Features of Paleozoic era

I. Paleozoic era :- This era produced revolutionary changes in the biosphere. Further this era saw the origin and the radiation of several groups of animals and plants that remained as the forefathers for the modern groups. Thus this era is known as the Cradle of ancient life.
1. Cambrian period :- (600 to 440 million years ago) The period preceeding cambrian is known as Pre-cambrian period. During precambiran time simple algae, protozoans, poriferans, annelids, were
well established. Thus the cambrian started with the plants and animals that were suceessful during the precambrian period. During cambrian among plants thallophytes were well establised. They diversified into various groups. (Chlorophyceae, Rhodophyceae etc.,). Among animals the aquatic arthropods
and echinoderms came to prominence. The fossils of such organism were obtained from several places.
2. Ordovician period :- (440 to 350 million years ago)
This period was marked by formation of coral rocks and molluscs and echinoderms. Among plants the semi terrestrial bryophytes were getting established. Interestingly this period saw the origin of first vertebrates. These were the now extinct agnatha. (Jawless, armoured fishes). The origin of early vertebrates was the major event that happened in the evolution of animals.Among arthopods, the trilobites were more prominent during this period.
3. Silurian period :- (350 to 315 million years ago)The oldest land plant originated in this period. These plants possesedconducting tissues. They colonised the land. Among invertebrates except forinsects all others flourised. The corals diversified. Several coral islands wereformed. Jawed fishes originated. The fishes developed scales and paried fins, for the first time jaws originated in fishes. Origin of paired fins and jaws is
considered as major events in chordate evolution.
4. Devonian Period :- (315 to 275 million years ago It is a significant period in the paleozoic era. During this period land living plants were more successful. The forests were filled with varieties of ferns and cycas. (non-flowering plants). Among aquatic animals fishes became dominant. They diversified by adapting themselves to live in various aquatic ecosystems. The forefathers of almost all modern fishes lived during
this period. Due to these reasons this period is called as the Age of fishes.
5. Mississippian Period :- (275 to 255 million years ago) Several changes happened to the land structure. There were massive upraising of land in several places. This resulted in the formation of several mountain ranges. Huge water bodies were broken into smaller lakes. These major changes on earth’s surface were known as revolutions(eg. Caledonian revolution). Such changes were the cause for the origin of lungs in fishes. Lungs evolved for the purpose of living temporaily on land. It helped such fishes to find new water bodies. Such practises encouraged the origin of the amphibians. The origin of land living amphibians were further increased by the proliferation of several land living insects.
6. Pennsylvanian :- (255 to 235 million years ago)
The land living forms became more successful during this period. There were huge forests of ferns and cycas. Due to geotectonic changes several forests got burried under the soil. Today’s coal and petroleum are obtained from such resources only. Hence the Pennsylvanian and the earlier Mississippian were collectively krown as Carboniferous (carbon bearing) period.
7. Permian Period :- (235 to 210 million years ago) It was the last period in the Paleozoic era. This period was marked by extinctions of several older groups of animals and plants. Nearly 60% of the organism that survived at that time became extinct. Some of the amphibians dramatically laid land eggs (cleidoic eggs). Specifically the group of organisms that laid such eggs are identified as Seymouria. These areconsidered as inter-connecting links between amphibians and reptiles.