The world's smallest known vertebrate, Paedophryne amauensis, is a frog species in the family Microhylidae discovered in the rain forests of Papua New Guinea by Chris Austin, curator of herpetology at LSU’s Museum of Natural Science. True to their name, they are certainly micro.
This "fly-sized beast" is only a hair smaller than the previous record holder -- a southeast Asian fish species Paedocypris progenetica, whose females measure about 7.9 millimeters.
From Newser.com: "At 0.27 inches long, Paedophryne amauensis is the smallest frog ever discovered and, by some measures, is the world's smallest vertebrate. The only smaller creature with a backbone is the male of a species of anglerfish, but they spend their lives fused to much larger females."