We’ve looked at the Cretaceous and Eocene fossils from the Badlands, as well as Oligocene fossils from the lower part of the Brule Formation, the Scenic Member, and seen that there are faunal differences between each unit. This continues as we move higher in the section, into the Poleslide Member and the Sharps Formation.
In the Poleslide we see the first appearance of the artiodactyl family Protoceratidae, specifically Protoceras celer (top; all images from SDSM). Protoceras is particularly common in certain beds in the Poleslide, with enough specimens known to determine characteristics such as sexual dimorphism. Below are male and female skulls of Protoceras:
Much less common were the hippo-like anthracotheres, such as Heptacodon:
Entelodonts were still diverse as well, and included some large taxa such as Megachoerus:
Rabbits and rodents continued to diversify and increase in abundance as well. In contrast, the perissodactyls declined somewhat. There were still rhinoceroses around, such as Subhyracodon (below), but they were not as common as in the older units.
Horses were still present as well, but the small Mesohippus was supplanted by the larger and higher-crowned Miohippus:
Many of the carnivores were quite similar to the earlier units, including Nimravus:
One new group of carnivores, the mustelids (weasels) were represented by Palaeogale:
The Badlands section, especially within the White Rover Group, is an interesting exercise in biostratigraphy and paleoecology. The changes from one unit to the next are not particularly dramatic, yet the Chadron fauna looks very different from the Poleslide fauna (try comparing the posts on those units without looking at the intervening post on the Scenic Member).
Over that period we see the loss of titanotheres and alligators, along with the rise of oreodonts, rabbits, and rodents, and higher in the section a move away from browsing rhinos and horses toward higher-crowned horses and protoceratids. The overall trend suggests a move toward a drier, less-forested environment. This is the same trend we see in the sediments, with thinner and more carbonate-rich paleosols.
We have actually already returned home from our trip, and I’ve discovered that it’s very difficult to keep up a blog while working 16-hour days! After leaving the Badlands we continued to the Black Hills and spent several days there, and I’ll be writing posts about that part of the trip as soon as I’m able.
We’ve also posted two more gigapans from the Badlands: