Mammals have an unusually dense and continuous fossil record, and are thus ideal for evolutionary studies. I am interested in understanding how evolution as a process acting on generation-to-generation scales of time yields the microevolutionary and macroevolutionary patterns we observe on longer historical and geological scales of time. Study of the evolutionary process and comparison of resulting patterns requires quantification of evolutionary change and comparison in terms of rate.
Field work with students in Wyoming is focused on bed-by-bed collecting of Paleocene and early Eocene vertebrates to provide detailed species-level evolutionary time series for quantification of evolutionary rates, and, simultaneously, a high-resolution stratigraphic record of the appearance of modern orders of mammals at the Paleocene-Eocene boundary (Perissodactyla, Primates, etc.). Our work has shown the appearance of several important modern orders to be synchronous and to coincide with an abrupt dwarfing event in mammals. In recent years we have been able to link the first appearances and dwarfing to a brief but important worldwide shift of carbon and oxygen isotopes and a rapid but short-lived event of global climate warming— the Paleocene-Eocene Thermal Maximum or PETM. In this instance, profound long-term higher-taxonomic faunal change resulted from a transient environmental perturbation affecting species over a broad geographic area.
Search for the origin of modern orders of mammals led to field work in the Paleocene and Eocene of South Asia, starting in the 1970s, which has yielded important new land-mammal faunas in Pakistan. Early whales (e.g., Pakicetus) were discovered there unexpectedly, which has diverted attention to middle and upper Eocene marine strata in Pakistan, Jordan, Egypt, and Tunisia. Field work in these Tethyan sediments has yielded important intermediate forms documenting the origin and early evolution of whales.
I remain interested in the origin of primates, the Eocene evolution of primates, and the origin of higher primates or Anthropoidea.
I teach an introductory minicourse on primate evolution (Geological Sciences 106) during the Fall or Winter terms, and a more advanced course on primate evolution (GS 438) or mammalian evolution (GS 439) during alternate Winter terms. In each, the primate and mammal fossil records provide an empirical basis for consideration of broader issues in the study of earth history and evolution. I also co-teach to a new Analytical Paleontology course (GS 510) in alternate years, and contribute regularly to our Friday noon Museum of Paleontology seminar on paleobiology and evolution (Fall and Winter terms: GS 536). Finally, supervision of undergraduate and graduate student research on mammals and evolution is an ongoing extension of classroom teaching.