Paradoxical frog (Pseudis paradoxa) is a member of the genus Pseudis, the swimming frog genus in the tree frog family, Hylidae. They are found in Argentina, Bolivia, Brazil, Colombia, French Guiana, Guyana, Paraguay, Peru, Suriname, Trinidad and Tobago, and Venezuela.
The frogs reach sizes of 1.7 to 2.5 inches but they have been known to get 2.9 inches long. What makes the Paradoxical frog interesting is that the tadpoles are bigger than the adult frogs. Tadpoles reach sizes of up to 7.8 inches long, roughly 3-4 times larger.
(images from http://www.itsnature.org/sea/other/paradoxical-frog/ and reddit)