HUTCHINSON, J.R.*; DONELAN, J.M.; ERICKSON, G.E.; VLIET, K.A.; KLEDZIK, D.; KRAM, R.; Stanford Univ.; Univ. of Alberta, Canada; Florida State Univ., Tallahassee; Univ. of Florida, Gainesville; St. Augustine Alligator Farm, Florida; Univ. of Colorado, Boulder; ; : The Biomechanics of Bounding Crocodiles
Aside from some mammals, crocodylians are the only major extant tetrapod group known to routinely use the bound and similar gaits such as galloping. Larger crocodiles do not bound or gallop; their fastest gaits are trots or high walks. To understand the biomechanics of bounding gaits, and how size limits crocodilian speed and gait, we measured joint kinematics and ground-reaction forces (GRFs) in a diversity of crocodylians (Alligator mississippiensis, Crocodylus cataphractus, C. niloticus, C. johnsoni, C. rhombifer, and Osteolaemus tetraspis; the latter four of which used bounding gaits). These crocodiles had a ten-fold range of size (3.9-43.2 kg); 85 trials from 15 individuals moving at various speeds were sampled.
Our data show that the bound was twice as fast as the trot (2.0 m/s vs. 1.0 m/s). The crocodiles typically used half-bound gaits, although we also recorded some rapid trots and transverse gallops. The GRFs demonstrated that the animals used their forelimbs to brake and their hindlimbs to accelerate. The peak GRFs were very high: up to 1.9x and 2.8x body weight for each pair of fore- and hindlimbs respectively. The positive external mechanical power output at these speeds was a surprisingly high 10-20 W/kg body mass. These data reveal some of the biomechanical requirements for fast terrestrial locomotion in crocodylians. Our data support the hypothesis that bounding is ancestral for the clade Crocodylia, perhaps secondarily lost in alligators, adult gavials, and large adult crocodiles.
