Prehistoric shark called Kentucky home 337 million years ago

A group of paleontologists, park rangers, and geologists have discovered a new species of ancient shark in the rock layers of Mammoth Cave National Park in Kentucky. It was uncovered in a large fossil deposit that includes at least 40 different species of shark and their relatives, and even well-preserved skeletal cartilage. 

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The new species is named Strigilodus tollesonae and is a petalodont shark. These extinct  sharks had petal-shaped teeth and lived about 337 million years ago. According to the National Park Service, it is more closely related to present day ratfish than sharks or rays and it was identified from teeth found in the cave’s walls. Strigilodus tollesonae likely had teeth that included one rounded cusp used for clipping and a long, ridge inert side that crushed prey the way molars do. Paleontologists believe that it likely lived like modern day skates and fed on worms, bivalves, and small fish. 

Strigilodus tollesonae translates to “Tolleson’s Scraper Tooth” and it is named after Mammoth Cave National park guide Kelli Tolleson for her work in the paleontological study that uncovered the new species. 

The limestone caves that make up the 400-mile long Mammoth Cave System were formed about 325-million-years ago during the Late Paleozoic. Geologists call this time period the Mississippian Period, when shallow seas covered much of North America including where Mammoth Cave is today. 

In 2019, the park began a major paleontological resources inventory to identify the numerous types of fossils associated with the rock layers. Mammoth Cave park staff reported a few fossil shark teeth that were exposed in the cave walls of Ste. Genevieve Limestone in several locations. Shark fossils can be difficult to come by, since shark skeletons are made of cartilage instead of bone. Cartilage is not as tough as bone, so it is generally not well-preserved in the fossil record. 

The team then brought in shark fossil specialist John-Paul Hodnett of the Maryland-National Capital Parks and Planning Commission to help identify the shark fossils. Hodnett and park rangers discovered and identified multiple different species of primitive sharks from the shark teeth and fine spine specimens in the rocks lining the cave passages.

“I am absolutely amazed at the diversity of sharks we see while exploring the passages that make up Mammoth Cave,” Hodnett said in a statement. “We can hardly move more than a couple of feet as another tooth or spine is spotted in the cave ceiling or wall. We are seeing a range of different species of chondrichthyans [cartilaginous fish] that fill a variety of ecological niches, from large predators to tiny little sharks that lived amongst the crinoid [sea lily] forest on the seafloor that was their habitat.”

[Related: This whale fossil could reveal evidence of a 15-million-year-old megalodon attack.]

In addition to Strigilodus tollesonae, the team have identified more than 40 different species of sharks and their relatives from Mammoth Cave specimens in the past 10 months. There appear to be at least six fossil shark species that are new to science. According to the team, those species will be described and named in an upcoming scientific publication.

The majority of the shark fossils have been discovered in areas of the park that are inaccessible to the public, so photographs, illustrations, and three-dimensional models have been made to display the discovery. The park also plans to celebrate the new shark fossils with multiple presentations and exhibits on Monday October 23.