. (editor), Proceedings of the Fifth International Conference on Creationism, Creation Science Fellowship, Pittsburgh, pp.465-477.

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Responses

  1. I would be curious to know how this scenario would fit within a YEC framework given that the model of Ali and Huber only works given timescales that are unacceptable to creation scientists.

  2. As I understand, Madagascar was shifted from where it is now and possibly closer together. They’re 250 miles apart right now, and surface ocean currents run anywhere from 1 MPH to 5.5 MPH. At 2.5 MPH, that’s about 4 days – easy survival for most animals even without fresh water. Several animals getting swept out to sea on a fallen tree by a storm could make it without problem.

    (I did a quick search, and modern ocean current speeds around Madagascar are around 2.5 MPH. Not that it helps us much about the speeds back then.)

    The floating mats, from what I’ve read, are considered to be multiple square miles in extent and would have some fresh water available trapped in the branches, leaves and roots. Hypothesized faster currents have been mentioned, and slightly closer continents have been used.

    A 2000 mile trip (just over half of the current distance) taken at a steady 5 MPH straight across from Europe to North America would be just over a month. Obviously ocean currents would have to be in drastically different directions from what we currently see.


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