In 1869, American geologist Alexander Winchell coined the name Mississippian
in 1869 for rock outcrops along the drainage basin of the Mississippi
River. He distinguished these limestone-rich Lower Carboniferous rock
layers from the coal-bearing beds of the Upper Carboniferous (or Pennsylvanian).
Because these two sets of rocks are easily distinguished in North
America, the terms Mississippian Epoch and Pennsylvanian Epoch are
commonly used by American geologists and paleontologists. This distinction
was less clearly marked in Europe, and the names Lower and Upper Carboniferious
were widely used. The European subdivision of the Carboniferous
has now been formally replaced by Mississippian and Pennsylvanian by the International
Commission on Stratigraphy.
The Mississippian world was rather uniformly warm, although yet another
ice age began toward the end. As more continents began to collide,
extensive mountain-building occurred. The tropical seas were home
to a great diversity of marine life, including many different kinds
of fishes, brachiopods, bryozoans, mollusks, and echinoderms. On land,
a major habitat division began between seed plants, which preferred
drier habitats and the lycopsids (club mosses), which preferred wetter
places. There were also the first significant radiations of terrestrial
tetrapods and winged insects. In the Pennsylvanian, vast coal swamps
would form, the feature for which the Carboniferous Period was named.