That's no tail on the Tailed Frog. It's not a mud flap, either. It's a . . . well, does the fact that it appears only on the male of the species provide the necessary information?
Tailed Frogs are unique among North American frogs. Whereas other species practice what's called external fertilization -- the female lays eggs, then the male fertilizes them -- Tailed Frogs copulate. This internal fertilization prevents the swift river waters in which these frogs conduct their business from washing away the sperm before it settles on the eggs.
The tadpoles of the species, both male and female, are also uniquely equipped. These Tailed Frogs-to-be have special suction-cup mouths that help them cling to rocks in the strong currents.
Click here to learn more about the Tailed Frog.