Two New Species of Carboniferous Ctenacanth Sharks Identified in the United States

A focused search for ancient marine vertebrates during a paleontological resource inventory of Mammoth Cave National Park has yielded a wealth of new fossil data. To date, paleontologists have identified marine vertebrate fossils from four primary horizons at the park, two of which are the first records of marine vertebrate fossils occurring in those horizons. Mammoth Cave sites have produced more than 70 species of ancient fish, about 90% representing cartilaginous fishes (sharks and kin), including two new species: Troglocladodus trimblei and Glikmanius careforum.

A reconstruction of the new ctenacanth sharks from Mammoth Cave National Park and northern Alabama: Glikmanius careforum is seen swimming in the foreground with two Troglocladodus trimblei swimming above. Image credit: Benji Paynose.

Mammoth Cave National Park, in central Kentucky, is home to the longest cave system in the world.

To date, more than 685 km (426 miles) of passageways have been mapped within 214 km2 that form the park. In addition, there are over 500 smaller caves within the park boundary.

These cave passages were formed through dissolution by underground rivers, streams, and other drainages that cut through a series of limestones, capped by a resistant sandstone, that date to 340 to 325 million years ago.

These passages opened a unique view of these limestones, which are time capsules holding a wealth of information on the ancient marine environments of their deposition.

Invertebrate fossils from these beds such as horn corals, fan-like bryozoans, brachiopods, gastropods, shelled cephalopods, and a diverse array of echinoderms have been found throughout the various formations that form the cave.

“Every new discovery at Mammoth Cave is possible due to collaborations,” said Superintendent Barclay Trimble.

“Our park team is honored to work alongside the National Park Service Paleontology Program and now the University of Alabama Geological Sciences Department whose coordinated efforts have made this latest announcement possible.”

Reconstruction of the shallow marine environment and its fauna of the Ste. Genevieve Formation at Mammoth Cave National Park, Kentucky. Image credit: Julius Csotonyi.

The two new species of ctenacanth sharks, Troglocladodus trimblei and Glikmanius careforum, would have hunted the ancient near-shore habitats that covered Kentucky and Alabama over 325 million years ago.

The area was once an ancient seaway that connected what is now eastern North America, Europe, and northern Africa, but would later disappear as the supercontinent Pangea formed.

Troglocladodus trimblei was identified from adult and juvenile teeth found within the St. Louis and Ste. Genevieve Formations of Mammoth Cave and the Bangor Formation.

The ancient shark is estimated to have reached about 3-3.7 m (10-12 feet) in length — about the size of an oceanic white tip shark.

Glikmanius careforum was identified primarily from teeth in the St. Louis, Ste. Geneveive, and Haney Formations at Mammoth Cave and the Hartselle and Bangor Formations of Alabama, but a partial set of jaws and gills of a young Glikmanius careforum was also found at Mammoth Cave.

The species was between 3 and 3.7 m in length; its jaw shape suggests it had a short head with a powerful bite for hunting smaller sharks, bony fish, and squid-like orthocones.

“The discovery pushes the origins of this ctenacanth shark back over 50 million years earlier than expected,” the paleontologists said.

The study was published in the journal Parks Stewardship Forum.

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J.M. Hodnett et al. 2024. Sharks in the dark: Paleontological resource inventory reveals multiple successive Mississippian Subperiod cartilaginous fish (Chondrichthyes) assemblages within Mammoth Cave National Park, Kentucky. Parks Stewardship Forum 40 (1); doi: 10.5070/P540162921

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