'Hairy' Fossil Shows Early Mammals Were Furry

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The newly discovered fossil is one of the best-preserved early mammal ancestors ever found, and provides some of the earliest evidence of pre-mammalian hair.
April Isch, University of Chicago

An extremely well-preserved rodentlike fossil recently discovered in China provides some of the best evidence yet for how the earliest human ancestors lived.

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Named Megaconus mammaliaformis, the animal closely resembled but predated true mammals, living about 165 million years ago in a humid world dominated by early dinosaurs. It is one of two recently described ancestral mammal fossils that provide a significant leap forward for research in early mammal evolution.

Until now, most knowledge of M. mammaliaformis has been based on isolated teeth remains that suggested that the animals were not highly evolved. But the newly discovered intact skeleton — complete with some of the earliest evidence of hair — shows that these animals were more complex than previously thought, the team reports in the Aug. 8 issue of the journal Nature.

"Research always assumed that these were primitive and not highly specialized, but this animal shows that they were already highly specialized and highly adapted to special feeding strategies," said Thomas Martin, a paleontologist at the University of Bonn in Germany and one of the authors of the paper.

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By closely examining the orientation of the animal's relatively flat teeth in relation to its jaw, the team determined that M. mammaliaformis evolved to grind plants, making it one of the earliest plant eaters in a world dominated by carnivores. [Image Gallery: Fantastic Fossils]

Hair impressions were also found on the fossil. The hair — which appears darker on the animal's back and lighter on its belly — are among the only premammalian hair impressions ever discovered. The hair likely evolved to keep the animals warm, which could indicate that it would otherwise lose heat quickly through a fast metabolism typical of modern rodents, Martin said.

"This is very important because the presence of hair was always postulated, but the direct evidence was never well preserved in fossils," Martin told LiveScience. "This is direct evidence, not just interpolated evidence."