• Grant Reed

About Crocodiles


Reptilia



Common Features Of Reptilia

Class reptilia:  are ectothermic, have a back-bone, breathe air and have internal fertilization of the egg.  The skin is covered in a protective layer of scales or scutes.


Common Features Of Crocodylia

Order crocodylia: this includes crocodiles, caimans, alligators and gavials; however, of these, the Nile crocodile is the only species found in southern Africa. Crocodylia have a four chambered heart, nictating membrane that closes over the eyes when submerging, their legs are short (relative to the body size) and they have a sprawled appearance when walking.


Crocodylia


History

F1 Crocodylia date back 135 to 65 million years. Although there is only one family (Crocodylidae) that falls under the order crocodylia, there are 21 different species to be found in the world and southern Africa has just one of these…the Nile crocodile


Physical Features

Crocodiles are covered in large olive green to grey scales on the back, a yellow belly and black bands across the tail; they can reach in excess of 6m in length (40% of this is the tail) and weigh up to 1000kg.


The eyes and nose and ears sit proud of the rest of the head; this adaptation allows a crocodile to keep these sensing organs above water whilst the rest of the body is submerged.


The upper jaw is fused with the rest of the skull and only the lower jaw can move independently. The head must be lifted to allow the bottom jaw to fall open (“mouth-gaping”) when basking in the sun.


These reptiles lack the vomeronasal organ.


Their sharp teeth are used to keep a firm grip on the prey. The 64-68 teeth are frequently replaced.   It has a long, spear-shaped tail, short legs and webbed hind feet. The oar like tail allows this reptile to move swiftly through the water using the webbed back feet as rudders.

Although not true of other reptilia, the crocodile, in line with mammals and birds, has a four-chambered heart.


Because the thick hide of the crocodile does not allow the fast transfer of the heat from the sun to the blood, the animal lies on the bank with its mouth open allowing the soft membrane to absorb heat and circulate it to the rest of the body…


Encountering Crocodiles

When in the vicinity of crocodile infested waters, care should be taken not to go into the water or close to the water’s edge as they are able to launch themselves three meters horizontally onto a bank with an exit speed of 70kph. Legs and arms hanging out of boats or makoros are a temptation to crocodiles cruising around below the surface


Although on land their speed is only 14kph, in the water their oar like tail propels them at great speed. Crocodiles quickly become aware of the habits of mammals, including man, and they will set up an ambush for prey that visits the site on a regular basis.


They are often seen during the day on sand banks basking in the sun with their mouths open: a) in the early morning and late afternoon this behavior allows the sun’s rays to heat up the blood just beneath the soft membrane. This warm blood circulates and heats up the rest of the body and b) on a hot day, the evaporation from the open mouth helps to cool the brain.  They are most active at night.


After dark they often, with their excellent night vision, hunt on land where they ambush prey.


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