In reading about the Precambrian Era, you discovered that fossils are more likely to form if organisms have hard parts. When organisms developed hard parts, the Paleozoic Era began. Fossils were then more easily preserved.
Era of Ancient Life
The Paleozoic Era, or era of ancient life, began about 544 million years ago. Warm, shallow seas covered much of Earth’s surface during early Paleozoic time. Because of this, most of the life-forms were marine, meaning they lived in the ocean. Trilobites were very common. Brachiopods and crinoids, which still exist today, were also very common. Although these animals may not be familiar to you, one type of animal you are familiar with, the fish, also evolved during this era.
The Paleozoic Era is broken into seven periods. The start of the Ordovician Period is marked by the beginning of the Appalachian Mountain building process. This was probably caused by the collision of the Eurasian or African continental plate with the North American Plate.
The first vertebrates, animals with backbones, developed during the Ordovician Period. Plant life moved from the oceans onto land during the Silurian Period. Fish became dominant in the Devonian Period. By this time plant life had developed on land, and animals began to move onto land as well.
Life on Land
One type of fish evolved a lung that enabled it to survive out of water. This fish had fins that allowed it to move across land. The fact that lungfish could move across land and breathe air has led scientists to theorize that lungfish and amphibians evolved from the same ancestor. Amphibians live on land and breathe air, but they must return to water to reproduce. Their eggs must be kept moist in water. They first appeared during the Devonian Period and became the dominant form of vertebrate life on land by the Mississippian Period.
Over time, one species of amphibian evolved an egg with a membrane that protected it from drying out. Because of this, the species no longer needed to return to water to reproduce. By the Pennsylvanian Period, reptiles had evolved, probably from the same ancestor as amphibians. Reptiles do not need to return to water to reproduce. Reptiles have skin with hard scales that prevent loss of body fluids. This adaptation enables them to survive farther from water. They can survive in relatively dry climates, whereas amphibians cannot.
End of an Era
Mass extinctions of many land and sea animals occurred, signaling the end of the Paleozoic Era. The cause of these extinctions may have been changes in the environment caused by plate tectonics. Near the end of the Permian Period, all continental plates came together to form the single landmass Pangaea and major glaciers formed.
1. How long ago did the Paleozoic Era begin in millions of years?
2. What did Earth’s surface look like? What were most of the creatures like?
3. What is a common animal that evolved during this era?
4. What was the Appalachian Mountain building process started by that happened during this era?
5. Plant life moved areas as well. Where did it move to?
6. After plant life moved to land, what happened to fish life?
7. What did certain fish possess that allowed them to live on land (two things)?
8. These fish, called lungfish, are theorized to be related to what other type of animal?
9. How did amphibians evolve into reptiles? Be specific.
10. What makes reptiles different than amphibians? Be specific.
11. Mass extinctions of many land and sea animals occurred near the end of the Paleozoic Era. What major geographic change occurred during this time?
12. What is the formal name given to the supercontinent and what formed along with it?
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