Figure 4. Orientation (u₃ vector) of the covariation plane for the HL (A) and FL (B) segment elevation angles.

For FL, the normal to the plane for both FL_upp and FL_low tri-segmental models are shown. Top panels: spatial distribution of the normal (u₃) to the covariation plane in all animals. Each vector u₃ yields one point corresponding to the projection of the plane normal onto the unit sphere, the axes of which are the direction cosines with the axes of segment elevation angles (u_3t, u_3s, u_3f). Positive direction of the semi-axes is indicated by arrow. Lower panels: u₃ vectors for different animals lay on the plane (perpendicular to the averaged u₁ vector across animals), α - angle of rotation of u₃ on this plane (α = 0 corresponds to the projection of the shank, upper arm and lower arm semi-axes on that plane for HL, FL_upp and FL_low, respectively). Animals are labeled as in Table 1 and different colors and markers refer to different taxonomic orders and species, respectively. Note a higher data dispersion for HL compared to FL across animals. Source files are available in the SourceData4-Figure4.zip file.

Figure 4—figure supplement 1. Reconstructed ancestral trait values of α for HL on a phylogeny.

Reconstructed ancestral states for a continuous trait, that is the angle α for HL (angle of rotation of u₃, Figure 4A), are plotted in a color scale with gradient projection onto the phylogenetic tree. Note that close relatives are not more similar than distant ones (except for birds), as also shown by the low phylogenetic signal (K = 0.1, see main text). Source files are available in the SourceData4-Figure 4—figure supplement 1—souce data 1.zip file.