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Otoliths are the bones least likely to be broken by physical trauma in vertebrates. While some animals have similarly sized bones elsewhere in their bodies, these tend to in the extremeties (feet and knuckles in particular) and more exposed to trauma than the otoliths, which are protected by the skull.

The next time someone threatens to break every bone in your body, it may or may not be comforting to realise that they probably don't include your otoliths in this threat.

The word "otolith" is formed from two Greek roots: otos (ear) and lithos (stone). An otolith ("earstone") is a small bone-like piece of calcium carbonate found in the ears of many vertebrates. It rests like a pebble in a small cavity lined with sensitive hairs, and its pressure on the hairs tells the brain which way is down. This information is crucial for a sense of balance.

Otoliths are found in the heads of all fish other than sharks, rays and lampreys, and are important tools for understanding the lives of fish and fish populations. Microscopic growth rings, like the rings found in trees, mark the otoliths and record the age and growth of a fish from hatching until death. These growth rings can be affected by many factors, including migration patterns and water temperatures.

Otoliths found in and around shipwrecks have been used to gather data about the species of fish that inhabited the area of the shipwreck two hundred (or more) years ago, enabling biologists to form conclusions about changes in oceanic environments.

Since the vestibular system of fish is similar to that of humans, otoliths from fish are also being used to study the effects of gravity removal on the vestibular system (which registers sensations of motion and balance). By recording data from the otolithic nerves of fish sent into space, researchers hope to gain a better understanding of the changes in signals sent by the inner ears of astronauts as they adapt to microgravity.


O"to*lith (?), O"to*lite (?), n. [Oto- + -lith, -lite.] Anat.

One of the small bones or particles of calcareous or other hard substance in the internal ear of vertebrates, and in the auditory organs of many invertebrates; an ear stone. Collectively, the otoliths are called ear sand and otoconite.


© Webster 1913.

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