Pacific Tailed Frog
Pacific Tailed Frog, Ascaphus truei. Although it may look like metamorphous leftovers - the tail is actually the manly bits, a 'copulatpry organ', that's used to fertilize a female's eggs internally. If the tailed frog reproduced using typical frog external fertilization, the fast moving water that they lay their eggs in would quickly wash away the male's sperm, leaving most eggs unfertilized. So the tailed frog's little tail may look unevolved or like a piece of tadpole after thought, but it's actually a habitat specific piece of anatomy.