Gigantic Tire-Sized Fossil Found In Natrona County

University of Wyoming professor Dr. Laura Vietti said the intact, 19-inch "tire-sized" ammonite fossil found by amateur rockhounds in Natrona County last weekend is "unusually rare."

Wendy Corr

May 17, 20224 min read

Giant fossil 2 5 17 22 scaled
(Cowboy State Daily Staff)

Amateur rockhounds discovered a colossal fossil while scouting around rural Natrona County this weekend.

Joe Ritz and three of his friends, all members of the Natrona County Rockhounds club in Casper, were rock hunting Sunday afternoon near Powder River, about an hour from Casper, when Ritz said something caught his eye.

“We were out looking for ammonites,” Ritz told Cowboy State Daily, referencing to a specific fossil, shaped like a coil, that between 450 and 66 million years ago were the shells that contained ocean-dwelling squids. 

“We went to a new area a guy was showing me, north of Powder River in that Natchez Dome area,” Ritz said. “And we were just out there looking, and I saw a piece of something that didn’t look quite right – because, I mean, the area is littered with fragments of them.”

Ritz said that as he started clearing the dirt from the object, he started seeing the distinctive ridges of the ammonite form.

“And then it looked like it was a whole piece,” he said, “and then we pried out the center of the rock. And that’s when we saw the inside coils and realized it was a whole ammonite, not just parts of one.”

But it wasn’t just any ammonite, which have been found in many sizes around the world – this fossil measured 19 inches across by 16 inches high. 

“I was with three other people when I found it,” Ritz said. “And we each have, like, a complete one, but they may be the size of your hand. I’ve never seen anything this large.”

“Very Rare”

The ammonite that Ritz found with his friends is an unusually large specimen, according to Dr. Laura Vietti, the geological museum and collections manager at the University of Wyoming.

“It’s very rare to find ammonites that large,” Dr. Vietti told Cowboy State Daily. “We have found larger in the state of Wyoming, but that’s definitely on the larger side, especially intact.”

Wyoming is a treasure trove for fossil hunters, according to noted Wyoming outdoorsman Paul Ulrich, whose family owns a commercial fossil quarry near Kemmerer in southwestern Wyoming.

“Wyoming, in scientific circles, is certainly ground zero, and has been for 100-plus years for fossil discoveries,” Ulrich said. 

“Wyoming has the best fossil record for vertebrates – animals that have a backbone,” said Dr. Vietti. “We also have a really rich invertebrate record, which includes these ammonites, which had tentacles, kind of like a squid stuck in a shelled body. And then on top of it all, we have a really deep record, meaning that we have fossils from almost every time period that there was life on Earth.”

Likely To Donate

In Ulrich’s opinion, Ritz’ discovery this weekend was a great find.

“That is an outstanding specimen,” Ulrich said, after viewing the photo. “Very well preserved, very beautiful, and certainly very large.”

What will Ritz do with the massive fossil that he is currently hauling around in the back seat of his vehicle?

“I’m going to take it to the rock club tonight and see if it needs some maintenance, or whatever it needs done to it, and then I don’t know,” he said. “I might donate it to the Tate (Geological Museum in Casper).” 

Whatever becomes of the fossil, Ritz said it’s important to share the find with others.

“I want people to see it,” he said. “That’s the cool thing about it – it was found here in the state, in Natrona County. I want people to be able to witness it. Maybe I’ll let the rock club display it and take it on shows or something like that. Like, I don’t need it in my house.”

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Wendy Corr

Broadcast Media Director