State Fossil Recalls ND’s Oceanic Past
Each state has its own designated coat of arms, seal, flag, official nickname, bird, flower, etc. Our nickname is the Prairie State; our state bird is the Western Meadowlark; our state flower is the Wild Prairie Rose.
But did you know that North Dakota has a state fossil? Our state was actually one of the first to recognize a fossil symbol, designating Teredo-bored petrified wood as such in 1967. Today, almost every state in the nation has designated state fossils, some also having state gems, rocks, formations and the like.
With the designation North Dakota made in 1967, they promoted Teredo-bored petrified wood to tourists, geologists, rock collectors and others, and the Smithsonian Institution made it part of its mineral collection. The fossilized wood belongs to a variety of species, including bald cypress, ginkgo, redwood, and magnolia trees.
During the Paleocene Epoch, from 66 to 56 million years ago, trees the Cannonball Sea covered the southwestern part of what would become North Dakota. When trees along its shores fell, becoming driftwood in the ocean waters, their wood was inundated by small, worm-shaped mollusks. These clams, ancestors of today’s oysters, clams and mussels, used their rasping shells to create long tunnels in the wood. The marine mollusks would live in the holes they created, supplementing their diets with nutrients from the wood while filter feeding.
Over many years, these holes were filled with sediments as they were covered by materials that saved them from the destructive forces of oxygen and insects. As they were buried by rich sediments,
dissolved solids replaced the plant material of the wood with inorganic minerals, preserving these Teredo holes as well as details of the bark, wood, and cellular structures.
The Cannonball for- mation which snakes through western North Dakota has been the source of most Teredobored petrified wood unearthed because this area was the location of the last sea to cover any part of North Dakota. Cannonball lies on top of the Hell Creek and Ludlow formations in southwestern North Dakota, known for their pristinely-preserved fossils that record millions of years of the land’s history. Other pieces of the fossil have been recovered in glacial gravel deposits in the state. However, these specimens are almost always small and heavily worn, leading geologists and paleontologists to assert that they originated in the Cannonball formation and were carried to other areas due to glacier activity.
Closer to home, the Pierre Formation that occupies counties in eastcentral North Dakota is another exclusively marine formation, one that was covered in waters as part of a massive inland sea in the early- to mid-Cretaceous period (the Western Interior Seaway). This formation covers the western half of Barnes County and the entirety of Stutsman county, as well as the North Dakota counties north and south of them. And although marine life has called this are home in days long past, Teredo-bored petrified wood is almost exclusively found in the Cannonball formation, since the Cannonball sea existed later in the Cretaceous than the Western Interior Seaway.
It’s strange to think about any part of North Dakota once being a tropical area, at the bottom of shallow, salty seawater—a lot has changed in the 60 million years since then. Next time you’re out in the open, take a moment to imagine the vast fields and prairie grasses as windswept ocean waves. Imagine those little clams living inside pieces of driftwood as they float by.
We’re lucky we have fossils like Teredobored petrified wood as evidence of that oceanic era, otherwise it might seem too bizarre to be true.