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Resar, Nicholas A.Reconstructing the Paleodiet of Ground Sloths Using Microwear Analysis
BS, Kent State University, 2012, College of Arts and Sciences / Department of Geology

Understanding the paleoecology of extinct xenarthrans, such as ground sloths, is complicated because they lack modern ecological analogues. Previous studies have applied functional morphology and biomechanical analyses to reconstruct the diet and lifestyle of ground sloths, yet the application of dental microwear as a proxy for feeding ecology in extinct xenarthrans remains understudied. Here, we hypothesize that dental microwear patterns can be used to reconstruct dietary niche partitioning among extinct ground sloths, thereby providing new evidence of feeding ecology in these animals.

In this study, 17 second molariforms from 5 taxa [Megalonyx, Acratocnus, Thinobadistes, Octodontotherium, Hapalops] were molded and cast for dental microwear analysis. Using scanning electron microscopy, two non-overlapping digital images of microwear on the occlusal surface of each tooth were captured at 500x magnification. In a blind study, each image was independently analyzed using the semi-automated software package, Microwear 4.02, which allows microwear features to be digitally counted and measured. As a baseline for reconstructing paleodiet, ground sloth microwear patterns were directly compared to microwear from living tree sloths and armadillos, which were analyzed separately using the same experimental design. Results suggest that ground sloths can be statistically differentiated based on a combination of the number of scratches and width of features. Number of scratches and feature width suggest that Megalonyx and Thinobadistes form the ends of the browser-grazer spectrum, respectively. Additionally, Acratocnus and Octodontotherium are here predicted to be mixed feeders, while Hapalops appears to be a grazer. These results support scanning electron microscopic analysis of dental microwear as a tool for reconstructing paleodiet in ground sloths. Further investigation should be into South American ground sloths to allow direct comparison with other methods of dietary reconstruction.

Committee:

Jeremy Green, Dr. (Advisor)

Subjects:

Paleoecology; Paleontology

Keywords:

ground sloth; microwear; scanning electron microscopy; diet; feeding ecology

Wayman, Matthew C.The Transfer of Volatiles Within Interacting Magmas and its Effect on the Magma Mingling Process
BS, Kent State University, 2011, College of Arts and Sciences / Department of Geology

The input of volatile-charged mafic magma into chemically evolved felsic magma reservoirs in the shallow crust leads to the exchange of heat and chemical components that may serve as the trigger for subsequent volcanic eruption. The exchange of volatiles, which occurs via diffusion and potentially through fluid movement, is particularly important to this process.

In order to simulate the magma mingling process and the role of volatiles within this process, we have conducted a series of hydrothermal experiments involving a hydrous basaltic-andesite glass containing trace olivine (prepared from a natural sample of Augustine volcano in Alaska’s Aleutian Arc) with crystal-deficient, anhydrous or hydrous Los Posos rhyolite glass (also natural) at 100 MPa. Some experiments were conducted under fluid-absent conditions while others involved O-H-Cl±S-bearing fluids. Temperature was varied during these experiments, with most beginning at 1100°C. Temperature was subsequently reduced to 800°C in several steps, where it remained until an isobaric quench. The run durations ranged from 25 to 125 hours.

The experimental products exhibit interesting textural and chemical features. The rhyolitic run product glass, whether hydrous or anhydrous initially, exhibits minimal crystallization throughout the experiments, whereas the starting basaltic-andesite glass shows significant crystallization of iron and titanium oxides, plagioclase, and pyroxene. The exchange of Cl between the two melts was significant for fluid-present and fluid-absent conditions, and the concentration of Cl in the more felsic melt was strongly controlled by well established Cl solubility relationships involving the cations Ca, Al, Na, and Mg and the presence or absence of S.

Committee:

Elizabeth Griffith, PhD (Committee Chair); James Webster, PhD (Advisor); Donald Palmer, PhD (Committee Member); Brett Ellman, PhD (Committee Member); Bentley Wall, PhD (Committee Member)

Subjects:

Geochemistry; Geology

Keywords:

volatile; volatiles; chlorine; magma; mingling; mixing; volcanology