Crocodilians, individually and collectively, have a diversity of locomotor patterns. When moving unhurried on land, a crocodile proceeds with a stately high walk but, if frightened it will plunge down an embankment in an inelegant belly crawl. A few species can even gallop across a beach with hare-like bounds. No crocodilian however shows any skills as a climber and certainly none has developed skills as an aerialist.
The high walk of the crocodilians is unique among the living reptiles. Turtles and lizards walk with a sprawled posture; the limbs project outward from the body, rather than downward, so that the body is hardly raised above the ground. In contrast, the limbs of a bird or mammal extend directly beneath the body and elevate it high off the ground. The high walk of crocodilians is much more similar to the mammalian walking posture than to the typical sprawled reptile one. Crocodilians hold their limbs nearly, although not completely, vertical beneath the body, resulting in an elevated posture that is high enough to raise much of the tail off the ground.
The walking gait of the crocodilians shows the same sequence of limb movements as in all four- limbed animals – right fore, left hind, left fore, right hind, and so on in sequence. This diagonal sequence provides a well- balanced tripod of support as the animal moves forward. With an increase in speed, the diagonally opposite limbs begin to move forward almost simultaneously and faster in a trot-like gait. The resulting bipedal support is less stable but the quick back and forth shift between diagonal support pairs establishes a dynamic equilibrium.
However, if the limbs move too fast this equilibrium is lost and the crocodilian, especially if it is an adult, appears to stumble into a new mode of locomotion, crashing onto its chest and belly with the limbs splayed to the sides. With side-to-side twists of the body and rowing-like swings of the limbs, the crocodilian thrashes and slides on its belly into the water. This belly crawl is most effective on steep shorelines for fast escape but can also be used to slip quietly into the water.
In smaller crocodiles the running gait can change into a bouncing gallop – the hind limbs push the crocodile forward in a leap; the body straightens; the forelimbs extend and catch the body at the end of the leap; the hind limbs swing forward as the back bends; and then the hind limbs leap the animal forward as the back bends. This bouncing gallop produces speeds of 3- 17 kilometers (2-10 miles) an hour, not the 15-30 kilometers (9 – 19 miles) an hour of some mammals, but consistently faster than the 0.3- 4.5 kilometers (0.2 – 3 miles) an hour of the crocodilian high walk.
Posted in Structure and Function