BONY FISHES BASED ON OTOLITHS AND OSTEOLOGICAL REMAINS FROM THE OLIGOCENE OF LOUISIANA

Oligocene marine vertebrates are extremely rare and poorly known in Louisiana although surface Oligocene marine strata have been recognized in the state for almost 140 years. Due to limited exposures of marine Oligocene sediments in Louisiana, collecting has concentrated on the type locality of the Rosefield Marl Beds (Rosefield Formation, Vicksburg Group) in Catahoula Parish since the early 1900's. New Oligocene fossil localities discovered since 2000 have provided additional information on the marine vertebrate assemblage, especially the bony fishes. Stratigraphic and paleontologic investigations indicated that the new locations correlate with the Rosefield Marl Beds, probably P19 planktonic foraminiferal zonation. Bulk sampling and systematic surface collecting have allowed a much better understanding of the actinopterygians in the Oligocene seas of Louisiana approximately 33-34 million years ago.

This study concentrates on describing the Oligocene marine bony fishes from Louisiana based on osteological remains and otoliths (earstones) with the otoliths providing the vast majority of the data. Before the examination of teleostean otoliths, the Oligocene marine bony fishes in Louisiana were virtually unknown and limited to a few taxa based on isolated skeletal remains (mainly teeth). The otoliths have allowed for an in-depth analysis and description of the Oligocene bony fish assemblage. Approximately 1200 teleostean otoliths and skeletal remains have been collected from four Oligocene localities in Louisiana and represent at least 19 families and 27 taxa of actinopterygians. Major constituents of the teleostean assemblage based on otoliths include clupeids (herrings), congrids (conger eels), ophiidids (cusk eels), bregmacerotids (codlets), sciaenids (drums), and paralichthyids (flatfish). Unfortunately, all of the localities have very shallow paleowater depths (probably less than 40 meters), which limits the diversity of the bony fishes present. Sciaenids are the most abundant representatives in the assemblage and include Sciaena pseudoradians, Aplodinotus distortus, and Aplodinotus gemma, all extinct drums. All of the taxa based on otoliths indicate fish from shallow marine to possibly estuarine conditions that preferred soft substratum in a tropical to subtropical climate.