Section 5: Mesozoic Era

Mosasaur

Figure 9. Mosasaur. This large marine lizard is shown swimming in the ocean that covered North Dakota 80 million years ago. Sharks and a seabird are also in the painting. (ND Geological Survey)

After the Paleozoic Era ended about 248 million years ago, the Mesozoic (mez-a-zoe-ik) Era began and lasted until about 65 million years ago, a length of about 183 million years. The Mesozoic Era is sometimes called the “Age of Reptiles” because during the millions of years of this era, many kinds of reptiles developed. Some were fish-like creatures that swam in the ocean waters, some were flying reptiles, and some lived on the land.

The most famous reptiles of all time were the dinosaurs. Fossils from more than a dozen different kinds of dinosaurs have been found in North Dakota.

Triceratops skull

Figure 11. Triceratops dinosaur skull, on display at the North Dakota Industrial Commission in Bismarck, North Dakota. (ND Geological Survey)

An example of a large sea reptile that lived in the area was the mosasaur (mos-a-sor). This giant lizard was a carnivore that hunted other marine (sea) animals.

One of the flying reptiles that lived in this area was the carnivorous Pteranodon (ter-an-a-don). It had a long neck, a long beak, and a wing-span of about 20 feet from tip to tip.

Triceratops

Figure 10. Triceratops dinosaurs in a swamp. Western North Dakota appeared like this 65 million years ago. (ND Geological Survey)

The most common dinosaur found in North Dakota was Triceratops (try-sair-a-tops). This strange-looking reptile had a huge head with a big horn above each eye and a smaller horn on its nose. It also had a bony plate at the back of its skull that looked like a high collar sticking up from its neck. It was an herbivore that could weigh as much as five tons (10,000 pounds).

Most of the dinosaurs that lived in North Dakota were herbivores, but one of the best-known carnivores was Tyrannosaurus (ty-ran-a-sor-us) rex, a huge dinosaur that walked on two powerful legs. A full-grown Tyrannosaurus rex was about 40 feet long, stood about 20 feet tall, and weighed about six tons (12,000 pounds). Its arms were only about three feet long.

Tyrannosaurus Rex

Figure 12. Tyrannosaurus rex. T. rex was a large, meat-eating dinosaur and lived in western North Dakota 65 million years ago. (ND Geological Survey)

Triceratops dig site

Figure 14. Triceratops dinosaur dig site (65 million years old) in the Hell Creek Formation near Marmarth, southwestern North Dakota. Shown are Triceratops ribs still in the ground. (ND Geological Survey)

Champosaur

Figure 13. Champsosaur (crocodile-like animal). Champsosaurs lived in North Dakota about 60 million years ago. (ND Geological Survey)

Tyrannosaurus rex had very strong jaws about four feet long, and it had 50 to 60 sharp teeth. Some of the teeth were about six to 10 inches long, and if teeth would break, new teeth would replace them. In one bite, the Tyrannosaurus rex could eat up to 500 pounds of meat.

Although not a dinosaur, one of the latest ancient reptiles to be dug up in North Dakota was at a site near Linton, North Dakota. It was a champsosaur (champ-sa-sor) which lived in swamps and looked something like a crocodile.

North Dakota Heritage Center & State Museum
Adaption Gallery: Geologic Time

Examples and exhibits of the mosasaur, Pteranodon, Triceratops, and champsosaur are on display in the Adaption Gallery: Geologic Time at the North Dakota Heritage Center & State Museum in Bismarck, North Dakota.

To learn more about the story of geology and early life in North Dakota, visit https://statemuseum.nd.gov/exhibits/adaptation-gallery. The Adaption Gallery: Geologic Time introduces visitors to North Dakota as it was in the geologic past.