Special Senses

The special sensory organs in cetaceans include the eyes, ears, and echolocation system. Unlike pinnipeds, cetaceans spend all their time in the water so their sensory systems do not need to function as well in air. Indeed, as fully aquatic animals, cetaceans have become superbly adapted to take advantage of the physical properties of water.

Most notably, odontocetes have evolved a sophisticated sensory system that relies on sound which travels 4-5 times faster in water than in air. The echolocation system of odontocetes (note mysticetes do not use sound the way that odontocetes do) varies in structure and performance across species but in general the system consists of a complex series of nasal air sacs which surround the blowhole. Air is passed across a set of phonic lips which are situated just deep to the blow hole. Sound is produced in an analogous manner to when you purse your lips and blow out, though their abilities far exceed what humans can produce! Directly in front of these air sacs is the melon (bulbous forehead) which consists of a sophisticated “lens” made of special fats and muscles and which is used to focus the sound leaving the head. The sound beam then moves out into the environment and will bounce off objects, sending a return beam back toward the animal. This beam is picked up by the lower jaw or perhaps the gular region of the head. The lower jaw is hollow and filled with specialized fats that conduct the sound directly to the ear bone. Echolocation helps odontocetes “see” their environment even when light is absent or poor.

During necropsy the nasal cavities and sinuses should be examined for nasal mites. The trachea and larynx can be removed by cutting along the inside of the lower jaw and removing the tongue then continuing to cut back along the throat. Though not usually necessary during a necropsy, the melon can be examined by cutting a cross section midway from where the melon meets the upper rostrum and the front of the skull.

For more information about cetacean sensory systems see Cranford et al., 1996 (echolocation), Mass and Supin, 2007 (eyes), and Ketten 1994 (ears).

Be sure to check back soon for detailed anatomical diagrams of the ear and head submitted by Israeli veterinary neurologist, Merav Shamir as well as detailed diagrams of the echolocation system submitted by Dr. Ted Cranford.

Detailed annotated images of the special sensory organs of a harbor porpoise are shown below.  CLICK on an image to see an enlarged view.