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

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.

KEYWORDS:

• Macrouridae
• sagittae
• deep-water paleoenvironment
• Northeast Pacific Ocean
• depth stratification

Acknowledgments

Appreciation is extended to the Green Diamond Resource Company (Seattle, WA) for graciously allowing collecting at UWBM locality B0403 in Mason County, WA, for this research. This investigation would not have been possible without the discovery and collection of the otoliths at the locality by J. Goedert. He also provided data on the location, stratigraphy, and other essential information for the study. Goedert is also thanked for his detailed review of an earlier draft of the manuscript. L. Guthrie (Lacey, Washington) and T. Iversen (Bremerton, Washington) provided field assistance in the collection of the otoliths for this investigation. The following people were especially helpful in the repositing of the otolith specimens at the University of Washington Burke Museum of Natural History and Culture, Seattle, WA: K. Anderson, Vertebrate Palaeontology Collections Manager, and C. Sidor, Curator of Vertebrate Palaeontology. Extant and fossil otoliths were supplied by D. Nolf (formerly of the Institut Royal des Sciences Naturelles de Belgique, Brussels, Belgium). We thank W. Schwarzhans (Natural History Museum of Denmark, Zoological Museum, Copenhagen, Denmark) who provided direction and made valuable suggestions regarding the taxonomy of the otoliths, and R. Long provided expertise and assistance in the development of the figures for the study.

Disclosure statement

No potential conflict of interest was reported by the author(s).