Otoliitit

Otoliitit, commonly referred to as otoliths in English, are calcified structures located in the inner ear of many vertebrates. In fishes, there are three paired otoliths—the sagittae, lapilli, and asterisci—each forming in the vestibular labyrinth. They grow throughout life as layers are added, creating growth rings that can be read much like tree rings. These rings enable scientists to estimate age, growth rate, and, with additional data, seasonal patterns of feeding and metabolism. Otoliths are composed mainly of calcium carbonate (predominantly aragonite) and an organic matrix; their composition and microstructure vary among species and environmental conditions. They are anchored within the otic capsule and move with the surrounding fluids as the fish perceives gravity and linear acceleration.

In mammals and other tetrapods, the term is sometimes used for the otoconia—tiny calcium carbonate crystals embedded in the gelatinous layer of the utricle and saccule, part of the vestibular system that detects linear acceleration and head position relative to gravity. Otoconia can be involved in balance disorders when displaced, such as benign paroxysmal positional vertigo.

Fossil otoliths, preserved as calcium carbonate fossils, are common in the fossil record and are used to identify fish taxa, reconstruct paleoecology, and study ancient oceans. Isotopic and trace element analyses of otoliths also provide environmental histories for individual fish and populations.

Etymology: from Greek oto- (ear) and lithos (stone).