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Crocodiles
Heike McGarry
Historical Geology
Spring 2006

                                  Crocodiles

 

 

Fossils from a real-life sea monster – a massive crocodile-like species have been unearthed in Patagonia, Argentina. The researchers name the marine reptile Godzilla which lived about 135 million years ago. This animal had a head like a carnivorous dinosaur and a tail like a fish. With its massive teeth, it preyed on other marine reptiles. It is one of the most evolved members of the crocodilian family. The creature’s skull is almost intact and this animal belongs to the crodyliforms, which includes today’s crocodiles and their extinct relatives. Marine crocs were abundant during the Jurassic period some 200 million to 145 million years ago and were distributed worldwide. This Dakosaurus andienis lived entirely in the water and measured 13 feet from nose to tail. It had four paddle-like limbs for stability and a fish-like tail propelled the beast through the water.

 

Crocodiles which are coldblooded and extremely sensitive to climate change survived and even flourished at the time the dinosaurs became extinct 65 million years ago. Dinosaurs disappeared at the boundary between the Cretaceous and Tertiary periods. Based on fossil evidence, the crocodiles showed no change in diversity or distribution across this K/T boundary. Crocodiles are coldblooded, so their body temperature is regulated by the surrounding environment. Crocodile fossils are only found in areas that had mild year-round temperatures. The fossil record of crocodilians starts at 100 million years ago shows that they are widely distributed and numerous across the K/T boundary. Along the border of Peru and Brazil a crew found a skull of the genus Purussaurus. This giant crocodilian stretched 39 feet in length and stood 8 feet tall. Purussaurus must have weighed 10,000 to 12,000 kilograms which would have been more massive than Tyrannosaurus rex. This carnivore ate birds, large turtles or rodents. These rodents reached the size of small cattle.

 

According to new crocodile fossils there must have been an ancient land bridge that linked South America with Indo-Pakistan which is thought to have gone through Antarctica or Australia. The Baurusuchus salgadoensis lived 90 million years ago in southeastern Brazil called Bauru Basin, 450 miles west of Rio de Janeiro. An adult measured about 10 feet from head to tail and weighed around 900 pounds. A new species of crocodile lived 40 million years ago in tropical Australia. It lived in the early Tertiary period, from 65 million years ago until five million years ago, during which time climate change possibly had a major impact on the evolution of the modern-day crocodile. Australia and Antarctica broke apart and most of eastern Australia became warmer, leading to an increase in rainforests which is an ideal environment for crocodiles.

 

Another fossil from New Mexico which is timed to have lived 210 million years ago was only 6 feet long, stood on its hind legs while keeping its tail erect. It had tiny arms, a long neck, huge eyes and no teeth. It is an example of convergence when two lineages evolve the same body plan. About 248 million years ago the fossilized remains of gigantic crocodiles have been discovered at the Big Bend National Park which had lengths of 40 to 50 feet and jaws studded with 6-inch teeth, they fed on different dinosaurs. They probably hunted by ambushing their prey.
 

 

Crocodiles (family crocodylidae) are the largest reptiles on earth. The African or Nile crocodile is one of the biggest, up to 18 feet long. Crocodiles are primordial. Crocodile fossils are from the Triassic, at least 206 million years ago. They were already an ancient group when dinosaurs went through the forests of the Jurassic. There have been some incidents where people died from crocodile attacks but vice versa the case is more severe. They were hunted for their skins and sport. In general, crocodiles are quiet and usually retreat back to water if approached. Crocodiles can move quickly and chase prey onto land. Their jaws are very powerful and their tails can be used as battering devices.

 

The crocodile has only 20 known species and is the least diverse of the three major reptile groups. They exist where conditions have remained the same and they are free of human interference. The crocodile is successful because it switches its feeding methods. It hunts fish, grabs birds at the surface, hides among the water edge vegetation to wait for a gazelle to come by, and when there is a chance for an ambush, the crocodile lunges forward, knocks the animal with its powerful tail and then drags it to water where it quickly drowns. Another way is to wait motionless for an animal to come to the water’s edge and grabs it by its nose where it is held to drown.

 

A hard-won carcass is usually dragged to some hiding place on a river bank until it is repe for the crocodile to taste it. They often leave their food to decompose because they cannot tear it into small enough pieces. Unable to chew, they bite off chunks by holding the carcass in their jaws while twisting it. A group of feeding crocodiles will thrash about taking turns at the meal. The crocodile’s teeth wear out but are replaced throughout the animal’s lifetime. The oldest recorded crocodilian reached the age of 68 years. They dig nests for their eggs, and the female watches over it. After three months, the babies hatch and are being carried by their mother in her mouth and are being released into the water. They feed on crustaceans and water insects until they can fend for themselves. Only two or three offspring survive due to many dangers. The sex of the embryonic reptile is determined by the temperature to which the egg is exposed during incubation.

 


 

Websites used:

http://www.friendsoftheenvironment.org/sawmillsinkfossi.htm

http://www.junglephotos.com/afric/afanimals/reptiles/crocodilenathist.shtml

http://new.nationalgeographic.com/news/2005/11/photogalleries/godzilla/

http://www.nps.gov/bibe/NR/dinosaur.htm

http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2006/01/26/MNGPEGT5FV1.DTL

http://www.crystalinks.com/fossilcrocodile.html

Science News November 9, 2001

http://chronicle.uchicago.edu/941110/crocodiles.shtml