Why the long teeth? Morphometric analysis suggests different selective pressures on functional occlusal traits in Plio-Pleistocene African suids

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.