SEPM Society for Sedimentary Geology announces that Dr. Jere Lipps (University of California, Berkeley, CA) has been awarded the 2010 Moore Medal for excellence in the study and application of paleontology.
Dr. Lipp's contributions to paleontology range across many fields, including micropaleontology, molluscan paleocommunities, general paleobiology (including organism responses to climate change), and temporal assessments ("temporal smearing") of extinction events owing to incompleteness of the fossil record (termed the "Signor-Lipps Effect"). He also has served the paleontological community as President of the Cushman Foundation for Foraminiferal Research, President of the Paleontological Society and Chair of the Association of North American Paleontological Societies, among others.
A brief synopsis of the Signor-Lipps effect goes a little something like this. When an organism dies, varying factors influence whether or not the organism will be preserved as a fossil. The potential that an organism will be, in whole or in part, fossilized can be referred to as 'preservation potential'. The preservation potential varies between species. For example, a clam lives its life buried in sediment. If it dies while still buried, it has a very good chance of becoming a fossil. A bird that lives in trees and flies around in the sky, will need to die and get transported to a location that is likely to be preserved. So the bird in this example has a lower preservation potential than a clam. Now expand this concept to discuss populations, rather than an individual. We see that rare species with relatively low preservation potentials aren't going to be fossilized as often as abundant species with high preservation potentials.
Now if we apply this concept to the study of extinction events (this is where the Signor-Lipps effect comes into play), we would expect to see certain species disappearing from the fossil record before other species. Regardless of the cause of the extinction. So rare species with low preservation potentials should disappear lower, in the stratigraphic record, than abundant species with high preservation potentials. This will give the appearance of a gradual extinction (where species diversity is declining over a period of time) even if the extinction event is catastrophic (where all the species disappear at once). The implication of this is that gradual extinctions are indistinguishable from catastrophic extinctions in the stratigraphic record. Here is a visual representation of this idea (from Williams, 1994):The larger the symbol the more rarely a species is preserved. The black box on the right is a representation of a stratigraphic column showing where each specimen was found. The lines leading to a symbol on the left give an approximate range of a species' duration. Rare species disappear from the rock record first, abundant species should disappear from the fossil record last. At this point, due to variable preservation potential within the fossil record, it is not possible for us to distinguish between a fast or slow extinction event. Jere Lipps was one of the first people to say it, so he deserves our congratulations.
Signor, P. W., and Lipps, J. H., 1982, Sampling bias, gradual extinction patterns, and catastrophes in the fossil record, Geological Implications of Impacts of Large Asteroids and Comets on the Earth: Special Paper - Geological Society of America, p. 291-296.
Williams,M.E., 1994, Catastrophic Versus Noncatastrophic Extinction of the Dinosaurs: Testing, Falsifiability, and the Burden of Proof: Journal of Paleonotology v.68 p.183-190.