Porpoises and dolphins
Porpoises (left) and dolphins (and whales) are all mammals that belong to the order Cetacea. The difference boils down to their faces, fins and bodies. Dolphins generally have prominent, long "beaks" and cone-shaped teeth. Porpoises have smaller mouths and spade-shaped teeth. Dolphins are generally leaner than porpoises, and have a curved dorsal fin, while porpoises are more robust and have a triangular dorsal fin.