Trait Measurements, Trait Evolution, and Trait-Dependent Diversification.

We compiled and measured four mandibular and dental traits for 69 species (1,119 specimens): LP3, LCM3, and HCM3, as proxies for diet (63, 67, 68); and LMRL, as proxy for body mass (69). For each species, a trait value corresponds to the species’ arithmetic mean and depends on the number of specimens available for each species. Measurements were taken in millimeters using a Nikon 10 measurescope (binocular microscope with measuring device) and a digital caliper or were taken directly from the literature (615 specimens measurements derived from the compilation of ref. 45, Dataset S3).

The distribution of trait values and ecological spaces over time were performed using R 4.1.3 software (94). They are based on the Dataset S4 combining the fossil species from Dataset S1, their lifespan (Te and Ts from PyRate), and the mean trait value (Dataset S3). All ecological spaces derive from a global PCA of the log-transformed traits (to linearize any allometry) and represent the species’ morphological repartition at given MP reference level(s). For the trait distributions over time (SI Appendix, Figs. S6–S8) and the Covar birth–death model (see below), diet traits were standardized by LMRL to reduce the effect of size on the data distribution.

We used the Covar birth–death model (6) with similar settings as in the BDS model to test for the influence of these four mandibulo-dental traits on the diversification dynamics of European artiodactyls on the Eocene–Oligocene interval. Under this model, changes in λ, μ, and q rates are correlated with changes in continuous (log-transformed) traits through estimated correlation parameters (αλ, αμ, and αq), with α > 0 indicating positive correlation between the trait value and a birth–death rate and conversely with α < 0. The correlation is considered significant when the 95% Credibility Interval (CI) does not overlap with 0. We performed the analyses for the all European artiodactyl dataset and for endemic and immigrant artiodactyl datasets.