Beluga whales are not porpoises, though they are often confused with them due to their shared classification as small-toothed whales. They belong to entirely separate scientific families, meaning the differences between them are fundamental. This distinction is based on millions of years of evolutionary history, resulting in clear differences in their anatomy, particularly their teeth and dorsal structures. Understanding their biological classification and physical characteristics reveals why these two Arctic-dwelling marine mammals are distinct species.
How Marine Mammals Are Classified
Beluga whales and porpoises are grouped together within the Order Cetacea, which includes all whales, dolphins, and porpoises. They both belong to the Suborder Odontocetes, or toothed whales, distinguishing them from the Mysticetes, or baleen whales. This shared suborder means they both use echolocation, possess teeth, and have a single blowhole.
The significant biological divergence occurs at the Family level, separating belugas and porpoises into distinct evolutionary branches. Beluga whales belong to the Family Monodontidae, along with the narwhal, meaning they are more closely related to each other than to any porpoise. Porpoises are classified under the Family Phocoenidae, which comprises seven different species.
Distinctive Traits of Beluga Whales
Beluga whales, whose scientific name Delphinapterus leucas translates to “white dolphin without a fin,” possess several unique traits. As adults, they are easily recognized by their pure white coloration, an adaptation that helps them camouflage in the icy Arctic and sub-Arctic waters they inhabit. This white color distinguishes them from the generally darker, gray-to-black porpoises.
A defining feature is the absence of a true dorsal fin; instead, belugas have a tough, low dorsal ridge running along their back. This lack of a fin allows them to swim easily under sheets of ice without injury and minimizes heat loss in frigid waters. Belugas also possess a highly flexible neck, a rare trait among cetaceans, because their seven neck vertebrae are not fused together. This flexibility allows them to turn their heads from side to side, which is useful when navigating shallow, complex environments.
Their teeth are distinct, being peg-shaped or conical, with an average of 34 to 40 teeth. Belugas use these teeth primarily for grasping and holding prey, such as fish and squid, which they typically swallow whole. They also have a prominent, bulbous forehead, known as a melon, which is highly flexible and changes shape to focus the sounds they use for echolocation.
Distinctive Traits of True Porpoises
True porpoises, members of the Phocoenidae family, are generally much smaller than beluga whales, with the largest species only reaching about 7.7 feet in length and 500 pounds. Their body shape is more robust and stocky compared to the sleek appearance of other cetaceans. Porpoises are characterized by a lack of a pronounced rostrum, or beak, giving them a more rounded head profile.
The primary physical difference from belugas lies in their dental structure and dorsal fin. Porpoises have distinctive spade-shaped teeth, which are flattened and blunt. This feature clearly separates them from the peg-like teeth of belugas and the conical teeth of dolphins. This unique tooth morphology defines the Phocoenidae family.
Unlike the beluga’s dorsal ridge, most porpoise species possess a small, triangular dorsal fin, often located near the middle of their back. However, some species, like the finless porpoise, lack a dorsal fin entirely. Their neck vertebrae are typically fused, meaning they cannot turn their heads with the same flexibility as a beluga whale.