Strategies of descent on vertical supports of various diameters by species.

A. Photographs illustrating the three different strategies of descent identified in this study. Black arrows represent the axis of the body regarding the support and the direction of the movement, and grey arrows represent the direction of the gaze. B. Proportions (in %) of each descent type (yellow = head-first descent, light green = side descent, and dark green = tail-first descent) occurring on each support category (vertical branches of large, medium, and small diameters represented by brown icons at the top of the graph), by species. Proportions of all individuals of the same species (n) were averaged. See Table S1 for details on the individuals studied, and Table S2 for the mean body masses (BM) references. NA = no data for the given condition. Results of statistical tests between support diameters (ANOVAs or MANOVAs on bootstrapped samples, confirmed by post hoc tests) are represented with annotations defined as NS (non-significant): p > 0.05, *: p < 0.05, **: p < 0.01, and ***: p < 0.001. See SuppTables A for associated p-values. C. Associated phylogeny of the species studied with branch length obtained from http://timetree.org 129. D. Photographs of individuals of various species descending vertical supports of different diameters.

Kinematics of locomotion during ascents and descents on vertical supports of varying diameters.

A. Mean absolute speeds by species during ascents and each descent strategy on the vertical supports of large, medium, and small diameters (represented by brown icons on the top left of the plots), with box plot representations of the medians for all species combined in ascents and each descent strategy. A. Mean relative speeds (based on individuals’ body length) by species during ascents and each descent strategy on each support type, with box plot representations of the medians for all species combined in ascents and each descent strategy. C. Mean duty factors by species, differentiating forelimbs (left box plots) and hindlimbs (right box plots), during ascents and each descent strategy on each support type, with box plot representations of the medians for all species combined in ascents and each descent strategy. Results of statistical tests between ascents and each descent strategy (two-sided Mann Whitney U tests) are represented with annotations defined as NS: p > 0.05, *: p < 0.05, **: p < 0.01, and ***: p < 0.001. See SuppTables B, C and D for associated p-values. Percentages correspond to the relative variation of each kinematic variable mean in each descent condition compared to ascents.

Proportions (in %) of gait types by support diameters for ascents and each descent strategies, for all phylogenetic groups.

Results of statistical tests on the fraction of symmetrical versus asymmetrical gaits by group between ascents and descents on each support (two-sided Wilcoxon signed rank tests) are represented with annotations defined as NS: p > 0.05, *: p < 0.05, **: p < 0.01, and ***: p < 0.001. NA = not applicable. DSDC: Diagonal sequence - diagonal couplet, LSDC: Lateral sequence – diagonal couplet, LSLC: Lateral sequence – lateral couplet. See SuppTables F for associated post hoc corrected p-values. See Fig. S1 for detailed proportions of gait types by species and support diameters.

Definitions of body measurements performed on extant and extinct individuals and calculation of limbs proportions.

Morphological correlates with vertical descents and prediction of descent strategy in extinct species.

Spearman correlations and associated corrected p-values between the proportion of head descents by extant species and A. the logarithm of mean body mass, B. the mean encephalization quotient (EQ), C. the leg to body length ratio (in %), and D. between the proportion of side descent in extant primate species only and the hallux to foot length ratio (in %). Each plot includes also the head descent proportion (A., B., C.) and side descent proportion (D.) of fossils predicted with the Schafer’s multiple imputation procedure. See Table 1 for body measurements definitions and Tables S2 and S3 for mean body masses, ECV and calculated EQ by species. See Fig. S3 for the plots of the percentage of head descent against the six other morphological variables analyzed by species, and SuppTables H and I for Spearman rhos and associated corrected p-values between each morphological variable and the proportion of respectively head (SuppTables H) and side descents (SuppTables I) on vertical supports. See Table S4 for calculated morphological variables of extinct species and SuppTable J for the resulting predictions of their descent behavior.

Phylogeny of studied species, including extant and extinct taxa, and representation of the best evolutionary model of head-first descent proportion.

We calculated a consensus tree for extant species based on 1000 trees from vertlife.org, to which we added extinct taxa using age and phylogenetic topology from literature. See Table S2. for estimated age of extinct species and associated references. The best evolutionary model of head-first descent proportion is an Ornstein-Uhlenbeck evolutionary model with two optimums (OUM) with a peak shift occurring at the node ‘plesiadapiformes + euprimates’. The associated theta peaks of head-first descent proportions of the two subgroups ‘plesidapiforms + euprimates’ vs ‘others’ are represented in red and black respectively.