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The Precambrian time soon came to an end and it was time to usher in a new period. The Palaeozoic Era was a time of great development with great activity occurring, it was the rise of life. Within the Palaeozoic Era there were many smaller periods:
1) Cambrian Period (about 540 - 500 MYA) where trilobites dominated the seas and the land still had no signs of life. 2) Ordovician Period (about 500 - 435 MYA) The first fish evolved 3)Silurian Period (about 435 - 410 MYA) The earliest land plants appear 4) Devonian Period (about 410 - 355 MYA) where fish dominated the oceans. Land was no longer left lifeless with an abundance of species starting to evolve. Spiders and mites were the first land creatures and the first amphibians started to evolve. Forests began to take form. 5) Carboniferous Period (about 355 - 295 MYA) saw insects flourish and the first reptiles evolve, Shrubs, ferns and trees dominate the land. 6) Permian Period (about 295 - 250 MYA) saw synapsids such as Dimetrodon and amphibians dominate the land. The Palaeozoic Era was a time of rapid growth and development. The oceans were now teaming with life and the land had a very diverse range of species living on it. Life was thriving in its new environment. However at the end of the Permian period, massive volcanic eruptions caused a mass extinction, wiping out 90% of marine life and 70% of land life. With such devastation and destruction, it was time to let go of the past and bring in a new Era. |
1) CAMBRIAN PERIODMost of the major groups of animals that exist today evolved in this period. This massive development in diversity only occurred in the seas, as life on land was still no where to be found. This explosion of life in the seas is referred to as the 'Cambrian explosion'. Soft bodied animals began to evolve into species that had hard bodies, for example the trilobites.
During the Cambrian most of the world's landmasses were united as the supercontinent Gondwana. This was surrounded by the vast Iapetus ocean. 3) SILURIAN PERIODAt the very end of the Ordovician period a large scale extinction occurred, resulting in a greatly reduced richness of animal life in the early stages of the Silurian period. However groups of animals such as molluscs, trilobites and graptolites that survived the extinction quickly recovered in a greater diversity. New aquatic animals such as sea urchins appeared for the first time, while jawless fish thrived and jawed fish diversified. Anthropods, the very first land living species started to evolve from their aquatic ancestors during this time.
The Silurian period also marked the beginning of true land plants. This was a critical time in the evolution of plants. The mosses that started to evolve during the Ordovician period had now become independent and no longer needed water to produce. This resulted in a widespread growth of plants inland. 5) CARBONIFEROUS PERIODAmniotes (vertebrates whose embryos are enclosed by a watertight membrane) evolved in this period. The land living vertebrates diversified while insects evolved. Spiders, scorpions and mites increased in size and diversity.
Lurking in the depths of the oceans were sharks and bony fish. Coral reefs of the time housed swimming molluscs and tiny little fish. Lush forests and floodplains developed rapidly in this age. Club mosses and horsetails were important components of these developing forests with some growing to enormous sizes. Towards the end of this period, the floodplains began to shrink as the climate became less wet. Club mosses were then replaced by ferns and seed ferns. |
2) ORDOVICIAN PERIODYet another burst of evolution in the Ordovician period gave life to thousands of new species. Many of these species were filter feeding that fed on increasing populations of plankton. Corals and bivalves provided the perfect home to swimming molluscs and other sea dwelling animals. The earliest jawed vertebrates (a group including sharks and bony fish) also appeared in this period.
Colonial blue-green algae were still widespread throughout this age. Most significantly, plants similar to mosses started to evolve during the later stage of the Ordovician period and began to spread across land. Until this burst of activity the land was barren, however these plants still relied heavily upon water as they needed it for reproduction. 4) DEVONIAN PERIODThis period was one of the most important periods in the evolution of vertebrates. During this time the first vertebrates with 4 limbs evolved from lobe-finned fish, spreading widely around the world by the end of the Devonian. Land-living arthropods increased in population and wingless insects started diversifying.
While ray-finned fish started becoming more important, heavily armoured jawless fish thrived in the oceans and jawed fish started becoming more abundant. Several groups of trilobites remained widespread and ammonoids and horseshoe crabs appeared. The most important steps so far in development of land plants occurred during this time. Leaves and roots evolved independently in a number of different species. Plant stems could now grow in length and diameter, resulting in far greater growth. Gigantic tree species started appearing, while horsetails, seed ferns and conifers started appearing later in the Devonian age. 6) PERMIAN PERIODThe primitive Synapsids were the most important and diverse land-living vertebrates of this era. Most were small to medium sized animals that had powerful skulls and sharp teeth. Reptiles and arthropods such as spiders and insects along with Synapsids thrived throughout this time.
Sponges and bryozoans built elaborate reefs that teamed with marine life. Shelled animals, new fish groups and some reptiles returned to find homes in the oceans. Plant communities during this time were similar to todays plants. The club mosses and horsetails that appeared in the previous period had now largely died out, being replaced by gymnosperms. Conifers flourished while cycads and gingkos evolved. Late during the Permian, conifers evolved to develop thick fleshy leaves protected by hairs to build tolerance to the hot and humid climate of the time. |
PERMIAN EXTINCTION
The greatest mass extinction took place at the end of the Permian period 250 million years ago. This had devastating effects on all life forms and due to this, scientists refer to this period as the "time of great dying". Scientists estimate that all but 5% of life was wiped out during this mass extinction. In the seas aquatic life was hit hard with reefs being destroyed, causing reef dwelling animals such as trilobites and sea scorpions to disappear. On land had the same fate with many reptile groups vanishing. It is unlikely that a single catastrophe was responsible for this mass extinction but rather a series of events leading up to it. Climate change and volcanic eruptions may have also contributed to the extinction.