Mass Extinctions’ Selectivity on the Diversity of Marine Modes of Life

Abstract:

A mass extinction is defined by a substantial increase in extinction rates, resulting in a loss of biological and ecological diversity. However, a mass extinction’s taxonomic severity does not always correlate with its ecological severity (Droser et al. 2009). Using the fossil record, one can reconstruct the relationships between extinct biota and past environments through extrapolating evidence of an organism’s feeding, tiering, and motility based on its functional morphology and analogies with its extant relatives. We used Bush, Bambach, and Daly’s conceptual model of marine ecospace to study marine modes of life. We looked at the number of different ecological modes over time, and observed that this curve roughly parallels Sepkoski’s generic diversity over time in that the number of ecological modes generally increases over time. Then we measured the selectivity of each mass extinction in log-odds using logistic regression. Here we compiled a “heat map” of the selectivity of 5 major mass extinctions based on the life mode of each marine genus in our dataset. Additionally, we looked at the standard deviation of the log-odds of extinction, which shows how uniform the selectivity of the mass extinction is across all life modes (i.e. a small standard deviation points to a more uniform selectivity among life modes). Ecological diversity was impacted by the mass extinctions: the end-Permian (Changhsingian) mass extinction had less variation in log-odds of extinction, whereas the other mass extinctions had a greater range of standard deviation of the log-odds of extinction. Three of the five mass extinctions (Famennian, Rhaetian, and Maastrichtian) were more ecologically selective than the others (Hirnantian and Changhsingian), which indicate that these two had factors that affected most marine life modes equally. In conclusion, not all mass extinctions had the same ecological effect.

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