The Carboniferous period dates from 360 million to 280 million years ago. It gets its name from the vast deposits of coal produced when fluctuating seas drowned the tropical forests that covered much of North America and Europe.
|Era||Period||Epoch||Million Years Before Present|
The later Paleozoic (286 million to 570 million years ago) was a world that would be recognizable to us. By this time the teeming marine and land plants had expelled enough oxygen to produce an atmosphere very similar to our own. Vast forests greened the supercontinent Pangaea and supported a thriving animal population. We would be struck by the sheer size and variety of the flora and fauna: horsetails and scale trees that stood from 50 to 100 feet tall and dragonflies with 2-foot wingspans. Drippingly humid and silent, the monotonously green rain forest abounded with scuttling creatures familiar and unfamiliar. Animals that swam, crawled, and flew populated the tropical swamps of the forest. Snails and cockroaches and myriapods made a living on the rich forest floor, along with 6-foot centipedes and crocodile-like amphibians.
By this time all the major characters of evolution had come into being. There would still be millennia of ingenious refinements of size and shape and function, variations on the main themes to exploit the new Devonian (408 million to 438 million years ago) environment of land and air. The Phylum Chordata, comprised of animals with backbones, had previously experimented with fishes and amphibians; now, in the Carboniferous period, the chordates would diverge into reptiles.
In a remarkable adaptation referred to as the amniote radiation, amphibians had evolved from needing large bodies of water in order to reproduce. The method was a semipermeable, shelled or leathery skinned egg filled with enough nutrients to sustain an embryo until it was fully developed. This dry-land form of reproduction necessitated yet another biological innovation, namely internal fertilization. These two features enabled the former amphibians to radiate out into every niche of the giant land mass, in turn encouraging further evolutionary branching. As the tetrapods (fourlimbed animals) spread through the luxuriant vegetation, they made adjustments in their dentition and digestive tracts to take advantage of the untapped food source on land.
Three distinct groups of reptiles emerged, differentiated by the number of small holes in the skull located behind the eyes at either side. Anapsids had no holes and included the turtles and their now-extinct relatives. Synapsids, with a single pair of temporal openings, included all of the mammal-like reptiles, now extinct, and their distant relatives, the true mammals. Diapsids were reptiles with two pairs of openings. Petrocalosaurus was a rapid, 16-inch insectivore whose genes gave rise to lizards, snakes, crocodiles, dinosaurs, and birds.
By the Carboniferous period, the constant ebb and flow of continental drift had once again pushed the land masses back together into one supercontinent, Pangaea, whose northern forests were periodically flooded by shallow tropical seas. The cycle of vegetation and flooding produced organic beds of peats that were compressed into coal layers over 3,000-feet thick. Exquisitely preserved fossils appear in this coal, especially near the Czech mining town of Nyrany. Here, hundreds of specimens have been collected, representing twenty amphibian and four reptile species as well as unusual fishes and small, shrimplike creatures.
In the Carboniferous seas, huge limestone reefs were being laid down by limy coral, brachiopod, and crinoid skeletons. These reefs were home to starfish, gastropods , and sea urchins, while giant coiled nautiloids and bony fish swam overhead.
see also Geological Time Scale.
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CARBONIFEROUS OR MISSISSIPPIAN AND PENNSYLVANIAN?
In the United States, the Carboniferous Period is usually broken down into two periods— Mississippian and Pennsylvanian. Sedimentary rocks that formed in shallow oceans characterize the Mississippian or "Lower Carboniferous." These rocks are usually found along the Mississippi River. Coal bearing sedimentary rocks that formed in swamps and river deltas characterize the Pennsylvanian or "Upper Carboniferous. These rocks are usually found in the northeastern United States.