Appendix S1. Full dataset of MC1 transformations with respect to the trapezium in gibbons (Hylobatidae) and rhesus macaques (Macaca mulatta). Rotation angles (in degrees °) and translation (in mm) are reported for each axis; x, y, and z represent the axes of the TMC joint. x: the dorsopalmar axis, rotation about x results in thumb abduction (−) - adduction (+), positive translation along x results in palmar translation; y: the proximodistal axis, rotation about y results in axial rotation (internal +, external -) of the MC1, positive translation along y results in proximal translation; z: the radioulnar axis, rotation about z results in flexion (+) – extension (−), positive translation along z results in radial translation. Axes in bold indicate the relevant rotation axis during each movement; x for abduction – adduction, z for flexion – extension.