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Living fossil birch mouse

birch mouse/Yuri Kimura/Southern Methodist University

In “Birch Mouse Ancestor Discovered in Inner Mongolia Is New Species of Rare ‘Living Fossil’”, we learn that tiny fossil teeth (ScienceDaily May 25, 2011)” found in Inner Mongolia are “a new species of birch mouse, indicating that ancestors of the small rodent are much older than previously reported”:17 million years old as opposed to the previous estimate of eight.

Kimura identified Sicista primus from 17 tiny teeth, whose size makes them difficult to find. A single molar is about the size of half a grain of rice. The teeth, however, are distinctive among the various genera of rodents known as Dipodidae. Cusps, valleys, ridges and other distinguishing characteristics on the surface of the teeth are identifiable through a microscope.

“We are very lucky to have these,” Kimura said. “Paleontologists usually look for bones, but a mouse is very tiny and its bones are very thin and fragile. The teeth, however, are preserved by enamel. Interestingly, small mammal teeth are very diverse in terms of their structure, so from that we can identify a species.

Question: Are living fossils getting found faster than they were decades ago,or are they just talked about more?


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