BRACHIOPOD ECOLOGY DURING THE LATE PALEOZOIC ICE AGE

The late Paleozoic ice age (LPIA) has much work written on it (e.g., Fielding et al. 2008 Geological Society of America Bull. XX). We add to this knowledge with our study of brachiopod ecology. In our study we used Relative Abundance Distributions (RADs) to distinguish assemblages suggesting simple division of resources (e.g., Geometric or Log-Series) from assemblages suggesting ecosystems structured by more complex interactions (e.g., Zipf and Lognormal). We used data from the Nebraska State Museum and PBDB data. Our goal is to see if changes in brachiopod ecology can be detected in the timescale of the LPIA.

Results suggest that models jump between simple and complex models during the transition between glaciation periods. The average temperature during these intervals plays the most correlated role (e.g., Isabel P. Montañez et al., 2007, Science315,87-91). All intervals of complex dominated ecology (Zipf and Lognormal) are times of warming (295ma-287ma, and 282ma–280ma.). Data from Oman and the north American midcontinent both had ratios around 4 to 1 complex vs simple (294ma-297ma). Eastern Australia had a ratio of 14 to 0 complex vs simple(281ma-282ma). During periods of stagnation or active cooling (287ma-284ma, and 283ma-280ma) we see that brachiopod ecology changes to a 1 to 1 complex vs simple ratio. This occurs in eastern Australia (281ma-282ma) and the north American midcontinent(285ma-284ma).

The result of this study is that brachiopod ecological structures become more complex during warming. The implications of this are that previously hard to date formations of this time could be better dated in terms of what time of glaciation they are in. This also could allow for geologists working at this time to better constrain the ice ages of different areas. And paleoecologists using brachiopods of this time should frame their understanding of ecological structures around these glaciations as they effect all communities worldwide.