NEW DISCOVERIES AND DATA FROM THE CRETACEOUS-PALEOGENE BOUNDARY SEQUENCE IN THE NORTHERN ATLANTIC COASTAL PLAIN: A SUMMARY OF 21ST CENTURY RESEARCH

Investigations into the Cretaceous – Paleogene (K /Pg) boundary stratigraphic sequence of the northeastern United States have increased and intensified since the beginning of the twenty-first century. The major faunal changes involved in the K/Pg mass extinction have been constrained by geochemical and micropaleontological studies as a result of a program of drill coring the K/Pg boundary in New Jersey by Rutgers University Department of Earth and Planetary Sciences. The resulting data has lent credence to evidence for an iridium excursion located in or near the basal Hornerstown Formation. Several major concentration of fossils are associated with this formation or are just below it, providing a record of the paleoecological and faunal transitions involved in the mass extinction event. Despite a long history of collecting from these beds, new discoveries and data continue to provide a framework for interpreting the paleontological record of this interval (Miller et al., 2010; Gallagher et al., 2012).

New discoveries include the naming of a new small crocodylian, Borealosuchus threensis, from the Inversand Pit at Sewell, NJ (Broschu et al., 2012), and the recent report of the first record of the small duraphagous mosasaur Carinodens belgicus, previously known only from Old World records, from the Severn Formation of late Maastrichtian age in Maryland (Mulder et al., 2013). Additionally new records of Paleocene shark occurrences help explicate the early evolution of lamnid sharks in the Paleocene. Older 19^th century fossil collections from the once-extensive marl mining industry can now be set within the geochemical, micropaleontological and taphonomic context of modern stratigraphic terminology. Collapse of the productive Mesozoic plankton assemblages at the K/Pg led to extinctions that reverberated through the K/Pg trophic structure, affecting organisms up to the apical predators, the mosasaurs. When mosasaurs disappeared, a trophic cascade of smaller predators became abundant, including crocodylians and lamnid sharks. Archaeocetes that originated in the Neogene are Elvis taxa, imitating the external morphology of mosasaurs and taking over the niche of large apical marine predator.