The Ordovician Period

The Ordovician Period in a Nut Shell

The Ordovician period brought about many new organisms and occured from 438-505 million years ago (according to the old
Earth belief). During this time, the Earth was covered mostly by water, thus the population of organisms consisted mainly of marine life. The Cephalopods dominated the seas, but were joined by sponges, coral,Trilobytes, Brachipods, algae and even some of the first jawless fish known ostracoderms. Here we will explore many of these different life forms.

Ostracoderms- The Jawless Fish

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The ostracoderms "are any of several groups of extinct, primitive, jawless fishes that were covered in an armor of bony plates." They were small, slow fishes that dwelled on the bottom of bodies of water. They had no lateral fins but had medial fins and used gills souly for breathing. Interestingly enough, they also had permanently open mouths. These creatures went extinct at the end of the Devonian period. As the image to the right shows, there are many different types of ostracoderms, and many more than are shown in this picture.The fish on the top almost resembles a lobster, and the one on the bottom resembles that of a shark. Today we see marine life that is armoured as well. Think about the crabs, lobsters, crayfish, even the clams and oysters.

This image is courtesy of www.blc.arizona.edu/courses/schaffer/182/Vertebrate

Cephalopods

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During the Ordovician period, the Cephalopods dominated the seas. ephalopods are a type of mollusk and include but are not limited to the following organisms: Octopus, squid, cuttlefish, and the nautilus. Each cephalopod shares one basic characteristic. They all have tentacles that surround their heads. They are also very intelligent for they have large brains. With their intelligence comes their ability to camouflage. The cephalopods are able to successfully analyze and adapt to their surroundings making it almost impossible for their predators to find them. Cephalopods are also carnivorous and consume other mollusks as well as fish, worms, and crustaceans, allof which they capture with their tentacles. The image at the left depicts a Nautilus.

This image is courtesy of : www.aquariumofpacific.org/onlinelearningcenter/full_description/

Cephalopods- Courtesy of http://www.youtube.com/watch?v=0GVaa91YFo
This video explores the world of the Cephalopods which were very abundant during the Ordovician Period. It talks about mainly their ability to camoflauge themselves.

Brachiopods

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Brachiopods are ocean dwelling bivalves (they have two shells). Many of them look very similar to clams and oysters but they are not related. These organisms were filter feeders that lived off of microscopic organisms and matter. They gather this food with a logophore. This is an organ that actually takes up about 2/3 of the space in the shell. It is a tube like organ that have hair-like cilia which move food into the mouth and down the logophore. Brachiopods are also unique in the way that they have a pedicle. The pedicle is a long fleshy appendage they use to burrow into the sea-floor. There are however some bivalves that do not posess this appendage.

This image shows many different varieties of the Brachiopods.

Image courtesy of http://etc.usf.edu/clipart/49200/49251_paleo_brach.htm

Trilobites

The trilobites were yet another organism that existed during the Ordovician period. Trilobites are part of the arthropod family and have hard segmented bodies and jointed legs. They are also one of the most diverse extinct animals. They have a three segmented body similar to many insects. The three segments include the cephalon (head), the thorax (midsection), and the pygidium (tail piece). Their name actually means "three lobed" and does not refer to their three segments. The three vertical lobes are the left pleural and right pleural lobes as well as the axial lobe.
The images below are courtesy of www.trilobites.info/trilobite.htm. The first image shows the three segments that make up each and every trilobite, and the second picture is of the three vertical lobes that make up trilobites.
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Citations:

Brachiopods: Bivalves With a Past. Copyright 2005 by fossil-facts-and-finds.com.
Kennedy, J. Cephalopods. About.com 2011. From www.marinelife.about.com/od/invertebrates/p/cephalopod.htm.
Gon, S. What are Trilobites? Copyright 1999-2001. Last updated Sept 6, 2011. www.trilobites.info/trilobite.htm
Ostracoderms. New World Encyclopedia. Last updated April 3, 2008. http://www.newworldencyclopedia.org/entry/Ostracoderm
The Ordovician Period. New World Encyclopedia. Last updated April 3, 2008. http://www.newworldencyclopedia.org/e