Assessing species diversity from insect trace fossils from the Cretaceous (Campanian) Two Medicine Formation, Choteau, Montana Open Access

Bradford, Maya (Spring 2020)

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This study follows two previous studies (Martin and Varricchio 2010; Freimuth and Varricchio 2019) that described insect trace fossil assemblages dominated by Rebuffoichnus sciuttoi and associated with dinosaur nesting sites from Two Medicine Formation calcareous paleosols. The paleosols are located in the paleontologically classic Willow Creek Anticline near Choteau, Montana, which is known for its abundant dinosaur nesting traces and body fossils. This study reviews 1,010 new cocoons collected from eight different localities within the Willow Creek Anticline area. A few cocoons display evidence of parasitoid behavior in the form of bore holes (Tombownichnus isp.), attached thin burrows, and smaller cocoons within cocoons. The most abundant cocoon is assignable to Fictovichnus sciuttoi and its size class and morphology are consistent across all three studies. The community of insect tracemakers represented by the trace fossils reviewed by this study, Martin and Varricchio (2010), and Freimuth and Varricchio (2019) likely comprised of at least three discrete species. 

Table of Contents

Chapter 1: Introduction..... 1

Chapter 2: Geologic Setting.... 3

Chapter 3: Methods and Results....7

Chapter 4: Discussion....14

Chapter 5: References.....22

Chapter 6: Appendix....25 

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