Upper Cambrian Chitons (Mollusca, Polyplacophora) from Missouri, USA John Pojeta, Jr., M. J. Vendrasco, and Guy Darrough Bulletins of American Paleontology Number 379, September 2010 BULLETINS OF AMERICAN PALEONTOLOGY Established 1895 Paula M. Mikkelsen Warren D. Allmon Editor-in-Chief Director Editorial Board Jason S. Anderson, University of Calgary Kenneth Angielczyk, Field Museum of Natural History Carlton Brett, University of Cincinnati Ann F. Budd, University of Iowa Peter Dodson, University of Pennsylvania J. Thomas Dutro Jr., United States Geological Survey Daniel Fisher, University of Michigan Dana H. Geary, University of Wisconsin-Madison Peter J. Harries, University of South Florida John Pojeta, United States Geological Survey Carrie E. Schweitzer, Kent State University Geerat J. Vermeij, University of California at Davis Emily H. 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Upper Cambrian Chitons (Mollusca, Polyplacophora) from Missouri, USA John Pojeta, Jr., M. J. Vendrasco, and Guy Darrough Bulletins of American Paleontology Number 379, September 2010 ISSN 007-5779 ISBN 978-0-87710-488-9 Library of Congress Catalog Card Number 2010935745 © 2010, Paleontological Research Institution, 1259 Trumansburg Road, Ithaca, New York 14850, U. S. A. UPPER CAMBRIAN CHITONS MOLLUSCA, POLYPLACOPHORA FROM MISSOURI, USA John Pojeta, Jr. U. S. Geological Survey and Department of Paleobiology, Smithsonian Institution, P. O. Box 37012, NHB MRC 121, Washington, DC 20013-7012, U.S.A.; email [email protected] M. J. Vendrasco Department of Biological Sciences (MH-282), California State University, Fullerton P. O. Box 6850, Fullerton, California 92834, U.S.A.; email [email protected], [email protected] and Guy Darrough 2075 Rosedale Court, Arnold, Missouri 63012, U.S.A.; email [email protected], [email protected] ABSTRACT Numerous new specimens reveal a greater presence of chitons in Upper Cambrian rocks than previously suspected. Evidence is presented showing that the chiton esthete sensory system is present in all chiton species in this study at the very beginning of the known polyplacophoran fossil record. Th e stratigraphic occurrences and paleobiogeography of Late Cambrian chitons are documented. Th e 14 previously-named families of Cambrian and Ordovician chitons are reviewed and analyzed. Aulochitonidae n. fam. is defi ned, based on Aulochiton n. gen.; A. sannerae n. sp. is also defi ned. Th e long misunderstood family Preacanthochitonidae and its type genus Preacanthochiton Bergenhayn, 1960, are placed in synonymy with Mattheviidae and Chelodes Davidson & King, 1874, respectively; Eochelodes Marek, 1962, also is placed in synonymy with Chelodes, and Elongata Stinchcomb & Darrough, 1995, is placed in synonymy with Hemithecella Ulrich & Bridge, 1941. At the species level, H. elongata Stinchcomb & Darrough, 1995, and Elongata perplexa Stinchcomb & Darrough, 1995, are placed in synonymy with H. eminensis Stinchcomb & Darrough, 1995. Th e Ordovician species H. abrupta Stinchcomb & Darrough, 1995, is transferred to the genus Chelodes as C. abrupta (Stinchcomb & Darrough, 1995). Th e Ordovician species Preacanthochiton baueri Hoare & Pojeta, 2006, is transferred to the genus Helminthochiton as H. ? baueri (Hoare & Pojeta, 2006). Th e Ordovician species H. marginatus Hoare & Pojeta, 2006, is transferred to the genus Litochiton as L. marginatus (Hoare & Pojeta, 2006). Matthevia walcotti Runnegar, Pojeta, Taylor, & Collins, 1979, is treated as a synonym of Hemithecella expansa Ulrich & Bridge, 1941. In addition, other multivalved Cambrian mollusks are discussed; within this group, Dycheiidae n. fam. is defi ned, as well as Paradycheia dorisae n. gen. and n. sp. Cladistic analysis indicates a close relationship among the genera here assigned to the Mattheviidae, and between Echinochiton Pojeta, Eernisse, Hoare, & Henderson, 2003, and mattheviids. Th e results suggest treating these taxa as stem-lineage chitons, and do not support the hypothesis that they are aplacophorans. INTRODUCTION ing Gasconade Dolomite. Th e Gunter Sandstone Member is Th is study deals with species belonging to Chelodes Davidson essentially equal to the Van Buren Formation of various au- & King, 1874 (= Preacanthochiton Bergenhayn, 1960; thors (Th ompson, 1991). Eochelodes Marek, 1962), Hemithecella Ulrich & Bridge 1941 All of our specimens are small, disarticulated, and pre- (= Elongata Stinchcomb & Darrough, 1995), Aulochiton n. served in white chert; most are molds, but some have the shell gen., and Paradycheia n. gen. All of the new material is from replaced by chert. Th e chert occurs as masses formed by si- the Upper Cambrian Eminence Dolomite of east-central licifi cation of coarse bioclastic molluscan grainstones that ac- Missouri, USA. (Text-fi g. 1). In this area, we use the stra- cumulated between domal stromatolites. Th e fauna collected tigraphy that was presented by Pojeta et al. (2005), in which with these multivalved mollusks is sparse (Pl. 1, Figs 1-7) and the Eminence Dolomite is Late Cambrian in age, as is the consists of (a) internal molds of indeterminate gastropods, (b) Gunter Sandstone Member the lowest member of the overly- the orthid brachiopod Finkelnburgia missouriensis Ulrich & 2 Bulletins of American Paleontology, No. MATERIAL AND METHODS In the fi eld, striking cherts with geology hammers results in sharp-edged fragments that "fl y" through the air and can pierce skin and/or damage eyes. Th us, care must be taken when collecting specimens preserved as chert. Appropriate clothing and eye protection are necessary. Part and counterpart of the same specimen are infre- quently collected, largely because either the internal or exter- nal portion shatters when the chert is struck with a hammer. Laboratory preparation is largely limited to using rock saws to reduce the amount of adhering rock and nipping the edges of the rock matrix with large steel wire cutters; these proce- dures expose more of the specimens and make them easier to photograph. For this study, we had 205 disarticulated specimens of multivalved mollusks. One hundred twenty-seven of the spec- imens were collected by Darrough over a period of 20 years; he also prepared these specimens. Darrough's collections were supplemented by 82 type, fi gured, or studied specimens used by Bergenhayn (1960) and Stinchcomb & Darrough (1995) in their monographs. Th e specimens studied by Bergenhayn (1960) were collected by E. O. Ulrich and his fi eld parties in the early part of the 20th century. Pojeta spent a week with Darrough in the fi eld and in Darrough's laboratory. COLLECTING LOCALITIES Darrough's collections came from three localities in Washington County, east-central Missouri, U.S.A (Text-fi g. 1). All collections are from the Eminence Dolomite. Th e lo- cality numbers are Darrough fi eld numbers: Locality 1: A road cut north of Potosi on State Highway Route 21, 3 km (1.9 mi) from the junction with State Highway Route 8; Sec. 1, T. 37 N., R. 2 E. Locality 2: A railroad cut north of Potosi where State Highway Route 21 crosses railroad tracks, 5.4 km (3.5 mi) from the junction with State Highway Route 8; Sec. 25, T. 38 N, R. 2 E. Locality 3: A road cut near Palmer and Berryman. Follow State Highway Route 8 west for 27 km (17 mi) from its junc- tion with State Highway Route 21 in Potosi. Turn south (left) Text-fi g. 1.—Outline map of the state of Missouri, USA, showing on Pigeons Roost Road (Machell Hollow) for 4.8 km (3 mi) the counties. Enlargement of Washington County shows the loca- and turn west (right) onto service road to exposures on both tions of our localities 1-3. Some of Ulrich's Missouri localities are in sides of the road; Sec. 33, T. 37 N., R. 1 W. the general area of east-central Missouri, and some of them are near Localities 1 and 2 can be plotted on the U.S. Geological Potosi and Palmer/Berryman. However, the information provided Survey Potosi 1:24,000 scale Topographic Map. Locality 3 can in the Ulrich locality register is not suffi cient to plot the exact places be plotted on the U.S. Geological Survey Berryman 1:24,000 from which his specimens came. scale Topographic Map. Cooper (1936, 1938), identifi ed by J. T. Dutro, Jr. (in litt., Ulrich Collecting Localities July 2007), (c) indeterminate trilobite fragments, examined Collections made by E. O. Ulrich and his fi eld parties between by John F. Taylor (in litt., July 2007), (d) and a poorly pre- 1905 and 1924, including some from east-central Missouri, served probable rostroconch. POJETA ET AL.: UPPER CAMBRIAN CHITONS 3 are listed in the Ulrich locality register at the U. S. National 1923)." Our localities 1 and 2 are near Potosi, Missouri. Museum of Natural History (USNM). Th e information is Ulrich locality 453n: "Ozarkian-Gasconade. Top of hill 2 here quoted from the register. Th is information is variable in miles south of Centerville. On Centerville-Ellington Road, clarity, but overall lacks specifi c locality details, and it was not Missouri. (Coll.[ectors] E. O. Ulrich and party, June 1923." possible to relocate Ulrich's exact localities.