Fish Otoliths collected from Berg in Belgium.These Otoliths date back to the Lutetian stage of the Eocene Epoch approximately 46 Mya. Otoliths are calcium carbonate structures which lie just behind the brain of fishes. They are commonly referred to as 'earstones' and aid with balance and orientation. Otoliths are actually comprised of growth rings so can be used to help infer the age and growth rate of the fish. These Otoliths approximately measure between 4 - 5 mm in diameter or length and are supplied in small plastic bags with an information label.