Mass extinctions and the Signor-Lipps effect. When a collection of taxa (e.g., species of dinosaurs or ammonites) are killed off simultaneously in a mass extinction, their last occurrences in the fossil record may nonetheless give the impression of a gradual extinction, due to the incompleteness of the fossil record (the Signor-Lipps effect). I develop methods for testing whether a mass (sudden) extincton has occurred, and for estimating the position and duration of such an extinction. Part of this work is joint with
Charles Marshall at Harvard University and
Phil Everson at Swarthmore.
Evolutionary trends. Large-scale trends in the history of life (such as increase in
body size, a.k.a. "Cope's Rule") may be a result of driven
mechanisms (e.g., selection) or passive mechanisms (e.g., diffusion away
from a lower bound). Several tests have been developed to categorize
a trend as either driven or passive, but real trends are
likely to be a combination of both types.
I have developed a new method, the Analysis of Skewness, to quantify the extent to which a trend
is a combination of driven and passive trends. I am
also a member of the
NESCent working group on
body size macroevolution and macroecology. 
Macroevolution. Using statistical analysis and paleontological databases, I study large-scale questions about the history of life. For instance, are mass extinctions merely larger manifestations of processes responsible for background extinction,
or are they a fundamentally different phenomenon?
Or, how many kinds of dinosaurs ever lived, and were dinosaurs already declining before an impact at the end of the Cretaceous Period caused their ultimate extinction?
Part of this work is joint with
Richard Bambach and
Andrew Knoll at Harvard University,
and
Peter Dodson at the University of Pennsylvania.
Dynamics of extinction in food webs.
The end-Permian mass extinction was the most severe in the history of life, but its causes remain enigmatic.
With
Peter Roopnarine of the California Academy of Sciences and
Ken Angielczyk of the Field Museum,
I study the dynamics of extinction in terrestrial ecosystems during the Permian.
Using models of Permian food webs, we explore how the extinction of primary producers (e.g. green plants) could have led to the collapse of terrestrial ecosystems.
More information: Publications | Media coverage | Talks | Lab members and collaborators
Funding from the following sources is gratefully acknowledged:
National Science Foundation
American Chemical Society Petroleum Research Fund
National Evolutionary Synthesis Center
Woodrow Wilson National Fellowship Foundation
Christian R. and Mary F. Lindback Foundation
NASA Space Grant program
Swarthmore College Research Fund
Opportunities for students: I will be hiring two summer student researchers in summer 2008. Please email me if you are interested. Due to grant restrictions, eligibility is limited to Swarthmore students (or recent alums). The preferred prerequisite is Stat 61, but some combination of Stat 11, Stat 31, Bio 2, computer programming, or other experience may suffice as well. Learn more about projects and publications by previous students.
Links:
Paleontology links |
Statistics and Mathematics links
Other areas of interest:
I am interested in how to effectively visualize high-dimensional datasets
using graphical methods such as parallel axis plots and data image plots, and more generally
in principles of effective graphical representation and communication.
Address 
Last update: July 24, 2008