The dolphin, an air-breathing marine mammal, possesses a respiratory opening called the blowhole, which is the functional equivalent of a human nose. This specialized adaptation migrated from the front of the head during evolution. It is the dolphin’s sole external nostril, allowing it to efficiently exchange air at the water’s surface. Unlike land mammals, dolphins must consciously decide to take every breath, making the blowhole a highly controlled structure.
The Blowhole: Location and Primary Function
The blowhole is located on the dorsal surface, or the top of the dolphin’s head. This positioning allows the animal to breathe while keeping the majority of its body submerged and maintaining forward motion. This location resulted from millions of years of evolution, where the ancestral nostril migrated backward and upward from the snout. The external opening is a crescent or comma-shaped muscular flap that provides a watertight seal when the dolphin is underwater.
The opening and closing of this structure is entirely voluntary, controlled by a developed set of muscles and a cartilaginous plug. When the dolphin surfaces, these muscles relax, and the flap opens for a rapid exchange of air. Dolphins are capable of completing the entire exhalation and inhalation process in as little as 0.3 seconds.
A network of specialized nerve endings surrounds the blowhole, helping the dolphin sense pressure changes. This signals when the opening is clear of water and safe to breathe. This rapid, efficient respiration is necessary for an active marine predator that must interrupt underwater activities to breathe. The primary function of the blowhole is respiratory, facilitating the intake of oxygen and the expulsion of carbon dioxide.
Internal Structures for Sound and Echolocation
The nasal passage beneath the blowhole contains internal structures separate from the breathing pathway, used exclusively for generating sound. Dolphins do not possess vocal cords like humans, so they produce clicks and whistles through a different mechanism. Sounds are created by forcing pressurized air through a specialized tissue complex known as the dorsal bursa, which includes the “phonic lips.”
As air is shuttled between complex air sacs in the nasal cavity, it passes the phonic lips, causing them to vibrate and produce high-frequency clicks. These short, broadband clicks, lasting about 50 to 128 microseconds, are the basis for the dolphin’s primary sensory tool: echolocation. Dolphins possess two sets of phonic lips, allowing them to produce clicks and whistles simultaneously.
The resulting clicks are projected forward into the water, where they strike objects and bounce back as echoes. By interpreting these returning echoes, the dolphin can determine the size, shape, distance, speed, and internal structure of objects. This complex sound generation process is distinct from the air movement used for breathing. This allows dolphins to echolocate while submerged without releasing air bubbles.
The Rostrum and Melon: Clarifying the Snout
The elongated snout of the dolphin, often mistaken for its nose, is composed of two main structures: the rostrum and the melon. The rostrum is the bony projection that forms the dolphin’s jaw structure and teeth. It is a physical platform and does not contain the respiratory or sound-producing organs.
The second structure, the melon, is the rounded, fatty forehead that sits directly in front of the blowhole. This mass of specialized fat, often called acoustic lipids, is connected to the internal sound-producing structures. The melon’s function is to act as an acoustic lens, focusing the high-frequency clicks generated by the phonic lips into a narrow, directional beam of sound.
The dolphin can subtly change the shape of the melon, allowing it to modulate and steer the sound beam toward objects. This focusing mechanism gives the dolphin its precise “acoustic vision” and is an integral part of its biosonar system. While the snout is a defining feature, the dolphin’s true nose is the blowhole on the top of its head.