Fish fossils from the Late Pennsylvanian and Early Permian of Southeastern Nebraska
Most of the vertebrate remains that have been found in the late Pennsylvanian and early Permian strata of southeastern Nebraska are elasmobranchs, a group of fishes that includes sharks, rays, chimaeroids, sawfish, and guitar fish. These fishes have wholly cartilaginous skeletons. Their placoid scales and teeth are similar to the teeth of higher vertebrates, having a layer of enamel covering a layer of dentine that encloses a pulp cavity. The most primitive elasmobrahchs have seven gill slits and more advanced forms have five. Elasmobranchs of the late Paleozoic seas filled several ecological niches and include forms that were carnivores with flesh cutting teeth, carnivores with teeth modified to crush shells, and teeth that may have functioned as filters to extract plankton including algae and small animals from the sea water. One form of tooth found in the Kiewitz Shale may have functioned much like the “beak” on the modern parrot fish that feeds on corals.
The late Pennsylvanian and early Permian rocks of southeastern Nebraska and the adjoining areas have produced some outstanding examples of fish fossils from black, offshore shale horizons that represent the deepest water during marine transgressions that have periodically covered the North American Midcontinent. These sedimentary deposits are called cyclothems and they include both continental and marine sequences.