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Geological Time - Paleozoic Era
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Paleozoic means "ancient life." The Paleozoic Era dawned about 550 million years ago. There was a great explosion of life in the seas and on dry land during this era. With the exception of rarely preserved soft bodied multicellular organisms, there was no documented complex life before the the Paleozoic Era. By it's close almost 200 million years later (245 million years ago) all of the major groups of animals (phylums) were well represented.

The Paleozoic divided is devided into six periods. During the early Paleozoic Era (Cambrian, The oldest was the Cambrian, Ordovician, and Silurian Periods, a large continent, known as Gondwanaland, was situated ofver the southern polar region. Marine life thrived during this time and invertebrates were especially widespread. Life diversified during the late Paleozoic (Devonian, Carboniferous and Permian Periods). At the end of this time, most of the land was joined in one supercontinent known as Pangea.

The phylum Arthropoda (invertebrates with segmented appendages) was, and still remains, one of Mother Nature's great success stories. The trilobites were the first arthropod to appear in the early Cambrian period and evolved to thousands of species which colonised the sea, land and air during the Paleozoic. They gave rise to modern day arthropods including insects, spiders and crustaceans. All of the trilobites died out at the end of the Paleozoic but the phylum Arthropoda remains the most diverse on Earth today.

Most other modern groups of invertebrates have their origins in the beginning of the Paleozoic Era. In addition to the arthropods, there were echinoderms (spiny skinned animals such as starfish), cnidarians (including corals, jellyfish and sea anemones), and mollusks (clams, snails and squids). The first vascular plants appeared during the Silurian Period, about 420 million years ago, and flourished during the Carboniferous.

The first animals with central nerve canal "chordates" appeared in the early Cambrian, about 550 million years ago, marking the beginning of vertebrate life. During the Paleozoic Era, fishes evolved from primitive jawless forms to complex bony types with lungs and specialized fins. Many of the early fishes became extinct before the end of the Paleozoic, but they set the stage for the great step in evolution from fishes to land animals.

The first tetropods (4 legged land vertebrates) emerged onto the land in the late Devonian, about 360 million years ago to feed on the vegetation that had developed. The first were amphibians (meaning "both lives"). They had the ability to live on the land but were dependent on the water for reproduction. Fifty million years of evolution improved the design for better terrestrial locomotion. The development of the hard shell egg eventually freed the amphibians from their dependency on the aquatic environs.

A mass extinctin of much of the life occurred at the very end of the Paleozoic. The few survivors emmerged setting the stage for "middle life" the Mesozoic Era, "The Age of the Dinosaurs."

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