Crocodiles – They Really Kill

Crocodile, after hearing this word the facial expression of our face changes automatically. They frighten us by their fierce appearance and killing activity. Crocodiles belong to the class Reptilia of the phylum Chordata. The order to which they belong is Crocodilia and the family is Crocodylidae. There are three members of the family Crocodylidae which are present today and they comprise crocodiles, alligators, gharials and caimans. They are large aquatic reptiles found throughout the tropics, Asia, Africa, America and Australia. They flourish well in the rivers, lakes, wetlands and sometimes in the brackish water. They are strictly carnivorous feeding on vertebrates including fishes, birds and mammals. Sometimes they are also seen to predate upon molluscs and crustaceans. They are believed to have evolved 200 million years ago.

The word crocodile has got its origin from the ancient Greek word crocodilos which was used for lizards. The crocodiles are among the most complex reptiles which have a completely four chambered heart and well developed cerebral cortex and complete diaphragm and muscles adapted for locomotion. The external morphology is best suited for its aquatic mode of life. The body is streamlined in shape which allows it to swim swiftly in water. They possess webbed feet which are a perfect adaptation for aquatic mode of life and it reduces resistance while swimming. In crocodiles the back portion of mouth bears a palatal flap which prevents the entry of water into the mouth when they are in water. The nostrils are closed when they are under water. The brain case is bony and lacks the supratemporal and postfrontal bones. Their tongues are attached to the mouth by a delicate membrane so they are unable to stick out their tongues.

The body is covered externally by scales which bear pores and are sensory in function and are analogous with the lateral line system in fishes. The pores are basically present on the upper and lower jaws. The scales are also believed to secrete an oily substance which helps in removing the dirt. The crocodiles remain without food for very short duration. They can hold the prey very tightly and can grab it immediately. They have very strong and sharp teeth that can be easily pierced into the body of the victim. The muscles of the jaws are very strong. The crocodiles are ambush hunters and they wait for their prey to come closer to them and when the prey comes closer to them they grab it with their strong jaws. They are cold blooded and the metabolic rate is very slow so can remain without food for a longer duration. Although they appear slow but they have been recorded attacking the sharks also. Many crocodiles have been observed to swallow stones and these stones act as parts helping in crushing of the food similar to the gizzard in birds.

Salt glands are also noticed to be present at the surface of tongues of the crocodiles but they are absolutely absent in the alligators. They have well developed hearing capacity and are also known to produce sounds when they become aggressive. Tympanic membranes are also present. Sometimes they are also known to consume smaller crocodiles. They are under protection in many parts of the world and are also farmed commercially in some places. Their hides are the source of leather for making hand bags, shoes and also they form a major part of delicacy in some countries. The commercially farmed species include the Nile crocodile and the Saltwater crocodile. A hybrid of the saltwater crocodile called the Siamese crocodile is also produced in the Asian farms.

The eggs of saltwater crocodile are marketed to different areas and it has resulted in the production of saltwater crocodile population in Australia. Generally it is believed that they have evolved from the dinosaurs and the birds so they are placed in the group Archosauria.

Crocodile embryos lack sex chromosomes. Sex is affected by temperature. Males develop at the temperature range of 31.6 °C and females develop at slightly lower and higher temperatures. The incubation period is of 80 days on an average but is also influenced by the temperature. The crocodiles can walk on the land with a speed of about 17km/hr as recorded in the Australian freshwater crocodile. Maximum speed various from species to species.

Crocodiles lack salt glands so release the body heat through their mouth and they often sleep with their mouths open. The body size varies from species to species. The larger species can reach a size of 4.85 meters with body weight up to 1,200 kilograms. They show well pronounced sexual dimorphism with males larger in size than females and grow rapidly in comparison to females. The crocodiles start with life span with an average size of only 20 cm and reach various sizes later on. The largest species of crocodiles is the saltwater crocodile species found in the northern Australia and the south-east Asia.

There is no specific method for determining the age of crocodiles. Scientists use their self predicted guesses for this purpose. Some believe that the lamellar growth rings present on the bones and teeth help in the age detection. Apart from these inaccuracies the average age of the oldest crocodile recorded is of 130 years. The crocodiles bear smooth skin of the belly and on the sides while the dorsal surface is hard characterized by the presence of bony osteoderms. The hard skin acts as a protective cover and also prevents excessive heat loss through the body.

Crocodiles are dangerous to human beings and have been known to kill many people in different parts of the globe. Records of human death by crocodiles are famous in Britain and Burma. Apart from their threatening nature they are also a source of economic importance. Their skin is the source of leather for making items of commercial importance and also they are consumed in some countries as favourite food.

The conclusion is that we must love crocodiles and save them from extinction.