What Was Helicoprion and How Did Its Spiral Teeth Work?

The Short Answer

Helicoprion was a 275-million-year-old marine predator closely related to ratfish, not sharks, that possessed a unique spiral whorl of over 150 teeth coiled inside its lower jaw — one of the most bizarre feeding structures ever found in the fossil record.

A Tooth Spiral That Defied Explanation for Over a Century

When Russian geologist Alexander Karpinsky first described Helicoprion in 1899, he had no idea what he was looking at. The fossil showed a dense, tightly coiled spiral of interlocking teeth — something with no parallel in the living world. For more than a hundred years, paleontologists debated where this structure actually sat in the animal’s body. Proposed locations included the snout, the tip of the lower jaw, the belly, and even external appendages. Without soft tissue or a complete skeleton to guide them, researchers were essentially guessing.

The confusion was not unreasonable. Helicoprion belonged to a group called eugeneodontids, fish whose bodies were composed almost entirely of cartilage. Cartilage rarely fossilizes. As a result, the tooth whorl is virtually all that survives. From that single spiraling structure, scientists had to reconstruct an entire animal.

CT Scanning Finally Solved the Mystery

The breakthrough came in 2013, when researchers at Idaho State University led by Leif Tapanila applied CT scanning technology to a remarkably well-preserved Helicoprion fossil from the Smithsonian Institution’s collection. The scans revealed something no one had anticipated: the tooth whorl sat deep inside the back of the lower jaw, and the upper jaw had no teeth whatsoever.

This dramatically changed how scientists understood the creature’s feeding mechanics. Rather than slicing prey between opposing rows of teeth, Helicoprion pressed food against soft cartilage with its rotating lower spiral. As the jaw closed, older teeth were pushed inward and downward into the coil, while new teeth continued to erupt at the outer edge. The whorl was not decorative — it was a self-sharpening biological cutting wheel. Prey, likely soft-bodied cephalopods such as ammonites, would have been caught and drawn inward as the spiral rotated.

Not a Shark — Something Far Stranger

A common misconception is that Helicoprion was a shark. It was not. Phylogenetic analysis places it firmly within the chimaera lineage — the same broad group as modern ratfish, also called ghost sharks. These animals are cartilaginous fish like sharks and rays, but they represent a separate evolutionary branch that split off hundreds of millions of years ago.

Helicoprion lived during the Permian period, between roughly 290 and 250 million years ago, in warm shallow seas that covered parts of what is now North America, Eastern Europe, and Asia. Fossils have been recovered from Idaho, Nevada, Russia, and Australia, among other locations. Size estimates based on tooth whorl proportions suggest some individuals reached lengths of 7 to 25 feet, though the absence of body fossils makes precise measurements difficult.

What Remains Unknown

Despite the 2013 findings, many questions about Helicoprion remain unanswered. The full shape of its body, the structure of its fins, and the precise mechanics of jaw articulation are still subjects of active research. Scientists have proposed multiple hypotheses for exactly how the jaw moved and how efficiently the whorl could process prey. The animal’s extinction at the end of the Permian — during Earth’s largest mass extinction event — also raises questions about whether its highly specialized anatomy contributed to its vulnerability.

Helicoprion stands as a reminder that evolution produces solutions to survival that no living creature has repeated. One jaw. One spiral. And a mystery that took 114 years to begin unraveling.