Sea Scorpion

Sea Scorpion Model (Pentecopterus decorahensis) 

Location: 700 College Drive, Decorah, IA. The exhibit is located in the Valders Hall of Science on the first floor.

The Sea Scorpion exhibit is free to visit.

Horseshoe crabs, scorpions, spiders, mites, and ticks are all creatures that, despite being relatively small - save perhaps for the horseshoe crab - are terrifying in their own right. Now imagine if one of those creatures was over 6 feet long! That privilege was given to those creatures’ ancestor, Decorah’s very own giant sea scorpion. 

The Pentecopterus decorahensis is a type of eurypterid, or sea scorpion, that swam the seas around 465 million years ago, making it the oldest known sea scorpion to date. Discovered in 2010 by a group of scientists, some of which worked with the late Decorah geologist Jean Young, Pentecopterus’s excavation site is the area known as the Decorah Impact Crater. The crater formed over half a billion years ago when an enormous meteorite hit the surface of the Earth; however, it was quickly filled and buried by sediment and seawater, leaving it hidden multiple layers beneath the surface of Decorah. Due to the crater’s location, it had a unique environment that permitted a variety of less common ancient species to live in, such as eurypterids and conodonts. Additionally, the crater's distinctive environment allowed for the extraordinary preservation of fossils, the greatest of which was the Pentecopterus. Due to the pristine state of the fossils, researchers found not only exoskeletons but also scales, follicles, and even stiff bristles that covered Pentecopterus. One exoskeleton, despite being compressed upon excavated rock, was able to be peeled off and studied under a microscope. This was possible due to the special shale unique to Winneshiek Country. Cleverly named “Winneshiek Shale,” it was layered perfectly year after year with no disturbances due to the lack of oxygen. With no oxygen, no worms, and no movement, this weird anoxic occurrence is what contributed to Pentecopterus’s pristine preservation. 

Pentecopterus decorahensis was not titled as such until 2015, five years after its initial discovery. Named by few of the scientists who discovered it and one who researched it, Pentecopterus decorahensis is an homage to the location of its discovery, its appearance, and its species. The genus, Pentecopterus, is inspired by the ancient Greek warship, the penteconter, while the suffix -pterus means wing and is commonly used in other genus of eurypterids. The genus pentecopterus stands out amongst eurypterids, however, as it contains only one species, P. decorahensis. Why is this sea scorpion the only species of its genus? As an apex predator, it may not have been too keen on sharing its title.

The excavation of the Decorah’s sea scorpion was possible only because of insistence from Jean Young to continue researching the strange shale present in Decorah. Alongside Huaibao Paul Liu and Robert McKay, Young gathered a number of pieces of evidence concerning the shale that eventually led to the hypothesis that the area was an impact crater. In 2010, Liu, McKay, and a team of researchers from University of Iowa, Yale, and the Iowa Geological Survey (IGS), received a grant to conduct their research on the Winneshiek fossil fauna and the structure of the crater impact. Sadly, Young passed away in 2007, before there was an opportunity to further explore the geology of the area, but both Liu and McKay credit her for discovering the first clue regarding the crater.

As both an incredible hunter and one of the largest of its kind, P. decorahensis was an apex predator of the Ordovician period. Now, however, its remains continue to be examined by researchers while its model sits in Luther College’s Valders Hall of Science. Rumor has it that its prey has changed from conodonts, phyllocarida, and jawless fish to the unsuspecting visitors wandering through Valders. Be especially wary if you’re an academic! After all, academics not only disrupted this creature’s over 400 million years of rest, they also disturbed the local biology when they built a temporary dam, diverting the Upper Iowa River to excavate. Perhaps this sea scorpion has risen from the past into a time of ecological uncertainty for which humans are most responsible.