By the close of the Paleozoic, the earth`s continents were amalgamated into the supercontinent Pangaea. By the end of the Triassic, Pangaea was beginning to break apart once more through rifting and drifting that ultimately led to the formation of the Atlantic Ocean. This reconfiguration of the biosphere`s substrate had a profound influence on the evolution of life and global diversity. I have been involved in studying the formation of a tropical seaway that I named the Hispanic Corridor which during the course of the Early and Middle Jurassic linked the Tethyan Ocean to the eastern Pacific. My work suggests that the seaway initially acted as a filter allowing the selective dispersal of organisms. I am currently collaborating with a group of geologists in China attempting to improve our biogeographic database for a critically important region, the eastern portal of Tethys.
Biogeography and terrane displacement:
Western North America consists of a collage of terranes whose origins and accretion to the continent are still the subject of debate. Patterns of endemism and diversity in ammonites and other molluscs appear to correlate well with paleolatitude in most parts of the world but in Canada and the United States the patterns are disrupted along the terrane boundaries. Restoring this biogeographic jigsaw puzzle has allowed us to place constraints upon tectonic models of terrane history. For example, quantitative analyses of biogeographic data using Monte Carlo methods indicate that the three main terranes that now form western Canada were already in the northeast Pacific by the Early Jurassic. This has been of particular help in resolving the north vs. south hemisphere ambiguity that is inherent in paleomagnetic data.
Resolving Jurassic time:
Geological time is measured in two main ways, namely, using the irreversible phenomena of organic evolution (biochronology and relative time) and the decay of radiogenic isotopes (geochronology and absolute time). Calibration of the time scales based on these two approaches is quite poor for certain intervals of the Phanerozoic and yet the calibration is central to ordering, correlating and quantifying many geologically and biologically important events and processes. Consequently, the problem of resolving Jurassic time has been a central theme of my research. In collaboration with a large group of researchers, I have been a leader in establishing an ammonite zonation for North America calibrated with a U-Pb chronology. In addition I have been involved in calibrating time scales based on microfossils (single celled organisms) and other fossil groups with the time scale based on ammonite evolution. This results in a timescale of maximum utility which has given me the opportunity to work with large geological mapping parties and also to contribute to the exploration for oil and strata-bound mineral deposits.
The 60 million years of Jurassic time were punctuated by numerous extinction events, three of which were of exceptional magnitude. For example, the extinction event that we now use to delineate the boundary between the Triassic and Jurassic periods almost resulted in the extinction of the ammonites. Only one small connection survived this event but the subsequent radiation was dramatic and the group reestablished itself to flourish until the end of the Cretaceous when it went the way of the dinosaurs. In collaboration with others, I am trying to document this event in detail, look for possible causes and, most importantly, try to understand the dynamics of recovery. I am using computer models to study the refilling of 'ammonite morphospace'. By mathematically defining the entire morphological spectrum that the group occupied throughout its history, we can then explore the path taken from crisis to recovery. This is providing insights into evolution and functional constraints.
This pioneering and award-winning database is the infrastructure of my research program. Beginning on the UBC mainframe in the early eighties and with subsequent transfers to UNIX and finally a PC platform, this database is now state-of-the-art. Containing morphologic, stratigraphic and geographic data for many thousands of ammonite specimens, AMMON allows us to track morphologic change in species and communities through space and time. Through several interactive modules it is possible to select any stored image and directly retrieve quantitative data relating to shell geometry and sculpture.
Invertebrate Paleontology, Stratigraphy; Ph.D. (McMaster University)