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11 of the smallest mammals in the world

By: Bryan Nelson on Nov. 17, 2010, 10:18 a.m.
Tree shrews

Photo: Paul J. Morris/Flickr

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Tree shrews

Not to be confused with the true shrews or elephant shrews, tree shrews are a group of mammals set apart.

In fact, they appear closely related to primates, though no clear fossil record of tree shrews exists. They've certainly got the brains to show for it; tree shrews have a greater brain-to-body-mass ratio than humans.

The smallest tree shrew in the world is the pen-tailed tree shrew, which can weigh as little as 25 grams and measure barely more than 10 centimeters.