Figure 1.  Marine Cretaceous exhibit, featuring the restored skeleton of the Cooperstown mosasaur, in the Corridor of Time at the North Dakota Heritage Center.

The marine Cretaceous exhibit (Fig. 1) is the first of several displays planned for the Corridor of Time, located at the entrance to the main exhibit gallery in the Heritage Center.  The Corridor of Time will trace the geological development of the State of North Dakota and history of life in North Dakota as known from the fossil record.  This story will begin about 550 million years ago during the Cambrian Period and end about 10,000 years ago at the end of the last Ice Age when humans first appeared in North Dakota.  The Corridor of Time will consist of several exhibits that will interpret the geological framework and dominant life forms that inhabited North Dakota at different times in the geologic past.

The Corridor of Time will provide an introduction to the remainder of the Heritage Center museum exhibits, which are devoted to the historical development of North Dakota from the time of the first appearance of humans in the state up to the present.   Briefly, in addition to the marine Cretaceous exhibit, the following other exhibits are currently being developed for the Corridor of Time.

North Dakota's Primordial Oceans

During most of time from about 550 million years ago until about 90 million years ago, shallow oceans covered North Dakota.  No rocks from this time are exposed at the surface of the earth in North Dakota, so information is sketchy about this long period in North Dakota's geological history.  Geological and paleontological information from this time is obtained by analysis of cylinders of rocks, called cores, which are brought to the surface during exploration for oil and gas by the petroleum companies.  These cores commonly exhibit features in the rocks that provide information about the geological conditions when the rock started forming in the bottom of the ocean.  Some core samples contain fossils of animals that lived in those oceans.  This exhibit will contain many cores that provide a record of the many oceanic, climatic, and life form changes through millions of years of this most ancient time in North Dakota's history.

Figure 2.  Triceratops skull display at the North Dakota Heritage Center.

This display will be concerned with life that inhabited a huge delta that occupied western North Dakota at the end of the Cretaceous Period about 65 million years ago.  This story is based on rocks and fossils of the Hell Creek Formation exposed in south-central and southwestern North Dakota.  Fossils of some of the largest animals ever to live in North Dakota, dinosaurs including Triceratops (Fig. 2), T. rex, hadrosaurs, and dromaeosaurs, will be featured.  Fossils of other members of the community that lived with the dinosaurs, including crocodiles, champsosaurs, turtles, mammals, freshwater snails and clams, and plants will be included. 

The North Dakota everglades exhibit will portray the geology of North Dakota and the prehistoric life that lived in North Dakota from about 65 to 50 million years ago. During this period, western North Dakota was mostly a lowland containing huge swamps and forests with a subtropical to tropical climate, not too different than areas of south Florida today.  The last of the dinosaurs had become extinct before this time and the dominant life forms in North Dakota were crocodiles, alligators, champsosaurs (Fig. 3A), and turtles (Fig. 3B), as indicated by fossils found in rocks deposited during the Paleocene Epoch. These rocks are extensively exposed in most of the badland areas of western North Dakota.  Fossils of other animals, such as mammals, clams, snails, and exotic plants, including redwood (Fig. 3C), bald cypress, ginkgo, and magnolia illustrate the diversity of life in North Dakota at this time.

3A.  Champsosaurus gigas on display at the North Dakota Heritage Center.	3B.  Soft-shelled turtle on display at the North Dakota Heritage Center	3C.  Dawn redwood, Metasequoia on display at the North Dakota Heritage Center.
Figures 3A - 3C.  Fossils of some of  the plants and animals that would have lived during the The North Dakota Everglades time in North Dakota.

North Dakota's Last Sea

     About 60 million years ago the last ocean to cover North Dakota, the Cannonball Sea, retreated from the upper mid-continent.  Fossils found in the rocks deposited in that sea, primarily exposed in south-central North Dakota, will be featured in this exhibit.  The remains of many kinds of animals that inhabited these shallow water marine environments have been found and will be exhibited including: teeth of sharks, rays, ratfish, other fish; shells of crabs, lobster, snails and clams; and North Dakota's state fossil, Teredo-bored petrified wood.

The North Dakota Savanna

     The humid, subtropical, swampy environment reflected by rocks and fossils in the North Dakota everglades exhibit gradually changed to drier, temperate conditions. Savanna habitats were established in North Dakota by at least 35 million years ago.  North Dakota's landscape was rather featureless and rivers and streams meandered across the savanna.  Little is known about plant life in North Dakota during this time because few plant fossils have been found.  Woody vegetation probably grew in the open savanna areas and forests were established along the watercourses.  Herds of exotic mammals roamed North Dakota indicated by abundant fossils found in the Chadron and Brule Formations in areas of western North Dakota. The remains of elephant-size titanotheres, rhinoceroses, camels, three-toed horses, sheep-like oreodonts, mongoose-like animals, saber-toothed cats, rabbits, and mice will be included in the exhibit.  Tortoise, lizard, and fish fossils will also be displayed.

Figure 4.  Skull of Bison latifrons, this bison had a horn spread of 200 cm and could stand 300 cm tall at the shoulder. North Dakota's Last Ice Age      The most important geologic event that shaped the present landscape of North Dakota is the movement of continental glaciers across North Dakota during the last Ice Age from about 2 million years ago to 10,000 years ago (Pleistocene Epoch).  Glaciers advanced and retreated into North Dakota from Canada several times during this period.  These glaciers molded the landscape and altered drainage patterns. They also affected the distribution of plants and animals.  During glacial maxima about 3/4 of North Dakota was covered by ice and most of the state was uninhabitable.  At the end of the glacial period, glaciers began to melt and life began to flourish south of the glaciers.  Forests were dominated by spruce and aspen trees, and large mammals, such as wooly mammoths, lived in the deglaciated areas.  Fossils in the Ice Age exhibit will include the remains of mammoths, the large Ice Age bison (Bison latifrons) (Fig. 4), with a horn span of more than seven feet, ground sloths, horses, and many other animals.  These fossils will accompany the Highgate mastodon skeleton already on exhibit at the Heritage Center.

Figure 5.  Map produced by the National  Geographic Society showing the Western  Interior Seaway that covered North Dakota  during the Cretaceous.

During the latter part of the Cretaceous Period, from about 90 million to about 65 million years ago, North Dakota was mostly covered by epicontinental seas that occupied the Western Interior Seaway (Fig. 5).  At times, these seas covered the entire North American mid-continent and connected the Gulf of Mexico with the Arctic Ocean.  The new marine Cretaceous exhibit is about that time in North Dakota's geologic past. This exhibit features the restored skeleton of a 23-foot-long mosasaur.  Mosasaurs were large marine lizards and the main predators in the seas.  Their bodies were streamlined and they possessed flippers.  They propelled themselves through the water by lateral movements of their body and tail.  The flippers were mostly used for steering.  Their heads were huge and equipped with large, conical teeth.  Although they became extinct at the end of the Cretaceous, like the last of the dinosaurs, mosasaurs were not dinosaurs.  They are categorized as varanid lizards and are related to the monitor lizards, such as the Komodo dragon that lives in Indonesia today. 

Figure 6.  Mike Hanson and Dennis Halvorson discovered the Cooperstown mosasaur.  Many assisted in the collection and excavation of the Cooperstown mosasaur skeleton including Mike Hanson, Dennis Halvorson, Gene Loge, Bev Tranby, Orville Tranby, Johnathan Campbell, and Scott Tranby.	Figure 7.  Michele Gutenkunst positioning mosasaur skull bones.

Included in this exhibit are fossils of other marine animals that lived with the mosasaur including remains of sharks, other fish, birds, corals, crabs, snails, and clams (see summer/fall 1996 NDGS Newsletter (vol. 23, no. 2 & 3)). Many of these fossils were found on the Jergen Soma property and the Soma family has donated them to the State Fossil Collection. 

Figure 8.  Johnathan Campbell painting the mosasaur skull cast in the NDGS Johnsrud Paleontology Laboratory at the Heritage Center.	Figure 9.  Shawn Holz arranging ammonite fossils in one of the display drawers for the Marine Cretaceous exhibit.

Fossils from other marine Cretaceous sites are also included in the exhibit.  Particularly impressive are the beautifully preserved ammonites (Fig. 9) found in the Fox Hills Formation near Linton, some of which were donated by Pat Liska and Duane Robey.   A large sandstone block, containing in situ clams (Panopia) collected from the Fox Hills Formation and donated by J. Mark Erickson, is displayed.  Many extraordinarily preserved clam, snail, and shark tooth fossils, from an important Logan County Fox Hills site, are included.  The sand covering the "ocean floor" part of the exhibit is 68-million-year-old beach sand from this Logan County site. 

Fossils in the marine Cretaceous exhibit show that the epicontinental seas that covered North Dakota during the Late Cretaceous were shallow, warm-water habitats that were teaming with life. 

We were fortunate to be able to commission David Miller, an artist specializing in prehistoric life habitat reconstructions from Bellingham, Washington, to create an image of life in the Pierre Sea 75 million years ago based on fossils from the Cooperstown fossil site.

On behalf of the North Dakota Geological Survey, I would again like to thank the people and organizations that donated fossil specimens and contributed funds, which made this exhibit possible.