Cephalopods from the Cretaceous-Paleogene (K-Pg) Boundary Interval on the Brazos River, Texas, and Extinction of the Ammonites

We report on new collections of cephalopods (ammonites and nautilids) from the Cretaceous-Paleogene (K-Pg) successions Corsicana Kincaid formations exposed along Brazos River in Falls County, Texas. An abundant fauna eight species comprising four genera ammonites is described Formation, including Discoscaphites mullinaxorum n. sp. The presence aptychi (probably lower jaws) Eubaculites, as well juvenile specimens, indicates a living population that experienced little postmortem drift. lytoceratid genus Gaudryceras also reported for first time area. Presence index taxon iris (Conrad, 1858) belongs to D. Range Zone, highest ammonite range zone North America. Correlation with existing microfossil data represents uppermost Maastrichtian, comparison published records further suggests this most diverse Zone yet Gulf Atlantic Coastal Plains Three are recorded basal units K-Pg event deposit at Brazos, which likely deposition immediate aftermath Chicxulub impact event. A single specimen nautilid Eutrephoceras Danian less than 300 kyr after boundary. These provide information differing fate these cephalopod groups during mass extinction add picture Maastrichtian faunas prior