Date of Award

Spring 1-1-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Jaelyn Eberle

Second Advisor

Jennifer Stempien

Third Advisor

Matt Sponheimer

Abstract

The Early Oligocene (Orellan) in the North American Western Interior is marked by a cooler and dryer climate than the late Eocene (Chadronian). New mammalian taxa appeared while other groups already present began to diversify. This study takes a closer look at the diversification of hornless ruminant artiodactyls present in the Latest Orellan Merycoidodon bullatus Interval Zone through an analysis of 70 specimens from three closely related species: Hypertragulus (27), Hypisodus (18), and Leptomeryx (25) from a single locality in Toadstool Geologic Park, Nebraska. Specifically, we took a closer look at the hypsodonty index, mesowear, and tooth volume, which have been used as proxies for paleodiet. Using a Keyence VHX-2000 Digital Microscope©, the lingual, labial, and occlusal view of the m3 of specimens was imaged and a series of up to 24 measurements were performed on each image. These measurements include length, width, and height of both the overall molar as well as the individual selenes and posterolophid. Values were then analyzed using JMP Statistical Software©, running an analysis of variance test. Results show the three artiodactyls are more distinct from each other in dietary niche than previously thought. The difference in the average hypsodonty index may be enough to categorize them into different feeding behavior groups. Additionally, the values group by species when hypsodonty index is plotted against tooth volume, potentially allowing identification morphometrically as a supplement to morphologically. Furthermore, a new formula to calculate the volume was derived to provide a more accurate value of tooth volume specific to the unique shape of the selenodont teeth possessed by ruminant artiodactyls. Part of this formula [A = (2W1L1)/3] focuses on the occlusal surface area where W1 and L1 represent and width and length respectively of any selene or posterolophid; values are summed together for a total occlusal surface area. The data also yielded a fourth way to calculate occlusal surface area, a modified formula used in previous studies. This study both explores how new technology and techniques can provide more accurate means of gathering measurements for non-destructive analysis and takes a closer look at dietary specialization of these artiodactyls that occurred in the same place at the same time.

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