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Crocodile – the semi-aquatic reptilian predator

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Description
    Crocodiles, represent large semiaquatic reptiles that live all over the tropical regions, for instance in Africa, Asia, America and Australia. The word “crocodile” is used for species that belong to the biological subfamily of Crocodylinae.

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However, this particular term is applied generally to all existing members of the Crocodilia order, such as Tomistoma, alligators, caimans of the Alligatoridae family, gharials of the Gavialidae family and the rest of the living species, and also the Crocodylomorpha fossils.
Even though the crocodiles resemble very much to alligators and gharial, they all appertain to different biological families. The gharial bears a snout that is narrow and it’s easier to recognize unlike the morphological variations that are harder to discern in both crocodiles and alligators. The most distinguished features that separate these species are lying perceptible in the form of their head. Crocodiles have heads that are narrower and longer and in a shape of V, while alligators and caimans have their snout shaped as U.
    In the Eocene epoch, crocodiles first began to separate from other crocodilians, approximately 55 million years ago.

     Today's ancestor crocodile, Sarcosuchus, was an extinct genus of crocodyliform and distant relative of today crocodile that lived 112 million years ago. It dates from the early Cretaceous Period of what is now Africa and is one of the largest giant crocodile-like reptiles that ever lived. It was almost twice as long as the modern saltwater crocodile and weighed approximately 8 to 10 tonnes.
      Until recently, all that was known of the species was a few fossilized teeth and armor plates.
Nowadays, the crocodiles might become extinct due to different factors, human being one and the most important; some of them being categorized as critically threatened.



Characteristics
    The physical features of a crocodile give it the ability to be a victorious predator. Crocodile’s external morphology represents a distinct evidence of its type of lifestyle defined by aquatic and predatory activities. Its aerodynamic body structure offers it the ability of swimming swiftly. When a crocodile swims, it always tucks its feet close to the body, diminishing in this way the water resistance, which enables it to swim faster. Crocodiles have webbed feet that gives them the ability to turn around faster and to make all kinds of sudden movements through water or to start swimming. The webbed feet don’t actually help the reptile to propel in the water. When it comes to shallower water, the webbed feet are of great use for crocodiles because they can move around just by stepping on the ground. These reptiles have a palatalized flap at the back of their mouth, which is a rigid tissue that prevents water from entering. The palatal flap follows a route from the nostrils all the way to the glottis that goes around the mouth. When submerging, crocodile’s nostrils aren’t opened anymore.

    Crocodilians are some sort of diapsid as archosaurs, though the skull’s post-orbital openings are decreased. The cranium walls are osseous but the supratemporal bone and the postfrontal one are absent. Crocodiles have confined tongues, which are kept in place by a tissue layer to limit their movement. Due to this, the reptiles can’t stick their tongues out. The belly of a crocodile’s body consists of smooth skin as well as its sides. On the other hand, the dorsal surfaces of its body are equipped with prominent osteoderms. The skin made of armor contains scales and is thick, and furrowed to offer protection. Still, even though the crocodiles have this kind of armor, they are capable of absorbing heat because they got some kind of web made of little capillaries that permits blood to absorb heat through the armored skin. The scales from the crocodile’s armor have pores that operate like sensors similarly to the lateral line of fishes. They can be visible on crocodilian’s upper jaw or lower one. There’s a chance that crocodiles produce secretions because they leave traces of a greasy substance, which seems like it removes the mud.



Size
    The size differs a lot among all species, for example the dwarf crocodile is the smallest reptile, while the saltwater crocodile is one of the largest reptilians. Species like Osteolaemus grow up to 1.5 or 1.9 when they become adult unlike the saltwater crocodile that only reaches an approximate size of 7 m, meaning 23 ft, and it weighs about 2,000 kg, which means 4,400 lb. Many other big species can grow to dimensions over 5.2 m, as in 17 ft long, and weigh more than 900 kg, meaning 2,000 lb.

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Crocodiles indicate obvious signs of sexual dimorphism because males grow more faster and larger than females. In spite of their large dimensions when they become adults, crocodiles begin their living at roughly 20 cm long, meaning 7.9 in. Between all species of crocodile, the largest one is the saltwater crocodile that lives in the East part of India, North of Australia, all over South-East Asia, and in all of the surrounding waters.
An estuarine-Siamese crocodile called Yai, which means “big” in Thai, is the largest reptilian ever kept in captivity in Thailand, at the Samutprakarn Crocodile Farm and Zoo. This crocodile has the size of 6 m, as in 20 ft, in length and the weight of 1,114.27 kg, meaning 2,456.5 lb. 

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    When it comes to the largest crocodile ever captured, then it is Lolong, measuring about 6.17 m, as in 20.2 ft, in length and weighting around 1,075 kg, as in 2,370 lb. It was captured in the province Agusan del Sul, in Philippines, by a team from National Geographic.



Teeth
    Being polyphyodonts, crocodiles got the ability of replacing each one of their 80 teeth about 50 times during their lifespan of 35-75 years. Beside the tooth that’s entirely grown, there exist a little substitute tooth and an odontogenic stem cell found in the dental lamina that can be activated at command.

 


Species
    In total, there are about 14 existent species that have been identified to date. However, there are some species belonging to the genus Osteolaemus that need to be verified more thoroughly and, for the time being, they are classified as monotypic.
•    Crocodylus acutus – better known as the American crocodile
•    Crocodylus cataphractus – more precisely the slender-snouted crocodile
•    Crocodylus intermedius – as in the Orinoco crocodile
•    Crocodylus johnsoni – the freshwater crocodile, also known as Johnstone’s crocodile
•    Crocodylus mindorensis – meaning the Philippine crocodile
•    Crocodylus moreletii – known as the Morelet’s crocodile as well as the Mexican crocodile
•    Crocodylus niloticus – this one is the Nile crocodile, called also African crocodile, or even the Black crocodile in some parts of Madagascar
•    Crocodylus novaeguinae – that means the New Guinea crocodile
•    Crocodylus palustris – known also as mugger or marsh, or the Indian crocodile
•    Crocodylus porosus –  is the saltwater crocodile or estuarine crocodile
•    Crocodylus rhombifer – the Cuban crocodile
•    Crocodylus siamenis – is the Siamese crocodile that probably is extinct now throughout the wild
•    Crocodylus suchus – the West African crocodile or desert, or the sacred crocodile
•    Osteolaemus tetraspis – is the dwarf crocodile (a genus specie that is under further studies, to find out if this represents actually two species or not)



Habitat
    Crocodiles live in most parts of Africa, Southern Sahara, Madagascar, India, Sri Lanka, South-East Asia, the East Indies, North of Australia, Mexico, Central America, the West Indies, and in North-South America.
Fourteen species of crocodiles are found in temperate climates throughout the world and they assemble their homes by sandy sea-coasts or where there are muddy river banks and, or in mangrove swamps that are salty.



Diet
    Crocodiles are predators that hunt by ambushing. They first lay in wait for the fishes, or other living animals, to approach them, and only afterwards they rush out to attack by surprise. When it comes to their daily meals, they usually eat fish, amphibians, crustaceans, mollusks, birds, reptiles, mammals and sometimes they even cannibalize by eating smaller crocodiles.

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Nonetheless, the meals of a crocodile vary with species, dimensions and also with age. Diet is greatly diversified as the slender-snouted crocodiles and the freshwater ones are mainly fish-eaters, while the Nile crocodile and the saltwater crocodile hunt big mammals like buffalo, deer or wild boar. Also, it depends a lot on the size and age of every individual among the same type of species.

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Younger crocodiles basically prey on invertebrates and little fish, and every once in awhile they hunt larger victims. Being cold-blooded reptiles, crocodiles have a slow metabolism in order to last a period of time without eating at all. Although crocodiles seem to be slow, they actually attack very fast and are leaders among the predators from their environment, and many species even attacked and killed sharks and prominent cats.



Reproduction
    Crocodile’s reproduction consists in laying eggs, which can be laid in a hole or in nests, differing from specie to specie. The period of nesting usually takes between a few weeks to 6 months. Crocodiles always mate in water, where they can be seen mating more than once. The eggs are laid usually during night time and this process lasts roughly 30-40 minutes. The number of laid eggs depends a lot on the type of specie; they vary between 7 and 95. However, the sex of the young crocodile cannot be found out at the time of fertilization but during the incubation because it depends a lot on the temperature at which the eggs are held. Normally, the incubation lasts about 80 days but if it’s affected by temperature and type of specie, it can vary between 65 to 95 days.



Interesting and fun facts
•    The first crocodile appeared when the dinosaurs did, about 240 million years ago; that’s why they are related. It had the size of 1 m, as in 3 ft, in length and could even run on 2 feet! This explains why now crocodiles have hind limbs that are longer than the fore ones.
•    Crocodiles swallow stones because they help their digestive systems. The stones also aid them to achieve a better balance.
•    Crocodiles are frequently hunted because of their valuable skin. The price of a crocodile skin is over $10,000.
•    Crocodiles often keep their mouth wide open in order to cool off, so this sometimes isn’t an aggressive position. Crocodiles sweat through their mouth.
•    When crocodiles submerge, a protective membrane covers their eyes.
•    In a park located in Ukraine, a crocodile accidentally swallowed a mobile phone that fell from a visitor. The mobile phone kept on ringing inside of it!
•    The expression “cry crocodile tears” comes from the myth according to which crocodiles weep when feasting on humans.
•    While eating, crocodiles need somehow to rip and tear apart flesh but because they cannot do just like other carnivores on land,they have another technique - The death roll- a strategic maneuver used to tear apart prey into chunks and make it easier for them to swallow.
•    When doing a death roll, a crocodile will grab onto a limb or part of another animal with its jaws and roll until the part they grabbed is ripped off.

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•    Although crocodiles are at the top of the food chain, sometimes the hunter becomes the hunted. Little Cayman often become prey themselves in front of a jaguar or anaconda.





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Sources
http://www.britannica.com/EBchecked/topic/143679/crocodile
http://en.wikipedia.org/wiki/Crocodile
http://animals.pawnation.com/crocodiles-natural-habitat-3107.html
http://www.livescience.com/28306-crocodiles.html
http://www.sophisticatededge.com/do-crocodiles-lay-eggs.html
http://news.softpedia.com/news/14-Amazing-Facts-About-Crocodiles-69931.shtml
http://channel.nationalgeographic.com/wild/built-for-the-kill/articles/crocodile-facts/
http://indervilla.com/home/Crocodile-Young-HD.jpg
http://www.serengetibook.com/wp-content/uploads/2011/01/shutterstock_13723087.jpg
http://topwalls.net/wp-content/uploads/2012/05/Eye-of-the-crocodile.jpg
http://upload.wikimedia.org/wikipedia/commons/e/eb/Kachikally_crocodile.jpg
http://dinolingo.files.wordpress.com/2011/05/crocodile-eat-mammal.jpg
http://media.pennlive.com/midstate_impact/photo/philippines-giant-crocjpg-018717eb9ba397f7.jpg
http://newswatch.nationalgeographic.com/files/2014/03/WW-QA-3-worlds-longest-alligator-02.jpg
http://www.youtube.com/watch?v=DBNYwxDZ_pA

Published by Claudia Barbu

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