Dolphins are highly intelligent, agile marine mammals recognized for their social behaviors and global distribution. They are a diverse group within the order Cetacea, which also includes whales and porpoises. Their sleek bodies and powerful movements enable efficient navigation of underwater landscapes.
Oceanic Dolphins
The majority of species commonly recognized as dolphins belong to the family Delphinidae. They vary widely in size and appearance, from smaller species like Hector’s dolphin to the largest, the orca. Their torpedo-shaped bodies make them efficient swimmers. They feature a prominent dorsal fin, which can be curved or hooked, and conical teeth suited for grasping prey such as fish and squid.
They inhabit diverse marine environments, from tropical to colder regions, including open oceans and coastal waters. They are highly social, living in groups called pods that can range from a few individuals to superpods of over a thousand. Within these pods, they communicate using clicks and whistles, and exhibit complex social behaviors like cooperative hunting and strong social bonds. The orca, Orcinus orca, despite its common name “killer whale,” is the largest member of the dolphin family, reaching lengths of up to 9.5 meters and weighing up to 10 tonnes. Orcas are apex predators with sophisticated hunting techniques and stable family groups, demonstrating a form of animal culture.
River Dolphins
River dolphins are a distinct group adapted to freshwater or brackish water environments. These species are found in specific river systems across South America and Asia. They have unique physical characteristics suited for murky habitats, such as smaller eyes, relying more on echolocation for navigation and hunting. They often have long beaks and flexible necks, which aid in maneuvering through submerged vegetation and catching prey in shallow, muddy waters.
Examples include the Amazon River dolphin (Inia geoffrensis), also known as the boto or pink river dolphin, which is the largest river dolphin species. Another notable species is the Ganges River dolphin (Platanista gangetica), found in the Ganges-Brahmaputra river systems, and is essentially blind, relying entirely on echolocation. Many river dolphin species face significant conservation challenges, often classified as critically endangered due to habitat destruction, pollution, and accidental entanglement in fishing nets.
Distinguishing Dolphins from Porpoises
While often confused, dolphins and porpoises belong to separate biological families: dolphins to Delphinidae and porpoises to Phocoenidae. Their teeth are a primary distinction; dolphins have conical teeth, whereas porpoises possess spade-shaped teeth. Their body shapes also differ: dolphins have more slender, streamlined bodies with curved or hooked dorsal fins and a pronounced snout or “beak.”
In contrast, porpoises have smaller, stockier bodies with rounded heads and a blunt, non-protruding snout. Their dorsal fins are triangular, though some species, like finless porpoises, lack a dorsal fin entirely. Porpoises are smaller in size compared to most dolphins and are more solitary or live in smaller groups, exhibiting shyer behavior and less surface activity. Notable porpoise species include the harbor porpoise and the critically endangered vaquita.