DOI: 10.5061/dryad.tmpg4f510
title: Why the long teeth? Morphometric analysis suggests different selective pressures on functional occlusal traits in Plio-Pleistocene African suids

description: Neogene and Pleistocene African suids displayed convergent evolutionary
 trends in the third molar (M3) morphology, with increasingly elongated and
 higher crowns through time. While these features can prevent premature
 loss of masticatory functionality and potentially increase long-term
 reproductive success, changes in dental occlusal traits such as enamel
 complexity and thickness can also improve chewing efficiency and increase
 short-term energetic return. While both long-term and short-term benefits
 can contribute to the thriving of a lineage, the selective pressures
 associated with each category can be different. To examine how crown
 elongation correlates with these functional occlusal traits, we selected
 M3s of Kolpochoerus, Notochoerus, and Metridiochoerus from Kenya and South
 Africa, dated between 3.0 Ma and 0.4 Ma. To account for dental wear, we
 used micro-CT imaging of unworn/slightly worn M3s to simulate wear
 progression within each tooth. We compared morphometric representatives of
 occlusal enamel complexity and thickness among the specimens following
 their respective wear trajectories. We found that M3 elongation correlates
 with higher occlusal complexity and thinner enamel in Notochoerus and
 Metridiochoerus lineages through time. In Kolpochoerus, enamel complexity
 and thickness were generally maintained through time, despite M3
 elongation. The differences in M3 morphometric trends suggest that
 Kolpochoerus likely experienced a different set of selective pressures on
 functional occlusal traits compared to Notochoerus and Metridiochoerus.
 The shared evolutionary trends of M3 specialization among Notochoerus and
 Metridiochoerus suggest similar selective pressures on their chewing
 efficiency and the possibility of a dietary niche overlap in more xeric
 habitats.
description: Micro-CT images of Kenyan and South African materials were
 collected using the Nikon XTH 225 high resolution X-ray CT scanner (2000 ×
 2000 pixels) at the Evolutionary Studies Institute, University of the
 Witwatersrand, South Africa, at 120-140 kV and 140-150 μA settings. The
 Sus scrofa specimens were scanned at PACEA / University of Bordeaux, using
 a General Electrics (GE) Vtome x|s X-ray microtomograph, at 100-120 kV and
 200 μA settings. The Phacochoerus africanus specimens were scanned at the
 National Institute of Applied Sciences of Lyon, using a GE Phoenix Nanotom
 180 at 150 kV and 90 μA. For fossil specimens, a 1 mm copper filter was
 used to limit the beam hardening effect. For extant specimens, a 0.1 mm
 copper filter was used. Within each specimen, between 8
 and 16 virtually simulated “occlusal surfaces” (slices) were created in
 Avizo 7.1 (Visualization Science Group) perpendicular to the growth axis
 of the tooth, using the mesial second pair of pillars as the reference.
 The number of simulated “occlusal surfaces” was determined based on the
 crown height of the specimen, and the spacing between “occlusal surfaces”
 is consistent within each specimen. After the slices were generated, they
 were manually processed in Adobe Photoshop CS6 to create segments of
 enamel, dentine, and coronal cementum if present (step by step Adobe
 Photoshop protocol is presented in Appendix S2). The segmented images were
 then exported to the open-source image analyzing software Fiji for
 measurements of occlusal features (step by step Fiji protocol is presented
 in the Supplementary document).
description: Please refer to ReadMe file.