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This succinct treatise presents an up-to-date assessment on the nature and evolutionary development of a phylum of extinct marine invertebrates. Conodonts are represented by a diverse array of tiny tooth-like fossils, and are widely used in stratigraphical correlation. They are also vital in the search for petroleum because the colors of fossils brought up in drill cores indicate potential oil reservoirs. Dr. Sweet, a leading researcher in the field, presents a novel view of the evolutionary history of the Conodonta besides examining their morphology, taxonomy, and paleoecology.
E-Book Content
THE CONODONTA G-
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Morphology,Taxonomy,Paleoecology,
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WALTERC.SWEEL TheOhioStateUniversity
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New York . Oxford
CLARENDON PRESS. OXFORD . 1988
PREFACE
Conodontsare common fossils.Almost anyone who dealson a regularbasiswith Paleozoicand Triassic marine rocks has probably seena few of them. Through the last 30 yedrs conodonts have come to be of exceptionalvalue in biostratigraphy, and they now have pride of place as index fossils in many parts of the geologic column. But conodonts are extinct and are unknowo to most neontologists.The sketchiness ofinformation about them in most texts on invertebrate paleontologymay result either fiom the fact that they are microfossils that haye only lately come to be important as stratigraphic tools, or from the fact that nothing quite like them exists today, so their zoologic relations axeuncertain. In this monograph, I provide a summary of information about a group with which I have worked all my adult life. Charts that name conodont-based biozones and show stratigraphic rangeofselected conodont speciesare included as Appendix B. However, I have purposely avoided a recap of conodont biostratigtaphy becauseit is constantly changing and cunent views are readily available in various other places.Instead, I focus here on the conodonts as a group of extinct animals, about which it is important to know as much as possible before assessing their distribution biostratigraphically. Of course, one takes considerablerisk in attempting such a summary, particularly of a group of animals known only from its fossil record, becausemost of what I think I know about conodontsasanimals is either conjecture or a highly personalinterpretation ofa still-irnperfect fossil record. So, with the caveal that whal followsis only one way of viewingan im-
portant group, I ofer my account of the Conodonta. For their "witting" or unwitting contributions to what I believe I know about the fascinating gtoup of extinct animals described on the following pages,I am gateful to a long list of my students and faculty colleaguesat The Ohio StateUniversity, especiallyStig M. Bergstrijm, and to members of the Pander Society, an intemational group of exceptionally goodnatured "conodontologists"that has met frequently and infomally thougl the last 20 years to share infomation about conodonts, argue conclusions,and correct the misapprehensionsof its seniormembers. Karen Tyler, faculty illustrator at The Ohio State University, drafted nea y all the figures from my very crude copy and assistedwith labeling others. Dr. Jerzy Dzik, of the Polish Acaderny of Sciences, Warszawa, provided about half the stippled drawings of conodonts that gace various figuresin Chapter 5- The anistry of tlrese two good friends is plainly evident in their work and is warmlY acknowledged. I am also grateful to Sue Shipley and David Little, of The Ohio State University, for their help in completing various parts of the manuscript and illustrations, and to Mark Klefner, who graciously cornpiled information on the range