As we continue our overview of Badlands fossils, the next unit above the Chadron Formation is the Scenic Member of the Brule Formation, which is Oligocene in age. If you just tabulate what fossils are present, the Scenic looks a lot like the Chadron. But that doesn’t reflect the differences in abundance, because the Scenic is all about the oreodonts.
Oreodonts were sheep-sized artiodactyls that were not particularly closely related to modern groups. They were present in the Chadron, but their diversity and particularly their abundance increases in the Scenic Member. Merycoidodon (top, from USNM) was particularly common. Miniochoerus (below, from SDSM) was also widespread, with several different species.
Other artiodactyls were also quite common, including the ruminant Leptomeryx (SDSM):
The camelid Poebrotherium (SDSM):
Some of the most spectacular artiodactyls were the omnivorous or carnivorous entelodonts, such as Archaeotherium (SDSM):
Other groups that saw tremendous increases in diversity were rodents such as Ischyromys and rabbits such as Palaeolagus (both SDSM):
Perissodactyls were still around, if not as common as artiodactyls. These included horses such as Mesohippus and rhinoceroses such as Hyracodon and Metamynodon (all SDSM):
Carnivores such as Hoplophoneus and Dinictis also continue into the Scenic Member (both SDSM):
So, other than the changes in relative abundance of certain groups, how exactly is the Scenic Member different from the Chadron Formation? Notably absent from the Scenic are titanotheres and alligators. The titanotheres disappear from North America all together at the end of the Chadron, and alligators are not seen in the White River Group again.