The Paleozoic era spanned from the Cambrian period to the Permian-Triassic extinction event, and saw the evolution of hard-shelled animals, land plants, and animals that could walk on land. Iconic animals include trilobites and sea scorpions. The era ended with a catastrophic extinction.
Paleozoic animals lived during the Paleozoic era, a huge span of time from the beginning of the Cambrian period 542 million years ago to the catastrophic Permian-Triassic extinction event about 251 million years ago. The era comprises six geological periods and, from youngest to oldest, they are: Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.
The Paleozoic was a time of extreme evolutionary change and the foundations of life as we know it were laid during this period. Immediately prior to the Paleozoic, there were few, if any, animals with hard shells, and as far as we know, there were no land plants or animals whatsoever. The largest early Paleozoic animal was probably no more than a few inches long, as early Ediacaran communities, which consisted of simple frond-like organisms up to about three feet long, were mostly extinct.
One of the first well-known Paleozoic animals, and indeed indicative of the beginning of the entire era, was the familiar trilobite, an extremely numerous arthropod that formed its own class, Trilobita. Trilobites were among the first animals to have hard shells, and their fossils are so plentiful that you can buy them today on eBay for $10 US dollars (USD) or less. Early trilobites also had compound eyes with calcite lenses, a feature unique to the group. For the time, this was an impressive evolutionary innovation.
About ten million years after the beginning of the Paleozoic, probably the most significant evolutionary radiation in the history of life occurred – the Cambrian explosion. The Cambrian explosion owes its name to the geologically sudden appearance of virtually all modern phyla, including vertebrates, represented by the first jawless fish, which would succeed for tens of millions of years, until being replaced by fish with jaws in the Ordovician.
Another of the Paleozoic’s iconic animals are the eurypterids, sea scorpions, which were career predators for virtually the entire Paleozoic era, only going extinct at the end. These scorpions are descendants of modern scorpions and some, such as Jaekelopterus, exceeded two meters in length. Although many paleontologists are probably disappointed that eurypterids aren’t around to study, most beachgoers would probably prefer they remain extinct.
The Paleozoic saw the evolution of the first terrestrial flora and fauna, which rapidly covered most of the earth’s surface during this period. Land plants evolved from green algae, at first only a few inches tall, until they developed vascular tissue, then became a few feet tall. After developing real wood, plants could really “break free”, growing many tens of meters in the last part of the Paleozoic. These land plants were joined by many Paleozoic animals that had evolved the ability to walk on land, with independent lineages of invertebrates (mostly insects and chelicerates such as mites) and vertebrates (fish started walking on land and became amphibians). By the end of the period, there were so many Paleozoic animals, accompanied by Paleozoic flora, that complex terrestrial ecosystems roughly analogous to those of all future eras were established.
The Paleozoic Era ended in a catastrophic extinction that wiped out 97% of marine genera and 70% of terrestrial vertebrate genera.
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