Edmontonian

Abstract: Latest Cretaceous (Maastrichtian) terrestrial vertebrates from western North America occur in two faunal provinces. The Triceratops fauna is found in Canada, Montana, and Wyoming; and the Alamosaurus fauna occurs in Utah, New Mexico, and Texas. Although the two faunas are thought to have been contemporaneous, only the Northern Province contains intercalated volcanic units that have been isotopically dated. The first isotopic age from within the southern province is presented. A single outcrop of distal tuff within the Upper Cretaceous Javelina Formation in northern Big Bend National Park, Texas, contains monazite with a U-Pb age of 69.0 ± 0.9 Ma (2 sigma). The age is from a 207Pb/204Pb vs. 235U/204Pb isochron, an approach chosen to avoid the effects of 230Th-derived excess 206Pb. The age falls within the boundary interval between the poorly calibrated Edmontonian and Lancian North American Land Mammal Ages. The tuff bed occurs approximately in the middle of the fluvio-lacustrine Javelina Formatio...

Abstract: Few latest Cretaceous mammalian faunas are known from the central part of the Western Interior of North America. Here we report a collection of 28 mammalian fossils (23 isolated teeth, 5 dentulous jaw fragments) from five Upper Cretaceous localities in and around the Pawnee National Grassland (Weld County) in the Cheyenne Basin, northeastern Colorado. At least 10 taxa are represented, including two new multituberculates, a neoplagiaulacid Parikimys carpenteri and a ?cimolomyid Paressonodon nelsoni, which has greatest affinities to Essonodon browni. The new specimens combine with a previously reported sample for a total of 40 mammalian specimens from the area. Using a subsurface model based on geophysical log data, we stratigraphically arranged the fossil localities relative to the top of the Fox Hills Sandstone. Our stratigraphically lowest site is 95 m above the datum and likely near the top of the Laramie Formation. Presence of Meniscoessus collomensis at this site implies a late ‘Edmontonian’ ...

Abstract: The Judithian (Late Cretaceous) stagodontid marsupial Eodelphis Matthew is known from two closely related species, E. cutleri and E. browni, which differ in size and proportions of P3 and robustness of the molars. P1 is shown to be two-rooted in both species and not only in E. cutleri, as previously believed. Known upper molars of Eodelphis lack a stylar cusp D, indicating that neither E. cutleri nor E. browni can be a part of the direct (species) ancestry of the later Cretaceous stagodontid Didelphodon. Evolution of the Stagodontidae probably included derivation of an E. cutleri-like radicle having robust premolars and molars from E. browni-like ancestors, present in North America by Aquilan time; development by the Edmontonian of specialized crushing premolars in primitive species of Didelphodon, descended from ancestors that were similar to E. cutleri in size but had a prominent stylar cusp D on the upper molars; and subsequent increase in size leading to Lancian D. vorax and D. padanicus. Contrary to ...

Abstract: The St. Mary River Formation (Fm) crops out in restricted parts of southwestern Alberta and northwestern Montana. Mammals are poorly known from the formation, but material collected from Alberta has played a role in recognizing an ‘Edmontonian’ Land Mammal Age between the better sampled Judithian (∼79–74 Ma) and Lancian (∼67–65 Ma) land mammal ages. New and well-preserved multituberculate and metatherian material collected from a single locality in the lower third of the St. Mary River Fm of Montana adds complexity to the interpretation of a discrete ‘Edmontonian’ Land Mammal Age. We report here three taxa of multituberculates (Paracimexomys propriscus, sp. nov., Nidimys occultus, gen. et sp. nov., and a primitive ptilodontoid of comparable size to the smallest species of Mesodma Jepsen, 1940, and Cimexomys Sloan and Van Valen, 1965) and two metatherian taxa (Leptalestes toevsi, sp. nov., and Turgidodon russelli). Paracimexomys propriscus and Turgidodon russelli are probably conspecific with Judi...