Geysers, Bison, Bears Oh My, but What About Yellowstone’s Fossils Oh Why?

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Yellowstone National Park is known for its unique hydrothermal features and array of animals and plants, but what about its fossils? From tiny invertebrates to large marine reptiles, Yellowstone’s boundaries include a wide range of paleontological resources that date back over 500 million years.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Megan Norr, Lead Physical Science Technician for the Geology Program at Yellowstone National Park.

A Ehmania walcotti trilobite from Yellowstone National Park

A Ehmania walcotti trilobite from Yellowstone National Park. Scale is in millimeters.  Specimen located at the Smithsonian National Museum of Natural History.

(Credit: Megan Noor, National Park Service. Public domain.)

Imagine Yellowstone, close to 500 million years ago, when the whole area was submerged by a shallow sea, and life was all about the water. Picture small organisms with armored shells (some the size of your fingernail), swimming, burrowing, and feeding in all depths of that shallow ocean.  These animals are known as trilobites—over twenty thousand different species existed, and they have been documented all over the world.

In Yellowstone National Park, trilobites were first described by Dr. William Holmes, who was part of the 1878 Hayden Survey to the region. They even have their own mountain and lake in Yellowstone named after them! Trilobites weren’t the only animals swimming around during that time. Brachiopods, with their lamp like shells, as well as sponges occupied that sea, too.

But what makes trilobites so significant to Yellowstone? Trilobites were such a diverse and well-adapted organism that they survived a span of more than 250 million years, until they became extinct at the end of the Permian geologic period. At that time, large environmental changes were affecting the whole planet, including volcanism and greenhouse gas emissions, which may have played a large role in wiping out not only trilobites but close to 95% of life on Earth.

A Ptychopariid trilobite from Yellowstone National Park

A Ptychopariid trilobite from Yellowstone National Park. Scale is in millimeters.  Specimen located at the Smithsonian National Museum of Natural History.

(Credit: Megan Noor, National Park Service. Public domain.)

Because of trilobites’ hard skeletons, they became fossilized when they died out, allowing paleontologists to discover and learn about their life habits and come to understand the environment in which they lived. Documenting trilobites in Yellowstone allows scientist to have a better grasp of the park’s vast geologic history. The presence of trilobites in the rocks of Yellowstone have helped geologists date, identify, and map the geologic history of the region.

Yellowstone National Park isn’t only home to geysers, bison, and bears, but encompasses a wide variety of natural and cultural resources, making it a unique landscape with a rich geologic history. The volcano tends to get a lot of attention, but that is a geologically recent feature. So, the next trip out to Yellowstone National Park, maybe take a hike to Trilobite Point and Trilobite Lake and think about the park’s paleontological resources, and the conditions that existed long before any volcanic eruptions occurred in the region. And if you find a fossil, enjoy it in place—collecting cultural and natural resources, including rocks and fossils, is illegal in Yellowstone National Park. Appreciate the geological story it tells and leave it for the next visitor to discover and enjoy!