Wall in Pennington County, South Dakota — The American Midwest (Upper Plains)
Mesoreodon
Photographed by William Fischer, Jr., September 19, 2026
1. Mesoreodon Marker
Oreodonts are among the most common vertebrate fossils found across the National Grasslands. This extinct animal had an unusual anatomy and does not resemble any animal species alive today. The closest comparisons might be a sheep, deer, or camel.
The Screaming Oreodont
Mesoreodon have been found with preserved ossified vocal cords; the only modern animal with ossified vocal cords are howler monkeys. Howler monkeys' deep, resonant calls can be heard from up to 3 miles away and are among the loudest sounds in nature. We can only imagine what sounds this little oreodont made!
Although oreodonts are presumed to have been herbivorous (plant eaters), they possess "caniform incisors" that resemble sharp canine teeth.
[Artist rendition of] Merycoidodon culbertsoni
Rockyford Ash
30 MILLION YEARS AGO
A thick layer of volcanic ash from an eruption in the Great Basin that was 5 to 6 times the size of Yellowstone! The environment would have consisted of open woodland, grasslands, and scrubland as the climate continued to dry and cool.
[Silhouette drawing] Rough estimate of Mesoreodant compared
this page online
Erected by US Forest Service and Badlands Natural History Association.
Topics. This historical marker is listed in these topic lists: Animals • Environment • Paleontology.
Location. 43° 59.453′ N, 102° 14.486′ W. Marker is in Wall, South Dakota, in Pennington County. It is at the intersection of Main Street and 7th Street, on the left when traveling south on Main Street. Marker is on the National Grasslands Visitor Center grounds. Touch for map. Marker is at or near this postal address: 708 Main Street, Wall SD 57790, United States of America. Touch for directions.
Regionally, this marker is in West River, in the Badlands, and in Greater Rapid City. It is also in the American Lewis & Clark Corridor, on the prairies, and on the Northern Plains. Globally, it is in North America, the Western Hemisphere, the Western World, and the Anglosphere. Historically, it finds itself in what was once Rupert’s Land and also the Louisiana Purchase.
Other nearby markers. At least 8 other markers are within walking distance of this marker: Hoplophoneus
Photographed by William Fischer, Jr., September 19, 2026
2. Mesoreodon Marker
Photographed by William Fischer, Jr., September 19, 2026
3. National Grasslands Visitor Center
Credits. This page was last revised on October 19, 2026. It was originally submitted on October 19, 2026, by William Fischer, Jr. of Reynoldsburg, Ohio. This page has been viewed 9 times since then. Photos: 1, 2, 3. submitted on October 19, 2026, by William Fischer, Jr. of Reynoldsburg, Ohio.
