Finding evidence of dinosaurs that once roamed Minnesota during the Mesozoic Era is difficult due to the geological record. Unlike states further west, Minnesota is not known for complete skeletons or large bonebeds. The state’s paleontological story centers on a few scattered, fragmented finds and an abundance of marine fossils, all of which point to a unique, water-dominated ancient environment.
Why Dinosaur Fossils Are Scarce in Minnesota
Dinosaur fossils are scarce because for much of the Mesozoic Era, the state was submerged beneath a vast body of water. During the Cretaceous Period, a massive inland sea called the Western Interior Seaway split North America, and its eastern margin covered much of what is now Minnesota. The sedimentary rocks deposited during this time were overwhelmingly marine, preserving sea creatures instead of terrestrial animals.
The state also experienced multiple episodes of glaciation during the Pleistocene Epoch, known as the Ice Age. These immense ice sheets acted like giant bulldozers, scraping away and eroding the younger sedimentary rock layers where dinosaur fossils would have been preserved. The glacial drift, a thick blanket of sediment left behind by the melting ice, now covers most of the state, making the few remaining Cretaceous deposits hard to access.
Much of the rock record from the Triassic, Jurassic, and Paleogene periods is entirely missing from Minnesota’s geology. The only widespread Mesozoic deposits are from the Cretaceous Period, and they are largely confined to the western and northeastern parts of the state. Even in these limited areas, the rocks are often buried deep beneath glacial till. This combination of a long-term marine environment and subsequent glacial erosion explains why finding a complete dinosaur skeleton in Minnesota is highly improbable.
The Limited Terrestrial Evidence Found
Despite the geological challenges, a few physical pieces of evidence confirm that dinosaurs did walk the land that is now Minnesota. These rare finds are typically fragmented and non-diagnostic, representing only a handful of documented specimens. The most significant discovery is a small, fully intact claw bone unearthed at the Hill Annex Mine State Park in the Iron Range.
This 90-million-year-old claw is believed to belong to a dromaeosaur, a type of carnivorous dinosaur related to Velociraptor. Other isolated finds include a dinosaurian tail vertebra centrum found in Crow Wing County, which dates to the Late Cretaceous period (approximately 70 to 65 million years ago). Researchers have also documented a serrated tooth, pointing to the presence of another type of meat-eating dinosaur.
Evidence of large plant-eating dinosaurs also exists, though not in the form of complete bones. Fragmented hadrosaur (duck-billed dinosaur) bones have been recovered from the Cretaceous Dakota Formation deposits. Trace fossils, such as footprints or trackways, have also been noted in the Dakota Formation, suggesting that a large ornithopod, likely a hadrosaur, once walked through the area. These scattered remains confirm that terrestrial dinosaurs existed in Minnesota, likely along the ancient shoreline of the seaway.
Minnesota’s Abundant Prehistoric Sea Life
Because Minnesota was largely covered by the Western Interior Seaway during the Age of Dinosaurs, the most abundant and well-preserved Mesozoic fossils are of marine life. The most common finds are the remains of invertebrates that thrived in the warm, shallow waters.
Ammonites, which were coiled-shelled relatives of modern squid and octopuses, are frequently found, along with clams, oysters, and snails. The Cretaceous deposits also yield an abundance of fossilized shark teeth, particularly those belonging to the genus Squalicorax. These teeth are resistant to decay and are easily preserved in the marine sediments.
The state’s ancient seas were also home to large marine reptiles. Fossils of mosasaurs and plesiosaurs, the dominant marine predators of the Late Cretaceous, have been recovered in the state’s western and northern Cretaceous rocks. Crocodiles, such as the ancient form Terminonaris, also swam in these waters.