Dental wear proxy correlation in a long-term feeding experiment on sheep (Ovis aries)

Abstract

Dietary reconstruction in vertebrates often relies on dental wear-based proxies. Although these proxies are widely applied, the contributions of physical and mechanical processes leading to meso- and microwear are still unclear. We tested their correlation using sheep (Ovis aries, n = 39) fed diets of varying abrasiveness for 17 months as a model. Volumetric crown tissue loss, mesowear change and dental microwear texture analysis (DMTA) were all applied to the same teeth. We hereby correlate: (i) 46 DMTA parameters with each other, for the maxillary molars (M1, M2, M3), and the second mandibular molar (m2); (ii) 10 mesowear variables to each other and to DMTA for M1, M2, M3 and m2; and (iii) volumetric crown tissue loss to mesowear and DMTA for M2. As expected, many DMTA parameters correlated strongly with each other, supporting the application of reduced parameter sets in future studies. Correlation results showed only few DMTA parameters correlated with volumetric tissue change and even less so with mesowear variables, with no correlation between mesowear and volumetric tissue change. These findings caution against interpreting DMTA and mesowear patterns in terms of actual tissue removal until these dental wear processes can be better understood at microscopic and macroscopic levels.

Keywords: absolute wear; diet reconstruction; feeding experiment; mesowear; microwear.

Figure 1.

Correlation matrix of all DMTA parameters applied to sheep molars (O. aries, n = 25) after a long-term feeding experiment on consistent diets (avoiding a discrepancy of wear proxies due to different time resolution). Correlations of the full DMTA parameter set were plotted as matrices for the maxillary right first molar M1 (a), the maxillary right second molar M2 (b), the maxillary right third molar M3 (c) and the mandibular right second molar m2 (d). DMTA parameters are sorted by functional group. Red coloration indicates a negative correlation whereas blue coloration indicates a positive correlation. The larger and darker the points in the matrix, the closer the correlation is to 1 or −1. For a full description of each parameter, see table 1. Note the general stability of correlations across teeth.

Figure 2.

Correlation matrix of dental wear parameters applied to sheep molars (O. aries, n = 25) after a long-term feeding experiment on consistent diets (avoiding a discrepancy of wear proxies due to different time resolution). Correlations of the reduced DMTA parameter set (one measure per functional DMTA group, from area to volume), mesowear scores (static scores for the end of the experiment; occlusal relief OR and cusp shape CS scores, for the anterior and posterior or the sharpest cusp, for the ordinal mesowear score; and the difference in mesowear scores between the start and the end of the experiment); and differences in crown and root volume between the start and the end of the experiment, plotted as matrices for the maxillary right first molar M1 (a), the maxillary right second molar M2 (b), the maxillary right third molar M3 (c) and the mandibular right second molar m2 (d). Crown and root volume differences were only measured in M2 (CrownDiff and RootDiff). DMTA parameters are sorted by functional group. Red coloration indicates a negative correlation, whereas blue coloration indicates a positive correlation. The larger and darker the points in the matrix, the closer the correlation is to 1 or −1. For a full description of each parameter, see table 1. Note the general stability of correlations across teeth, and the paucity of correlations between DMTA parameters and measurements of change of a tooth over time. For r values, see electronic supplementary material, S1.

Figure 3.

Scatterplots representing correlations between mesowear and dental microwear texture parameters in the maxillary right second molar of sheep (O. aries, n = 25) after a long-term feeding experiment. Dental microtexture parameters: Smc, plateau size; Sdq, slope. Mesowear parameters: OR, occlusal relief; ORdiff, difference in OR scores between the first and last timepoints of the experiment; CSP, cusp shape of the posterior cusp. For a full description of each parameter, see table 1.

Figure 4.

Scatterplots representing correlations between crown tissue loss (CrownDiff) and dental microwear texture parameters in the maxillary right second molar of sheep (O. aries, n = 25) after a long-term feeding experiment. Dental microtexture parameters: mea, area; Asfc, complexity; Spc, peak sharpness; Sdq, slope. CrownDiff (mm³) is the difference in tooth crown volume between the first and last timepoints of the experiment. For a full description of each parameter, see table 1.