Monday, February 05, 2007

Forward into the Palaeocene!

New primate fossils have been found pushing the existence of these critters back to the Palaeocene. In an article in Foxnews, two new skeletons of plesiadapiforms have been found. These forms were originally thought to be primates but then reclassified as primate-like mammals. Now it seems, that designation may have been wrong.

[Jonathan] Bloch recently caught a lucky break when he made the rare discovery of nearly complete skeletons of two plesiadapiform species, now named Ignacius clarkforkensis and Dryomomys szalayi, embedded in limestone outside Yellowstone National Park.

By analyzing the skeletons and comparing them to more than 85 modern and extinct primate species, the researchers showed that plesiadapiforms look a lot more like primates than paleoanthropologists had imagined — and look nothing like flying lemurs, Bloch said.

This is exciting because it addresses the origin of our first precursors at a time when the dinosaurs had finally given way to the mammals. The article goes on to say:

Primates must have acquired their traits gradually, because plesiadapiforms have some, but not all, of the characteristics of later primates, Bloch and Sargis said.

"In the past, people had hypothesized that all of these kinds of primate features evolved as a single complex of features at one time, whereas what we're finding is throughout those first 10 million years of primate evolution, these features were evolving piecemeal, kind of one-by-one, accruing through time," Sargis said.

Bloch and Sargis's skeletal analysis shows that flying lemurs and another modern, non-primate mammal, the tree shrew, are primates' closest living relatives.

DNA studies of all three types of mammals — primates, flying lemurs, and tree shrews — confirm Bloch and Sargis's finding.

"So all three of those groups," Sargis said, "you can trace back to a single common ancestor.

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