Idaho No. 5 is returning to the Idaho Museum of Natural History after disappearing for more than six decades

POCATELLO — A quick glance at his inbox late at night nearly caused Lev Tabanella to fall out of bed.

Looking at his phone screen, director of the Idaho Museum of Natural History and professor of earth sciences at Idaho State University, he ran across the words in an email from a colleague in Copenhagen, Denmark: “A few years ago in our group, I came across a specimen of the toothworm referred to as With Helicoprion ergasaminon by Bendix-Almgreen It doesn’t seem to belong to our group, so I hope you can help us find its right home again.

“I have a habit of waking up in the middle of the night,” Tabanella said. “I check my email to reset my mind and go back to sleep. The first thing that came to mind after I read the email was ‘Oh my God, I can’t believe it’, and I thought I had read it wrong. I went back and re-read the statement two or three times to make sure I made sure I got it right, and the fossil they were talking about was the one I was thinking about. Once I gathered my mental map, I had a hard time falling back asleep.

The fossil specimen is what remains of the fiercest animal that inhabited the seas more than 250 million years ago: Helicoprion ergassaminon. Measuring more than 30 feet long, this stunted great white shark possessed a mouth full of teeth the size of large steak knives, and was the largest predator on the planet.

“This thing is king,” Tabanella said. “It swam and fed on nautiloids — squid with a shell two feet or larger — and ate other sharks, and perhaps each other. In eastern Idaho, we find their fossils in what remains of the Phosphorus Sea, a large tropical gulf on America’s west coast.” North America in prehistoric times. Given the many fossils we’ve found here, we believe the area served as a nursery for sharks much like the waters of Massachusetts’ Cape Cod are for great white sharks today.

Related | A new shark fossil has been donated to the Idaho Museum of Natural History

The Idaho Museum of Natural History has more than 90 specimens of Helicoprion sharks, but for Tabanella and others in his field, this fossil is different. It is the fossil specimen that proves that Helicoprion ergasamenon is a completely new species. This ancient being, called the holotype, is sacred to people like Tabanilla.

“We measure everything we can on the fossil to get an idea of ​​what we are looking at. “In the case of prehistoric sharks, we count the teeth, measure the height and width of the teeth, the thickness of the enamel, etc.,” Tabanella explains. “When we finish All together, we can say: “We’re looking at a species we already know,” or if the measurements don’t match anything else, we’ll say: “It’s a completely new species, this fossil is the holotype, and future discoveries should be checked against this specimen to find out.” Whether they are of the same type.

The fossil is slightly larger than a dinner plate, and features distinct impressions of more than 100 sharp Helicoprion ergassaminon teeth arranged in a spiral pattern — also known as circularity — in the limestone. The sample was recovered from the ground at the long-closed Gay Mine east of Fort Hall, Idaho, by Walter Youngquist, a University of Iowa graduate who taught at the University of Idaho in the 1950s. In 1953, Youngquist left academia and headed to Peru to work as a petroleum geologist, according to Susan Ewing’s account in her book “Shark Revival.” Before leaving, Youngquist sent his collection of Helicoprion fossils, including what later became the model Helicoprion ergasamenon, to the University of Iowa, where it ended up in the hands of William Furnish, a professor in the school’s paleontology department.

“In 1961, Furnish sent the fossils to Svend Erik Bendix Almgren, the world’s foremost expert on Helicoprion sharks living in Denmark, on loan,” Tapanella said. “These types of fossils were not Furnish’s specialty, and he probably just wanted to get them into the hands of someone who studies sharks.”

In 1966, Bendix Almgren published “New Investigations on Helicoprion from the Phosphorus Formation of Southeastern Idaho, USA”, in which he analyzed 10 specimens found throughout the region. In his paper, he gave the fossil a name — Idaho No. 5 — and a hallowed place in the annals of paleontology by using it to establish Helicoprion ergasamenon as a type of ring-toothed shark. The Danish paleontologist chose the name “ergassaminon”, a translation of a Greek word meaning “one who has done work”, in honor of the “distinctive wear marks” found on the shark’s teeth.

“Of the three species of Helicoprion sharks, Ergasamenon is the only one named using a fossil found in Idaho,” Tapanella said.

Helicopter shark, photograph by the artist
Artistic depiction of a Helicoprion bird. | Stock image

In Denmark, Idaho No. 5 has found a home at the Natural History Museum of Denmark, hidden among 14 million animal skins, insects, plants, fossils, meteorites and more from around the world.

“Museums have a habit of not throwing things away for good reason, and it’s relatively common for museums to have things they don’t know they have,” Tabanella said. “It’s like a junk drawer at home: you don’t know what’s in there until you move. Fortunately, over the years, we’ve gotten better with changing tracking systems and practices.

In 2017, Idaho No. 5 was rediscovered when staff at the Natural History Museum of Denmark were cataloging all of the museum’s fossilized vertebrates and entering the specimens into a new database system.

“My colleague Anne-Elise Schröder noticed the writing on the fossil, and the paper notes next to it,” said Bent Lindo, collections manager at the Natural History Museum of Denmark. “She correctly identified it as most likely not belonging to our collections here in Copenhagen and reported it to me instead. She placed the fossil in our separate area in order to ‘deal with specimens of uncertain provenance when there is time’, but unfortunately I was unable to follow it up.” Never because there is other work in the way.

Fast forward to early 2023, when Tabanella emailed Lindo about a close relative of helicoprion: the sarcoprion. He asked Tabanella about coming to Copenhagen to study the holotype of Sarcoprion edax and three other specimens.

“When Leif contacted us, his email signature said ‘Director of the Idaho Museum of Natural History’ and I thought, ‘Wait, haven’t we gotten this specimen from Idaho yet?’ Better send pictures and ask him about them. “Maybe he can help us get it back into the right group,” Lindo said.

In his response dated February 9, Lindo told Tabanella that his organization could help with sarcoprion samples. Ultimately, Lindo began the process of bringing back a piece of Idaho history that had been missing for more than 60 years, “Who/what organization should we contact about bringing back this specimen (Helicoprion ergassaminon)?”

“Bendix-Almgren mentioned Idaho Building 5 as the property of Idaho State College, the old nickname for Indiana State University, in his 1966 paper,” Tabanella said. “Some of the labels also mention Idaho State College and the Idaho State Museum. Additionally, another label says that Idaho No. 5 was at one time in the possession of Andrei Izotov, a professor of geology at Idaho State College. Putting it all together, we know that Idaho House No. 5 is located in Pocatello.

In July, Idaho No. 5 returned home to Pocatello. Today, you can find them in the “This Is Idaho” exhibit at the Idaho Museum of Natural History, along with more than 700 other items that each offer a unique window into the Gem State’s past.

“The story of Idaho No. 5 is far from over,” Tabanella said. “We are pulling DNA from fossils that would have been thought impossible just a few years ago, so there’s no telling what Idaho No. 5 might reveal to us in the years to come. However, for now, we’re thrilled to have Idaho Home No. 5.

For more information about the ISU Department of Geosciences and the Idaho Museum of Natural History, visit and

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