For one thing, because they were so broad and relatively flat, drops in sea level should have had more drastic effects on epicontinental seas because large regions could have been drained entirely in a short amount of time. On the other hand, the sluggish circulation associated with epicontinental seas may have inhibited the spread of the waterborne effects of such events as volcanic eruptions and asteroid impacts, which may have been more effective killing agents in open oceans.
In their research, Miller and Foote assembled data on the occurrences of marine genera from the Paleobiology Database (http://paleodb.org) for the Permian through Cretaceous periods, during which both major settings are well preserved in the fossil record. From that, they determined whether these occurrences were from epicontinental seas or open-ocean-facing settings, and they then compared extinction and origination rates in the two settings throughout the interval.
"This was a particularly juicy interval to work with, because it includes three of The Big Five, including the Late Permian mass extinction, the largest extinction in the history of marine animal life, and the end-Cretaceous event, which also did in the dinosaurs and has been associated previously with the impact of a big comet or asteroid," Miller says.
Miller and Foote found that, while extinction rates in the two settings did not generally differ from one another during "background" times between mass extinctions, there was a strikingly different pattern for the mass extinctions: extinctions rates during mass extinctions were significantly higher in open-ocean-facing settings than in epicontinental seas, indicating that open-ocean settings were more susceptible to t
|Contact: Wendy Beckman|
University of Cincinnati