Wednesday, July 28, 2010

One Ought Not Hype the Roos

This cladistic diagram of marsupials, showing the branching that took them from a common ancestor in South America to their present variety, is attached to a write-up of a scientific finding that is, unfortunately, overdramatized:
More than 300 marsupial species live in the Americas and Australia. The critters are famous for their pouches, built-in baby carriers where they keep and feed their young. They are the closest kin of placental mammals, such as humans, but they branched off to form their own group 130 million years ago. They settled predominantly in South America and Australia, which at the time were part of a supercontintent known as Gondwana.

DNA sequencing and the fossil record tell two different stories of how that settlement went down. The DNA suggests that a single South American ancestor swept into Australia before the continents drifted apart, and the marsupials on each continent then evolved on their own. Fossils, however, support a more complicated picture in which some ancestors made the return journey to South America, meaning that some South American species might have arisen in Australia.
Fascinating, but the article could do better to emphasize that the two land-masses involved belong in scare-quotes. The combination of plate techtonics and time has a way of doing this to land masses.

Back in the heady days of a few hundred million yesteryears, going from "Australia" to "South America" was hardly the dramatic peregrination we picture when imagining a little marsupial family making its way through thousands of miles of rough, windy, shark-infested seas, clinging to a forlorn patch of soil and driftwood, arguing over which of them will be forced to eat the other when starvation sets in.

Back then it would have been more like crossing from Oklahoma to Kansas, or maybe from Oklahoma to Nebraska by way of Kansas, which -- trust me on this -- is not a dramatic thing to do.

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