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uncommon dinosaurs
by Sean Harvey
Historical Geology
Spring 2008

 Uncommon Dinosaurs

            There are many types of dinosaurs and they can be broken down into numerous categories.  Dinosaurs are prehistoric animals that evolved over a time frame of 185 million years.  Because the dinosaurs are extinct creatures now they are ever changing discoveries that changes how dinosaurs are classified. The following chart illustrates how dinosaurs are classified currently.

Dinosaur groups


            Dinosaurs evolved in a multitude of directions and with the many different parallel, convergent and divergent evolutionary paths there are some species that look completely different from one another, but are quite the same in many aspects.  There are many recognized dinosaurs when spoken of such as the Tyrannosaurus Rex and the Triceratops; however, there are more then just these nine or so common dinosaurs.  In the following paragraphs some of these uncommon dinosaurs will be uncovered with some interesting facts.

            Here in Arizona there is a dinosaur discovery that much resembles a crocodile and reached up to the length of ten feet.  This dinosaur was called the Arizonasaurus.   The Arizonasaurus had a large fin on itís back to regulate the body heat.  This was thought to be a prehistoric predator and lived in hot desert ecosystem.


            Shonisauarus is a swimming reptile that was considered to dolphin-like.  This animal grew to the amazing size of fifty feet!  This reptile had four large fins to help stabilize its body and had a small fin on top if its back. Not a dinosaur, but from the age of dinosaurs.



Another dinosaur that resembles the Velociraptor which was made famous through the movie Jurassic Park is the Eoraptor.  This dinosaur hunted in packs and is about the size of a fox.  It is about 3 and Ĺ feet long.  This dinosaur was very dexterous and worked well in the hunting environment.  This dinosaur had very strong hind legs and razor sharp teeth to shred through its prey.

Dinosaur pictures


            The Corythosaurus had a large fin on the top of its head and stood on its hind legs like many other dinosaurs.  This was a very commonly found animal from the Cretaceous period.  This dinosaur was in Jurassic Park for a short scene or two. This dinosaur had a large beak on the skull with many interlocking teeth in the back of its jaw.  This dinosaur was believed to be a herd dinosaur and able to communicate to like animals through a uniquely designed nasal passage.

Corythosaurus dinosaur


             In great contrast to the Tyrannosaurus Rex there was one of the smallest dinosaurs to ever exists, Nanosaurus.  This dinosaur was approximately two feet high and four feet long.  This dinosaur was also a herbivore. Not much is known about this dinosaur.

Dinosaur Facts


            Lastly, the Guanlong which is related to the Tyrannosaurus Rex was a medium sized dinosaur reaching about ten feet in length and also had a large protruding head plate.  It is made of a softer bone which may have been used to protect a specialized organ.  There is not much information on this dinosaur even though there has been a full discovery of its bone structure.  This dinosaur was found in China.  This animal was believed to have been carnivorous and very fierce predator.



These dinosaurs above are just the many hundreds of species the evolutionary path of life traveled down.  From big lizards to small - from flying, running and swimming they conquered the world as their own.  These dinosaurs came to be extinct with the rest of their brothers and sisters by a nine mile thick meteorite striking around the Gulf of Mexico.  This meteorite has yet to be proven that it has made the dinosaurs extinct; however, the evidence shows that this is a very logical theory.  This meteorite was believed to have stuck half on land and half on water.


            This meteorite was believed to have killed all large animals and the only survivors would be small mammals that lived off roots under ground.  These animals are responsible for the recovery of living life on earth today.

Resources: Dinosaur Facts. 2007.

Reed, Wicander and Monroe, James. Historical Geology.  Thomson Brooks/Cole. 2007. 5th ed. Dinosaur Dig. San Diego Natural History Museum.  Dinosaur Museum. 10 Surprising Dinosaur Facts. MSN Encarta. Dinosaur Facts.