Growth patterns and biological information in fossil fish otoliths

Teleost otoliths are located in the membranous labyrinth and are mainly com posed of aragonite and a small amount of organic matrix. Their rhythmic gro wth may provide important data about age, growth, maturity, and life-histor y events. This article presents insights into paleoecological and evolutionary detail s from a study of the otolith microstructure of Trisopterus kasselensis, Tr isopterus sculptus, and Pterothrissus umbonatus (Oligo-Miocene, North Sea B asin). Otoliths of Recent Trisopterus minutus were analyzed using the same methods (light and electron microscopy, thin slides) as a basis for compari son with the fossil sample. Growth structures similar in size and aspect to the seasonal and daily grow th increments in living fish indicate both individual age and early life tr ansitions in habitat and life strategy suggesting planktonic larvae and ben thic juveniles. The aspect of rhythmic growth patterns is due to lunar peri odicity, a common feature in fish otoliths. Moreover, fossil Trisopterus sh ow an phylo genetic increase in otolith-and consequently-somatic growth, in dicating a change of life strategy during evolution (Oligocene to Recent). Thus the internal structure of fossil otoliths allows the determination of growth, age composition, and early life history of fossil fish, as well as their direct comparison with living relatives.