2000 GSA Annual Meeting -- Reno, Nevada
2000 GSA Annual Meeting -- Reno, Nevada
Author(s): REES, Peter McA. (rees@plates.uchicago.edu), McGOWAN, Alistair J., and ZIEGLER, Alfred M., Dept. of Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637
Keywords: paleobotany, paleogeography, paleoclimate, Permo-Triassic, extinctions
There are two extreme approaches to compiling and analyzing fossil data for elucidating patterns of evolution and extinction: (1) treating the entire global fossil record for a given time interval as a single parameter, and (2) making detailed studies of a particular region and extrapolating the findings to assume similar conditions for the whole world. Although the Permo-Triassic mass extinction has been well documented among marine taxa and terrestrial vertebrates, the response of the terrestrial flora has been less closely examined. To address the questions of the rapidity and severity of the extinction, a generic level floral database was compiled and analyzed. The database is global in coverage, comprising Permian and Triassic localities, and 10144 occurrences of 819 genera. Analysis of this dataset reveals that there was a sharp decline in generic diversity at the close of the Permian, followed by an Early Triassic recovery period of low diversity, after which diversity increased to pre-boundary levels. Genera in the database were also assigned to 12 coarser morphological categories (morphocats). The analysis was rerun to investigate how the diversity patterns of the different morphocats varied through the Permian and Triassic. Our preliminary results show that certain morphocats (e.g., pteridosperms, cordaites, and glossopterids) which had been major components of Permian vegetation underwent a marked decline towards the end of the period. Conversely others (e.g., ferns, cycads, and ginkgophytes) became more abundant in the Triassic. The taxonomic diversity patterns are informative as measures of how severely the terrestrial flora was affected by the Permo-Triassic event. However, such patterns say little about the process(es) driving the mass extinction. So we also studied the geographic distributions of the morphocats to determine the extent to which latitudinal and climatic factors controlled spatial/temporal variations in the composition and diversity of floral assemblages. Such an approach enables a more complete understanding of evolutionary and extinction processes through time by viewing them from a geographical and climate change perspective.
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