Scientists think that all members of the Carnivora family (cats, dogs, bears, weasels, etc.) are descended from the humble little Miacid clan. Though these hunters don't look all that intimidating, their success speaks for itself. Miacids roamed the planet for over 29 million years, which is an insanely good run, before diversifying into the dozens of carnivorous mammal families we know and love today. If you have ever owned a cat, a dog, or even a ferret, you have this Eocene predator to thank for him/her.
Image via Stitch0626.