National Park Service researchers have identified a previously unknown shark species in the limestone walls of Mammoth Cave, the world’s longest known cave system. The animal, named Macadens olsoni, measured less than one foot long and swam the warm, shallow waters that covered this region roughly 340 million years ago.
The find emerged during a broader survey of cave passages cut through the Ste. Genevieve Formation, a layer of carbonate rock deposited during the Carboniferous Period. Embedded within that rock, scientists spotted a curved spiral of teeth — known as a tooth whorl — distinct from any catalogued species. Microscopic analysis confirmed the teeth belonged to a new genus and species.
“This discovery is a remarkable addition to our understanding of ancient marine life and underscores the importance of preserving and studying our natural history,” said Superintendent Barclay Trimble.
Unlike modern sharks with conveyor‑belt rows of blade‑shaped teeth, Macadens carried a single, crescent‑shaped dental spiral suited for crushing. Researchers believe the tiny predator targeted soft‑shelled prey such as mollusks, worms and other invertebrates that crawled across Carboniferous sea floors.
The genus name “Macadens” is a nod to Mammoth Cave’s informal abbreviation, while the species name also honors Rickard Olson, a retired park scientist who spent decades mapping subterranean passages and recording stray fossils. Olson’s field logs guided recent inventory crews to layers rich in marine material.
Macadens joins the 70-plus distinct fish species catalogued in Mammoth Cave to date, including over 40 sharks or shark‑like relatives registered in the past 10 months alone. Among them is Rotuladens, a recently reclassified species once filed under Helodus and renamed for its wheel‑shaped teeth.
Although Mammoth Cave’s passages formed only 10 million to 15 million years ago — long after dinosaurs vanished — the limestone itself preserves a reef ecosystem that flourished 320 million to 360 million years ago. Rainwater percolating through fractures later dissolved the rock, opening the hollow corridors that now expose the fossils.
Mapping crews have traced 426 miles of passages so far, with new extensions logged each year. Every fresh tunnel can reveal additional windows into the Mississippian Sea that blanketed what is now central Kentucky.
To minimize damage, researchers document fossils in place before carefully extracting small samples for laboratory scans. Portable 3‑D imaging rigs record tooth position, surrounding sediment texture and any associated skeletal fragments. Back in the lab, high‑resolution micro‑CT helps reconstruct the jaw’s shape without dislodging fragile material.
Park officials say the discovery will feed into public programs that already bring school groups underground to learn about geology and evolution. Specimens not required for further study will remain where they are, marked for future tours and protected by federal regulations.
Next steps
Scientists plan to publish a formal description of Macadens olsoni in a peer‑reviewed journal later this year, complete with detailed imagery of the tooth whorl. The team will also analyze trace elements in the fossilized dentine to reconstruct seawater chemistry during the Carboniferous, a period of significant climate and sea‑level shifts.
Meanwhile, cavers continue to extend the known boundaries of Mammoth Cave. Each newly charted corridor offers fresh exposure of the Ste. Genevieve Formation, raising the prospect of more discoveries.
For visitors on surface trails, the park’s landscape may appear calm. Deep below, however, the rock still tell of a time when Kentucky sat near the equator, waves lapped over coral reefs and even a shark smaller than a school‑ruled notebook found a place in a bustling marine community.
“This finding not only enhances our knowledge of ancient marine ecosystems but also emphasizes the critical role of paleontological research in our national parks,” Trimble said. “Every discovery connects the past with the present and offers invaluable educational opportunities for students and the public.”
