![]() This research may have implications for understanding evolutionary and ecological processes, like adaptive radiations and recovery from mass extinctions. The results suggest that dental morphological diversification of placental mammals lagged several hundred thousand years behind taxonomic diversification, which immediately followed the K-T boundary (Wilson 2004, in prep.). I have also estimated changes in body size in these paleocommunities. Specifically, I have applied geometric morphometrics to therian molars and multituberculate fourth premolars to quantify changes in the dental morphological disparity and morphospace occupation of mammal paleocommunities across the K-T boundary in the Hell Creek study system (Wilson 2003, 2004). I am tracking morphological patterns of mammal paleocommunities across the K-T boundary to infer the pattern and timing of ecological expansion in placental mammals after the K-T boundary. The predicted pattern of increasing species richness of placentals has been broadly documented (e.g., Stucky 1990, Alroy 1999), but the pattern of the morphological diversification expected from the ecological diversification has not been directly quantified.Īn upper molar of the metatherian Glasbius with homologous landmarks. It has long been held that following the K-T extinction of non-avian dinosaurs, placental mammals rapidly invaded a wide array of ecological niches via in situ evolution and immigration. Paleocene ecological expansion of placentals Future work will improve the temporal resolution of the chrono-stratigraphic framework, develop a local climate signal, improve the density of fossil sampling, incorporate other fossil taxa (plants, molluscs), and draw comparisons with other study areas.Ĭollaborators: W.A. Whereas the results are consistent with a sudden exinction from an extra-terrestrial impact non-linear response to long-term causes or multiple short-term causes cannot be rejected. Dramatic changes in mammal and turtle paleocommunities occur within the last 100 thousand years of the Cretaceous. Results show no evidence of long-term changes in paleocommunities leading up to the K-T boundary, although some changes in relative abundances, taxonomic composition, and body sizes likely reflect normal responses to background levels of climate change. Changes in mammal, turtle, and amphibian paleo-communities leading up to the K-T boundary have been compared to published floral and paleoclimatic data from the same region. 2003).įossil localities have been integrated into a temporal framework based on stratigraphic position. 2007) and southwestern North Dakota (plants & temperature: Wilf et al. Data are from northeastern Montana (mammals: Wilson 2005 turtles: Hutchison et al. It includes vertebrate microfossils collected by our field crews over the past 10 years, and those amassed during the 30+ years of collecting prior to my involvement (Archibald 1982, Clemens 2002, Wilson 2004, 2005, Clemens and Wilson 2009).Ĭhanges in taxonomic richness during the ~2 million years leading up to the K-T boundary. We have compiled a large fossil database ( PaleOasys) of latest Cretaceous and earliest Paleocene vertebrate faunas from the Hell Creek Formation and Tullock Member of the Fort Union Formation of northeastern Montana. The K-T boundary section in northeastern Montana is a standard for examining patterns in the terrestrial realm, but few studies have examined the biotic changes at ecologically relevant spatial and temporal scales leading up to and across the K-T boundary. Substantial evidence supports an extra-terrestrial impact at the K-T boundary, but the causes, timing, and extent of the associated mass extinction remain unclear. Badland exposures of the Hell Creek Formation in northeastern Montana.
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