Chondrichthyans from the Lower Clayton Limestone Unit of the Midway Group (Paleocene) near Malvern, Arkansas, USA, with comments on the K/Pg boundary

Abstract

The Lower Clayton Limestone Unit (LCLU) of the Midway Group (Paleocene) near Malvern, Arkansas, USA contains an assemblage of chondrichthyans recently exposed by excavation for highway stabilization. Chondrichthyan teeth in this assemblage belong to at least 12 taxa including: Ginglymostoma subafricanum, Carcharias cf. whitei, Carcharias sp., Odontaspis winkleri, Palaeohypotodus rutori, Palaeogaleus vincenti, Dasyatis cf. hexagonalis, Dasyatis sp., Hypolophites sp., Myliobatis sp., Rhinoptera sp., and an indeterminate chimaerid. Locally, these chondrichthyans occur within a stratigraphic section directly above the Cretaceous–Paleogene (K/Pg) boundary that also contains chondrichthyans. This occurrence is uncommon in the global fossil record and provides an opportunity to (1) assess chondrichthyan diversity across the K/Pg boundary in the Malvern region and Gulf Coastal Plain of southwestern Arkansas and (2) evaluate the timing of marginal to shallow marine chondrichthyan faunal turnover and extinction at a proximal location ≈ 1500 km from the Chicxulub, Mexico, K/Pg impact site. Observed patterns within this K/Pg stratigraphic section indicate that changes in chondrichthyan assemblages are primarily the result of sea-level cyclicity and habitat losses that occurred across several million years.