Idaho No. 5 returns to Idaho Museum of Natural History after being gone over six decades - East Idaho News
Fossil Found

Idaho No. 5 returns to Idaho Museum of Natural History after being gone over six decades

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POCATELLO –– A late-night glance at his inbox almost caused Leif Tapanila to fall out of bed.

Looking at the screen of his phone, the director of the Idaho Museum of Natural History and professor of geosciences at Idaho State University scrolled through the words in an email from a colleague in Copenhagen, Denmark: “Some years ago in our collection, I came across a specimen of tooth whorl referred to Helicoprion ergasaminon by Bendix-Almgreen. It appears not to belong to our collection, so I hope you can help us find its correct home again.”

“I have this habit of waking up in the middle of the night,” said Tapanila. “I check my email to reset my brain and go back to sleep. My first thought after I read the email was, ‘Wuh-what, I can’t believe it,’ and I thought I had read it wrong. I went back and reread the statement two or three more times to ensure I understood it correctly, and the fossil they were talking about was the one I was thinking of. Once I put my mental map together, I had a tough time going back to sleep.”

The fossil specimen is what remains of the fiercest animal to inhabit the seas more than 250 million years ago: Helicoprion ergassaminon. Dwarfing a great white shark at more than 30 feet in length and sporting a mouthful of teeth the size of big steak knives, it was the largest predator on the planet.

Helicoprion ergassaminon fossil

”This thing is king,” Tapanila said. “It would swim around feasting on nautiloids – squids with a shell two feet or larger – eating other sharks, maybe even snacking on each other. In East Idaho, we find their fossils in what’s left of the Phosphoria Sea, a large tropical bay on the west coast of prehistoric North America. Because of the many fossils we’ve found here, we think the area was a shark nursery like the waters of Cape Cod in Massachusetts are for today’s great white sharks.”

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The Idaho Museum of Natural History has more than 90 specimens of Helicoprion sharks, but, for Tapanila and others in his field, this fossil is different. It’s the specimen — the fossil that proved that Helicoprion ergassaminon is an entirely new species. This ancient object, called a holotype, is sacred to folks like Tapanila.

“We measure everything we can on a fossil to get an idea of what we are looking at. In the case of prehistoric sharks, we count the teeth, measure tooth height, width, the enamel’s thickness, and on and on,” explains Tapanila. “When it’s all done, we can say, ‘We are looking at a species we already know about,’ or if the measurements don’t match anything else, we’ll say, ‘It’s a brand new species, this fossil is the holotype, and future discoveries need to be checked against this specimen to see if they’re the same species.’”

A little bigger than a dinner plate, the fossil features the distinct impressions of more than 100 of Helicoprion ergassaminon’s razor-sharp teeth arranged in a spiral pattern – also known as a whorl – in limestone. The specimen was plucked from the ground at the long-closed Gay Mine east of Fort Hall, Idaho, by Walter Youngquist, a graduate of the University of Iowa who was teaching 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, “Resurrecting the Shark.” Before he left, Youngquist sent his collection of Helicoprion fossils, including what later became the Helicoprion ergassaminon holotype, to the University of Iowa, where they ended up in the hands of William Furnish, a professor in the school’s paleontology department.

“In 1961, the fossils were sent by Furnish to Svend Erik Bendix-Almgreen, the world’s foremost expert on Helicoprion sharks who lives in Denmark, on loan,” said Tapanila. “These types of fossils weren’t Furnish’s specialty, and he probably just wanted to get them in the hands of someone studying sharks.”

In 1966, Bendix-Almgreen published “New Investigations On Helicoprion From The Phosphoria Formation Of South-East Idaho, U.S.A.,” analyzing 10 specimens found around the region. In the paper, he gives the fossil a name – Idaho No. 5 – and a hallowed status in the annals of paleontology by using it to establish Helicoprion ergassaminon as a species of whorl-toothed shark. The Danish paleontologist chose the name “ergassaminon,” a translation of a Greek word meaning “the one, who has done work,” as an homage to the “distinct wearing marks” found on the shark’s teeth.

“Of the three species of Helicoprion sharks, ergassaminon is the only one that’s been named using a fossil found in Idaho,” Tapanila said.

Helicoprion shark, artist's depiction
Artist’s depiction of a Helicoprion. | Stock image

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

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

In 2017, Idaho No. 5 was re-discovered 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 Ane Elise Schrøder noticed the writing on the fossil, and the paper notes alongside it,” said Bent Lindow, collections manager with the Natural History Museum of Denmark. “She correctly identified it as most likely not belonging to our collections here in Copenhagen and instead notified me. I put the fossil in our separate area for ‘specimens with uncertain provenance to be dealt with when there is time,’ but unfortunately never got around to following up on it due to other work getting in the way.”

Fast forward to early 2023, when Tapanila emailed Lindow about a close cousin of the Helicoprion: Sarcoprion. Tapanila asked about coming to Copenhagen to study the holotype for Sarcoprion edax and three other specimens.

“When Leif contacted us, his email signature had ‘Director, Idaho Museum of Natural History’ and I thought, “Wait, haven’t we still got that specimen from Idaho sitting around? Better send photos and ask him about it. He can probably help us get it back to the right collection,’” Lindow said.

In his response on February 9, Lindow let Tapanila know his institution can help with the Sarcoprion specimens. At the end, Lindow set in motion the return of a piece of Idaho’s history that’s been missing for more than 60 years, “Who/which institution should we contact about returning of this (Helicoprion ergassaminon) specimen?”

“Bendix-Almgreen stated Idaho No. 5 is the property of Idaho State College, ISU’s old moniker, in his 1966 paper,” said Tapanila. “Some labels also refer to Idaho State College and Idaho State Museum. Plus, another label says Idaho No. 5 was, at one time, in the possession of Andrei Isotoff, professor of geology at Idaho State College. Putting it together, we know Idaho No. 5’s home is in Pocatello.”

In July, Idaho No. 5 returned home to Pocatello. Today, you can find it in the “This is Idaho” exhibit at the Idaho Museum of Natural History, with over 700 other items each offering their unique window into The Gem’s State’s past

“Idaho No. 5’s story isn’t over,” said Tapanila. “We’re pulling DNA from fossils that was thought to have been impossible just a few short years ago, so there’s no telling what Idaho No. 5 might reveal to us in the years ahead. Right now, though, we’re just happy to have Idaho No. 5 home.”

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