The Silurian Period-the era of fishes and coral reefs
The Silurian period (about 417 to 443 millions of years ago), known for remarkable formation of coral reefs and fish gains its prominence as one of the significant parts of the Palaeozoic Era. Considerable changes occurred in the Earth at that time and these had their impact to shape the environmental and life in new forms. In the Silurian period climate of the earth gains a stabilized position and marked the end of climatic fluctuations which were erratic. The Silurian period also witnessed melting of large glaciers giving rise to the levels of major seas.
Lifeform and Species of the Silurian period
Due to rising levels of seas fishes and coral reefs had gained a remarkable evolution. There were significant appearances of jawless fishes, freshwater fishes and fishes with jaws. This period also marks formation of life on land with species related to centipedes and spiders. Fossils of vascular plants also denote the existence of the same in the Silurian period.
Coral reefs flourished during the Silurian period
Oldest fossils of coral reefs like brachiopods and crinoids mark the existence of these coral reefs in the Silurian period. At this time of Silurian era reefs formed in abundance mainly in the areas of Illinois and Wisconsin in North America. These areas were covered by tropical and shallow seas which paved the ways for the reefs to flourish.
Rugose corals and Tabulet corals were the dominant reefs formed in the Silurian period. Chains of tabulet reefs often resembled organ pipe clumps while the rugose corals came in shapes of bulls horn. These reefs finally formed a nice place for the fish to hide.
Fishes appeared in extensive ranges
Among the most notable species of fishes of the Silurian period were the jawless, freshwater and fishes with jaws. Jawless fish were known to come at the earlier part of the Silurian period and often regarded as vertebrates of the earliest forms, which are animals with soft cartilage backbones. Freshwater and fishes with jaws were thought to appear at the middle and later part of the period.
Extinct of the Silurian period- Crinoids
Though enjoyed a dominant position in the Silurian period Crinoids are not in existence today. They existed till the Permo-Triassic and then suffered from a complete extinction. Even, most of the Paleozoic limestones were made formed of the skeletal fragments of these crinoids.
Extinct of the Silurian period- Brachiopoda
Though these creatures suffered from obscurity but they did not suffer from complete extinction like the Crinoids. There are 300 living species of these reefs though they are rare in seas of today.
Life on the land during the Silurian period
Primitive plants like Mosses grew in abundant. These plants were responsible to turn rocks into soil and did the works of lichen. From the fossils gathered it was seen that these mosses were also the hubs of early insects. Cooksonia, a strange plant, began to grow on the lichen made soil. These plants had no leaves but only stems.