Otolith

An otolith (Ancient Greek: ὠτο-, ōto- ear + λῐ́θος, líthos, a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule and utricle, in turn, together make the otolith organs. These organs are what allows an organism, including humans, to perceive linear acceleration, both horizontally and vertically (gravity). They have been identified in both extinct and extant vertebrates.

Counting the annual growth rings on the otoliths is a common technique in estimating the age of fish.