Crocodylian locomotory patterns can be broken down into two different categories: Aquatic and Terrestrial. Since crocodylians are semi-aquatic animals, they have adapted to both life on land and life in the water. Even with this in mind though, there are some forms of locomotion one would not expect from a crocodylian.
Now the common analogy used for the belly crawl is that of the way in which a lizard moves. It is usually stated that when a lizard moves with its splayed limbs, it doesn't raise its body that far off the ground and is usually stuck dragging its stomach and tail behind, but this is only a half truth. Some of the shorter legged lizards such as anguids, have bodies that are very long, and legs that are very short. The effect of this bodyplan is, of course, that the lizards drag most of their bodies on the ground when walking. On the other hand, we have more common longer legged lizards such as the varanids and iguanians, which are able to not only carry their bodies off the ground, but also around two thirds of their tails too. Turtles, with the exception of the fully aquatic variety, are all able to carry their bodies off the ground.Then of course there are snakes, but they sort of speak for themselves in that department.
The belly crawl is the most commonly seen form of locomotion in crocodylians, not so much for its frequency of use, as it is the times at which they usually viewed (e.g. resting and sliding into the water).
One of the more popular characteristics of being a reptile is that of having a sprawling stance, but not all reptiles are the same, and here one witnessess one of the transitional elements of crocodylians. For along with the more typically seen sprawling gait, crocodylians can also walk in a near to fully erect stance (depending on species). They accomplish this by using a suite of characteristics which one can learn about here.Crocodylians use the "high walk", as it is termed, to traverse longer distances than would be comfortably possible with the belly crawl. By raising their bodies this much higher above the ground, they are able to see farther and avoid obstacles such as rocks and sticks. By having the legs directly underneath the body, these animals can more easily support their great bulk.
High walks generally don't go very far or very fast. They tend to be used just to get from one basking spot to another or to the water. Still there are instances where crocodylians (e.g. Mugger & Nile crocs) have traversed many miles overland. Their "high walks" make this mode possible.
Of course seeing pictures of crocodylians galloping, while cool, is nothing compared to actually seeing them in action. So for those who are interested, Adam Britton of crocodilian.com has taken digital movies of a Crocodylus johnstoni in a gallop along with other movies of croc behaviour.To view the movies head on over to crocodilian.com's crocs on film site.
The gallop of a crocodylian is different from that of a horse and looks more like that of a cat. It is still quite a sight and produces speeds of up to 3-17 kilometers (2-10 miles) per hour. The gallop is never (or at least has never been observed) used in hunting and is employed only by a crocodile that is frightened and attempting to flee. This form of locomotion is seen in the smaller species of crocodylian and can probably be used in the young of all species, but as the animals get bigger the chances of them doing this falls shorter. To date, there has been no documented case of a galloping adult.
To accomplish this the croc firmly places its hindlegs on the ground and lifts first up with its forelegs and then its hind. This is the same way as a dog or cat would do it, just on a MUCH larger scale. This is probably used to get things hanging in branches and such, maybe even a low flying bird. Both juvenile and adults Colombian crocs have been seen doing this, although it gets increasingly rarer the larger the adult.
The tail is either not moving (if in calm water) or is in a constant state of flux (if in moving water) as the crocodylian continually makes minute changes to compensate for the moving water. The entire upper portion of the body is usually out of the water and the animal can just basically observe everything thats going on. By making slight kicks to the side with its legs and by swishing the tail slightly the animal is capable of turning itself around.All of this is for relaxation purposes only and is never used in hunting or hiding (since the main goal of both is to stay hidden). The other position crocodylians stay in above water is the one used in hunting. The body is held near vertical underwater while the upper portion of the head (containing the five basic senses) on top. The limbs are either held away or underneath the body for stabilzation purposes and the tail doesn't move (or moves slightly). In this position the crocodylian can survey its potential prey without getting caught. The vertical position allows better control for diving which just so happens to be next.
When moving fast or against a current, crocodylians tuck their limbs to their body and use the tail as the main propulsionary unit. This is decreases drag from the limbs and increases underwater speed. Hunting crocodylians employ this mode when moving into a new position quickly and dealing with fast moving water. For the most part crocodylians avoid areas with fast moving or choppy water. This probably has to do with taking in air. Whereas a crocodylian in need of a breath can just stick the tip of its noise out in calm water, it needs to raise the entire head up in choppy water. So crocodylians probably aim for the calm water just for the ease of breathing. A crocodylian that is moving very fast underwater will be undulating its entire body. The speeds reached are pretty impressive, around 50 kilometers (30 mph's) per hour.
Crocodylians lack fins, and many of their slow underwater maneuvers don't involve the limbs. This ability of crocodylians to slowly dive, pitch and roll, without the aid of their limbs, or tails, has puzzled scientists.Recently a paper by Uriona and Farmer (2008) found that crocodylians are able to accomplish this amazing feat by actually moving their lungs!
Special muscles along the body (the M.diaphragmaticus, M.ischiopubis, M.rectus abdominis, M.intercostalis internus and M.transversus abdominis), which are normally associated with respiration, have been exapted in crocodylians for use underwater. By moving the lungs to different parts of the body cavity, crocodylians are able to change their local density distribution.For instance, by moving their lungs towards the rear of their body cavity, the rear end of the animal becomes less dense, and starts to float to the surface. The front of the animal, meanwhile, is now denser than before, and starts to sink.
By doing this internally a crocodile can dive underwater without moving any external bodypart. This reduces turbulence in the water, thus allowing crocodylians to better sneak up on unwary prey.
Leaping, lunging and tail walking