Bearpaw Shale and the Inland Ocean

The panel's crocodile has a precise origin. In the summer of 1903 John Bell Hatcher, on a Geological Survey reconnaissance with T. W. Stanton, found scutes lying on the ground on Willow Creek, then in Fergus County, and carried a couple back to the Carnegie Museum. A collector sent that fall gathered vertebrae, ribs and several hundred fragments. Hatcher died in 1904, and in 1909 W. J. Holland named the animal Deinosuchus hatcheri for him. The bones lay in the Judith River beds beneath the Bearpaw, and teeth found in North Carolina in the 1850s were probably Deinosuchus too.

What the plaque says

Bearpaw Shale and the Inland Ocean The black shale rocks seen in this area represent the muddy sediments deposited by the last ocean to exist in Montana. The shale, known by geologists as the Bearpaw Shale contains fossils of sea-going creatures that lived and died some 70 million years ago. Twenty foot long swimming reptiles like Mososaurus and Tylosaurus fed on fishes and ammonites, relatives of squids and octopi. The remains of the gigantic coiled ammonites called Placentaceras and the straight shelled ammonites called Baculites are often found in these shale deposits. This inland ocean extended north to south, from the Gulf of Mexico to the Arctic Ocean, and divided North America into two subcontinents. Dinosaurs roamed the lands, and alligators and turtles inhabited the streams and rivers. But, one of the largest animals to live in this area was a gigantic, forty foot long crocodile called Deinosuchus that lived in the coastal waters of the inland seaway. The first remains of this animal were found near here. In the early 1900s, geologists learned that geological structures called anticlines, a kind of large wrinkle in the rock strata, were good places to drill for oil. Geologists also realized that certain parts of anticlines were better than others, and that the good spots were beneath structures they called domes. Here at the Mosby rest area you are standing on a part of the Mosby Dome, of the Cat Creek Anticline.

Where it stands

More markers nearby

• Kerchival City — steps away
• Fort Musselshell — steps away