Carboniferous Period 359 to 299 mya
The Carboniferous takes its name from the coal (made mostly of carbon) which formed during this period, coal derived plants which continued to evolve and grow larger. On land the insects evolved wings and amphibian vertebrates followed this new food source onto the land.
At the end of the period life suffered a mass extinction event.
The southern supercontinent Gondwana saw massive glaciers.
Early in the Carboniferous, the ocean separating Euramerica from Gondwana began to close, creating the Variscan and Appalachian mountains.
There were glaciers on Gondwana in the south and the Earth was subject to glacial periods.
During the Carboniferous Period, ferns the size of trees were common. They had solved most of the problems of living on land but were still tied to moist ground for their reproduction. Many ferns grew in swamps. They grew from a small underground growth called a prothallus. The sperm swam from one prothallus to fertilize the egg on another. Without water or wet ground they could not reproduce.
Reconstruction of Lepidodendron or “Scale Tree” in Carboniferous swamp
When they died some ferns fell into the swamp. Decomposition could not happen because there was no oxygen in this water so the plants were buried and eventually turned into the stone we call coal.
The ferns we see today are still among the most primitive of plants. Their fronds uncurl and carry spores on their undersides.
Once the plants and arthropods were there was plenty of food for any which could manage to come out of the water. Some fish lived in ponds which dried up in summer. Their swim bladders evolved into lungs which they used to breathe air. They used their fins to crawl from one pond to another and these evolved into legs, two at the front and two at the back.
The vertebrates which emerged from the water and became land animals around 350 mya we call amphibians “am-fib-ee-ans”. Their name means “both lives” because they lived both in water and on land at different times in their lives.
Image of early temnospondyl courtesy of Dmitry Bogdanov
Early amphibians such as the temnospondyl shown here first appeared in the Early Carboniferous around 330 mya.
Leaving the water was one of the greatest steps ever taken by our ancestors. It needed changes in every part of the body. The most obvious changes were the appearance of legs and the ability to breathe. Other changes were not so obvious but were just as important. For example the way the flowed round the body had to change.
Amphibians were still not totally free from the water. They needed to return to it to (like the and the before them). Their eggs were laid and in water and the young developed in the water just like their ancestors. But when amphibians grew up they left the water to live on the land. Most frogs and newts are still at this stage of evolution.
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