The 89th Annual Meeting of the American Association of Physical Anthropologists (2020)

Strong dental trait correspondence between the outer enamel surface (OES) and the enamel-dentine junction (EDJ) in the Great Ape Dental Scoring System


1Anatomy and Neuroscience, The University of Melbourne, 2Medical School, Australian National University

April 18, 2020 29, Platinum Ballroom Add to calendar

The EDJ provides an accurate morphological record of the fully formed tooth on the basement membrane. However, enamel deposition toward the end of tooth formation can obscure dental morphology at the OES. As non-metric dental traits at the OES play a key role in differentiating hominoid species and determining their phylogeny, we test the role of enamel deposition in the manifestation of dental traits by comparing the expression of dental traits at the OES and EDJ in the Great Ape Dental Scoring System. This is a newly devised set of reference plaques showing dental trait expression in extant great apes, with application for fossil hominoid systematics.

We micro-CT scanned 254 teeth from 11 gorillas and nine chimpanzees and segmented the enamel and dentine tissues to generate surface meshes. We scored 185 graded traits on incisors, canines, premolars, and molars. A trait with identical score at the OES and EDJ was marked as ‘true’ correspondence; a score deviating by one was recorded as ‘graded’ correspondence. Other trait correspondences were disregarded.

We found that ‘true’ correspondence in gorillas was 68%, but in chimpanzees was 66%, and explained this by the thinner enamel in gorilla dentition. Protrusions such as cingula, tubercles, cones and crests had stronger true correspondence in gorillas. In chimpanzees, foveae, wrinkles and accessory ridges had stronger true correspondence, fitting with their crenulated dental morphology. In both taxa, 95% of the traits showed ‘graded’ correspondence. This clarifies the role of enamel deposition and validates the Great Ape Dental Scoring System.

Funded by the L.S.B Leakey Foundation

Slides/Poster (pdf)