Which marine mammal order includes whales, dolphins, and porpoises? The answer is Cetacea.
Cetacea is the scientific group containing all living whales, dolphins, and porpoises. These animals are fully aquatic mammals: they breathe air with lungs, give birth to live young, nurse them, and propel themselves with horizontally oriented tail flukes rather than fish-like vertical tails.
Living cetaceans are commonly divided into two major groups. Baleen whales, such as blue whales and humpback whales, filter food through baleen plates. Toothed whales, including dolphins, porpoises, sperm whales, and beaked whales, generally use teeth and many also use echolocation. Although “whale” is often used for larger species, dolphins and porpoises are cetaceans too.
A common classification mix-up is treating Cetacea as a separate mammalian order in every modern taxonomy. Many current systems place cetaceans within the larger order Cetartiodactyla, alongside even-toed ungulates and close to hippopotamuses. In traditional quiz and textbook usage, however, Cetacea is accepted as the order-level name for this distinctive marine mammal lineage.