Publication Date

2025

Document Type

Dissertation/Thesis

First Advisor

Naples, Virginia L.

Second Advisor

Goodwin, Mark

Degree Name

Ph.D. (Doctor of Philosophy)

Legacy Department

Department of Biological Sciences

Abstract

The Hell Creek Formation of the Northern Great Plains records one of the greatest mass extinction events in Earth’s history, bringing to a close the reign of the dinosaurs at the end of the Cretaceous period. This rock unit comprises one of the most studied geological formations in the world and is one of the few locations on the planet that preserve terrestrial deposits containing ejecta from the bolide impact that slammed into the Yucatan Peninsula 66 million years ago. This profound event in the geologic record has led to numerous studies of paleobiotas, climate change, ecosystem recovery dynamics, and dinosaur diversity, evolution and paleobiology. While the Hell Creek Formation has been well studied for over a century, most of our knowledge comes from two intensely studied regions in eastern Montana and the western Dakotas within the Williston Basin.

This dissertation focuses on exposures of the Hell Creek Formation in Carter County, Montana where the formation has received much less attention. The thickness of the formation in the region of the study area reaches ~150 meters of which ~120 meters were mapped allowing for the dividing up of the unit into a lower, middle and upper portion based on traceable beds in the study area. Using the microvertebrate fossil collected over 23 years by crews from the Burpee Museum of Natural History in Rockford, Illinois, 25,000 fossil specimens were examined and 15,000 identified to class. The microsites where the specimens were collected were put into a stratigraphic framework for the first time to document the vertebrate biostratigraphy of the Hell Creek Formation in Carter County, as well as analyze community structure and diversity through the final 1.5 – 2 million years of the Cretaceous Period.

Species richness and community structure remained consistent throughout the lower and middle Hell Creek Formation whereas it dipped in the upper Hell Creek Formation in the study area. Relative abundance and heterogeneity indices varied across the section with evenness dipping in the middle Hell Creek Formation and spiking in the upper Hell Creek Formation. Dominance measures reflected similar data showing more dominant species in the middle Hell Creek and decreasing in the upper. Overall, species diversity in Carter County, Montana was relatively high and was consistent with other areas of Hell Creek Formation deposition in Montana and the Dakotas.

Lissamphibia (caudate and allocaudates) were examined to further investigate community structured and faunal change and to assess potential links to climate change based on their ecophysiology. Because they breathe through their skin, lissamphibians are the first to feel the effects of climate change. In the study area, lissamphibia were relatively diverse with eight species collected from sediments in the study area. Scapherpeton tectum is the most abundant throughout the formation, however it declines from 80% in the lower to 45% the upper. Opisthotriton kayi is the second most abundant salamander, however it’s abundance increases throughout the Hell Creek Formation in the study area from 15% in the lower to 36% in the upper Hell Creek microsites. Together, the species richness is higher than what has been reported from exposures in the Dakotas, however it falls slightly lower than those to the north near the Fort Peck Reservoir north of Jordan, Montana.

Diversity measures and relative abundance data suggest that the vertebrate community in Carter County, Montana largely resembles those in other region of Hell Creek Formation exposures with similar results in heterogeneity indices. The community appears to be stable from the bottom of the formation to the few remaining beds of the upper Hell Creek Formation.

Extent

201 pages

Language

en

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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