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TORONTOTORONTO Vol. 8, No. 9 September 1998 See titles/ authors database GSA TODAY — http://www. A Publication of the Geological Society of America geosociety.org Technical Program Schedule A New Look at Evolutionary Rates 1998 — page 19 Annual Preregistration in Deep Time: Uniting Paleontology Deadline and High-Precision Geochronology Meeting — September 18 Samuel A. Bowring, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 54-1124, 77 Massachusetts Avenue, Cambridge, MA 02139, [email protected]. Douglas H. Erwin, Department of Paleobiology, MRC-121, National Museum of Natural History, Washington, DC 20560, [email protected] Figure 1. The Permian- Triassic boundary at Meishan, China, showing dates for the ash beds described in Bowring et al. (1998). The end Permian mass extinction is recorded within the last 1 m below the lowest ash bed (left). This ash bed lies about 10 cm below the Permian-Triassic boundary as defined on the basis of conodonts, and just below the major isotopic excursion. The upper two ash beds are in Lower Triassic strata. ABSTRACT stratigraphic data with new U-Pb zircon and geochronologists offers the prospect dates for the late Neoproterozoic and of accurately assessing the rates of evo- It is now possible to routinely Early Cambrian has demonstrated that lutionary processes, from speciation determine the age of 200–600-m.y.-old the soft-bodied Ediacaran fossils imme- to evolutionary radiations and mass ex- volcanic rocks interlayered with fossil- diately underlie the Cambrian, that the tinctions, throughout the Phanerozoic. bearing deposits to uncertainties of less base of the Cambrian is much younger than 1 m.y. with uranium-lead zircon “How fast, as a matter of fact, do animals than previously recognized, and that geochronology. This level of precision, evolve in nature? That is the fundamental the Cambrian explosion lasted 10 m.y. coupled with the recognition that vol- observational problem that the geneticist or less. Other recent studies have shown canic ash beds are much more common asks the paleontologist” (Simpson, 1944). the Middle and Late Cambrian each in fossiliferous rocks than previously lasted only about 10 m.y., suggesting realized, opens new opportunities for that the duration of the included trilo- INTRODUCTION the study of evolutionary rates in deep bite zones was similar to those of Juras- time. It is now possible to constrain Answers to Simpson’s question about sic ammonites. Recent data from the rates of evolutionary radiations, mass evolutionary rates have generally lacked Late Permian and earliest Triassic of extinctions, and other evolutionary precision, particularly for the pre-Ceno- south China now constrain the duration events as well as evaluate potentially zoic. Although many paleontological of the most profound mass extinction diachronous biostratigraphic bound- in the history of life to less than 1 m.y. aries. For example, a combination of Collaboration between paleontologists detailed biostratigraphic and chemo- Evolutionary Rates continued on p. 2 IN THIS ISSUE GSA TODAY September Vol. 8, No. 9 1998 A New Look at Evolutionary Rates in 1998 Annual Meeting—Toronto Deep Time: Uniting Paleontology and Late-Breaking Research Sessions ........ 17 GSA TODAY (ISSN 1052-5173) is published monthly High-Precision Geochronology ...... 1 Program Calendar ...................... 19 by The Geological Society of America, Inc., with offices at 3300 Short Courses .......................... 24 In Memoriam .......................... 2 Penrose Place, Boulder, Colorado. Mailing address: P.O. Box Grad School Information Forum ......... 25 9140, Boulder, CO 80301-9140, U.S.A. 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Miller, Department of Geology, Box 117-B, Vanderbilt Evolutionary Rates continued from p. 1 Rates of some evolutionary and geo- University, Nashville, TN 37235. logical processes can be determined for the Forum Editor: Bruce F. Molnia, U.S. Geological Survey, issues have revolved around evolutionary Cenozoic with some precision by means MS 917, National Center, Reston, VA 22092 Director of Publications: Peggy S. Lehr rates, the inadequacies of the geologic of a variety of techniques (e.g., climatic Managing Editor: Faith Rogers time scale have generally precluded their cyclicity, paleomagnetic reversals; Hilgen Assistant Editor: Vanessa Carney Production Manager: Jon Olsen resolution. Yet, accurate