Earth and Atmospheric Sciences, Department of

 

First Advisor

Ross Secord

Committee Members

Amy Chew, David Harwood, R. Matt Joeckel

Date of this Version

7-2024

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Geosciences

Under the supervision of Professor Ross Secord

Lincoln, Nebraska, July 2024

Comments

Copyright 2024, John Colter Johnson. Used by permission

Abstract

Esthonyx is an early Eocene tillodont found in North America, Europe, and India. The genus was named by Edward Drinker (E. D.) Cope in 1874 based on specimens from the San Jose Formation in New Mexico. Since then, several species of Esthonyx have been described from North America alone. The best record of Esthonyx comes from the central Bighorn Basin (BHB) in Wyoming, where it appears in 220 localities in a 640 m-thick stratigraphic succession. Since the last summary of Esthonyx in the BHB, several hundred new specimens have been collected and curated at the Denver Museum of Nature and Science and the Smithsonian National Museum of Natural History. Herein, I revise the taxonomy and stratigraphic distribution of Esthonyx in the central BHB. I also compare taxonomy and body mass changes with the paleoclimate record, including two hyperthermals recently identified in the study area. I identify three species of Esthonyx in the Wasatchian sequence: E. spatularius Cope, 1880, E. bisulcatus Cope, 1874, and E. acutidens Cope, 1881, using previous diagnoses, novel character combinations, and character quantifications. Additional undescribed species of Esthonyx may be present in the study area. My results slightly extend the stratigraphic ranges of the three species described by previous studies, but they also reveal a strong correlation between smaller body size in E. bisulcatus and the ETM2 and H2 hyperthermals.

Advisor: Ross Secord

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