Fossil Bony Fish Ear Bones

Otoliths ("ear bones") occur in all vertebrates, including humans, whales, and dolphins [see my previous posts: Fossil whale ear bone, August 15, 2014; Fossil dolphin ear bones, Oct. 4, 2015] for these latter two examples) and allow for perception of linear acceleration, both horizontally and vertically. Otoliths are not skeletal components; rather they form as three separate bones (in each ear) within the auditory capsules. Their composition is calcium carbonate (mainly the mineral aragonite). They can also be fossilized and many are microscopic in size. Some, however, can be macroscopic in size.

Otoliths of modern-bony fish (teleosts) can be common in Tertiary freshwater and marine environments. The shapes and proportions of otoliths vary with fish species. Fish from reef or rocky bottom habitats (snappers, groupers) have larger otoliths than open-clean fish (tuna, mackeral). The growth rings in otoliths are similar to tree rings, in that they can be used to estimate the age of fish, as well to determine early life transitions from planktic larvae to benthic juveniles. The stable isotopes of oxygen and carbon found in the otoliths can be used to determine ancient temperatures of their environments. 

Front, side, and back views (in vertical order) of a matched pair of macroscopic left-and-right otoliths (24 mm long and 7 mm thick) from a 1-meter long, 40-pound White Sea Bass from the northern Gulf of California, Mexico.