Fossil Gives Teeth to Evolutionary Theory

Article excerpt

A fossil of a tiny, furry mammal that scurried around China 165 million years ago holds a missing piece to a controversial evolutionary theory, a Carnegie Museum of Natural History paleontologist said Wednesday.

Zhe-Xi Luo, curator of vertebrate paleontology at the Oakland museum, and Chinese colleagues published a paper in the journal Nature that explains how the teeth of the mole-like Pseudotribos support the theory of convergent evolution -- the idea that animals not closely related independently develop similar characteristics because they are useful to survival.

"This animal that they found -- Pseudotribos -- is actually the most recent and probably one of the most important pieces of this new picture that's emerging," said Richard Cifelli, associate curator of vertebrate paleontology at the Oklahoma Museum of Natural History, who has researched convergent evolution but was not involved in Luo's research.

Modern mammals, including humans, have versions of tribosphenic molars, those with three points that resemble a three-peaked mountain. The molars enable animals to grind and cut food. For the molars to work, animals need an upper and lower tooth.

Pseudotribos had this type of molar, but the location of the peaks on its teeth are the reverse of those in modern mammals -- something Luo's team dubbed "pseudo-tribosphenic," giving the mammal its name. It is the first time both upper and lower tribosphenic molars were found in such an old fossil.

Despite the differing shape, Pseudotribos's molars and the molars of modern mammals function the same.

Luo found that Pseudotribos, which was less than six inches long and weighed less than a pound, died out and is not the direct ancestor of any living mammal. …