The paradoxical frog measures only about 8 cm in length, while its tadpoles can grow up to 22 cm.
The paradoxical frog (Pseudis paradoxa), also known as the shrinking frog, is found in northern South America and Trinidad. It primarily feeds on invertebrates, mainly insects. While this may seem typical, this species is unlike most other frogs. This unusual amphibian actually shrinks as it matures.
During its larval stage, it is significantly larger than in its adult form. Specifically, the tadpoles of the paradoxical frog are 3 to 4 times larger than the adult. While the tadpoles can reach a length of 22 cm, the fully grown frog measures only 8 cm. Some other species in the Pseudis genus also experience this unusual size change, but the paradoxical frog holds the record for having the largest tadpoles.
So why are the tadpoles of the paradoxical frog so large? According to a study published in The Herpetological Journal in 2009, the growth rate of the tadpoles is similar to that of other species, but they continue growing and developing for an extended period. By the time they undergo metamorphosis into adult frogs, males have already begun producing sperm, and females are developing eggs—something that usually occurs during the juvenile frog stage.
In a study on another species within the Pseudis genus, researchers examined the skeletal development of its tadpoles and found that their skeletons were nearly or fully developed by the end of metamorphosis.
The tadpoles’ enormous size is mainly due to their long tails. Just before metamorphosis, their snout-to-vent length (SVL) is already similar to that of the adult frog.
For most frog species, individuals are small immediately after metamorphosis but continue growing over time. However, because the tadpoles of the paradoxical frog grow for a much longer period than other species and are already well-developed when metamorphosis occurs, the adult frog undergoes very little, if any, further growth. The loss of the tail results in the frog shrinking in size.
