CONTRIBUTIONS FROM THE MUSEUM OF PALEONTOLOGY UNIVERSITY OF MICHIGAN VOL. XD, No. 8, pp. 113-173 (7 pls., 16 figs.) JULY 1, 1955 LOWER MISSISSIPPIAN CEPHALOPODS OF MICHIGAN PART 111. AMMONOIDS AND SUMMARY BY A. K. MILLER and H. F. GARNER MUSEUM OF PALEONTOLOGY UNIVERSITY OF MICHIGAN ANN ARBOR CONTRIBUTIONS FROM THE MUSEUM OF PALEONTOLOGY Director: LEWISB. KELLUM The series of contributions from the Museum of Paleontology is a medium for the publication of papers based chiefly upon the collections in the Museum. When the number of pages issued is sufficient to make a volume, a title page and a table of contents will be sent to libraries on the mailing list, and to individuals upon request. A list of the separate papers may also be obtained. Correspondence should be directed to the Museum of Paleontology, University of Michigan, Ann Arbor, Michigan. VOLS.11-XI. Parts of volumes may be obtained if available. VOLUMEXI1 1. Four New Species of Rugose Corals of the Middle Devonian Genus Eridophyl- lum, from New York, Michigan, and Ohio, by Erwin C. Stumm. Pages 1-11, with 2 plates. 2. Ornamentation as a Character in Specific Differentiation of Ostracods, by Robert V. Kesling. Pages 13-21, with 2 plates. 3. Mississippian Megaspores from Michigan and Adjacent States, by William G. Chaloner. Pages 23-35, with 2 plates. 4. A Tertiary Azolla from British Columbia, by Chester A. Arnold. Pages 37-45. with 2 plates. 5. Pleistocene Vertebrates from the Upper Becerra (Becerra Superior) Forma- tion, Valley of Tequixquiac, Mexico, with Notes on other Pleistocene Forms, by Claude W. Hibbard. Pages 47-96, with 9 plates. 6. Three New Species of the Cystid Genus Lipsanocystis from the Middle Devon- ian Traverse Group of Michigan, by Erwin C. Stumm. Pages 97-103, with 2 plates. 7. A New Occurrence of Sernitextdaria thomasi Miller and Carmer, 1933, by Murray J. Copeland and Robert V. Kesling. Pages 105-112, with 1 plate. 8. Lower Mississippian Cephalopods of Michigan. Part 111, Ammonoids and Summary, by A. K. Miller and H. F. Garner. Pages 113-173, with 7 plates. LOWER MISSISSIPPIAN CEPHALOPODS OF MICHIGAN PART I11 . AMMONOIDS AND SUMMARY BY A. K . MILLER and H . F . GARNER CONTENTS Introduction .............................................................. 113 The cephalopod fauna and its significance .................................... 114 Systematic descriptions .................................................... 120 Genus Gattendorfia Schindewolf ......................................... 120 Gattendorfia andrewsi (Winchell) .................................... 121 Gattendorfia ohiensis (Winchell) ..................................... 122 Gattendorfia? shumardiuna (Winchell) ............................... 124 Gattendorfia stummi Miller and Garner. sp. nov ......................... 125 Gattendorfza? sp. [of Michigan] ...................................... 126 Gattendorfia? sp. [of Ohio] .......................................... 128 Genus Kazakhstania Librovitch .......................................... 129 Kazakhstania americanu Miller and Garner. sp. nov ..................... 129 Genus Imitoceras Schindewolf ........................................... 132 Imitoceras romingeri (Winchell) ..................................... 132 Im~itocerasrotatorium (de Koninck) .................................. 133 Genus Miinsteroceras Hyatt ............................................. 135 Mumsteroceras oweni (Hall) ......................................... 138 Miinsteroceras pergibbosum Miller and Garner. sp. nov ................. 140 Munsteroceras? pygmaeum (Winchell) ................................ 142 Genus Beyrichoceras Foord .............................................. 143 Beyrichoceras allei (Wichell) ........................................ 144 Genus Merocaites Schindewolf ......................................... 149 Merocanites houghtoni (Winchell) .................................... 150 Merocanites marshallensis (Winchell) ................................. 154 Addendum ................................................................ 157 Literature cited ............................................................ 157 Plates ............................................................. (after 161 Comprehensive index to Parts I. 11. and I11 .................................. 169 INTRODUCTION HIS report on the ammonoids concludes the authors' study of the TLower Mississippian cephalopods of Michigan. Part I dealt with the orthoconic nautiloids . It was published as Article 7 of Volume X of the Contributions from the Museum of Paleontology of the University of Michigan in April. 1953 .Part I1 described the coiled nautiloids and appeared as Article 6 of Volume XI of the same series in November. 1953 . The present 113 MILLER AND GARNER paper, Part 111, in addition to a review of the ammonoids contains a summary of the authors' views in regard to the entire cephalopod fauna and a comprehensive index to the three parts. The Michigan cephalopod collections that are now available were assembled during most of the past century and all are housed in the Museum of Paleontology at the University of Michigan. From 1861 to 1870 Winchell published several accounts of the stratigraphy of the Lower Penin- sula and the fossils known at that time. His descriptions of the species, unfortunately, were not accompanied by illustrations, which makes their identification difficult, and his work on the stratigraphy has to a considerable extent been superceded, especially by that of Monnett in 1948. Both Michi- gan Lower Mississippian formations that carry cephalopods, the Coldwater shale and the Marshall sandstone, are extremely fossiliferous, and particu- larly is this true of the Marshall. The fauna, though predominantly mollus- can, is quite varied and other fossil groups, besides cephalopods, merit the careful attention of future workers. Acknowledgments are due to Dr. G. M. Ehlers and Dr. E. C. Stumm, of the University of Michigan, and to Dr. W. A. Kelly, of Michigan State Col- lege, for facilitating our study in many ways. The photographs for the accompanying plates were retouched by Messrs. Howard E. Webster and Frederick D. Leach. The completion of the report was made financially possible by the Graduate College of the State University of Iowa. Unless otherwise indicated, all specimens described are deposited in the Museum of Paleontology, University of Michigan, and the catalogue numbers refer to the collections in that institution. Localities given without a state designation are to be understood to be in Michigan. THE CEPHALOPOD FAUNA AND ITS SIGNIFICANCE We believe that the cephalopods of the Coldwater shale and the Marshall sandstone constitute a single fauna. Although the Coldwater shale is strati- graphically older than the Marshall sandstone, the two formations are locally gradational both lithologically and paleontologically. Fossils are not nearly as abundant in the Coldwater as in the Marshall, but in the younger formation they tend to be more fragmentary and less well pre- served. The differences between the assemblages from the two formations are largely, if not wholly, due to ecology (as reflected by the lithology) rather than to age, for the Coldwater consists for the most part of well- indurated gray shale, whereas the Marshall is predominantly of sandstone which is ferruginous and locally conglomeratic or calcareous. The strati- graphic and geographic distribution of the cephalopods in the Lower CEPHALOPODS OF MICHIGAN 115 Mississippian of Michigan is given in Table I. For the convenience of the reader, the species and the localities are arranged alphabetically. As may be seen from this table, a few species of cephalopods, representing at least four genera, are common to the Coldwater and the Marshall formations. Certain of these, for example the orthoconic nautiloids, are perhaps not stratigraphically very significant. But the presence of such distinctive species as the ammonoid Beyrichoceras allei and the coiled nautiloid Vestinautilus altidmsalis in both formations indicates that the two formations are of similar age. With the possible exception of Cycloceras, every cephalopod genus known from the Coldwater occurs in the Marshall. The fact that the younger Marshall has yielded representatives of seven, possibly eight, genera not known from the Coldwater can hardly be explained as entirely due to the relative dearth of specimens from the older formation. There was presumably early in Marshall time an incursion of new faunal elements into the Michigan Basin. It should be emphasized that all of the many cephalopods known from Marshall, Michigan, came from a thickness of only 4% feet of strata. Indeed, every species listed from there is repre- sented in a single 6-inch bed of extremely fossiliferous limonitic sandstone in the very small quarry that is the type locality of the Marshall sandstone. The Michigan depositional basin existed before and after the Missis- sippian period. The Coldwater shale is of much greater areal extent than the Marshall sandstone, which suggests that the sea in the basin was becoming progressively smaller and shallower. In post-Marshall Missis- sippian times the sea was at least temporarily isolated and more or less locally desiccated, as the presence of evaporites in the later Mississippian strata indicates. Even so, some sea must have remained, for at Grand Rapids, on the western edge of the basin, the Point au Gres limestone of Meramec or possibly Chester age, has yielded a small marine fauna which includes