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The Paleozoic Era began 541 million years ago and ended about 252 million years ago. In other words, its duration was approximately 290 million years. It ranges from the appearance of animals with shells or exoskeletons, to the emergence of the first amphibians and reptiles.
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The Cambrian period, part of the Paleozoic era, produced the most intense burst of evolution ever known. The Cambrian Explosion saw an incredible diversity of life emerge, including many major animal groups alive today. Among them were the chordates, to which vertebrates (animals with backbones) such as humans belong.
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During the Ordovician period, part of the Paleozoic era, a rich variety of marine life flourished in the vast seas and the first primitive plants began to appear on land—before the second largest mass extinction of all time ended the period.
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The Silurian Period occurred from 443 million to 416 million years ago. ... It followed the Ordovician Period and preceded the Devonian Period. During this time, continental landmasses were low and sea levels were rising. This meant rich shallow sea ecosystems with new ecological niches.
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The Devonian, part of the Paleozoic era, is otherwise known as the Age of Fishes, as it spawned a remarkable variety of fish. The most formidable of them were the armored placoderms, a group that first appeared during the Silurian with powerful jaws lined with bladelike plates that acted as teeth.
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The later half of the period experienced glaciations, low sea level, and mountain building as the continents collided to form Pangaea. A minor marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred at the end of the period, caused by climate change.
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During the Permian Period, Earth's crustal plates formed a single, massive continent called Pangaea. In the correspondingly large ocean, Panthalassa, marine organisms such as brachiopods, gastropods, cephalopods (nautiloids and ammonoids), and crinoids were present. On land, reptiles replaced amphibians in abundance.
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The Mesozoic era is divided into three periods: Triassic, Jurassic, and Cretaceous. Flowering plants and new types of insects proliferate. More modern teleost fish are beginning to appear. Ammonites, belemnites, rudist bivalves, echinoids, and sponges are common.
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During the Triassic, the first dinosaurs walked on the land, the first pterosaurs sailed through the skies, and the first ichthyosaurs and plesiosaurs swam in the oceans. The lineage of many modern-day reptiles began in the Triassic Period, including crocodiles, lizards, and turtles
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This period is characterized by the hegemony of the great dinosaurs and by the split of Pangea into the Laurasia and Gondwana continents. From the latter Australia was split off (in the Upper Jurassic and early Cretaceous), just as Laurasia split into North America and Eurasia.
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During this period, oceans formed as land shifted and broke out of one big supercontinent into smaller ones. Continents were on the move in the Cretaceous, busy remodeling the shape and tone of life on Earth.
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This period began 65 million years ago and ended roughly 1.8 million years ago and bore witness to some major geological, biological and climatological events. This included the current configuration of the continents, the cooling of global temperatures, and the rise of mammals as the planet's dominant vertebrates.
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The Mesozoic era is divided into three periods: Triassic, Jurassic, and Cretaceous. Flowering plants and new types of insects proliferate. More modern teleost fish are beginning to appear. Ammonites, belemnites, rudist bivalves, echinoids, and sponges are common.
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The Quaternary Period is famous for the many cycles of glacial growth and retreat, the extinction of many species of large mammals and birds, and the spread of humans. The Quaternary Period is divided into two epochs, from youngest to oldest: the Holocene and Pleistocene.
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