The incredible shrinking frog
In the lakes, ponds, and slow-moving rivers of the Amazon Basin lives a frog that breaks a fundamental rule of growth. The paradoxical frog, Pseudis paradoxa, starts life as a tadpole of enormous size, only to shrink as it reaches adulthood. The tadpole can reach a length of up to 27 centimeters (10.6 inches), holding the record for the world's longest tadpole. The adult frog, however, measures a mere 3.4 to 7.6 centimeters long.
This "reverse metamorphosis" is what gives the frog its name. Early naturalists were so baffled by the size difference that they initially believed the frog must metamorphose into the giant tadpole, which then became a fish, unable to accept that shrinkage was possible. The reason for this biological puzzle lies in the tadpole's anatomy. The vast majority of its length comes from a large, muscular tail. Its actual body, or snout-vent length, is comparable to that of the final adult form even before metamorphosis begins. The process of absorbing the massive tail accounts for the dramatic reduction in overall length. Unlike other frogs that grow substantially after becoming froglets, the paradoxical frog does little to no growing after it loses its tail.