Abstract This paper presents breakthroughs in the chronostratigraphy of the heretofore poorly constrained Yellow Cat Member of the Cedar Mountain Formation, which is an important record of terrestrial environments, ecosystems and global change in the ancient North American Cordilleran foreland. Zircon populations from 10 stratigraphic horizons in the Yellow Cat Member yield youngest single-grain ages ranging from 142.5 ± 2.7 to 133.7 ± 2.7 Ma (Berriasian–late Valanginian); those from one mudstone palaeosol yield a robust Concordia Age of 136.3 ± 1.3 (Valanginian). Additionally, a new palynoflora – one of a few to be published from the Cedar Mountain Formation – is assigned to the middle Berriasian to early Hauterivian stages, based on the presence of Foraminisporis wonthaggiensis and Trilobosporites sp. cf. T. canadensis , and the absence of F . asymmetricus , Appendicisporites spp. and angiosperms. Furthermore, these chronostratigraphic data allow us to interpret part of the so-called ‘Weissert Event’ C-isotope excursion (Valanginian) in a new C-isotope profile through a palaeosol-bearing alluvial succession in the Yellow Cat Member. This research extends a firm understanding of the formation further back into the Early Cretaceous than was the case previously (except for ostracod biostratigraphy) and sets the stage for future advancements.

Abstract The Lagerstätte at Ashfall Fossil Beds—the result of supervolcanic eruption—preserves a mass-death assemblage of articulated skeletons of reptiles, birds, and mammals in a 3-m-thick pure volcanic ash near the base of the Cap Rock Member of the Ash Hollow Formation in Antelope County, Nebraska. The ash originated from the Bruneau-Jarbidge caldera in southwest Idaho, some 1600 km away, and it is geochemically matched with the Ibex Hollow tuff (11.93 Ma). Ashfall is a critical Clarendonian North American Land Mammal Age locality. More than 20 taxa—predominantly medium- and large-sized ungulates preserved in three dimensions—are buried in a late Miocene paleodepression (waterhole) filled with tephra reworked from the landscape by wind and water. Smaller taxa, such as birds, turtles, and moschids, died shortly after the pyroclastic airfall event and their remains are preserved in the basal ash. Remains from the medium-sized ungulates (equids and camelids) are separated from the underlying smaller skeletons by several centimeters of ash, indicating that these animals died at a slightly later time. In turn, more than 100 mostly intact skeletons of the barrel-bodied rhinoceros, Teleoceras major , overlie the remains of the medium-sized taxa. Pathologic bone on the limbs and skulls of the horses, camels, and rhinos suggests short-term survival and slow death several weeks or months after the pyroclastic airfall event. Exquisite preservation in an information-rich context allows aspects of the behavior, social structure, intraspecific variability, and pathology of extinct species to be reconstructed.