The Belly Crawl
The High Walk
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. Still there are some forms of locomotion that one really doesn't expect from a crocodile.
Even though they have been described as slow moving and lumbering animals when on land, I have never looked at crocodylians that way. To me everything from their amazing gallops to the common belly crawl, has always looked majestic and graceful. Anyway let's get down to the meat of this shall we.
The belly crawl is the one that most people view crocodylians as moving. In the belly crawl the legs are splayed out to the sides and move about in an oar like fashion. This is normally done slowly and for a short distance (it's mainly used to get in the water). But crocodylians are also able to move fast in a belly crawl. In this process the animal both moves it's body sinuously and slightly up and down. The legs still move sideways, but in a more diagonal progression so that the body rises up and down as the animal moves. The faster the crocodylian goes, the more sinuous the movements. A fast moving crocodylian in a belly crawl has it's entire body thrashing from side
to side, which migh look ungainly at first, but when one sees the distance covered by it, this "ungainly" movement becomes quite fluid.
Now many scientists, when attempting to explain this belly crawl, refer to to the way that most reptiles move. They state that when a lizard moves with it's splayed limbs, it doesn't raise it's body that far off the ground and is usually stuck dragging it behind. This is only a half truth. Some of the shorter legged lizards such as lizards in the Anguid family have bodies that are real long, and legs that are real short. The effect of this is, of course, that they drag most of their bodies on the ground when walking. On the other hand, we have the more common longer legged lizards such as the varanids, 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. And then of course we have snakes, but they sort of speak for themselves in that department.
At any rate the belly crawl is the most commonly seen in crocodylians, not so much for it's frequency of use, just that the times that we usually view these animals are when they are resting and sliding into the water. Below is an example:
This is one of the strangest ways of beating around the bush that I have ever read about in scientific literature. One of the old characteristics of a reptile was that of a sprawling animal. And for years this worked out nicely, but then when people started to take a closer look at reptiles (crocodylians in particular) they noticed that some of them did walk upright and therefore couldn't be called a reptile. Well rather then just dumping this stupid classification mistake (which later did happen) they danced around it and stated that crocodylians don't really walk erect and instead walk semi-erect. This was based on the fact that the humerus (your upper arm) sticks out and to the side when walking and the the
femur (the upper leg bone) stuck out just ever so slightly. Well, if we are to believe this lie then we would have to call sauropods and ceratopsians (both deinosaurs) sprawlers. Why, because sauropod legs do stick out from the hip just ever so slightly. So slight in fact that it is unnoticeable when covered in flesh and muscle. As for ceratopsians their forelegs stick out from the sides a bit making them look like they are in the middle of a push up. Yet, when deinosaur hips and legs were found it was finally realized that some reptiles had an erect stance and that was finally dropped. Still for some reason science will not acknowledge the fact that crocodylians have an upright stance. They refuse to admit that these animals
walk erectly when they want to. So that's the backstory to it.
The way that crocodylians are able to accomplish this erect walk is in their ankle arrangement. Most animals have their ankle bones(tarsals) arranged in manner so that the foot can only move in two linear directions. This forces either a full sprawling posture ala lizards, or a fully erect posture ala birds. With the crocodylians though (and this is where the transitional bit comes in) their ankles are arranged in a much different manner. Their upper (proximal) bones of the ankle are split up and arranged so that the joint passes between them instead of between the proximal and distal (lower) bones like in lizards. The astragalus (a proximal ankle bone) moves with the shank (lower leg) while the calcaneum (the other proximal ankle bone which is equivalant to the heel bone in our feet) moves with the foot.
The calcaneum also bears a socket in which a peg in the astragalus fits. What this means is that instead of using only one form of locomotion, crocodylians are able to employ both forms. When belly crawling the femur is pushed out horizontally and the foot must come down at an angle more flush with the side of the shank. Now in order to do the high walk the foot must be able to swivel 900 to come underneath the shank and in line with the newly positioned leg. So can you guess what the peg and socket do. If you said swivel then your right. They allow the ankle to swivel into it's new position and hold itself in place as the animal moves. Pretty damn amazing isn't it?
Yup, you heard right, crocodylians gallop. This is the most amazing form of crocodylian locomotion, for unlike the usual ways of walking employed by most vertebrates, where the legs move - right fore - left hind - left fore - right hind - and so on producing a stable tripod stance, in the gallop the legs move completely different. In this gait the back limbs shove off pushing the animal up and forward. Then the back straightens and the arms outstretch to catch the body as it reaches the ground (Fig.1). Now the back bends and the hind limbs swing forward to grip the ground and shoot the animal forward again (Fig.2).
So now instead of the stable tripod, the animal is in the more unstable bipodal position with only two legs touching the ground at one time
and the severly unstable (cause nothings touching) "no-pod" position in which the entire body is suspended in the air.
The gallop of a crocodylian is different from that of a horse and looks more like that of a bounding rabbit. It's 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 by a crocodile that is freaked out and attempting to escape from danger. 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, but then I wouldn't put anything past a crocodylian.
Yes we're still talking about crocodylians. This is a behaviour that has been observed in the Colombian crocodile (Crocodylus rhombifer) although there is no reason to doubt that it happens in other crocodylians too.
Basically what happens is the croc firmly placing it's hindlegs on the ground and lifting first up with it's forelegs and then it's hind. 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.
Good luck finding any of this in scientific literature. Crocodylians and climbing don't exactly go hand in hand, but there are cases of climbing animals. These are mostly seen in alligatoroids (probably due to the more coverage given to them) and in youngsters at that. The animals don't usually climb too high (which is good since they lack any grasping appendages) and it is probably done to get a better basking spot and avoid predators. Crocodylians have been seen climbing everything from ferns and other low hanging brush, to potted plants and chain linked fence.
And that will do it for the terrestrial locomotion now on to...
This form of locomotion probably deserves the most coverage, since this is what crocodylians are most adapted to, but I personally don't find it as interesting as their terrestrial modes, but thats me (NOTE: Just because I don't find it that interesting doesn't mean it's not interesting)
When crocodylians are swimming around lazily enjoying the day they can be seen on the surface of the water with their arms and legs outstretched to keep them from rolling over. 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 it's 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 it's potential prey without getting caught. The vertical position allows better control for diving which just so happens to be next.
Crocodylians underwater move in two different ways. The first way is by means of the limbs. In this form the tail becomes secondary. The crocodylian basically just walks along the bottom of the river or lake bed, taking the normal step and kicking off almost like it were walking on land. Sometimes the crocodylian will only use it's longer hindlegs for this and leave the forelegs tucked near the body. This form of locomotion is for relaxation purposes mostly and can only be done in areas without any strong currents. For strong currents crocodylians do something different.
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 helpful for getting 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 it's 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 it's entire body. The speeds reached are pretty impressive, around 50 kilometers (30 mph's) per hour. A crocodylian underwater is not to be messed with; that's for sure.
Leaping, lunging and tail walking
Seeing as how these last three involve both being below and above the water I figured that they deserved their own section.
This occurs when the crocodylian has built up enough speed underwater that it can launch itself up and out at any object in it's way. This is mainly used to attack oncoming rivals during the mating season. The animal can close the gap faster this way the underwater (it's a friction thing). It is also used for fast attacks on shore animals. This usually happens when the animal has detected the crocodylian's presence and is attempting to flee. A leap can carry a crocodylian several times it's length onto shore.
This is a lot like leaping except it's used to grab prey near the water. The animal digs it's hindlegs in the embankment and curls the tail. Then at the right moment it surges forward by rotating the legs back and unfurling the tail. The main difference between this and leaping is that it's done from a stationary position. A crocodylian doing this can cover many feet in mere seconds. Once beaching itself the crocodylian may continue it's attempt to capture it's prey by once again swinging the rear legs forward and launching itself forward some more. It may even anchor it's head to the ground in the process of swinging the legs forward as it continues it's attempt. Eventually this might be turned into a run. By doing this crocodylians have been seen running near vertical up small cliffs reaching in upwards of 1.5 meters (5 feet). Mind you this is all going
on in seconds of time. One minute a the animal is in the water and the next it could be 6 or 7 meters (about 20-30 feet) from the water. Scary isn't it.
This form of movement is the one that the tourist industry loves. It is used by crocodylians attempting to snatch low flying birds and animal in trees. Oh and of course lunchmeat held out by tour operators on tour boats in Australia. In order to do this the croc usually will station itself vertically underwater with the tail curved back against the ground and the legs tensed up like springs. When the animal spots it's prey above the water it jumps with it's hind legs and pushes off with it's tail. This shoots the animal straight up and at it's prey. These tail walks can take a crocodylian many feet into the air. Young animals are able to shoot their entire bodies out of the air plus several feet more.
Adults are usually capable of getting all the way up to their hind legs.
The difference in height achieved by both young and old is probably nill. A crocodylian doing this
is pretty good at judging the distance needed to reach it's prefered prey. Tail walking can even be done when moving although the angle needed to be reached is so steep that it could only be done in deep water. By doing this with the momentum achieved by swimming the animals can reach even loftier heights.
One last thing about the tail walk. It's the equivalant of the terrestrial gallop. Absolutely amazing to see, but very rare indeed. Unless of course your on a tour boat:)