Tuesday, March 8, 2011

Zombie taxa

The dinosaurs all died out at the end of the Mesozoic, about 60 million years earlier.  Or did they...

Numerous dinosaur teeth have actually been found in much more recent rock formations, well into the Paeleogene. There are a number of explanations for this.

One explanation is that we are entirely wrong about the extinction of the dinosaurs. They did not go extinct at the end of the Cretaceous and persisted much longer, perhaps to the modern day! But for some mysterious reason their bones stopped being preserved and they just left teeth and claws.

An entirely different explanation, and dare I say a much more plausible one, is that in some taxa fossil structures may be eroded out of one layer and then re-deposited in a younger layer. Given that our fossil record of dinosaurs post-Cretaceous consists of just the sort of a structures (teeth) we'd expect to be washed out and re-preserved the evidence is consistent with this hypothesis.

This hypothesis also predicts that even today we would find structures like dinosaur teeth washed out of sediments and being preserved in brand new depositions. Yes, yes we do. Such taxa are known as zombie taxa.

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