Dolphins are members of several families of small- to moderate-sized toothed whales. The family of true, or oceangoing, dolphins contains about 35 species of river dolphin belong to three other families. Dolphins are similar to porpoises, but whereas dolphins generally (but not always) have beak-shaped snouts and pointed teeth, porpoises are generally smaller and have rounded snouts and spade- or chisel-shaped teeth. Until quite recently, and particularly in the United States, the term porpoise was used for any small, toothed whale.