Date of Award

Spring 1-1-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Jaelyn J. Eberle

Second Advisor

Talia S. Karim

Third Advisor

Thomas E. Williamson

Abstract

Early and middle Paleocene mammalian faunas are documented throughout the North American Western Interior. Faunas near, or spanning, the Torrejonian-Tiffanian transition have been reported by others from Wyoming’s Hanna, Carbon, and Bighorn basins and are important for assessing this transition period which has many overlapping mammalian occurrences. Reported here is a later Torrejonian (To2 or To3) mammalian fauna from the upper China Butte Member of the Fort Union Formation in Wyoming’s Great Divide and Washakie Basins (GDB & WB). The GDB & WB assemblage is comprised of isolated mammal teeth, collected primarily from anthill localities, and is a representation of some of the smallest members of the fauna due to the selection bias of their insect gatherers. The Torrejonian assemblage from the GDB & WB is comprised of at least 12 mammalian species from seven orders, identified primarily by comparison with specimens and casts from multiple institutions as well as the literature. Faunal affinities with Swain Quarry in the Washakie Basin suggest that these assemblages are temporally correlative, corroborating stratigraphic relationships hypothesized by others. The marsupial, Swaindelphys cifelli, previously documented only from Swain Quarry, is found in the late Torrejonian assemblage from one of the localities from the Great Divide Basin. Occurring taxa with wider ranges (both temporal and geographic), such as the large multituberculate Ptilodus mediaevus, show particular morphologic resemblance to the fossils from Swain Quarry. In the GDB & WB assemblage, there are teeth of multiple small neoplagiaulacids, including Krauseia clemensi, which also occurs at Swain Quarry. The presence of Mixodectes malaris suggests a minimum age for the GDB & WB localities in south-central Wyoming, specifically that they are of the To2 interval zone of the Torrejonian: M. malaris has a first occurrence in the To2, has only questionable identifications in the To3, and is not documented from the Tiffanian. The known temporal ranges of many taxa identified from this assemblage, such as Krauseia clemensi, the cimolestid Acmeodon secans, the paromomyoid Paromomys maturus, and the ‘condylarths’ Haplaletes disceptatrix and Litomylus dissentaneous suggest that the GDB & WB faunal assemblage cannot be older than To2. The carnivore Simpsonictis tenuis and the cimolestid Gelastops parcus would have their known first occurrences adjusted from the To3 to the To2 if this fauna is To2. The absence of characteristic Tiffanian taxa, such as members of the Plesiadapoidea, also suggests that the GDB & WB faunal assemblage is of a later Torrejonian age. This is the first of this age to be described which includes mammalian fossils from the Great Divide Basin, and is important for furthering our understanding of North American mammalian diversity and evolution during the early Paleocene.

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