The terms whale and dolphin describe different marine mammals, but they belong to the same biological group, the infraorder Cetacea. Cetaceans are warm-blooded, air-breathing aquatic mammals, including whales, dolphins, and porpoises. While the names are frequently employed based on overall size, clear biological distinctions exist within this single family tree. Understanding the scientific classification and anatomical features reveals the differences between the two groups.
The Cetacean Family Tree
The Cetacea infraorder is divided into two main suborders: Odontocetes (toothed whales) and Mysticetes (baleen whales). All dolphins are classified as a type of toothed whale, belonging to the Delphinidae family. Biologically, every dolphin is considered a whale, but only a few species of whales are considered dolphins.
The Odontocetes suborder encompasses approximately 75 species, including all dolphins and larger animals like the sperm whale and the orca. The orca, often called the killer whale, is actually the largest species of dolphin. These toothed whales are distinct from the Mysticetes suborder, which contains about 15 species and includes massive filter feeders like the humpback and blue whales. The common distinction between a “whale” and a “dolphin” is primarily a non-scientific one, generally separating smaller, streamlined toothed whales (dolphins) from the larger members of the group and all baleen whales.
Comparing Scale and Physical Form
Size is the most recognizable difference between the two groups. While dolphins are relatively small compared to the great whales, the largest dolphin, the orca, can reach 8.2 meters (27 feet) and weigh over 6,000 kilograms. The smallest dolphin, such as the Maui’s dolphin, measures about 1.7 meters long.
This scale is dwarfed by the Mysticetes, or baleen whales, often called the “great whales” due to their sheer bulk. The blue whale, the largest animal on Earth, grows up to 30 meters (98 feet) in length and weighs over 180,000 kilograms. Dolphins generally possess a sleek, torpedo-shaped body built for agility and speed in pursuit of prey.
Large whales, especially baleen species, are built for massive size and endurance rather than extreme maneuverability. While dolphins are lean and agile, many great whales are robust and proportionally wider. The contrast is clear when comparing a common dolphin to the massive, relatively slower-moving body of a humpback whale.
Key Anatomical Differences
An anatomical trait separating the two suborders is their feeding method, reflected in their mouth structure. All dolphins and other toothed whales possess uniform, conical teeth, used to grasp prey like fish and squid before swallowing it whole. Mysticetes have no teeth; instead, they feature large plates of baleen. These keratin structures hang from the upper jaw and act as a sieve to filter small organisms like krill and plankton.
The shape of the head is another distinguishing characteristic. Most dolphin species have a pronounced snout, or rostrum, which aids in their streamlined shape. Many large whales, especially baleen species, have blunter, broader heads that lack this defined beak structure, like the large, bowed lower jaw of the right whale.
Dolphins typically have a prominent, curved, and triangular dorsal fin relative to their body size. Conversely, many large whales have dorsal fins that are much smaller in proportion to their massive bodies, or they may have only a small ridge or no dorsal fin at all, such as the bowhead whale. Finally, all toothed whales possess a single blowhole, while all baleen whales have two blowholes situated side-by-side.