© 2023
Prairie Public NewsRoom
Play Live Radio
Next Up:
0:00 0:00
Available On Air Stations



Today we’re bringing you a glimpse of what our state was like before humans came. On this day, 75 million years ago, the area around Cooperstown was under salt water.

Actually, a shallow, sub-tropical sea covered almost the entire state. The Pierre Sea was part of the Western Interior Seaway, which divided the North American continent right down the center, connecting the Arctic Ocean with the Gulf of Mexico.

But back to Cooperstown 75 million years ago. On a typical day, sand-tiger sharks, dogfish sharks, and two types of cow sharks were trying to “out-lunch” each other. Since both types of cow sharks are now extinct, a person could surmise that one of the other types was winning.

The water in that area was only about 100 yards deep, and the sharks’ entrees included numerous types of bony fish, including the salmon-like Enchodus. Down on the seabed, coral and different types of seaweed were sheltering snails, tusk shells, clams, starfish, sea urchins, shrimp, crabs and lobsters.

There were also cephalopods, which include creatures like the octopus, squid and the chambered nautilus. It’s the cephalopods that give away the time period, which was Campanian; some refer to it as the golden age of the duckbilled dinosaurs.

On the sea’s surface were turtles and hesperornithids. That last one was a seabird that couldn’t fly. At 6_ feet tall, it had powerful legs similar to the modern loon. It also had teeth.

Now we get to one of the creepier predators: the carnivorous mosasaur. These marine reptiles lived during the same time as the dinosaurs, but they’re in a different classification more closely related to monitor lizards, like the Komodo dragons of Indonesia. Mosasaurs had powerful toothy jaws like those of alligators and crocodiles, but they didn’t have legs. They had flippers, and they propelled through coastal waters in the same way a snake moves.

Mike Hanson and Dennis Halvorson of Cooperstown found the jaw of a mosasaur in the Sheyenne River valley around 1993, and John Hoganson, of the North Dakota Geological Survey, came out to investigate. To make a long story short, at least 12 mosasaurs have now been found in that area. Two separate species were identified, but there was one that was different.

The unusual one was found on Beverly and Orville Tranby’s property, and it was almost completely intact. To their great credit, the Tranbys, as well as Bev’s sisters, donated it to the State Fossil Collection for further study. The entire skeleton turned out to be 23 feet long, with the skull alone being 3 feet. The specimen was identified as a type of Plioplatecarpus, but its unusually large size and unique bone structure revealed it to be a new species not found anywhere else in the world. Some of its bones had tooth marks, and thousands of dogfish shark teeth found with the skeleton paint a pretty clear picture of the lizard’s last moments: sharks lose a lot of teeth when they’re attacking and feeding.

After two years of intensive restoration, this one-of-a-kind mosasaur is now suspended in mid-air in the impressive Corridor of Time display at the Heritage Center in Bismarck. The restoration was funded only through private donations and volunteer help, so we’re fortunate that it happened at all. To learn more, go to the website for the ND Geological Survey. And remember… do something good for the earth today and always.

Written by Merry Helm