Trilobites

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Trilobites

Trilobites are extinct sea creatures that were one of the first forms of life on earth.

They ruled the world before the time of the dinosaurs, from the Cambrian Period to the

Permian Period (between 245 and 600 million years ago). Trilobites are the only extinct

form of Arthropods (invertebrate animals having jointed bodies and legs),and were related

to the lobster and crab. Their closest living relative today is the horseshoe crab.The name

Trilobite refers to it's three lobes, or body sections, consisting of a central axial lobe, and

two pleural lobes on the sides. The three main parts of it's body are called the

Cephalon,(head) the Thorax (body), and the Pygidium (tail). There are 8 Main Orders of

trilobites, and over 15,000 different species, many of which have a stratigraphic value,

especially those found within Cambrian and Ordovician rocks. It is the fact that trilobites

are found world wide which makes some of them serve as excellent index fossils, and it is

their short life periods which allows precise dates and correlation’s to be made about the

rocks in which they are found.

Most trilobites were sea floor dwellers, living in the soft sediments, while others

were free swimming. They appear to have been exclusively marine organisms since the

fossilized remains of trilobites are always found in rock containing fossils of other

salt-water animals, e.g. brachiopods, crinoids, and corals. Trilobites ranged in size from

1/4 of an inch,and smaller, to almost 3 feet long. Trilobites were also the first creatures to

develop eyes and sensory organs. Trilobites had two compound eyes. In some trilobites,

the eyes had densely packed lenses and may have served merely as a light sensitive

warning...

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...ve found them a

good source of food. The Trilobites fought back for a time, growing spines during the

Devonian period but these were no match for the larger predators.

The fossilized remains of trilobites are useful because they help scientists develop

relative time scales for the ancient marine environment. Because trilobites evolved quickly

and were widely distributed, comparing the trilobite fossils found in rock layers in different

regions of the earth can indicate which rock layer is older than the other. Trilobite fossils

are particularly helpful in developing time scales for the early Paleozoic era. Trilobites

were highly successful bottom dwelling sea organisms with over 10,000 species. They

thrived for 300 million years as the most abundant and successful ocean animal through

the Cambrian period until they bit the cosmic dust in the Permian era.

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