Background
Following the extinction of the dinosaurs at the end of the Cretaceous period, the Paleogene, which constitutes the first part of the Cenozoic period (aka "Age of Mammals"), consisted of 40 million years of dramatic and dynamic changes in the earth's climate and ecological communities. In contrast to the wholesale reorganization of the continental land masses that had occurred repeatedly throughout earth's history, by the beginning of the Paleogene the general configuration of the continents had begun to look fairly modern. Nonetheless, important changes in the location and interconnection of seaways, raising of major mountain ranges, and significant episodes of volcanism continued to occur throughout the Paleogene. These events, as well as natural ticks and oscillations in the operation of the earth's chemical and climate systems, were responsible for a number of discrete and continuous changes in global climate during the Paleogene. The continued work of paleoclimatologists is revealing a number of rapid episodes of Paleogene global warming, as well as million-year shifts that linked early Paleogene times, during which tropical warmth spread from pole to pole, and the late Paleogene, when near-modern seasonal climates were established and the accumulation of our modern polar ice caps began.
During this same interval of time, terrestrial mammals were evolving and diversifying from the small, rodent-like forms that had co-existed with the dinosaurs to a more diverse assemblage of forms and body sizes that, by the end of the Paleogene, included representatives of all the major, modern groups. For more than 100 years, paleontologists have recognized that many of these changes do not show up in the fossil record as gradual changes in morphology or community composition through time, but rather as evolutionary "events" featuring the simultaneous appearance of several new taxa. In many cases, it appears that these events are not local, but regional or global in nature, with identical or similar species first appearing in rocks of similar age at many locations worldwide. These events constitute the mechanism by which modern mammalian communities evolved, and their apparently discrete and global nature suggests that some external, global factor may have set the pace and nature of mammalian evolution during the early Paleogene.
Together with collaborators at the University of California, University of New Hampshire, American Museum, Louisiana State University, and Chinese Academy of Sciences, I am studying the pattern and timing of these events. By studying fossil sites worldwide using modern methods of geochronology, we are attempting to answer fundamental questions about evolutionary events in the early Paleogene mammal record, including 1) are changes in mammalian fauna compositions truly synchronous at a global scale, 2) if not, is the modernization of mammal faunas during the Paleogene being driven or paced by the origination of new groups in one or more unique regions of the globe, or 3) if so, what is driving the synchronous appearance of new groups in the fossil mammal record, and are these events related to known, episodes of global climatic and environmental change during the early Paleogene.
Project Status
Coming soon...