AN ELASMOBRANCH ASSEMBLAGE FROM THE DANIAN (EARLY PALEOCENE) OF MISSISSIPPI

Less than a half dozen local elasmobranch assemblages have been adequately characterized from the Danian (Early Paleocene) of North America and none thus far from the eastern Gulf Coastal Plain. The published assemblages vary in their taxonomic composition, and only three document a dozen or more species. Preliminary investigations in the Clayton Formation in the vicinity of Starkville, Oktibbeha County, Mississippi, have yielded at least a dozen elasmobranch taxa from a discrete horizon. Unfortunately, the preservation of teeth with intact roots, particularly among large lamniforms, is infrequent, thus identification is not always easy or complete. The Starkville selachian taxa include Hexanchus, Squalus, Heterodontus, orectolobiforms, odontaspidids, otodontids, Scyliorhinus, and triakids. Compared to the volume of matrix processed and quantity of selachian teeth recovered thus far, batoids are surprisingly rare. A single dasyatid tooth and two associated fragments of a large myliobatiform caudal barb are all that represent this group. The Starkville site has a few taxa in common with published Danian assemblages in New Jersey, along the Potomac River, and even the northeast Atlantic. However, there are notable compositional differences with unpublished synchronous elasmobranch associations in the adjacent coastal plain states of Arkansas and Alabama.

The age of the Starkville assemblage is based, in part, on certain associated early Midway (Danian) mollusks, namely the oysters Pycnodonte pulaskensis (Harris) and Ostrea crenulimarginata Gabb, the arcoid clam Cucullaea macrodonta Whitfield, and the nautiloid Hercoglossa ulrichi (White). Elasmobranch and bony fish teeth, vertebral centra, and coprolites occur sparingly within lenses of phosphate nodules ~3.0 m above the K-Pg boundary and represent a condensed bed within a glauconitic, marly shale probably attributable to transgressive deposits. Also suggestive of transgressive deposits, specifically eastern Gulf Coastal Plain sequence TP1.1b, is the relative abundance of the clam tube Teredolites (Pholadida: Teredinidae). Of the phosphatic nodules, a significant portion represents indurated, reworked macroinfaunal traces; phosphatic clasts in general, including vertebrate fossils, are regularly encrusted by foraminiferans.