Professor, Department of Earth and Environmental Sciences
Contact
385-08 John T. Tate Hall
116 Church Street Se
Minneapolis, MN 55455
Affiliations
Professor, Department of Earth and Environmental Sciences
My research has three broad focuses. The first is using stable isotope measurements of biogenic and sedimentary materials to answer questions in paleobiology and paleoclimatology. A selection of planned and on-going stable isotope projects include: tracking changes in North American deer ecology from the Late Pleistocene to the Recent using carbon, oxygen, and nitrogen isotope measurements of teeth and bones; studying the ecology of Late Pleistocene North American mammoths and mastodons and Eurasian mammoths, including the latest surviving population from Wrangel Island north of Siberia, using carbon, oxygen, and nitrogen isotope measurements of tusks and teeth (in collaboration with Dan Fisher at the University of Michigan); and tracking the expansion of grasslands and concurrent changes in ecology among Miocene mammals of the Great Plains using carbon and oxygen isotope measurements of soil carbonate nodules and herbivore teeth. Future work may include development of compound-specific techniques for application to paleontological material.
A second focus is exploring the role of stratigraphic data in phylogenetic analysis through the use of computer simulated evolutionary histories. Stratocladistics, which incorporates stratigraphic range data into the logic of traditional cladistic analysis, is still a controversial method. However, stratocladistic analysis of simulated character data sets and stratigraphic ranges has been shown to lead to more accurate estimates of simulated phylogenies than traditional cladistic analysis of simulated character data sets alone (see Fox et al., 1999). On-going simulation studies focus on the sensitivity of both stratocladistics and cladistics to tree shape, variable preservation probability, variable character evolution probabilities through time, taxon sampling, stratigraphic resolution, and missing data.
The third focus of my research (in collaboration with Catherine Badgley at the University of Michigan) is on the ecological biogeography of modern North American mammals in relation to the spatial variation in climate. The frequency of modern mammal species in body size and dietary categories shows striking correlations with climatic variables and, in parts of the continent formerly covered by the Laurentide (continental) ice sheet, the time since deglaciation. Continuing work on the biogeography of mammals will include development of transfer functions to estimate paleoclimatic variables from the ecological characteristics of fossil mammalian faunas and comparisons between the modern mammalian faunas of North American and Africa, continents with quite different faunal and climatic histories over the last several million years.
PhD, 1999, University of Michigan