Fig. 1. Kinematic landmarks and angles used to describe hindlimb movements in alligators during locomotion. (A) Three-dimensional coordinates were digitized for one trunk landmark (T), and landmarks for the hip joint (H; on both sides: H left, H right); the knee (K), the ankle (A) and foot (F; on the skin on the lateral aspect of the metatarsal-tarsal articulation). (B) Three-dimensional angles were calculated for femoral retraction angle (the angle between landmarks T-H right-K indicating primarily femoral retraction/protraction movements); knee angle (angle H-K-A indicating knee flexion and extension), and ankle angle (angle K-A-F indicating foot flexion and extension). (C) Femoral adduction angle (angle H left-H right-K) was calculated to quantify the degree of hip adduction relative to a transverse line through the acetabula. (D) Ground reaction forces in body weight units (BWU) of a typical trial indicating key kinetic events: peak vertical force, peak braking force, braking-to-propulsive transition (zero fore-aft force), peak propulsive force and peak lateral force.