April 1 2009

12:00 LSB 2320

John Alroy
National Center for Ecological Analysis & Synthesis

The dynamics of evolution and extinction in the Phanerozoic fossil record


The Phanerozoic marine invertebrate diversity curve has been used for decades to frame research in quantitative palebiology. Most versions of this curve depict little change during the Paleozoic and Mesozoic apart from the Cambro-Ordovician radiation and end-Permian extinction, but also show a mysteriously steep late Cretaceous and Cenozoic radiation. This pattern was derived from older literature compilations that only recorded first and last appearances of families or genera, making it impossible to correct for biases in the fossil record. Research over the past decade has come to rely more and more on the Paleobiology Database (, which records contextual data about individual fossil collections and thereby makes it possible to standardize sampling levels. In this talk I introduce the PaleoDB and discuss sampling standardization protocols. These algorithms are still in a state of flux, and because the results depend on methodological choices there is much to say on the topic. However, all methods of standardization suggest that the Cretaceous-Cenozoic radiation is an artifact of variation through time in the quality and quantity of fossil data. Instead, diversity has changed very little since the early Paleozoic, and seems to have done so independently of CO2 levels and glaciation cycles. The new data also make it possible to employ better origination and extinction rate equations. The resulting turnover rates demonstrate the mechanisms that hold diversity within narrow limits: density dependence of extinction rates and huge jumps in origination rates that follow major mass extinctions. Similar evidence is provided by the fossil record of North American mammals. If there is time I will briefly touch upon several other projects related to mammalian paleoecology and the calibration of vertebrate molecular clocks.











































































































































































































































































































































































































































































































































































































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