The Paleozoic is the time period from 542 million years ago and 251 million years ago. During this period there was an explosion of life in the seas and on land. Life began in the seas and then spread to the land. Primitive plants covered the continents like great forests and many of these plants formed the coal beds of Europe and eastern North America.
Shown below are the Paleozoic displays in the Raymond M. Alf Museum of Paleontology on the campus of the The Webb Schools, a private residential high school, in Claremont, California.
According to a display at the Raymond M. Alf Museum of Paleontology:
“Insects, fish, reptiles, amphibians, trees, ferns, and much more emerged during the Paleozoic. Animals took their first steps onto dry ground. Tropical coral reefs covered much of what is now the continental United States.”
The Paleozoic is divided into six geologic periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.
Shown below are the Paleozoic displays in the Raymond M. Alf Museum of Paleontology on the campus of the The Webb Schools, a private residential high school, in Claremont, California.
The bottom four fossils shown above are crinoids, cousins to starfish, sea urchins, and sand dollars. All of these date to about 330 million years ago.
Shown above is an illustration by John Sibbick.
Shown above are Eurypterids (sea scorpions) which date to about 425 million years ago.
Shown above is Scaumenacia (early lungfish) from 380 million years ago
Shown above is Eusthenopteron from 385 million years ago. This fish had well-developed limbs, but these were probably used for swimming rather than walking.
Shown above is Tiktaalik from about 375 million years ago. This represents a transition between fish and tetrapods.
Shown above is a Diplocaulus skull cast and a Dissorophid skeleton, both from about 270 million years ago. These are both aquatic tetrapods from the Permian Period.
Shown above are a cockroach cast (top) and plant impressions from about 300 million years ago.
According to the Museum display:
“The earliest forests would have been an otherworldly sight. Ferns and primitive trees—some towering over 100 feet tall—carpeted the landscape. Giant millipede-like animals up to 8 feet in length munched their way through the ground cover, which giant cockroaches scurried through dead vegetation on the forest floor and dragonflies buzzed through the trees.”
Shown above a tribolites, marine anthropods which flourished worldwide during the Paleozoic. They lived along the ocean floor.
Mass Extinction
At the close of the Permian Period, 251 million years, there was a mass extinction. According to the Museum display:
“The Permian-Triassic extinction resulted in the extinction of 95 percent of all marine species and 70 percent of all terrestrial vertebrates. Trilobites and eurypterids which had flourished for over 200 million years went completely extinct, and many other groups were decimated. The ancestors of mammals, dinosaurs, and lizards barely survived.”
There have been a number of hypotheses regarding the cause of the extinction, including volcanism, glaciation, asteroid impact, and changes in atmospheric composition or ocean circulation patterns.