Susan M. Kidwell William Rainey Harper Professor, Department of the Geophysical Sciences, Committee on Evolutionary Biology, and the College Fellow, American Academy of Arts and Sciences Department of the Geophysical Sciences 5734 S. Ellis Ave. HGS 261 Chicago, IL 60637 USA Phone: 773/702-3008 E-mail: skidwell@uchicago.edu Publications Courses Advisees

My primary research interest is in quantifying and understanding the archival quality of the sedimentary geologic record, with the dual aims of (1) acquiring insights into the dynamics of record accumulation and (2) developing protocols, preferably quantitative, for the interpretation of geohistorical records. How and why does grain supply and removal vary in time and space within local basins, across tectonic and latitudinal/ climatic/ productivity gradients, and over geologic time? What are net accrual rates and their determinants? What are the consequences for the quality of environmental and biological information captured by sedimentary deposits? What are the tangible signatures of records having low resolution or biased information?

My research was initially entirely stratigraphic and field-based, focusing on the recognition, analysis and genesis of unconformities and condensed intervals. I was particularly interested in the association of skeletal material with such features, both as a means of reconstructing the duration and dynamics of intervals of low/zero sediment accumulation and erosion (as an aid to basin analysis), and as a source of insights into bias of paleontologic information. This launched a series of comparative studies of basins in various tectonic, nutrient, and climatic/latitudinal settings. However, stratigraphic patterns of skeletal preservation and concentration, including secular trends through the Phanerozoic, raised a series of hypotheses best tested in the lab and in modern environments. Actualistic studies thus started to become an important component of my research and student-advising effort ~15 years ago, and now dominate my research program. Questions under investigation – using manipulative, time-lapse, and capture-recapture experiments, statistical evaluation of observational data, dating and other direct analysis of skeletal remains, and meta-analysis—include:

• How in fact do skeletal disintegration rates vary as a function of shell mineralogy and microstructure, animal bauplan, water oxygenation/temperature/microbial activity, sediment chemistry and mass properties, and along gradients of nutrients/organic-supply and seasonality (latitude)?
• What are maximum shell ages within surficial sediments (scales of time-averaging), what is the thickness-scale of mixed zones with age-homogeneous remains, and how do these vary among geologic settings and for different animal groups?
• Given the array of skeletal types input into systems, and the array of physical, chemical and biological agents acting on skeletal remains, what are per capita and per taxon capture rates during the initial stage of forming a sedimentary record, and what is the net compositional fidelity, spatial fidelity, and temporal resolution of skeletal death assemblages?

The top priority in my current research is meta-analysis of molluscan “live-dead” studies, using and further enlarging my digital database to quantify how well death assemblages from surficial sediments of modern seafloors capture the taxonomic composition, relative abundance, species richness, body-size distribution, etc of local living communities (3rd bullet above). Analysis of an initial set of 85 live-dead datasets, generated during a sabbatical in 2000, found high agreement in species rank-order and richness once sample-size and sample-processing issues were controlled for, and this has unleashed – for better or worse – paleobiologic interpretation of abundance patterns in marine fossil data. Fortunately, it has also inspired a new generation of live-dead studies and modeling efforts (both among former Chicago students and others) to test meta-analytic hypotheses of mesh-size effects, cumulative pooling of live-censuses, and relationships between rarity and shell-durability and the rapid fading of dead cohorts. I am currently in the process of freezing the database, now doubled in size, and am adding species-level meta-data on shell mineralogy and microstructure, body sizes, life-habits, etc. This will permit tests of intrinsic factors in live-dead agreement, tests of new metrics (evenness, trophic composition, etc), and tests in narrower environmental ranges (for example, I now have 37 open-shelf datasets rather than only 16, much improving statistical power). My current NSF grant supports student assistance with meta-data generation. It also supports a post-doc (Tom Rothfus) for a data- and sample-rescue effort in US coastal waters. Tom and I will be using 30 years of live survey data generated by municipal biologists in southern California, including ~a decade of semi-annual monitoring data near several wastewater outfalls, to test for cumulative live-dead agreement, taphonomic inertia in the face of local environmental changes, and scales of time-averaging in an area where improved insights into benthic community health has high societal value. We thus have both basic and applied research aims for this project.

A strong motivator of actualistic taphonomic research, both for me and for advisees working on their own projects, are the potential applications to conservation biology. That is, to what extent can we use data from skeletal death assemblages to complement or substitute for “live” data, especially in areas where biodiversity is still unknown or where human impacts on natural communities are underway or imminent? This would much simplify and possibly improve biodiversity inventories: dead skeletal material is abundant relative to live individuals, and samples are easier to transport and store for analysis by taxonomists off-site. Moreover, if we can quantify taphonomic inertia relative to environmental change and have confidence that their fidelity persists down-core, then death assemblages become a powerful means of establishing natural variability in communities and of distinguishing anthropogenic versus natural causes of recent community change. This new motivation to apply death assemblages to conservation and the evaluation of human legacies does not replace but simply supplements my interest in earth-science applications, and in fact I anticipate eventually shifting to basic research in “actuo-stratigraphy” and sedimentary modeling in order to resolve questions about the behavior of death assemblages below the surficial mixed zone.

October 19, 2005

Education:

• Ph.D., Yale University 1982