Skinny 'Shrew' Is Oldest True Mammal

A shrew-like animal that snagged insects from ferns lining the shores of freshwater lakes 160 million years ago, might be one of the first "true" mammals to walk the Earth, back when the dinosaurs roamed, a new fossil suggests.

The new fossil, discovered in what is now Liaoning Province in China, is the oldest evidence of the divergence of these "true" or placental mammals from their marsupial counterparts, and indicates the mammalian lineage was evolving faster than expected during the Jurassic Period.

http://www.livescience.com/15734-oldest-placental-mammal.html