Fossil of new shark species found in Mammoth Cave

Published 3:32 pm Thursday, October 12, 2023

By Jake Moore, Bowling Green Daily News

While the land and underground passageways of Mammoth Cave National Park are now traversed by tourists, guides and the occasional bat, millions of years ago the region was more popular among aquatic visitors.

On Wednesday, the park announced – National Fossil Day – that the fossil of a never-before-seen species of prehistoric shark had been discovered inside the cave’s rock layers.

Dubbed Strigilodus tollesonae, a kind of petal-toothed shark, the cartilaginous creature was identified following the discovery of the teeth of both an adult and juvenile of the species.

The fossils were accounted for as part of an ongoing paleontological resources inventory (PRI) coordinated by Mammoth Cave and the National Park Service’ Paleontology Program.

The PRI began in 2019 after J.P. Hodnett, a shark fossil specialist of the Maryland-National Capital Parks and Planning Commission, was shown photos of a skull of Saivodus striatus, a shark he called the “Megalodon of its time,” that was found in the cave system.

“It kind of started a boom of everybody checking out every passage in Mammoth Cave, and they’re finding shark fossils,” Hodnett said. “It turns out, Mammoth Cave has one of the richest Mississippian-age shark localities probably in the country, if not the world.”

Hodnett said the reason for this shark abundance is likely due to the series of seaways and embayments that crisscrossed the region in the Mississippian Period more than 300 million years ago, a time when Kentucky was a warm ocean.

“What Mammoth Cave represents is kind of the timing when (the continents) were starting to close up to form Pangea, and these sharks (were) adapting to their environments changing,” Hodnett said.

The freshly identified shark lived approximately 340 million to 345 million years ago in the middle Mississippian Period, which Hodnett said was the “perfect habitat for all different varieties of sharks.”

“It was probably fish heaven at this time,” Hodnett said, referring to the buffet of small invertebrate life that populated the waters back then. “It was just living the best sharky life you can think of.”

Hodnett said the Strigilodus tollesonae was originally thought to be a Janassa, a similar genus of extinct fish. But the pronounced V-shaped grooves on the shark’s teeth led Hodnett to believe he was dealing with a unique specimen.

“As we started to delve into the nitty-gritty details of what makes a Janassa a Janassa, we’re realizing then that our shark from Mammoth Cave has some special features,” Hodnett said. “This is a relative of Janassa, and it also helps us redefine the family a little bit.”

He added that the Strigilodus tollesonae is older than Janassa by about 5 million years.

Hodnett said the shark likely operated its mouth like a pair of tweezers, crushing prey with its petal-shaped teeth. Complete Janassa fossils give clues to how the Mammoth Cave shark might have lived, including a diet of shrimps, worms and small fish.

Hodnett said Strigilodus tollesonae is “species No. 1 that is brand new” to be found in the cave, but he expects that number to keep growing as work continues. Its name translates to “Tolleson’s Scraper Tooth,” honoring park guide Kelli Tolleson, who assisted in the shark’s discovery.

“(Tolleson) was extremely instrumental in our survey,” Hodnett said. “She had a great understanding of the local geology and cave sites.”

Tolleson, a Mammoth Cave guide for about five years now, said the honor was kept as a surprise.

“It definitely brought a tear to my eye. I won’t lie about that,” she said.

Tolleson worked with a team of other park employees, volunteers and research specialists to identify fossils, photographing and measuring notable finds to show to Hodnett.

“We work hand-in-hand with the researchers trying to identify stratigraphic layers in which we found fossils before, and then we figure out which passages in the cave are carved through those layers,” Tolleson said.

Tolleson said shark teeth are easy to spot thanks to the shine coming from their enamel, a trick picked up from Hodnett.

She and her fellow team members have found so many fossils that she honestly couldn’t remember the moment that the new shark’s teeth were found in the cave ceiling.

“Some of these passages – especially where that particular one was found – are just littered with so many of these fossils,” Tolleson said.

Once a fossil of interest is found, she said it usually doesn’t take more than a dental pick to retrieve it from its crumbly limestone bed.

“What else would you use to scrape around your teeth?” Tolleson said.

Tolleson said the full PRI report will be released in the coming months.

“Overall, the whole program is basically about establishing a baseline, so then that will help us manage fossil resources for the future,” she said. “It’ll help us educate the public and really understand the scientific importance here.”

The park will celebrate the discovery, along with other cave fossils, with a special event Oct. 23. More details will be released closer to that date.