States commonly designate symbols like birds, flowers, and trees to honor their natural heritage. Many states also select a fossil to represent their deep geological past and the ancient life that once flourished within their borders. Wisconsin has formally recognized its own state fossil, choosing a common but scientifically significant specimen. This organism speaks directly to the region’s history as a submerged seabed and its rich paleontological record.
The Official State Fossil
Wisconsin’s state fossil is the trilobite species Calymene celebra. This organism belongs to an extinct group of marine arthropods, distant relatives of modern crustaceans and insects, that dominated ancient oceans for hundreds of millions of years. The name “trilobite” refers to the three distinct lobes that divide the creature’s body lengthwise: a central axial lobe and two pleural lobes.
Calymene celebra was a relatively small member of this group, commonly measuring between one and two inches in length. Its body was highly segmented and featured a tough exoskeleton that the animal shed periodically as it grew. A notable characteristic is its ability to enroll, or curl up, into a ball shape for defense, similar to a modern pill bug. This species thrived during the Paleozoic Era, being most abundant in rocks dating to the Silurian period, roughly 443 to 419 million years ago.
Geological Context in Wisconsin
The presence of Calymene celebra in Wisconsin’s bedrock is direct evidence that the area’s geography was once vastly different. During the Silurian period, the entire region was submerged beneath a warm, shallow, saltwater sea. This environment was ideal for sustaining a diverse community of bottom-dwelling invertebrates, including corals, crinoids, brachiopods, and trilobites.
The fossil remains of these organisms were deposited and preserved within the accumulating marine sediment. Over millions of years, these sediments hardened and transformed into the rock formations visible today, primarily limestone and dolomite. The best and most numerous examples of Calymene celebra fossils are found in the Niagara Dolomite. This rock unit surfaces across much of eastern Wisconsin, particularly along the Door Peninsula and southward toward the Illinois border.
The Path to Designation
The movement to designate a state fossil was championed by the Wisconsin Geological Society and others promoting the state’s geological heritage. Initial campaigns in the early 1980s proposed a generic trilobite. However, paleontologists suggested that designating a specific species would be more scientifically meaningful, leading to the selection of Calymene celebra. This species is well-documented and abundant in the state’s Silurian formations.
The legislative process culminated in 1985 when the Wisconsin State Legislature officially adopted Calymene celebra as the state fossil. The designation was formalized under Wisconsin Act 162, a measure intended to encourage public interest in geology and paleontology. The decision favored the common and scientifically relevant trilobite over other contenders, such as the Ice Age mastodon.