Vertebrate Paleontology of the Cretaceous/Tertiary Transition of Big Bend National Park, Texas (Lancian, Puercan, Mammalia, Dinosauria, Paleomagnetism).

Screen washing of material from new and previously known fossil localities in Late Cretaceous/early Tertiary deposits in Big Bend National Park, Texas resulted in establishing the presence of sediments of early Paleocene (Puercan) age in the upper Javelina Member of the Tornillo Formation. Deposition of the Tornillo Formation was probably continuous across the Cretaceous/Tertiary boundary. Preliminary paleomagnetic zonation indicates that the highest occurrence of dinosaurs at Bid Bend is in a reversed interval. At least part of the early mafic stage of Laramide magmatism in the Big Bend area was post-early Paleocene in age. A new Maastrichtian locality in the upper Aguja Formation yielded a diverse fauna including the first ankylosaurid dinosaur and the first Cretaceous mammals known from Big Bend. A new genus of cimolomyid multituberculate was recovered from this locality. Four localities in the upper Javelina Member of the Tornillo Formation that contain Puercan mammals are described. Puercan faunas include a new ray, the earliest known scolecophidian snake, a new genus of mioclaenid condylarth, and a new species of Ptilodus, Stygimys Viridomys, and Protictis. A new multituberculate family is defined. Mixodectes malaris and Palaechthon nacimienti are present in deposits of late Puercan age at Big Band. A new ray was found at localities of Tiffanian age. Re-examination of fossils from TMM locality 40147 in the lower Black Peaks Member of the Tornillo Formation shows that the locality is Torrejonian in age. TMM locality 41274 is early Tiffanian in age