The Mississipian Period (after the U.S. state of Mississippi) extends from about 363 mya until 323 mya.
In Europe, the Mississippian and Pennsylvanian Periods are joined into a single period called the Carboniferous, and can be quite naturally be subdivided into three epochs. In the U.S., this timespan can only be divided into two subgroups, subdivided by a withdrawl of seas from the North American continent.
The Mississippian fossil record is almost entirely marine. Shallow, warm-water seas covered much of the North American continent, which was equatorially located at the time.
Classic Fossil-Bearing Sites
Mazon Creek, Illinois
A 46 km, 360 million year old, impact structure is found in Quebec, Canada, and a second Canadian impact is found on the north shore of Lake Superior at Slate Island. This structure is about 30 km in diameter and has been dated to some time less than 350 mya.
Laurasia and Gondwana
During the Carboniferous, the world's continents were combined into two large supercontinents. The northernmost, extending across the equator and into subtropical northern latitudes has been called Laurasia. The current continents of North America, Europe and Asia made up this body.
The southern supercontinent, extending from southern subtropical latitudes to almost antarctic latitudes has been named Gondwana, and was comprised of what was to become South America, Africa, India, Australia, and Antarctia.
The Age of Crinoids
The Mississippian has sometimes been called the "Age of Crinoids," due to the numbers of fossils of these stalked echinoderms found in the strata of the period. Crinoids were filter feeders that lived in the warm water surrounding Laurasia.