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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