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February 10, 2013 in City

This 2012 artist’s rendering shows a hypothetical placental mammal ancestor, a small animal that lived on Earth 65 million years ago.

Associated Press photo

Shown here is a fossil of a shrew-sized Cretaceous-age animal, Ukhaatherium nessovi, which is one of the many mammals used in a mammal tree-of-life study released Thursday. The fossil was discovered in 1994 in the Gobi Desert by the Mongolian Academy and the American Museum of Natural History.