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CROCODILIA Kingdom: Animalia Phylum: Chordata Class: Reptilia Order: Crocodylia OVERVIEW: The order of Crocodilia is a relatively select group that has existed for millions of years and in modern days has continuing success in its body plan and systems. Crocodilia is a unique group, on the first glance you would assume that it is purely reptile but it actually shares a more recent ancestor with birds and even tetra pods. In the following sections we will explore various aspects of crocodilian including Development and life cycle, physiology, habitat, ecology and diversity. DEVELOPMENT AND LIFE CYCLE Of all the great attributes that crocodilians have their development and life cycle is the only real flaw. When crocodiles and alligators breed it is one of the only occasions that when audible noise is made. When the eggs are fertilized the mother carries them until they are only a few cells big. The mother then lays 20-50 eggs in a nest of leaves and organic debris. The eggs form a white strip which eventually spreads to cover the egg and then harden. The eggs are incubated for 72-90 days. Even under the watchful eye of the mother the eggs are still vulnerable to scavengers. The sex of the crocodiles and alligators is determined by the temperature of the nest. Unlike turtles whose sex is determined in a ratio, crocodiles are entirely male or female causing an in-balance of sexes, for instance in one area of Louisiana females outnumbered males 5 to 1. When the eggs are ready to hatch the hatchlings bellow until their mother comes and carefully uncovers the nest. It has been documented that for hatchlings having trouble getting out of their shell the mother will put the eggs in her mouth and gently crushes it with her tongue to let the hatchling out. Once the hatchlings have escaped their shells they have a race to the water before other lizards and birds eat them. Once they get to the water they then have to avoid large fish, birds that hunt in the water and other crocodiles. The fact is that the highest mortality is during the first few months of the crocodilians life. As the crocodiles grow larger there survivability increases as well. They reach sexual maturity around 6 or 7 years old and have a life expectancy of 70 to 100 years old. PHYSIOLOGY The physiology of the crocodilians is largely unchanged for over 200 million years ago. They share the most recent common ancestor with birds although they appear very different. Crocodilians are very long and narrow with a semi-erect or sprawled posture. For the most part they move over the earth by sliding on their bellies but can also erect themselves and move relatively quickly. For example an Australian species can gallop over uneven terrain at speeds as high as 10 miles per hour. The skull is very complex with the nostrils and the eyes on the same plane and a second palate allowing the crocodile to breathe when its mouth is full of food or water. It’s jaws are surrounded by huge muscles which deliver a crushing pressure and grip although all that power is focused on closing the jaw and keeping it closed it is not very strong when it comes to opening its mouth. Crocodilians have teeth which are set into sockets similar to humans. Unlike humans they have thousands of replacement teeth growing one right underneath the other. When they are young crocodilians can replace lost teeth as fast as one a month however as they get older this slows to about 3 years. In the end crocodilians that survive to old age are more likely to die from starvation because of no teeth than any other cause. Crocodilians have two sets of eyelids one solid and the other translucent for under water use. Internally they are very similar to birds and mammals including being the only reptiles with a four chambered heart, however they do not have a bladder. As simple as they may seem their ankles are highly developed for semi aquatic life. Their skin contains an amino acid called keratin which is found in feathers, hooves, hair and finger nails. HABITAT Crocodilians are wide spread across tropic and sub tropic zones. They are found from the Nile River to South East Asia, From Australia to South America to the southern United States. They live partly in the water and partly out living on coasts and in swamps, Rivers and even lakes. Crocodiles can survive out in the open ocean for weeks at a time even catching pray while at sea, this is how it is believed they became so wide spread. ECOLOGY Crocodilians are the masters of their territory. Growing from the most helpless of beginnings they become unbeatable with no natural predators once they reach maturity. They young start out eating flies and spiders and small aquatic insects then progress to small fish and frogs, to prey as big as Cattle and people. They roam their territory unchecked by other species. The only threat that crocodilians have is human. Their scale like skin is very desirable for hand bags, hats and boots making them a wanted commodity.
DIVERSTIY There are essentially 3 different divisions in the crocodilian group, Alligators, Caimans which are the new world version of Alligators, and Crocodiles. There are also a number of species in each group. In the United States there are one species of each, the American alligator and the American crocodile. Crocodiles are very large and very aggressive and are found in warmer climates than crocodiles although they do overlap. The largest species of crocodile is the Salt Water Crocodile which get as long as 20 feet and weighing as much as 2,900 pounds. They are extremely aggressive and will attack anything when hungry. Alligators are much smaller and calmer but still deadly although they don’t normally attack humans. To distinguish between a crocodile and an alligator, crocodiles have relatively narrow pointed snout with the fourth tooth exposed when the jaw is shut. The alligator has a snout that is wider and more rounded with no teeth visible when the jaws are closed. SOURCES CITED: TEXT: http://en.wikipedia.org/wiki/Crocodilia http://www.crocosauruscove.com/crocodiles/lifecycle.htm http://www.sandiegozoo.org/animalbytes/t-crocodile.html PHOTO’S: http://animals.nationalgeographic.com/animals/printable/american-crocodile.html http://www.lpzoo.com/animals/factsheet.php?contentID=21 http://www.arkive.org/nile-crocodile/crocodylus-niloticus/image-G33472.html http://myanimalblog.wordpress.com/2008/02/17/my-first-post-alligator/alligator/ |