Fossils of the Central Lowland

Paleozoic fossils

The Central Lowland region composes the middle part of the North American continent, centered on the Mississippi River Valley. This region as a whole includes abundant and extensive fossils from the early Paleozoic, especially in the midwestern states, demonstrating that the area was covered by a warm, shallow sea during much of this time. The portion of the Central Lowland region represented in the northwest-central states—eastern Nebraska, eastern South Dakota, and eastern North Dakota—has very few Paleozoic rocks at the surface. 

Cores drilled in eastern parts of the Dakotas have yielded marine fossils of early and middle Paleozoic age from the subsurface similar to those found elsewhere in the Central Lowland region, revealing that these areas were also covered by the same warm, shallow sea. Fossils and other subsurface information indicate that coral reefs were well developed in what is now North Dakota during parts of the Silurian and Devonian.

Pennsylvanian rocks outcrop in easternmost Nebraska and contain a diversity of marine fossils, including foraminifera, brachiopods, bryozoans, cephalopods, crinoids, gastropods, bivalves, trilobites, corals, and the teeth of early sharks. The Beil Limestone, for example, is a rock layer containing abundant corals; it occurs in Cass County, Nebraska, and also extends into Mills and Montgomery counties in Iowa, Holt County in Missouri, and Doniphan, Atchison, Greenwood, and Douglas counties in Kansas.

Mesozoic fossils

The northeastern corner of North Dakota (Pembina County) contains the Central Lowland’s only Jurassic bedrock. By that time, a shallow sea had flooded the region again, and fossil marine gastropods, bivalves, and crinoids are found in the state’s Jurassic deposits.

Cretaceous rocks occurring in the Central Lowland, as well as the few Cenozoic deposits that extend into northeastern Nebraska, are identical to those found in the Great Plains region.