The story
Helicoprion was a large fish of the Permian, about 290 to 270 million years ago, known for a circular saw-like whorl of teeth. Russian geologist Alexander Karpinsky named it in 1899 from a whorl found in the Ural Mountains, and similar fossils later turned up in Idaho, Australia and elsewhere. Early scientists suggested the whorl sat on the snout, the back, the tail or a fin.
CT scans of a whorl from Idaho, published in 2013 by Leif Tapanila and colleagues, settled the question. The whorl filled the lower jaw, with the jaw joint just behind it, and new teeth were added at the centre while older ones were kept inside, curling in. The animal is not a true shark but belongs to a related group, the eugeneodontids, close to the ratfish. It probably ate soft prey such as squid-like cephalopods, which the spiral sliced. The teeth in the whorl were not shed but stayed locked in place as it grew, so the size of the spiral records the growth of the animal itself.
Why it mattered
- Helicoprion shows how unusual early cartilaginous fish were, far beyond today's shark shapes.
- The solution of its jaw puzzle by CT scanning shows how technology reshapes old fossils.
- It reminds us that the 'shark' look has evolved several times.
Sources
- Idaho State University researchers solve mysteries of ancient shark with spiral-toothed jaw Idaho State University
- Buzzsaw Jaw Helicoprion Was a Freaky Ratfish National Geographic
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