Trapped for 325 Million Years, Two Strange Sea Monsters Resurfaced From the Depths of the Earth’s Longest Cave

Deep beneath Kentucky’s rolling hills, in the dark reaches of Mammoth Cave National Park, paleontologists have unearthed the fossilized remains of two never-before-seen prehistoric shark species. Preserved in limestone for over 325 million years, the discovery opens a rare and vivid window into a vanished Carboniferous sea that once covered much of inland North America.

The two sharks—Troglocladodus trimblei and Glikmanius careforum—belong to an extinct group of ancient predators known as ctenacanths. Found inside the largest cave system on Earth, the fossils were recovered as part of the U.S. National Park Service’s sweeping Paleontological Resource Inventory, a long-running federal program documenting fossil records across more than 270 parks.

The site’s uniquely stable, low-oxygen environment allowed not only bone but also fine anatomical structures to be preserved—an extremely rare occurrence in the fossil record. These cave-stored sharks are offering researchers a new baseline for understanding early shark evolution, biodiversity, and predator-prey dynamics in the Paleozoic Era.

Yet beyond the species themselves, the real breakthrough may lie in where they were found. As subterranean paleontology expands, sites like Mammoth Cave are reshaping what scientists thought was possible in fossil preservation and discovery.

The Sharks That Time Forgot

The newly described species are members of the ctenacanthiformes, a lineage of sharks that flourished hundreds of millions of years ago but vanished entirely without leaving modern descendants. Unlike today’s sharks, ctenacanths bore comb-like dorsal spines and a body structure not found in any extant marine species.

Troglocladodus trimblei, the smaller of the two, measured around 3.5 meters and had forked, recurved teeth—suggesting it preyed on soft-bodied marine life through fast, ambush-style attacks. Glikmanius careforum, the more robust predator, featured a crushing bite capable of breaking through bone and the hard shells of orthocones, an extinct group of mollusks.

The anatomical adaptations of both species suggest a diverse and highly specialized Carboniferous marine ecosystem, in which multiple shark species occupied different ecological niches. Their reconstruction, based on anatomical comparisons and digital modeling, shows a scene of predators swimming above coral-like reefs in shallow tropical seas—seas that no longer exist, but once covered the very ground now traversed by park visitors.

Preserved in the Stone Veins of the Planet

The discovery site itself is central to the fossils’ remarkable state. Mammoth Cave spans over 676 kilometers of mapped passageways through Mississippian-era limestone, rock formed during a time when the region was submerged beneath a tropical archipelago.

The anoxic cave environment, sealed from surface weathering and microbial activity, acted as a natural deep-time archive. As the National Park Service outlines, such conditions are ideal for preserving fine-scale structures that often degrade in more exposed settings.

The find was part of a larger scientific effort under the Paleontological Resources Preservation Act, which mandates fossil surveys in federally managed lands. These inventories compile data not only through field expeditions, but also from museum collections, archival records, and expert interviews.

Shark fossils from the Carboniferous are not rare—but specimens this complete, from this period, and found in situ in a cave, are virtually unheard of. The cave’s limestone walls, once part of a seafloor, now offer one of the best-preserved glimpses into that lost marine realm.

Ancient Oceans Beneath America’s Heartland

During the late Paleozoic, much of present-day North America was part of a vast, shallow tropical sea. This marine corridor connected what are now the United States, Europe, and North Africa, forming an ecosystem teeming with primitive coral reefs, mollusks, and cartilaginous fish.

As tectonic plates shifted and sea levels dropped during the formation of Pangaea, these habitats disappeared, leaving behind isolated fossil-rich formations. Kentucky, northern Alabama, and southern Indiana are now considered key regions for reconstructing this ancient ocean’s biodiversity.

The Journal of Paleontology has documented several significant shark finds in the area, including a 330-million-year-old specimen nearly rivaling a modern great white in size. These new species from Mammoth Cave add critical data points to that record, particularly in the study of extinct shark diversity and morphology.