Key Mammalian Characteristics
Whales are classified as mammals, based on distinct biological features that set them apart from fish. Whales are endothermic, maintaining a consistent internal body temperature. This contrasts with most fish, which are ectothermic and rely on external sources for temperature regulation. Whales also possess lungs and breathe air directly from the atmosphere, surfacing regularly.
Unlike fish, which typically lay eggs, whales reproduce through live birth. After birth, the mothers nurse their young with milk produced by mammary glands. Whale milk is highly concentrated with fat and protein, allowing calves to grow rapidly in their early stages. While adult whales appear hairless, some species possess sparse hairs around their jaws or snout, particularly during embryonic development.
The Order Cetacea
Whales, along with dolphins and porpoises, belong to the scientific order Cetacea, a group of fully aquatic mammals. This order is defined by adaptations for marine environments. Cetaceans possess streamlined, fusiform bodies, efficient for movement through water. Their front limbs have evolved into paddle-shaped flippers, used primarily for steering and stability.
A distinguishing feature of cetaceans is their horizontal tail flukes, which move up and down for forward thrust. This contrasts with the vertical tail fins of fish, which typically move side to side for propulsion. Cetaceans also breathe through one or two blowholes located on the top of their heads, allowing them to surface for air without fully exposing their heads. Cetaceans evolved from terrestrial, hoofed ancestors, transitioning to a fully aquatic existence over millions of years.
Diverse Whale Groups
Within the order Cetacea, whales are divided into two main suborders, distinguished by feeding mechanisms and physical characteristics. One group is the Mysticeti, known as baleen whales, including species like the blue, humpback, and gray whale. These whales lack teeth and instead possess baleen plates—large, keratinous structures hanging from their upper jaw—to filter small organisms like krill and fish from the water. Mysticetes typically have two blowholes and are generally larger than toothed whales.
The second group is the Odontoceti, or toothed whales, which encompasses species like the sperm whale, orca, and various dolphins and porpoises. Odontocetes possess teeth to grasp and tear prey, such as fish, squid, and sometimes other marine mammals. These whales typically have a single blowhole and often exhibit complex social behaviors within their pods. Their feeding strategies vary, from hunting in coordinated groups to deep-sea diving for giant squid.