| My goal in research is to understand the interaction between environmental change and biological evolution using fossils and the sedimentary rock record. How does environmental change influence local and global diversity and ecology? And conversely, how does ecological change affect the physical environment? I am focused primarily on finding answers to these questions on two timescales: 1) the timescale of catastrophic extinction events and their immediate aftermaths (up to a few million years); and 2) the timescale of geological periods and eras (tens to hundreds of millions of years). My research combines micro-scale work on the petrography and geochemistry of individual limestone samples and mineral phases with macro-scale work on the stratigraphy and paleontology of carbonate platforms. In addition to field and laboratory study, I also compile literature-based data and use theoretical models to help constrain interpretation of field-based data. |
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Current Research Areas
I. Recovery from the end-Permian mass extinction |
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One focus of my current research is field-based examination of biological evolution and environmental change associated with the end-Permian extinction and its aftermath. Extinction at the end of the Permian Period reduced global marine diversity at the species level by a factor of 10 over an interval shorter (and likely much shorter) than 500,000 years. The subsequent five million years are characterized by instability of the global carbon cycle and limited biological recovery. Carbon cycle stabilization early in the Middle Triassic coincides with accelerated biological recovery, suggesting an intimate link between biological evolution and carbon cycling. In collaboration with Daniel Lehrmann, Wei Jiayong, Demir Altiner, and Hiroyoshi Sano, I have been engaged in field studies of the Permian-Triassic boundary and Lower-Middle Triassic recovery interval in China, Turkey, and Japan to develop detailed carbon isotopic and fossil occurrence records across a range of environments and localities. The figure below illustrates the pattern and is taken from my recent publication with collaborators in Science magazine (Payne et al., 2004) based upon data from the Great Bank of Guizhou, in Guizhou Province, southern China.
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II. Evolution of body size |
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One pattern of particular interest across the end-Permian extinction is the loss of large species in many higher taxa, the best documented of which are gastropods. I am interested in several aspects of body size evolution. For example, what is the relationship between predation pressure and the evolution of body size in prey taxa? Growth to large size provides many organisms with substantial protection from predators. However, for many marine invertebrates it is not yet well known how the much the evolution of large size has been driven by predatory pressure. Another set of open questions is: What controls which taxa evolve toward large size and which do not? Is body size strongly conserved over long intervals of time – i.e., is it easy to evolve large species from small ancestors and vice versa, or does this only happen at times of low biodiversity? These questions can be explored by compiling size data from the published paleontological literature as well as by compiling size data from new collections and can be studied at local, regional, and global geographic scales. The figure to the right illustrates the largest gastropod species illustrated or described in the published literature through the Permian-Triassic interval from my recent paper in Paleobiology.
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III. The abundance of animals through geological time |
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Numerous paleontologists have suggested that the total abundance (or biomass) of animals has increased substantially over the course of the past 550 million years, perhaps driven by gradual or episodic increases in nutrient supply and food availability. Quantification of these changes has been difficult, however, as the concentration of fossils in a given locality or a given bed often largely reflects sedimentary and taphonomic processes rather than the density or abundance of organisms in the community that produced the shells. However, quantification of fossil abundance as a fraction of rock volume averaged over long temporal and spatial scales and compared across carefully controlled depositional environments may hold potential for quantifying short-term and long-term changes in fossil abundance. Recent work by Michal Kowalewski and Susan Kidwell, among others, has shown that the duration of time-averaging in brachiopods and bivalves (the most abundant fossils of Paleozoic and post-Paleozoic shallow marine strata) is quite similar, suggesting that increase in shell-bed thickness through time does not merely reflect changes in the duration of time-averaging. I have been working to quantify changes in fossil abundance across the end-Permian mass extinction as part of my field studies in south China, Turkey, and Japan, and have also been collaborating with Seth Finnegan to develop a theoretical framework to better understand the controls on long-term changes in animal abundance. |
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