Analyses
We used phylogenetic comparative methods, using a tree pruned from Pyron
& Burbrink (2014). If species were not present in this tree, we used
the closest relative (Supplementary material 2). We tested whether tooth
curvature length, the mean degree of curvature, and the maximum degree
of curvature were correlated with one another using Pearson correlation
tests (function cor.test from the ‘stats’ package). We then
tested whether these measurements were associated with our factors using
the function phylANOVA of the package ‘phytools’ using 1000
simulations and a Holm correction for the post hoc pairwise t-tests. The
normality of the data distribution was checked using a Shapiro test and
variables were log-transformed to ensure normality when necessary. We
used the function procD.pgls in ‘geomorph’ (Adams, 2014) to run
phylogenetic ANCOVAs and ANOVAs to test the link between tooth shape and
our different dietary constraints. For ANCOVAs, we used the
log-transformed centroid size of the tooth as a covariate. Since our
predictive factors are not entirely independent from one another, we
performed one model per factor. We compared the fit of our different
models using the function model.comparison in the ‘RRPP’ package
(Collyer & Adams, 2022), that calculated the log-likelihood of each
model. Statistical significance was tested by performing 10000
permutations. We performed subsequent post-hoc pairwise comparisons
using the pairwise function in ‘RRPP’ on the best models. All
geometric morphometric, statistical analyses and visualizations were
performed in R version 3.4.4 (R Core Team, 2018) (R code and data
available in Supplementary Material), except the landmark acquisition
performed in MorphoDig (Lebrun, 2017). To highlight shape differences
between ecological groups, we used mesh deformation of the template
specimen toward the mean landmark configuration for each group, using
the plotRefToTarget function of the ‘geomorph’ package. We also
used the function spheres3d from the ‘rgl’ package that allows to
visualize both the inner and outer surfaces of the teeth, providing
information on teeth thickness (Fig. 5).