My research involves using the fossil record to study macroevolutionary patterns and processes. A central part of my research involves reconstructing phylogenetic patterns in arthropods, especially trilobites. I am also interested in the role that earth history changes, such as tectonic changes and climatic changes, play in influencing evolution. For this reason a central part of my research involves paleobiogeography.

The Lieberman Lab

I have used phylogenetic biogeographic approaches to determine the relationship between earth history change and evolution and also to reconstruct the sequence of Paleozoic tectonic events. One of the time intervals my research has focused on is the Cambrian radiation: that key episode in the history of life when diverse, abundant animal remains appear in the fossil record. I have conducted phylogenetic analyses of the diverse olenellid trilobites and used these to study evolutionary and biogeographic patterns during the radiation.

Phylogenetic and biogeographic patterns suggest that the radiation of trilobites may have been underway in the late Neoproterozoic before the group becomes manifest in the fossil record; these patterns also suggest that the breakup of a supercontinent at the end of the Neoproterozoic had an important effect on the topology of the Cambrian radiation. I've also used probabilistic models to study how fast the rates of evolution were during this interval and the results suggest that rates of evolution were high at the time but not so high that new rules of evolution need to be invoked to explain the Cambrian radiation.

With support from the National Science Foundation we studied evolutionary and biogeographic patterns in a Middle Cambrian soft-bodied fauna from Utah. This work was conducted with my former post-doc, Jon Hendricks, and involves collaboration with Derek Briggs, Bob Gaines, and Mary Droser.  We have described new taxa from these localities and have also conducted phylogenetic analyses on a series of new arachnomorph taxa that have been recovered from these localities.  In addition we conducted biogeographic studies on these taxa using phylogenetic biogeographic analyses and Geographic Information Systems (GIS), the latter in conjunction with Alycia Stigall at Ohio University.  Finally, we documented beautifully preserved jellyfish from the Middle Cambrian of Utah.  These appear to represent modern crown groups, including modern orders, families, and in one case a genus.  This work has also been made possible through the generous contributions of specimens by the Gunther family, and Sue Halgedahl and Richard Jarrard, along with the insight and assistance of Richard Robison.

I am very much interested in paleobiogeographic studies and this has formed an important component of my research. This not only includes my research described above under the heading of the Cambrian radiation but various other theoretical and practical applications. Much of this research has involved phylogenetic approaches.

This research has also included applying Geographic Information Systems (GIS) and Ecological Niche Modeling (ENM) to study biogeographic patterns in deep time using the fossil record. Some of this work was done in conjunction with my former student Alycia Stigall, who is now an associate professor at Ohio University, and involved exploring ecology and evolution during the Late Devonian biodiversity crisis. Other research with her and my former post-doc Jon Hendricks involving a GIS based analysis of paleobiogeographic and evolutionary patterns in Cambrian Burgess Shale type faunas is provided above under the heading of research on the Cambrian radiation.

My lab has also been very interested in using GIS to explore the role that competition plays in influencing macroevolution. My current student Cori Myers and I conducted a GIS based analysis of the charismatic marine vertebrate fauna of the Cretaceous Western Interior Seaway. Our results suggest that in the Cretaceous, and perhaps in general at the grand scale of the history of life, environmental factors played a much more prominent role in structuring geographic distributions, and causing extinction, than interspecific competition. We are continuing to do ENM based work on this fascinating time period.

In collaboration with Adrian Melott and other scientists, and with support from NASA, we have been conducting research investigating the nature of the late Ordovician mass extinction and the extent to which it may have been precipitated by a Gamma Ray Burst. This research is described more fully at: http://kusmos.phsx.ku.edu/~melott/Astrobiology.htm

NewScientist

As part of my research interests in macroevolution and biogeography, one of the topics I have considered is the evidence that at the large scale physical factors play a fundamental role in influencing macroevolution. This has included investigating the evidence that there is a fundamental connection between carbon dioxide levels and rates of evolution and extinction; this work was conducted in collaboration with Bob Goldstein and my former student, Jim Cornette; we found strong evidence that carbon dioxide levels and rates of macroevolution are significantly coupled. In addition, in work led by Jim Cornette, I investigated the extent to which the history of Phanerozoic diversity can be modeled as a random walk; we found strong evidence that except for the last 75 million years life largely follows a trajectory indistinguishable from a random walk. This does not mean that the history of diversity over the last 520 million years is random, and instead it may be that diversity is largely tracking environmental variables that themselves are following a random walk pattern. Most recently, and associated with my work in the area of astrobiology described above, I have been collaborating with Adrian Melott to consider the evidence that there are large scale cycles in biodiversity, possibly associated with astrophysical phenomena.

Information on various trilobite species, especially emphasizing cheirurids but including many other clades, is available at the link above. This includes geographic distributions, phylogenetic patterns, and photographs.

We have been funded by NSF, through their RevSys program in Systematic Biology, to investigate phylogenetic patterns in a diverse clade of phacopid trilobites, the cheirurids. The other PI on the grant is Jonathan Adrain at the University of Iowa. We are using the phylogenies to produce a stable, modern classification for the group, and also to understand biogeographic patterns and macroevolution in this major invertebrate clade. This includes a consideration of patterns of speciation and extinction during a key episode in the history of life, the Late Ordovician mass extinction. I am working closely with Ph.D. students Curtis Congreve and Wes Gapp. We have produced a phylogenetic hypothesis for the Deiphonine trilobites, a subfamily of Cheiruridae and conducted a biogeographic analysis on the group. This work has been published in the Journal of Paleontology. We have also produced a phylogenetic hypothesis for the Sphaerexochinae. We have also investigated phylogenetic patterns in a closely related group of trilobites, the Homalonotidae. These have a different life history strategy than many cheirurids and also occupy different environments. Thus they provide an excellent point of comparison to consider macroevolutionary patterns and processes and how these may vary among trilobite groups. Finally, with Francine Abe, who recently completed her Ph.D. with honors, I have been investigating phylogenetic, biogeographic, morphometric, and macroevolutionary patterns and processes in another group of phacopid trilobites, the calmoniids. Patterns in these suggest that geological and geographic complexity plays an important role in spurring evolutionary radiations.