Many people automatically think that there is a clear separation between dolphins and whales. While they each have some distinct characteristics, their DNA tells a different story. Modern day science relies on genetic relatedness to determine taxonomic groupings and relationships. So when is a whale not a whale? To answer that question we must look at the taxonomic relationships to answer this question.
Cetaceans belong to the infraorder cetacean. An Infraorder is simply a further separation of order in the animal kingdom. In relation to oteher animals, cetaceans are most closely related to the hippopotamus. And their ancestral characteristics are shared with pigs and camels.
The phylogram shows the placement of Cetacea in relation to other taxon groups.
Within the Cetaceans are broken up into two groups – Mysticeti (Baleen whales) or true whales and the Odontoceti tooth whales. Each branch is further divided into groups. The tooth whales have characteristics such as teeth, which the Baleen whales don’t have. The tooth whales are broken into groups that include some whales and all of the dolphin subgroups The Monodontidae or unusual whales include the beluga and narwhal. The other groups are comprised of dolphins and porpoises. Delphinidae or ocean dolphins are a particular interesting group.
The Delphinidae make up a large group of cetaceans that includes dolphins and some whales. But wait a minute doesn’t Delphinidae contain oceanic dolphins? I am glad you asked. This group defines the question when is a whale not a whale? Within this group the Delphinae contain the dolphins and Globicephalonae contain whales. These whale by definition are actually dolphins.