Dall's porpoises were named after William H. Dall, an American zoologist who was one of the first to identify the species through detailed notes and drawings. Rooster tails are one way that scientists identify Dall's porpoises. Dall's porpoises are black with a striking white patch on the belly and flank. They have a small triangular dorsal fin and the posterior margin of the tail flukes are fringed with a grayish-white band. However, each word refers to a specific family and should not be used interchangeably.
Dolphins usually have beaks and more noticeable dorsal fins.
Porpoises are usually smaller than dolphins and usually don't have pronounced melons or beaks. If you are lucky enough to look into a dolphin or porpoise mouth, you can tell the difference between the two families as dolphins have rather pointed teeth while porpoise teeth are shaped like spades. Unless you know a lot about dolphins and porpoises it is easy to confuse them. This site was created by Laura Drumm and the National Marine Mammal Laboratory .