Itty bitty fur balls
Though small size may seem like a meager trait, in the biological world it can come with some big advantages.
Small mammals can occupy ecological niches which are inaccessible to larger animals, and their petite frames make it easier to hide undetected, burrow into minor crevices or climb upon the flimsiest of branches.
They're also incredibly cute, like this baby pygmy marmoset (pictured). Here's our list of some of the world's smallest mammals.
Editor's Note: This gallery has been updated since it was originally published in November 2010.