The immediate, scientifically accurate answer to whether a dolphin is a whale is yes: dolphins are technically a specific type of whale. The terms “whale” and “dolphin” are informal names, not distinct taxonomic groups. From a biological perspective, all dolphins are considered smaller, toothed members of the broader whale family tree.
The Scientific Classification of Cetaceans
All whales, dolphins, and porpoises belong to the single taxonomic group, the infraorder Cetacea. This means all cetaceans share a common ancestor. Scientists estimate there are about 90 living species within this group.
The infraorder Cetacea is divided into two parvorders, representing the two main evolutionary branches. The first is Mysticeti, which includes the baleen whales. These whales are characterized by plates of keratin called baleen, which they use to filter small food items like krill from the water. This group includes the blue whale, humpback whale, and gray whale.
The second parvorder is Odontoceti, which are the toothed whales. These animals possess teeth, which they use to hunt and consume larger prey like fish and squid. The Odontoceti group contains approximately 75 species and includes all dolphins and porpoises, as well as larger animals like the sperm whale and beluga whale.
Dolphins belong to several families within the Odontoceti, most notably Delphinidae, which includes all oceanic dolphins, such as the common bottlenose dolphin. Because the scientific classification places dolphins within the Odontoceti parvorder, and Odontoceti is a branch of Cetacea, dolphins are formally considered toothed whales.
Defining Dolphins Versus Whales
The distinction between a dolphin and a whale in common language is based largely on size and specific family grouping, rather than a major scientific split. The term “dolphin” is reserved for smaller cetaceans, especially those in the Delphinidae family, which are usually under 13 feet in length. The term “whale” is applied to the larger cetacean species.
This size-based distinction leads to confusing nomenclature, such as the orca, commonly known as the killer whale. Despite its name, the orca is the largest member of the Delphinidae family, making it the largest species of dolphin. Orcas are classified as dolphins due to their close genetic ties and anatomical characteristics, even though their immense size causes them to be called “whales.”
Other physical features help differentiate the common groups, though they do not create a taxonomic boundary. Dolphins often have a pronounced, beak-like snout (rostrum) and conical teeth. Porpoises, another small Odontocete, have spade-shaped teeth and a shorter, rounded head. Toothed whales have a single blowhole, while baleen whales possess two blowholes.
Shared Mammalian Characteristics
The unity of all cetaceans is rooted in their shared biology as fully aquatic mammals. Like all mammals, they are warm-blooded, meaning they regulate their internal body temperature independently of the surrounding cold water. This thermoregulation is aided by a thick layer of fat called blubber that insulates their bodies.
All cetaceans must surface to breathe air, using a specialized nostril on the top of their head called a blowhole. They reproduce by giving birth to live young, which they nurse with milk produced by mammary glands. These traits trace their evolutionary history back about 50 million years to land-dwelling ancestors related to modern hippos.