In the second part of the Paleozoic, the emergent lands are divided into two continents, Laurasia in the north and Gondwana in the south, which are dressed in green with huge forests of plants with seeds.
At this time the expansion of life on the continents was consolidated. However, the Paleozoic Era ended with the greatest mass extinction in Earth's history, that of the Permian-Triassic, which caused the disappearance of 70% of terrestrial species and 90% of marine ones.
Devonian: amphibians, insects and plants with seeds
The Devonian period, which began 420 million years ago, is characterized by the appearance of several types of fish, which included sharks, dipnoos, armored fish and a primitive form of fish with hard scales. The first amphibians probably evolved from these last ones, appeared about 365 million years ago.
There were also corals, starfish, sponges and trilobites, as well as some terrestrial arthropods, including the first known insect, although without wings. Woody plants developed and, at the end of the Devonian, other land plants such as ferns, horsetails and scaly trees related to the current ones selagos.
In the Devonian appeared the first plants with seeds, which spread rapidly forming immense forests.
There was a lot of tectonic activity, since Gondwana and Laurusia pushed themselves without truce. Towards the end of the period there was a new mass extinction due to the cooling of the climate that affected, above all, marine life.
Carboniferous, the diversity of life
Some 359 million years ago, some land plants began to diversify and increase in size, especially in swampy areas. Huge forests prospered and were buried in successive strata that, over time, became coal. That's why it's called Carboniferous.
A group of sharks, the cestraciontes, predominated among the large marine organisms. The most notable land animals were a kind of amphibious lizards that came from the dipnoos.
In the second part of the Carboniferous, reptiles emerged, which evolved from amphibians and were already terrestrial. Other animals of this period were arachnids, snakes, scorpions, more than 800 species of frogs and huge insects, the largest that have existed.
The largest plants were scaly trees, whose trunks measured more than 1.8 meters at the base and were 30 meters high. There were also some in this period gymnosperms primitives and the first true conifer, an advanced form of gymnosperm that consisted of a vascular plant with seeds, but without flowers.
Of the ancient land masses only the protocontinent of Siberia was north of the tropics, reaching almost to the north pole. Gondwana, who understood what would become South America, Africa, India, Australia and Antarctica, was entirely in the southern hemisphere and encompassed a vast area centered in the immediate vicinity of the pole. The Carboniferous period ended with a great glaciation.
Permian: reptiles and Pangea
The last period of the Paleozoic, the Permian, began 299 million years ago. Events as relevant as the disappearance of a large part of marine organisms and the rapid evolution and expansion of reptiles occurred, diversified into two types: lizards similar to lizards, completely terrestrial, and slow semi-aquatic reptiles.
A small group of reptiles, teriodontes or teriodontos (Theriodontia, beast teeth in Greek), were the origin of mammals and, therefore, our ancestors. The vegetation of this period, very abundant, was constituted mainly by ferns and conifers.
The final part of the Paleozoic was a period of widespread agitation of the earth's crust, in which continents emerged from beneath the shallow seas of the preceding carboniferous. The accumulated deposits in geosinclinal pits were put under pressure and elevated in the form of mountainous systems: the Appalachians of the center and the south in North America, and the Urals in what would later be the territory occupied by Russia.
Europe and Asia joined while to the west a collision between continental plates connected North America with the continent of Gondwana. At the end of the Permian period and, therefore, of the Paleozoic Era, all the continental land masses gathered in one, called Pangea.
• Chronology of glaciations
• Pangea, all the land
• Coal formation in Barruelo de Santullán
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