INITIAL STUDIES OF FISH OTOLITHS AID IN UNDERSTANDING THE JONES BRANCH SITE (LATE OLIGOCENE) IN SOUTHEASTERN MISSISSIPPI

Initial investigations by the Mississippi Museum of Natural Science (MMNS) of the Jones Branch Site (latest Oligocene, Catahoula Formation) near Waynesboro, Mississippi, indicated the presence of teleostean fish otoliths in silty to fine-sandy, lignitic shell hash seams in the lower portion of the formation. Subsequent bulk sampling by the author as well as the MMNS material has produced approximately 200 otoliths thus far. While not a large number, it is sufficient to provide salient stratigraphical and paleoenvironmental information about the site. Various processes, especially leaching, have adversely affected the preservation of the aragonitic otoliths. However in spite of the preservation, taxonomic identification of the vast majority of the otolith specimens is possible. Initial results based on the otoliths indicate an assemblage of very low diversity (n < 10) that is dominated by members of the family Sciaenidae (drums). Various sciaenid species compose more than 95% of the otoliths recovered thus far. The sciaenids represent taxa that are common in the Gulf Coast Oligocene and include Aplodinotus distortus, Aplodinotus gemma, and Sciaena pseudoradians. Although the sciaenid otoliths range from approximately 1.5 to 10 mm, the predominant size is quite small (< 5 mm). Therefore, the otolith assemblage appears to be strongly dominated by juvenile drums. The sciaenid taxa coupled with their age (juveniles) are a strong indicator of nearshore marine waters, estuarine passes, and possibly, even fresh water. The sciaenid taxa represented at Jones Branch were probably estuarine-dependent for reproduction. The preliminary paleoenvironmental parameters suggested by the otoliths will be compared to the paleoecological settings ascertained by the analysis of other fossil groups at the site. Collecting and analysis of additional otoliths as well as other marine and terrestrial vertebrates such as sharks, rays, amphibians, reptiles, and mammals are continuing at the Jones Branch Site.