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The Ability of Mosasaurs to Produce Unique Puncture Marks on Ammonite Shells

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The Ability of Mosasaurs to Produce Unique Puncture Marks on Ammonite Shells THE ABILITY OF MOSASAURS TO PRODUCE UNIQUE PUNCTURE MARKS ON AMMONITE SHELLS Steven Daniel King A Thesis Submitted to the Graduate College at Bowling Green State University in partial fulfillment of the requirements of the degree of MASTER OF SCIENCE August 2009 Committee: Margaret Mary Yacobucci, Advisor James Evans Daniel Mark Pavuk ©2009 Steven Daniel King All Rights Reserved iii Abstract: Margaret Mary Yacobucci, Advisor The purpose of this study was to test the claim that certain types of unique puncture marks on ammonite shells could be produced by mosasaur bites. These unique puncture marks are double puncture marks, which are two adjacent holes set within the same indented rim, and puncture marks on only one flank of an ammonite’s shell. The common interpretation of puncture marks in ammonite shells is that they were bite marks from mosasaurs, however, this idea has been challenged, in part with the claim that these two unique types of puncture marks could not be produced by a mosasaur’s bite. To answer this question, this study was divided into two parts. The first part involved measuring the position and orientation of teeth from 202 mosasaur jaw bones and jaw fragments to determine if any had teeth that were crooked enough that they would have tips that were adjacent to one another. Additionally, the distribution and variety of tooth orientations were compared among several mosasaur genera. These comparisons were accomplished by performing univariate statistics using the PAST software package. The second part of this study was to build a replica of a mosasaur skull and use it to crush modern Nautilus shells, to see if puncture marks on only one side of a shell could be experimentally produced. The mosasaur Prognathodon overtoni was used as the model for this replica as this genus is thought to have been the mosasaur most likely responsible for the puncture marks on ammonite shells. The skull replica was made of steel and was used to crush twenty-two Nautilus shells. The crushed shells were then examined and compared to ammonite puncture marks and previous tests in which Nautilus shells were crushed. The results of this study showed that there are a range of tooth orientations in mosasaurs and that in rare cases, adjacent teeth can be found whose tips are close enough to have produced double puncture marks. In addition, the skull replica succeeded in producing iv puncture marks restricted to one flank of a Nautilus shell’s phragmocone when a partial bite force was applied. These results strengthen the claim that mosasaurs were responsible for the puncture marks found on ammonite shells. v Acknowledgments: I would like to thank Dr. Richard and Mrs. Mary Ann Hoare for providing funding for this project through the Richard D. Hoare Research Scholarship. These funds were essential for providing transportation costs needed to travel to several museums to complete this study. I would like to thank Caleb Cook for his help in creating the mosasaur skull replica. Caleb provided the necessary materials, tools, and abilities needed to take the skull replica from an idea to a physical model. I would like to thank Charles Codding for permitting the use of and help in operating a Tinius- Olsen press. This press was used to measure forces needed to crush Nautilus shells, which was a valuable part of this study. Finally, I would like to thank Dr. Peg. Naturally, since she is my advisor, it would seem obvious that I would have to rely on her help, but I want to thank her for her guidance as I learned, and continue to learn how to properly do research. vi Table of Contents: 1. Introduction 1 2. Background 2 3. Previous Tests 5 4. Research Objectives 8 5. Methods 8 6. Results 20 Tooth Morphometrics 20 Shell Crushing 22 7. Discussion 24 8. Conclusion 29 Works Cited 30 Appendix A: Tables of Tooth Measurements and Transformation to Bookstein Coordinates 56 Appendix B: Description of Crushed Nautilus Shells 120 vii Figures: Figure Page 1. A Placenticeras specimen with puncture marks 32 2. Reconstruction of Tylosaurus, a common mosasaur 33 3. Example of a double puncture mark in an ammonite shell 34 4. Coordinate system for tooth morphometrics 35 5. Streptostyly in a mosasaur’s skull 36 6. Mandibular movement in a mosasaur’s jaw 37 7. Pattern used for the construction of the skull replica 38 8. The complete skull replica 39 9. Plot of complete and chipped tooth pairs for the maxilla 41 10. Plot of complete and chipped tooth pairs for the dentary 42 11. Plot of tooth tips in the dentary with convex hulls 45 12. Plot of tooth tips in the maxilla with convex hulls 46 13. Distance between the tips of the teeth in the tooth pairs 47 14. Tooth pair in a Platecarpus sp. whose teeth tips are very close to each other 48 15. Tooth pair in an unknown mosasaur whose tips are close to each other 49 16. New tooth occupying the same socket as an old tooth 50 viii 17. Crushed remains of dry Nautilus shells 51 18. Puncture marks on specimen 12 partway through crushing 52 19. Puncture marks on specimen 19 partway through crushing 52 20. Close up of a puncture mark made in a wet Nautilus shell 54 21. Close up of a puncture mark made in a dry Nautilus shell 55 B1. Orientations of skull used to crush shells 129 B2. Final results for specimen 1 130 B3. Final results for specimen 2 130 B4. Final results for specimen 3 131 B5. Final results for specimen 4 132 B6. Final results for specimen 5 133 B7. Final results for specimen 6 134 B8. Final results for specimen 7 134 B9. Final results for specimen 8 135 B10. Final results for specimen 9 136 B11. Final results for specimen 10 137 B12. Final results for specimen 11 138 B13. Specimen 12 partway through crushing 138 ix B14. Final results for specimen 12 139 B15. Final results for specimen 13 140 B16. Specimen 14 partway through crushing 140 B17. Final results for specimen 14 141 B18. Specimen 15 partway through crushing 142 B19. Final results for specimen 15 142 B20. Final results for specimen 16 143 B21. Final results for specimen 17 143 B22. Final results for specimen 18 144 B23. Specimen 19 partway through crushing 144 B24. Final results for specimen 19 145 B25. Final results for specimen 20 145 x Tables: Tables Page 1. Experimental plan for the crushing of the wet Nautilus shells 40 2. Statistics for the distribution of the tooth tips in tooth pairs in the dentary 43 3. Statistics for the distribution of the tooth tips in tooth pairs in the maxilla 44 4. Results of bite force measurements 53 A1. Tooth measurements 58 A2. Complete and chipped adjacent tooth pairs 109 A3. Original coordinates and Bookstein coordinates for all tooth pairs in the dentary 113 A4. Original coordinates and Bookstein coordinates for tooth pairs in the maxilla and premaxilla 116 A5. Calculations of the tooth tips in tooth pairs 119 Introduction: Determining predator/prey relationships in the fossil record can be difficult. Sometimes, direct evidence of these sorts of relationships can be found, in the form of stomach contents, for instance. One interesting type of evidence for predator/prey relationships that may be found in the fossil record is puncture marks found in ammonite shells. The first ammonite with puncture marks was described by Kauffman and Kesling (1960). This ammonite was a Placenticeras from the Campanian Pierre Shale near Scenic, South Dakota. This specimen had numerous puncture marks in the shell and part of the body chamber was crushed. Many of these puncture marks were in obvious rows and had matching rows on the opposite side, indicating that they were produced by some sort of predator. The presence of smaller tooth marks that appear to have been caused by pterygoid teeth led Kauffman and Kesling (1960) to identify a mosasaur as the predator responsible, because mosasaurs were the only marine predators with pterygoid teeth in the Western Interior Seaway, which covered much of central North America during the Late Cretaceous. More ammonites have been found with puncture marks since that time. Additional Placenticeras specimens with puncture marks have been found in the Bearpaw Formation (which is thought to be equivalent to the Pierre Shale) of Alberta (Hewitt and Westermann 1990 and Tsujita and Westermann 1998) and the ammonite Sphenodiscus has been found with puncture marks in the Severn Formation in Maryland (Bukowski and Bond 1989). Other types of ammonites, such as Baculites and Metoicoceras, have been found with marks that may have been made by mosasaurs (Kauffman 1990). However, this study will focus on puncture marks found in Placenticeras and Sphenodiscus as these are the two most common ammonites found with puncture marks. In addition, the marks on the Metoicoceras specimen indicate that the predator was a Globidens (Kauffman 1990), a mosasaur with rounded, blunt teeth that appears to have been a crushing specialist, whereas the puncture marks in Placenticeras and Sphenodiscus are typically round holes, indicating that the mosasaur that attacked 2 them had conical teeth (the more common style of mosasaur teeth). Placenticeras and Sphenodiscus specimens with puncture marks range from the Santonian to the Maastrichtian (Kauffman 1990) and they appear to be restricted to places that were once covered by the Western Interior Seaway. Figure 1 illustrates a typical Placenticeras specimen with puncture marks. Since their discovery and initial interpretation as bite marks made by mosasaurs, the puncture marks on ammonites have been considered a classic example of predator-prey interactions in the fossil record.
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