Frogs are amphibians belonging to the order anura. The anuran group has nearly 2,700 species throughout the world and includes both frogs and toads. The word anura means "without a tail," and the term applies to most adult frogs. The anura are distinguished from tailed amphibians (urodeles) such as salamanders because the latter retain a tail as an adult.

One of the most studied and best understood frogs is the northern leopard frog, Rana pipiens. This species is well-known to most children, to people who love the outdoors, and to scientists. Leopard frogs live throughout much of the United States as well as Canada and northern Mexico. Inhabiting a diverse array of environmental conditions, the order anura exhibits an impressive display of anatomical and behavioral variations among its members. Despite such diversity, the leopard frog is often used as a model that represents all members of the group.

Leopard...