Fig. 2. (A) Data collection setup, illustrating how forelimb force data were collected (first contact with force platform). In this diagram, the opossum is moving up the incline, and a single forelimb has stepped onto the force plate. (B,C) Digitized landmarks and the calculation of overall limb excursion angles. Protraction angle was measured at touchdown, retraction angle was measured at lift-off, and mediolateral angles were measured at both events.