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Elasmobranch and Osteichthyan Fauna of the Rattlesnake Mountain Sandstone, Aguja Formation (Upper Cretaceous; Campanian), West Texas. by Joseph A. Schubert, B.A., B.S. A Thesis In Geoscience Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of Master of Sciences Approved Thomas M. Lehman Chair of Committee James E. Barrick Sankar Chatterjee Dominick Casadonte Interim Dean of the Graduate School May, 2013 Copyright 2013, Joseph A. Schubert Texas Tech University, Joseph A. Schubert, May 2013 ACKNOWLEDGEMENTS Thank you to Dr. Tom Lehman for his knowledge and help throughout the project, Steve and Jen Wick of the Ten Bits Ranch without whose fossil microsite, none of this would be possible, Dr. Mark Grimson and the Texas Tech Imaging Center for use of the Hitachi SEM, and Alton and Linda Schubert for their unwavering support. ii Texas Tech University, Joseph A. Schubert, May 2013 TABLE OF CONTENTS Acknowledgements ii Abstract vi List of Figures viii 1. Introduction 1 Geologic Setting and Regional Stratigraphy 2 Stratigraphy of the Ten Bits Microsite 4 Methods 5 Tooth Morphology and Nomenclature 6 Rostral Teeth 8 Placoid Scales and Dermal Denticles 9 2. Systematic Paleontology 15 Hybodontidae 15 Lonchidiidae 16 Ginglymostomatidae 18 Orectolobidae 23 Squatinidae 24 Cretoxythinidae 26 Anacoracidae 27 Mitsukurinidae 31 Rhinobatidae 33 Hypsobatidae 35 Sclerorhynchidae 36 iii Texas Tech University, Joseph A. Schubert, May 2013 Ptychotrigonidae 42 Rhombodontidae 47 Myliobatidae 49 Trigonodontidae 55 Albulidae 55 Phyllodontidae 56 Semionotidae 58 Osteichthyes 58 Testudines 63 Mosasauridae 64 Crocodylia 65 Reptilia 65 Coprolites 66 3. Discussion 77 The Ten Bits Fauna 77 Ten Bits and Terlingua Microsites Compared 79 Paleobiogeography of the Western Interior Seaway 80 Comparison with the Judith River Fauna 82 Comparison with the Pictured Cliffs Fauna 83 Comparison with Blufftown Fauna 84 Comparison with the Black Creek Fauna 85 Characteristics of the Gulf Coast and Atlantic Fauna 86 4. Conclusions 93 iv Texas Tech University, Joseph A. Schubert, May 2013 References 97 v Texas Tech University, Joseph A. Schubert, May 2013 ABSTRACT A thin granular conglomerate within the Rattlesnake Mountain sandstone member of the Upper Cretaceous Aguja Formation on Ten Bits Ranch in Brewster County, Texas preserves a diverse assemblage of small teeth, denticles, vertebrae, and other bones of chondrichthyan and osteichthyan fishes. This thin layer of teeth and bones probably represents a winnowed lag deposit, concentrated by wave action in a coastal marine environment. The deposit, referred to herein as the "Ten Bits Microsite" is highly fossiliferous; screen-washing methods yielded about 5000 specimens. Chondrichthyan fishes are represented by 23 species,while identifiable osteichthyan fishes represent four species. Two of the three most abundantly occurring chondrichthyan species (Scapanorhynchus texanus and Ischyrhiza mira) are also the most common species in other middle to Late Campanian marine vertebrate faunas along the Gulf of Mexico, and Atlantic Coastal Plain. Ptychotrygon agujaenisis is abundant at Ten Bits, but unknown in correlative marine faunas elsewhere. The abundance and diversity of ptychotrigonid rays may be a unique feature of the Ten Bits fauna. The most common osteichthyan fishes found in the Ten Bits fauna (Paralbula casei and Albula sp.) are also reported elsewhere in Gulf and Atlantic Coastal Plain faunas, but they are rare there and subordinate to bony fishes not recovered at Ten Bits. Paralbula casei is a common bony fish found in marine vertebrate faunas of the Western Interior. The most common chondrichthyan fishes found in Western Interior faunas are either unknown or rare in the Ten Bits fauna, and the common Western Interior ray vi Texas Tech University, Joseph A. Schubert, May 2013 Myledaphus bipartitis does not occur at Ten Bits or any other Gulf or Atlantic Coast fauna. These differences probably reflect latitudinal variation, oceanic water circulation pattern, or variation in other environmental conditions between the Western Interior Seaway and the Gulf or Atlantic Coast that restricted the distributions of some marine fish species. The similarities between the Ten Bits fauna and those of the Atlantic and Gulf Coast indicate that western Texas was more closely allied biogeographically with that province than with the Western Interior of North America. One species tentatively identified in the Ten Bits fauna on the basis of a single tooth, Igdabatus indicus, is otherwise known only from Africa and Asia. If this identification is correct, it would represent the only known occurrence of the species in North America. This could reflect the chance preservation of a single individual outside of its normal range. Western Texas may have been near the northern limits of the range for tropical marine vertebrate species. vii Texas Tech University, Joseph A. Schubert, May 2013 LIST OF FIGURES 1. General geologic map of the Big Bend region of Texas. 11 2. Stratigraphic Relation of the Aguja and Pen Formations. 12 3. Stratigraphic section of the Aguja Formation. 13 4. Diagram of sawfish, tooth and denticle terminology. 14 5. Selachiian teeth. 68 6. Selachiian and Batoid teeth. 70 7. Batoid teeth . 72 8. Osteichthyan teeth. 74 9. Indeterminate rostral spines and Reptilia. 76 10. Late Cretaceous paleogeographic map of North America. 88 11. Paleogeographic map of North America during Campanian. 89 12. Paleogeographic reconstruction of the Western Interior during Campanian time. 90 13. Ten Bits Ranch Chondrichthyans Assemblage. 91 14. Ten Bits Ranch Osteichthyans Assemblage. 92 viii Texas Tech University, Joseph A. Schubert, May 2013 CHAPTER 1 INTRODUCTION Remains of fossil sharks and bony fishes are relatively common in Upper Cretaceous marine strata throughout western North America. Although similar remains have been reported from the Upper Cretaceous Aguja Formation in the Big Bend region of West Texas, only a few specimens from the upper part of the formation have been illustrated (e.g., Rowe et al., 1992), and no thorough account of the Aguja shark and bony fish material has been presented. The Aguja fauna is of particular interest because it provides a sample from the southernmost Late Cretaceous biome in the Western Interior Seaway of North America (Lehman, 1997). Contemporaneous shark and fish assemblages are known from sites farther north on the Great Plains, and also farther east on the Atlantic and Gulf Coastal Plains. The Aguja fauna offers an opportunity to compare the marine vertebrate faunas in these separate biogeographic provinces. The primary goal of the present report is to provide systematic descriptions and illustrations of a diverse shark and bony fish assemblage recently recovered from the middle part of the Aguja Formation (Rattlesnake Mountain sandstone member). The shark and fish assemblage described in this report was collected at a site on the Ten Bits Ranch, about 15 km north of Study Butte in Brewster County, Texas (Fig. 1). The site is referred to here as the "Ten Bits Microsite" and was discovered by the owner of ranch, Mr. Steve Wick, who made the initial collection from the site and granted permission to undertake the present study. Subsequent study revealed that this 1 Texas Tech University, Joseph A. Schubert, May 2013 site is almost certainly the same one mentioned by McNulty and Slaughter (1972) that yielded the type specimens of the batoid chondrichthyan Ptychotrygon agujaensis. Specimens collected for the present study are catalogued at the Vertebrate Paleontology Laboratory of the Texas Memorial Museum in Austin, Texas and assigned to site TMM - 46018. Exact locality information is available at the Vertebrate Paleontology Laboratory. Geologic Setting and Regional Stratigraphy During Late Cretaceous (Campanian) time the Big Bend region of West Texas lay along the western edge of a shallow epicontinental sea, known as the Western Interior Seaway, that extended from the Gulf of Mexico northward through Montana and Canada. Throughout the Campanian Stage, transgressive and regressive cycles resulted in deposition of intertonguing marine and coastal sediments all along the western side of the Seaway (e.g., Kauffman, 1984). The Aguja Formation is an eastward-thinning series of paralic and marine sandstones that is interbedded with shale and lignite, and reflects deposition in varied shallow marine and coastal plain environments (Lehman, 1985). The fossil vertebrate fauna of the Aguja Formation is well known and includes a wide variety of terrestrial and marine animals (Rowe et al., 1992). However, the marine fauna has not been as extensively studied as the dinosaurs, crocodylians, and turtles. Lehman (1985) separated the Aguja Formation into several informal members that reflect two major progradational intervals separated by a transgressive marine interval (Fig. 2). The basal sandstone member intertongues with marine shale of the 2 Texas Tech University, Joseph A. Schubert, May 2013 underlying Pen Formation, and consists of fine-grained fossiliferous sandstone that records the initial progradational event in the Big Bend region (Bohannon, 1987). The lower shale member is composed of interbedded carbonaceous shale and lignite deposited landward of the prograding shoreline (Record, 1988). The Rattlesnake Mountain sandstone member is a thin transgressive sandstone interval that represents a shallow marine shelf environment (Macon, 1994).

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