Storied fossil found near Stillwater in the running for official state designation

Aquatic creature from half a billion years ago could become Minnesota’s designated state fossil.




2 minute read

The original Dikelocephalus minnesotensis fossil found near Stillwater by David Dale Owen in 1852, now at the Smithsonian Museum of Natural History. (Justin Tweet/National Park Service)

A fossilized 500-million-year-old sea creature first found on the banks of the St. Croix River near Stillwater could become Minnesota’s official state fossil. Minnesota is one of only seven states that doesn’t have an official fossil, and the Science Museum of Minnesota is currently leading an effort to pick one.

Among the museum’s recommendations is Dikelocephalus minnesotensis, which was first discovered during an 1852 geological expedition to the region. The foot-long early animal lived in what’s now the St. Croix Valley when the area was under a shallow sea, a time period called the Cambrian Era. The seas laid down the sediments that became the sandstone commonly seen along the river, and buried some aquatic inhabitants in the process.

Justin Tweet, a National Park Service scientist who has surveyed the St. Croix Valley as well as the Mississippi River National Recreation Area and many other National Park sites says Dikelocephalus minnesotensis is a good candidate for state fossil.

“It’s definitely Minnesotan (says so right there in the species name), it’s got a historical hook, it’s reasonably well-known, it’s not teeny-tiny like most of Minnesota’s fossil invertebrates (D. minnesotensis is downright big for a trilobite, topping out longer than 12 in/30 cm), and trilobites are pretty charismatic as fossils,” he wrote in 2017. “Another point of interest: although a couple of other states have trilobites as state fossils, D. minnesotensis would be the only Cambrian state fossil.”

The fossil was first documented by David Dale Owen based on fossils found he and his team found during extensive geological surveys made on travels through the region between 1847 and 1850 sponsored by the Treasury Department. A description of the new fossil was published in 1852.

“The principal distinctions between this and the other species of the genus are its larger size, less convexity of the glabella, the greater extent and slightly concave shovel shaped area expanded in front of the glabella with the greater size of the caudal flap, and the shortness of the caudal spines set wide apart and projecting vertically backwards five or sometimes six segments in the axal lobe of the pygidium since the terminal and largest lobe is usually though obscurely divided by a faint furrow,” Owen wrote in his description. (I don’t understand hardly any of it, but the people who need to do.)

There are several other fascinating fossils under consideration, including a large cat whose fossils are found in Fillmore County; an extinct shark and a large crocodile relative found in the Mesabi Iron Range; photosynthesizing bacteria found in northern Minnesota; a mammoth found in central and southern Minnesota; a sea animal reaching up to ten feet in length found in the Twin Cities area; and a bison found in central and southern Minnesota.

Additional Minnesota state fossil suggestions can be submitted to the Science Museum with this form.


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One response to “Storied fossil found near Stillwater in the running for official state designation”

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    Mark Hove