[F] Pierre Shale - Nebraska - South Dakota - Wyoming - US
Nebraska - South Dakota - Wyoming - US
This mile-thick layer of dark gray mudstone and shale accumulated at the bottom of the Cretaceous Western Interior Seaway. Clams, ammonites, and baculites are the most common fossils. Their distribution tells that for millions of years, this seaway connected the Gulf of Mexico to the Arctic Ocean and covered all of what today is Colorado.
Claosaurus affinis - South Dakota - Hadrosauridae Nomina Dubia - Cretaceous Late Campanian
Hesperornis bairdi ~/~ - South Dakota - Ornithurae [Hesperonithiformes] - Cretaceous Late Campanian
Hesperornis chowi ~/~ - South Dakota - Ornithurae [Hesperonithiformes] - Cretaceous Late Campanian
Hesperornis macdonaldi ~/~ - South Dakota - Ornithurae [Hesperonithiformes] - Cretaceous Late Campanian
Hesperornis mengeli ~/~ - South Dakota - Ornithurae [Hesperonithiformes] - Cretaceous Late Campanian
Hesperornis regalis ~/~ - Nebraska - Ornithurae [Hesperonithiformes] - Cretaceous Late Coniacian Santonian Campanian Maastrichtian
Undescribed hadrosaurid - Wyoming - Ornithopoda - Cretaceous Late Campanian