Scientists have found ancient nail tooth shark fossils deep inside Mammoth Cave in Kentucky, revealing new information about a mysterious group of extinct predators.
Tiny Ancient Shark with Nail-Like Teeth Discovered in Kentucky’s Mammoth Cave
Deep within the vast passages of Kentucky’s Mammoth Cave, scientists have uncovered fossils of a previously unknown species of ancient shark, notable for its nail-shaped teeth and tiny size.
Named Clavusodens mcginnisi, or McGinnis’ nail tooth, this miniature shark swam the seas approximately 340 million years ago. It belonged to a family of sharks called obruchevodid petalodonts, often nicknamed “chipmunk sharks” because of their small stature and distinct dentition.
According to the National Park Service (NPS), these ancient sharks only grew to about 3 to 4 inches (7.5 to 10 cm) long and likely fed on small crustaceans, worms, and other seafloor creatures. Their diminutive size may have been an evolutionary advantage, helping them avoid larger predators.
The discovery was officially introduced in a study published on January 24 in the Journal of Paleontology. The species name honors David McGinnis, a retired superintendent of the National Park Service, and its teeth’s resemblance to iron nails inspired the rest of the name.
Researchers extracted the fossils from the Ste. Genevieve Formation inside Mammoth Cave, a vast system known as the world’s longest cave and a rich source of ancient fish fossils, with over 70 species identified so far.
These rocks, shaped by underground rivers and streams, preserve marine sediments dating back to the Carboniferous period (about 359 to 299 million years ago). Since 2019, scientists have been carefully documenting fossil finds within the cave, working under challenging conditions that often require crawling through tight spaces and navigating low ceilings.
“Many of these sites have low ceilings requiring crawling for long distances on hands and knees, and at times belly crawling,” researchers noted in the study. “The fish fossils are frequently encountered in the cave ceilings or walls.”
The fossils of Clavusodens mcginnisi, estimated to be 330.9 to 323.2 million years old, are the oldest known specimens of their shark group. Scientists believe these sharks may have thrived in reef-like environments, possibly among crinoids (sea lilies) — marine animals that attached themselves to the seafloor like plants. However, further research is needed to confirm this habitat theory.
“The fossil discoveries in Mammoth Cave continue to reveal a wealth of new information about ancient shark species,” said Barclay Trimble, superintendent of Mammoth Cave National Park. “Researchers and volunteers have collected samples from both the main Mammoth Cave system and smaller, isolated caves throughout the park, providing new data on ancient sharks and revealing several species that are completely new to science.”
This extraordinary discovery adds another piece to the puzzle of ancient marine life, giving scientists deeper insights into prehistoric ecosystems and the remarkable creatures that once inhabited them.