The enigmatic occurrence, size distribution, and significance of a new macrourid species, Nezumia armentrouti, based on otoliths from the Lincoln Creek Formation (upper Oligocene Section), Washington State, USA

Abstract

ABSTRACT Teleostean otoliths (112 sagittae) from the Lincoln Creek Formation (upper Oligocene), Washington State, U.S.A., were identified as Nezumia armentrouti n. sp. except for two specimens. The preponderance of one species (98.21%) is very unusual. Equally puzzling is the size of the otoliths that represents almost exclusively large, mature fishes (extant N. aequalis used as an analogue). Otoliths do not reflect various ages (sizes), and there appears to be an absence of larval, juvenile, or subadult representatives. The restricted range (97.32% of specimens 8.1–16.1 mm) of the otolith lengths (and corresponding fish length) is attributed to depth stratification, which is well-known in extant macrourids. Otoliths may be the result of piscivorous predators and subsequent excretion. However, the unusual occurrence of the otoliths (single, or at most, two specimens often associated with thin bone beds) may indicate a different process such as the death and decay of individual fish. This investigation is highly significant on many fronts including the first fossil occurrence of the benthopelagic deep-sea Nezumia in North America (excluding the Caribbean), possible evidence of depth stratification in the paleoenvironment based on otolith length, and otoliths from an outer shelf/shelf break to upper slope paleoenvironment (200–600 m), which are extremely rare in the published fossil record.