What ended the Carboniferous Period?
The formation of Pangea signaled the end of the Carboniferous Period. Pangea caused a great upheaval on land and in the sea, and set up the basis for new species of plants and animals.

Pennsylvanian Period (Upper Carboniferous) 325-286 mya

Major Adaptive Radiations
A new group of tetrapods, the diapsids, enters the scene. These are the ancestors of reptiles, and actually the diapsids divides into two groups, the 1) marine reptiles, snakes, and lizards and 2) the archosuars, which includes crocodiles, dinosaurs and birds.
Amphibians also flourish. The major ancient amphibian groups appear.
Arthropods discover that spores are yummy.
 

Fauna
Shallow water covered most of the planet, except for Pangea. Attached filter feeders, such as bryozoas were in abundance. The ostracoderms, or armored fish, of the Devonian Period become extinct and are replaced by more modern looking fish.  Millipedes, scorpions, and spiders also begin to play a larger role in the ecosystem. Insects with wings that do not fold back, such as Dragonflies, radiate and thrive.
Tetrapods become more diverse, with their body shapes becoming less like fish and growing sprawling limbs and flattened heads. The first land snails occur.
Amphibiamus

Flora
Swamp forests with highly diverse vegetation become common. In the swamps are lycopods, or seedless plants, that grew to 35 feet tall. Some of the swamp plants had large tops and laterally spreading roots which were ideally suited to the wide, flat, poorly drained land surfaces. These plants grew densely in bogs and swamps along the flood plains, estuaries and shorelines of lakes, and possibly in coastal areas. Ferns become very important. Sphenophytes, the ancestor to Equisetum, appears and flourished, producing trees up to 100 feet tall.
Coal Swamp, common in the Pennsylvanian.

Continental Drift
The Carboniferous was marked by the progressive formation of the supercontinent Pangea. The present day Northern Hemisphere mandamuses moved towards the equator to form Laurasia and to join the large Southern Hemisphere land mass Gondwana. The collision between Siberia and Eastern Europe created the Ural Mountains, and China was formed with the collision of several microcontinents and Siberia. The collision between Gondwana and Laurasia led to the formation of the Appalachian belt in North America and the Hercynian Mountains in Europe. Gondwana also shifted towards the equator while the continents moved from east to west.
Coal beds, which can be up to eleven to twelve meters thick, characterize the Upper Carboniferous. The forests of seedless vascular plants that existed in the tropical swamp forests of Europe and North America provided the organic material that became coal. Dead plants did not completely decay and were turned to peat in these swamp forests. When the sea covered these swamps, marine sediments covered the peat. Eventually, heat and pressure transformed these organic remains into coal.
 
 

Mississippian Period (Lower Carboniferous) 360-325 mya

Climate
The climate during the early Carboniferous Period was uniformly tropical. There were no distinct seasons. This is due to the vast oceans that covered everything except the massive land masses Laurassia and Gondwana.

Adaptive Radiation
Terrestrial radiation occurred because of drying trends that were the result of large glaciers, most of which originated in the South Pole of the time. As the glaciers passed over the land, they absorbed the majority of the water in the shallow oceans, which resulted in the extinction of shallow marine vertebrates such as bryozoans, the swamps dried up, and terrestrial land increased.
Freshwater clams first appear along with an increase in  bony fish, and shark diversity.
The first conifers appear.
By far, the most important structure to come about during the Mississippian Period was the amniotic egg. As the atmosphere became more arid, there came a need for a reproductive structure that could stand the pressures. The amniotic egg, seen in the picture below, has an outer shell that prevents drying and membranes that nourish and protect the embryo.

 

Continental Drift
Near the end of the Mississippian, uplift and erosion of the continents occurred, causing an increase in the number of flood plains and deltas present. The Missisippian Period is known for its limestone deposits, which is a result of the crinoids, lime-crusted green algae, and calcium carbonate shaped by waves. During the late Early Carboniferous, East Gondwanaland, for the first time since Early Paleozoic, began to drift toward the South Pole.  By early Late Carboniferous, the South American-North African margin of Gondwanaland had collided with the northern Devonian supercontinent of Euramerica becomes Laurasia by the late Carboniferous.

Fauna
corals, crinoids, and bryzoans
Freshwater clams first appear along with an increase in bony fish, and shark diversity.

Flora
Mostly shrub bushes, about 2 meters tall
Lycopsids and calamite trees

Glossary
calamite- horsetails
crinoids- marine organisms with calcium shells
tetrapods- Organisms with four limbs

Sources Cited
http://www.kheper.auz.com/gaia/Paleozoic/Carboniferous/Mississippian.htm
http://www.ucmp.berkeley.edu/carboniferous
Chaloner, W.G. 1991. Fossil evidence for plant-arthropod interactions in the Palaeozoic and Mesozoic. Phil. Trans. R.Soc.
    Lond. 333:177-186
Daeschler, E.B., Neil Shubin 1995. Tetrapod Origins. Paleobiology 21:404-409.