Taxonomic and ecologic implications of mammoth molar morphology as measured via computed tomography (CT)
Open Access
- Author:
- Smith, Gregory James
- Graduate Program:
- Geosciences
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 15, 2015
- Committee Members:
- Russell W Graham, Thesis Advisor/Co-Advisor
Eric S Post, Thesis Advisor/Co-Advisor
MARK E PATZKOWSKY, Thesis Advisor/Co-Advisor
Timothy Michael Ryan, Thesis Advisor/Co-Advisor - Keywords:
- Mammoth
taxonomy
ecology
teeth
molar
morphology
computed tomography
CT
paleontology
geology
quaternary
pleistocene - Abstract:
- Two Late Pleistocene species of Mammuthus, M. columbi and M. primigenius, prove difficult to identify on the basis of their third molar (M3) morphology alone due to the effects of dental wear. A newly-erupted, relatively unworn M3 exhibits drastically different characters than that tooth would after a lifetime of wear. On a highly-worn molar, the lophs that comprise the occlusal surface are more broadly spaced and the enamel ridges thicken in comparison to these respective characters on an unworn molar. Since Mammuthus taxonomy depends on the lamellar frequency (# of lophs/decimeter of occlusal surface) and enamel thickness of the third molar, given the effects of wear it becomes apparent that these taxonomic characters are variable throughout the tooth’s life. Therefore, employing static taxonomic identifications that are based on dynamic attributes is a fundamentally flawed practice. To help resolve the relationship between M. columbi and M. primigenius, I quantified the proportions of the characters that comprise the occlusal surface of Mammuthus third molars. Using computed tomography (CT), I digitized a sample of teeth from both species, creating models of continual wear via the removal of slices from the occlusal surface to the base of the crown. At each time slice, I calculated the occlusal enamel percentage, enamel thickness, and lamellar frequency of the exposed surface of the tooth. I then examined the relationship between relative wear percentage and dental characters to determine if there was a separation between the two species of mammoth with wear. My results demonstrate a prevalence of intraspecific variation, making a consistent separation of species difficult. In the absence of accompanying cranial morphologies or molecular data, delineation of the North American mammoth species based solely on molar morphology remains challenging, if not impossible. Additionally, the scatter in enamel values in M. columbi molars is indicative of a less phenotypically stable organism, suggesting that M. primigenius was the mammoth with a more highly conserved niche.