Mosasaurs were huge marine lizards, up to 40 feet in length, that inhabited the world's oceans during the cretaceous. This skeleton is one of the mosasaurs called Plioplatecarpus that inhabited the Pierre Sea about 75 million years ago. It was discovered in 1995 by Mike Hanson and Dennis Halvorson on Orville and Beverly Tranby's farm in the Sheyenne River Valley near Cooperstown, in Griggs County, ND. The mosasaur exhibit and other paleontological exhibits in the North Dakota Heritage Center, Pembina State Museum, and at State Historic Sites administered by the State Historical Society have been developed in collaboration with the North Dakota Geological Survey (NDGS) through the NDGS Fossil Resource Management Program. The North Dakota State Fossil Collection and the NDGS state paleontologist are located in the North Dakota Heritage Center.

Mosasaur Fast Facts

• Mosasaurs were huge, some as long as 40 feet, and inhabited the world's oceans during the Cretaceous Period from about 90 million years to 65 million years ago. They were a large group of reptiles which included several species.
• Nicknamed the "Tyrannosaurus rex of the Sea," after the fearsome land dinosaur. Their prey probably included other mosasaurs, fish, turtles and invertebrates.
• Although not a dinosaur, these lizard-like reptiles lived at the same time and became extinct when the dinosaurs did. They existed about 25 million years.
• The 23-foot-long mosasaur on permanent exhibit at the North Dakota Heritage Center in Bismarck beginning July 9 was discovered in 1995 near Cooperstown, North Dakota.
• The Marine Cretaceous exhibit, which also tells the story of other sea creatures that lived at the same time, is a joint project of the State Historical Society of North Dakota and North Dakota Geological Survey.
• The fossil at the North Dakota Heritage Center is of the genus, or group, of mosasaurs known as Plioplatecarpus, and is a new species of this genus that has not been found anywhere else in the world. It is also 25 percent larger than any other known mosasaur in this Plioplatecarpus group.
• After it died, its carcass was scavenged by dogfish sharks, as indicated by the tens of thousands of dogfish shark teeth found with the mosasaur skeleton and gnaw marks on some of its bones.
• Other creatures that lived in the oceans that covered North Dakota during the time of the mosasaurs included sharks, rays, plesiosaurs, turtles, sea birds and invertebrates such as snails, lobsters, corals and clams.
• Mosasaurs are believed to be closely related to the largest known lizards alive today, the Komodo dragons of Indonesia that measure up to 10 feet.
• The mosasaur fossil at the North Dakota Heritage Center was discovered by Mike Hanson and Dennis Halvorson of Cooperstown, N.D. The remains were found on the land of Orville and Beverly Tranby of Cooperstown, who, along with Beverly's sisters, Gloria Thompson of Warren, Minn., Jacqueline Evenson of Edmonton, Alberta, Canada, and Susan Wilhelm of Princeton, Minn., donated the historic find to the North Dakota State Fossil Collection for study and exhibit.