Montana Governor and First Lady's Math and Science Initiative
The Great Inland Ocean
Columbus Rest Area east of Columbus on Interstate 90
For over sixty million years during the Cretaceous
Period, much of eastern Montana was
underwater, covered by an vast inland sea. As
the Rocky Mountains formed to the west, it created a
broad, flat coastal plain that was home to many different
species of dinosaurs. Indeed, the long life of the sea saw
the rise and extinction of many dinosaur species until
it finally receded from Montana about 65 million years
ago at the end of the Cretaceous Period. The sediments
deposited underwater or along the sea’s coast formed
the spectacular sandstone rimrocks in the Yellowstone
River valley between Columbus and Billings.
The sea was shallow and warm, probably no more
than a few hundred feet deep. But it was home to a
wide variety of aquatic life. Oysters lived in dense
banks along the shore, while tentacled ammonites
fed on monster clams that lived in the shallow water
offshore; sharks also cruised the shallows preying
on whatever animals appeared tasty to them. For
several million years, two predators, synonymous with
prehistoric sea creatures, were at the top of the food
chain in the sea: the long-necked Plesiosaurs and the
snakelike Mosasaurs. Neither animals were dinosaurs,
but were air-breathing reptiles who had adapted to
living in the oceans. Both were carnivores that ate just
about anything they could seize and swallow. Fossils of
Plesiosaurs and Mosasaurs have been found throughout
eastern Montana.
The Great Island Seaway Road Sign
A Brief History
For centuries, the sandstone rimrocks along the Yellowstone River guided travelers between the mountains and the buffalo country to the east. In 1912, regional Good Roads enthusiasts and county officials created one of the first interstate highways in the United States, the Yellowstone Trail, an interconnected network of county roads blazed by distinctive chrome yellow signs with black arrows. The 4,000-mile highway connected Plymouth Rock, Massachusetts and Seattle, Washington with a branch to Yellowstone National Park. Later re-designated U.S. Highway 10, Interstate 90 bypassed it in 1971.
Jack Horner and Nancy Schweitzer
 First Lady Nancy Schweitzer Jack Horner, Curator of Paleontology, Museum of the Rockies |
October 2006 |
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