Collaborative Research: Recovery of Vertebrate Faunas after the K/T Boundary, Tullock Formation, Eastern Montana

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Swisher 9505766 The first objective of the project will be to refine the stratigraphic correlations of over 100 Early Paleocene vertebrate fossil localities in eastern Montana already discovered and sampled. Here widespread coal/lignite beds bracketing many fossil localities contain interbeds of sanidine-bearing bentonites excellent for 40Ar/39Ar dating with a potential resolution of 0.1%. Preliminary studies using criteria described by Swisher et al. (1993) indicate that high resolution 40Ar/39Ar age determinations, in conjunction with microprobe analysis of interbedded volcanics and detailed magnetostratigraphies, are capable of providing precise identifications of individual coal/lignite beds throughout the area. The resulting chronology will provide the basis for testing hypotheses of correlation of Early Paleocene local faunas from Montana with those known from New Mexico, Alberta, and intervening areas. Interpretations of the processes and rates of biotic recovery after mass extinctions involve competing hypotheses concerning the relative significance of local survival, cladogenic diversification, and immigration from refuge areas. Our preliminary results show the Early Paleocene, Puercan North American Land Mammal Age (NALMA), as recognized in eastern Montana, had a duration of ca. 1 Ma. Puercan and early Torrejonian NALMA (Middle Paleocene) local faunas can be ordered in at least four temporal units. Analysis of the systematic relationships of the mammals and other vertebrates in these stratigraphically well-controlled local faunas will provide the basis for much more refined tests of hypotheses concerning the evolutionary processes operative during the recovery of the terrestrial biota after the Cretaceous mass extinction than previously possible. Locality and systematic data will continue to be recorded in computer-based curatorial systems at the University of California Museum of Paleontology and will be readily available to the research community.