Fig. 2. Frames from video footage of swimming turtles during forelimb protraction (recovery phase). (A–C) Trachemys scripta, lateral view. (D–F) T. scripta, ventral view. (G–I) Apalone spinifera, ventral view. (J–L) A. spinifera, lateral view. The grid scale is 1 cm in each frame. Movements of the left forelimb were analyzed; thus, in lateral views, the focal forelimb is the one closest to the viewer, but in ventral views (which were filmed using a mirror) the focal forelimb is the one closest to the bottom of the video frame. Lateral and ventral views for each species are from the same experimental trial. Images in each column depict an approximately equivalent instant in the locomotor cycle: left-hand column (A,D,G,J), early recovery phase; center column (B,E,H,K), mid recovery phase; right-hand column (C,F,I,L), late recovery phase. The white arrow in K points to the forelimb in A. spinifera, which is difficult to see in still lateral frames while the forefoot is feathered. Note that video frames illustrated in Fig. 3 depict thrust phase from the same swimming trials, so that sequential viewing of Fig. 2 and Fig. 3 will allow examination of entire kinematic cycles for turtle forelimbs during swimming.
