Paleozoic Era

From an explosion of early life to the greatest extinction in history, the Paleozoic was a time of change. During this earliest era, living things developed vertebral columns and hard body parts like jaws, bones and teeth. Fish evolved, and plants and animals started the move from the ocean onto dry land. Most plants and animals from this time are extinct in our modern world, which is why the Paleozoic is named for “ancient life."

The 6 periods in this era are described below, as shown in the "Fossils Tell a Scientific Story" exhibit in the Hall of Evolution. Click on images to enlarge.

 

Cambrian Period (600 to 500 million years ago)

Cambrian Period case with specimens in museumAll Cambrian Period fossils come from rocks formed in aquatic environments. Hard-shelled creatures dominated the sea bottom. Most abundant were the trilobites, arthropods distantly related to horseshoe crabs. Snails, lamp-shells (brachiopods), mollusks, graptolites, and marine worms were also common. Traces of primitive jawless armored fish have been found in late Cambrian Period rocks, indicating that backboned animals developed during this period.

Ordovician Period (500 to 435 million years ago)

Ordovician Period case with specimens in museumDuring the Ordovician Period the land was still barren, but life was abundant in shallow seas which covered what is now the State of Michigan. Trilobites and brachiopods were common. Squid-like shelled cephalopods probably fed on these creatures. Crinoids, often called “sea lilies,” were animals that resembled plants. In the Ordovician Period, the continental masses on earth were drifting together to form two “supercontinents,” Laurasia in the north and Gondwanaland in the south.

Silurian Period (435 to 410 million years ago)

Silurian Period Triassic Period case with specimens in museumThe evolution of colonial corals led to the formation of great coral reefs, similar to those found in tropical oceans today. These reefs, teeming with life, existed in many parts of North America, including Michigan and Ohio. Large predatory arthropods called eurypterids and primitive jawed fish may have fed on the many kinds of trilobites. Life began to invade the land at this time, as shown by fossils of primitive terrestrial plants and scorpion-like animals that probably lived near the shoreline.

Devonian Period (410 to 360 million years ago)

Devonian Period case with specimens in museumTwo great “supercontinents” met to form the single landmass called Pangaea (“all Earth”). The Devonian Period is often called the “age of fishes” due to the rapid evolution and radiation of various fish types. Giant armored fish, sharks, and the ancestors of today’s “bony fish” were all present. The “lobe-finned” fish gave rise to the first land vertebrates, the amphibians, in the late Devonian Period. With the development of larger land plants, the first forests (made up of scale trees, giant “horsetails,” and ferns) spread across warm lowlands, providing early land animals with new habitats.

Carboniferous Period (360 to 290 million years ago)

Carboniferous Period case with specimens in museumThe Carboniferous Period is named for coal deposits which formed from the accumulation of plant debris in vast swamp forests. Amphibians diversified into several groups one of which evolved increased agility and the ability to lay shelled eggs on land -- thus becoming the first reptiles. Insects, already abundant, developed wings and became the first flying animals.Some geologists split this period into the “Mississippian” and “Pennsylvanian” Periods, based on rock exposures in the eastern United States.

Permian Period (290 to 240 million years ago)

Permian Period case with specimens in museumDuring the Permian Period the climate became cooler and drier -- glaciers formed on the southern parts of Pangaea, and shallow seas retreated from the continent. Trilobites and some other sea animals disappeared. Reptiles dominated the land as amphibians declined. The end of the Permian Period was a time of extinction and transition throughout the world.

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