Fossils
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Fossil Types (Tour Map symbol 'F')
Ammonite (similar to the chambered Nautilus) and clam shells are abundant in the Belle Fourche shale of the mid-Cretaceous period. They can be seen on the eastern beach margins of the Belle Fourche reservoir when the water level is low. Wave action usually washes them out of slumped cliff sections.
The Pierre shale was formed from sediments laid down in a Cretaceous sea. Fossils commonly found in these sediments are fragments of the hard parts of clams, belemnites (similar to squids), ammonites, and larger marine animals like the reptile mosasaur which is on display at the South Dakota School of Mines and Technology (SDSM&T) Museum in Rapid City. Occasionally, coral is also found.
Fossils remains of large terrestrial animals are found in the Hell Creek formation deposited during the late Cretaceous period. Dinosaur fossil bones notably that of Tyrannosaurus rex (T. rex) and Triceratops spp. and remains of other animals such as fresh water turtles are the most numerous. The most intact T. rex skeleton named 'Sue' was discovered near the Ziebach-Perkins county line and is displayed in the Field Museum in Chicago. Another excellent T. rex skeleton, 'Stan', was excavated in Harding county. A replica of 'Stan' is on display at the Kirby Science Discovery Center in Sioux Falls. The SDSM&T Museum in Rapid City and the Grand River Museum in Lemmon have many fine fossil models and specimens on exhibit.
The White River formation of the Tertiary period was deposited in a terrestrial environment. The hard parts of land animals of various sizes and types can be found as well as turtles and some freshwater fish skeletons that are excavated in the Badlands and surrounding areas as well. Displays of titanothere and oreodont skeletons and other land animals are displayed at the SDSM&T in Rapid City. Several casts of smaller land animal skeletons are also on display along the Fossil Exhibit Trail on the Badlands Loop Road in the Badlands National Park.
Parts of petrified tree trunks and branches can be found in the Fort Union formation of the Tertiary period either embedded in parent rock, or weathered out. An excellent selection of petrified wood (logs, branches, and cones) is arranged in the City Park in Lemmon. Local gardens and other parks in northwestern South Dakota proudly display their most beautiful specimens.
