A previously unknown species of ancient shark has been discovered in Kentucky's Mammoth Cave National Park, home to the world's longest cave system.
The system, which is located in the state's south-central region, extends for more than 400 miles and features a series of large underground passages. The system's rocks date to the Mississippian period (359 to 323 million years ago), around the time that the supercontinent Pangea was forming. For much of this period, the stretch of land that is now Kentucky, then located south of the equator, was covered by shallow tropical seas.
The unique environment within the Mammoth Cave system has resulted in the extraordinary preservation of ancient shark fossils. To date, more than 100 species of ancient cartilaginous fishes—a group that includes sharks, rays and skates—have been identified there.
The Mississippian rocks that form the Mammoth Cave system are divided into several layers called, from oldest to youngest, the St. Louis Formation, St. Genevieve Formation, the Girkin Formation and Big Clifty Sandstone. The older St. Louis and St. Genevieve formations contain the greatest diversity of ancient sharks.
Researchers identified the ancient shark species after finding several small, spoon-like teeth in a cave wall, the National Park Service (NPS) said Wednesday, which was National Fossil Day.
The teeth were uncovered during an ongoing research project known as a paleontological resources inventory (PRI) that is being coordinated by officials from the Mammoth Cave park and the NPS Paleontology Program.
Scientists have named the new shark species Strigilodus tollesonae. The creature is a kind of petalodont ("petal-toothed"), an extinct group of cartilaginous marine fish found in what is now the United States and Europe.
An NPS spokesperson told Newsweek, "The teeth of Strigilodus tollesonae were discovered within the St. Genevieve Formation rock layer at Mammoth Cave National Park. This would place it as living approximately 340 to 320 million years ago."
In a press release, Barclay Trimble, the park's superintendent, said, "We are excited to finally announce the discovery of our first new shark species at Mammoth Cave on National Fossil Day."
He went on: "Teams of geologists, paleontologists, park staff, and volunteers have been hard at work deep inside the cave identifying and collecting fossils since the paleontological resources inventory began in 2019. Their important research allows us to better understand the scope, significance, distribution, and management issues associated with the fossil record found within Mammoth Cave."
Strigilodus tollesonae is more closely related to modern ratfish than other present-day sharks and rays, according to researchers.
The teeth of this shark that have been found so far represent all possible tooth positions in the mouths of both adults and juveniles of this species. It appears that the teeth were arranged in a fan-like structure. The characteristics of the fossils indicate that the shark may have lived like modern skates, feeding on snails, bivalves, soft-bodied worms and smaller fish.
The shark's name translates to "Tolleson's scraper tooth" in Latin. The species was named in honor of Mammoth Cave guide Kelli Tolleson, who played a significant role in the PRI.
Tolleson uncovered several important fossil sites in the Mammoth Cave park, many of which are difficult to access. Sometimes researchers must crawl for long distances through small openings to reach them.
Update 10/13/23, 1:29 p.m. ET: This article was updated with comment from the National Park Service.
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Aristos is a Newsweek science reporter with the London, U.K., bureau. He reports on science and health topics, including; animal, ... Read more
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