Causes and consequences of extinction: Some Lessons from the Marine Fossil Record
Seth Finnegan, California Institute of Technology
Extinction is the ultimate fate of all species, and more than 99% of all species that have ever existed on Earth are now extinct. However, the fossil record tell us that extinction is not a random process -extinction risk is nonrandomly distributed across different groups of organisms, different environments, and different time intervals. The marine fossil record shows evidence of a long-term decline in extinction rates from the appearance of skeletonized animals (> 500 million years ago) to the present, but this trend in interrupted by mass extinctions -comparatively short intervals of very elevated extinction. Although it has periodically been suggested that all mass extinctions may have a common cause, a growing body of work demonstrates that this is unlikely -different events are associated with different types of environmental perturbations, often show idiosyncratic patterns of selective extinction, and may unfold over widely varying timescales. Some mass extinctions are characterized by apparent shifts in selective regime -traits that influence extinction risk during intervals of normal, or “background” extinction may not be important determinants of risk during a mass extinction, and previously unimportant traits may assume a new prominence. By depleting or even removing ecologically dominant incumbent groups, mass extinctions can precipitate wholesale reorganizations of ecosystem structure and facilitate the diversification of previously obscure groups. Although many interesting patterns have been documented, major questions about extinction mechanisms remain open for many events. I will discuss these and other issues in the context of my own work on patterns of extinction selectivity over the past 542 million years and, in particular, during the Late Ordovician mass extinction (ca. 444 million years ago).
Background Review Article:
Jablonski, David. Lessons from the past: Evolutionary impacts of mass extinctions.
Proceedings of the National Academy of Sciences of the United States of America, Vol. 98, No. 10. (May 2001), pp. 5393-5398.