Application of micro-CT and Elliptic Fourier Analysis on Molar Outline Shape for Group Discrimination of Notoungulates
Mammal teeth commonly possess a crown shape that is unique to each species, and, as a result, taxonomic identification of mammals relies heavily upon dental analysis. Ever-growing (hypselodont) cheek teeth, acquired convergently within numerous lineages of Cenozoic (66 Ma – present) mammals, retard wear associated with abrasive diets. Four major groups of notoungulates, a diverse group of extinct South American herbivorous mammals that flourished during the Cenozoic, acquired hypselodont cheek teeth. Simplification of crown morphology is a developmental consequence of hypselodonty, leaving tooth crown outline as a potential metric for taxonomic identification. One concern with this approach is that crown outline is prone to change, however, the inclusion of all possible crown outlines along the height of each tooth may effectively capture intraspecific variability. This study tests the power of crown outline shape analysis to discriminate among notoungulate genera/species. Micro-computed tomography, a non-destructive technique to visualize the internal structure of materials, was used to scan eight notoungulate specimens from five genera. From those eight specimens, 18 molars were reconstructed and analyzed. Teeth were sectioned digitally to ascertain how tooth outline would have changed during wear. Sections parallel to the occlusal surface for each tooth were subjected to elliptic Fourier analysis (EFA) to compare outline shape. Examination of the set of outlines from each tooth reveals that ontogenetic variation of crown outline along the height of a tooth is less than intraspecific variation, indicating that tooth crown outline can reliably discriminate among notoungulate groups.