WINNERS AND LOSERS: VERTEBRATE FAUNAL SUCCESSION IN THE LATE CRETACEOUS- PALEOCENE INTERVAL OF NEW JERSEY

Interpretations of large scale evolutionary events such as mass extinctions depend upon our knowledge of the nature of the fossil record. Microstratigraphic and taphonomic sampling of fossil assemblages from the Campanian, Maastrichtiam, Danian and Thanetian stages in the New Jersey coastal plain deposits reveal victims and survivors of the K/T boundary mass extinction in this region. Among chondrichthyans, mitsukurinids and chimaerids migrated to offshore environments by the early Paleocene. Large lamnid sharks appear by the Thanetian with the radiation of Paleocarcharodon and Otodus. Smaller shark teeth are common throughout this interval. Some shark tooth concentrations may represent secondary reworkings of teeth originally shed during mating seasons at breeding sites. Bony fishes were also affected at the K/T boundary, with the disappearance of typical Cretaceous forms such as Xiphactinus and Enchodus. Sea turtles and softshell turtles experience some significant reductions in diversity across the K/T datum. Only one taxon (Osteopygis) out of thirteen species present in the Late Cretaceous continues upward above the basal Hornerstown Formation; loses include members of the pleurodires, toxochelyids, protostegids, and adocids. Crocodilians replace mosasaurs as the dominant marine predators after the K/T event. In Late Cretaceous marine deposits, crocodilian remains are relatively rare, but are very common in estuarine environments. Mosasaurs tend to dominate near-shore and offshore marine deposits until late in the Maastrichtian. Crocodile remains increase in abundance in the marine realm in the Paleocene Hornerstown Formation. Plesiosaurs also persist into the Maastrichtian, but are not nearly as common as mosasaurs. Dinosaur remains are found in seven Upper Cretaceous formations, and reach their peak abundance and diversity in the Campanian; the youngest forms are Late Maastrichtian partial skeletons found in the Navesink/New Egypt facies. From what little evidence available for Paleocene terrestrial forms, it would appear that large snakes and crocodilians replaced dinosaurs as major reptilian predators. Crocodilian expansion in the Paleocene may have been the result of their ability to exploit diverse food resources in a wide variety of environments, including terrestrial, freshwater, estuarine, and marine habitats.