Meeting Abstract
Enamel patterns on the occlusal surfaces of equid teeth are asserted to have tribal-level differences. The most notable example compares the Equini and Hipparionini, where Equini have higher crowned teeth with less enamel-band complexity and less total occlusal enamel than Hipparionini. While previous work has successfully quantified differences in enamel band shape by dividing the length of enamel band by the square root of the tooth surface area (Occlusal Enamel Index, OEI), we have discovered that OEI only partially removes the effect of body size. Because enamel band length scales allometrically, body size still has an influence on OEI, with larger individuals having relatively longer enamel bands than smaller individuals. Fractal dimensionality (D) can be scaled to any level, so we have used it to quantify occlusal enamel complexity while completely eliminating the effects of scaling from body size. To test the hypothesis of tribal-level complexity differences between Equini and Hipparionini, we digitally traced a sample of 58 teeth; 18 Hipparionini and 40 Equini. We restricted our sampling to the P3-M2 to eliminate the effect of tooth position. After calculating the D of these teeth with the fractal box method, we performed a nested two-way analysis of co-variance (ANCOVA) with taxonomy as a nested independent factor, true occlusal area (TOA) as a continuous independent factor, and D as the dependent factor. The ANCOVA indicates that tribe (p=0.0002), genus nested within tribe (p=0.0219), and species nested within genus and tribe (p=0.0030) are significant. TOA (p=0.2968) is not significant. Our results suggest that, as expected, D is independent of body size and that complexity is the product of evolutionary relatedness and differs from previous analyses where the tribal level was not significant.
