Uneven distribution of enamel in the tooth crown of the hypsodont Plains Zebra Equus quagga

Unworn teeth of herbivorous mammals are not immediately functional. They have to get in wear to expose enamel ridges which can then act as shear-cutting blades to disintegrate the food. We use the Plains Zebra (Equus quagga) as a hypsodont, herbivorous model organism to investigate how initial wear of the tooth crown is controlled by underlying structures. We find that the enamel proportion is smaller at the apical part of the tooth crown in all upper tooth positions. Measurements of enamel thickness on the first molar show that the outer enamel band is widest in the lower half of the tooth crown, where enamel content is also highest. We therefore find evidence that the distribution of enamel within the tooth crown is uneven and lower enamel content at the apex promotes early wear. This gradient in enamel distribution is less pronounced in the last molar (txM3), which has also a higher overall enamel content. The M3 is thus hypothesised to have a slightly different functional trait in mastication, resisting highest bite forces along the tooth row and maintaining functionality while anterior teeth are already worn down.