A Blog by Brian Switek

Buzzsaw Jaw Helicoprion Was a Freaky Ratfish

Of all the vexing fossil mysteries that have confounded paleontologists, few have been as persistent as that of Helicoprion – the name given to petrified whorls of elongate teeth that look like 270 million year old renditions on the theme of buzzsaw. What sort of animal did this Paleozoic remnant belong to, and where did the circular blade actually fit on the animal? Today, Idaho State University paleontologist Leif Tapanila and coauthors announce the answer to a conundrum that has puzzled paleontologists for over a century.

Russian geologist Alexander Petrovich Karpinsky coined the name Helicoprion in 1899. Even though the coiled fossils superficially resembled the shelled ammonites and nautilus paleontologists often found in the marine fossil record, Karpinsky realized that the petrifications were actually part of a shark-like fish. But there was no obvious indication of where such an unusual feeding apparatus might fit. Karpinsky’s best guess was that Helicoprion bore the toothy spiral on its nose, like a permanently-tensed party favor studded with a fearsomely pointed dentition.

Other paleontologists disagreed. While the American paleontologist Charles Rochester Eastman unabashedly praised the depth of scope of Karpinsky’s monograph – “not one in one hundred essays on paleontological subjects receives anything like the elaborate care and finish” that Karpinsky gave “the remarkable ichthyodorulites” called Helicoprion – the researcher brushed aside his colleague’s spiral-snouted restoration. “Few will be prepared to admit, however, that this highly fanciful sketch can be taken seriously, and, therefore, the least said about it the better,” Eastman wrote. Instead, the American paleoichthyologist pointed out that the “teeth” might actually be spines that jutted from elsewhere on the prehistoric shark’s body. (Karpinksy soon considered another alternative placement, too, with the whorl hanging off the putative shark’s tail.) Lacking a well-preserved Helicoprion with a whorl in place, though, the prehistoric enigma remained open to anyone who wanted to approach the problem.

A gallery of Helicoprion hypotheses. Artwork © Ray Troll 2013.
A gallery of Helicoprion hypotheses. Artwork © Ray Troll 2013.

Paleontologists and ichthyologists weren’t shy about proffering new ideas on the nature of Helicoprion. Over a century of speculation produced visions of sharks with whorls hanging off their snouts, lower jaws, dorsal fins, caudal fins, and even embedded deep in their throats. (Click on the image above, by Ray Troll, for a look at the gallery of hypotheses.) Even after paleontologists generally agreed that the teeth belonged at the tip of a long lower jaw, artists and scientists still played with what leeway they had. Was the fearsome spiral fully enclosed in the jaw, or did it hang down awkwardly in an external coil? The true anatomy of Helicoprion was frustratingly difficult to pin down.

When I wrote about Helicoprion in 2011, I highlighted the end-of-the-jaw placement for the tooth whorl as the most likely arrangement. But artist and major Helicoprion fan Ray Troll quickly got in touch with me to say  that the classic image probably wasn’t correct, after all. New research was set to give Helicoprion a major makeover. That study has just been published today in Biology Letters, and focuses on a specimen found decades ago.

In 1966, paleontologist Svend Erik Bendix-Almgreen described a Helicoprion fossil that had been found 16 years earlier in the Waterloo Phosphate mine near Montpelier, Idaho. This specimen was special. Not only did it display a lovely tooth whorl – which Bendix-Almgreen suggested fit at the end of an elongate lower jaw – but the fossil also contained bits of cartilage from the upper jaw and skull.

Despite the extra material, though, Bendix-Almgreen thought that the specimen had been disarticulated and crushed so extensively that properly reassembling Helicoprion was impossible. The jaws sat in the Idaho Museum of Natural History for decades, one of thirty jaws in the institution’s collections, until student Jesse Pruitt started asking curator Leif Tapanila about the strange Permian fish. “He started poking around and asking questions about Helicoprion jaws,” Tapanila says, about “why the jaws were this way and not that.” In particular, Tapanila recalls, Pruitt wanted to know whether the coiled tooth row was a real feature of a living animal or something that happened after death – an artifact of death rather than a representation of life.

Tapanila and Pruitt concluded that the Helicoprion whorls really did have their buzzsaw shape in life, but they didn’t stop there. Along with their colleagues and input from Ray Troll, the researchers launched a new, detailed investigation into the museum’s Helicoprion stores. The fossil Bendix-Almgreen described, in particular, seemed to have the potential to yield new clues through CT scans that could visualize the internal secrets of the specimen. The scans, taken at the University of Texas High-Resolution X-ray CT Facility in Austin, “came out brilliant” Tapanila says. Not only was the fossil in better shape than expected, but the specimen elucidated two critical facets of the animal – that Helicoprion didn’t have an elongated jaw, and that it wasn’t really a shark.

How the jaw of Helicoprion was arranged. Artwork © Ray Troll 2013.
How the jaw of Helicoprion was arranged. Artwork © Ray Troll 2013.

Contrary to the popular long-jaw restorations, the tooth whorl of Helicoprion totally filled the lower jaw. The jaw joint sat right behind the weapon, and the spiral dentition was buttressed by jaw cartilage on either side. And, even stranger, Helicoprion didn’t have any upper teeth to speak of. The spiral of continually-added teeth was the creature’s entire dental armament.

Scraps of Helicoprion skull indicate that the fish wasn’t really a shark, either. Of course, as Tapanila points out, the word “shark” doesn’t have the simple definition we might expect. “‘Shark’ doesn’t have biological meaning anymore,” Tapanila told me, confiding “If I talk to a fish expert, and I say ‘shark,’ they get very angry.” Ichthyologists are rapidly rearranging the fish family tree and the definitions for different groups. All the same, the skull cartilage of Helicoprion included a very specific double connection that is characteristic of a group of cartilaginous fish called Euchondrocephali – commonly known as ratfish and chimeras.

Helicoprion was not a buzzsaw predecessor to great white or tiger sharks. The fish belonged to the lineage one branch over, near the evolutionary split where the ancestors of living sharks and ratfish parted ways. (And this pulls other weird prehistoric fish with fearsome teeth – such as the scissor-jawed Edestus – away from the shark line and into the ratfish line.) In general form, Tapanila and Troll expect, Helicoprion was an archaic member of the wider ratfish group that looked quite shark-like. And these predators reached impressive sizes.  Tapanila estimates that a large Helicoprion would have been about 20 to 25 feet long.

A new look for Helicoprion. Artwork © Ray Troll 2013.
A new look for Helicoprion. Artwork © Ray Troll 2013.

After over 100 years, the mystery of the Helicoprion jaw is solved. That doesn’t make the prehistoric fish any less enigmatic. With only a single blade of teeth, how did Helicoprion actually catch and consume prey? Tapanila and other researchers are only just starting to investigate this question. Based on the new restoration, Tapanila suggests that “The analogy to a circular saw is almost perfect.” Not only was the tooth whorl shaped like a saw, but, Tapanila points out, “as the jaw closed [the tooth whorl] rotated the teeth backwards in a rotational saw motion.” Such a strategy would have worked well on squid and other soft-bodied cephalopods of the 270 million year old seas. But even with this realization, we are still left with the question of how such a strange arrangement – singular in the history of life on Earth – evolved in the first place.

Tapanila and colleagues are keeping after the enigmas surrounding the fish through studying Helicoprion fossils found in Idaho and elsewhere, including a lower jaw that’s even bigger than the one used in the new Biology Letters study. “You know the line from JAWS, ‘You’re going to need a bigger boat’? Well, I need a bigger CT machine,” Tapanila says. “I have the world’s largest Helicoprion specimen in the world sitting in my museum, and I see evidence for jaws.” The two-foot-wide jaw is too big for a conventional CT scanner, though. “It’s got all the features we hope,” Tapanila says, “but it’s massive, so I need to bring it to [a facility in] Pasadena.” That giant jaw will yield additional clues, and raise new questions. Tapanila suspects that the larger jaw belonged to a different species of Helicoprion than the one he and his team previously scanned, and the features of the bigger jaw might provide new information about how these buzzsaw fish differed across species and body sizes. There are still many secrets to draw out from the jaws of Helicoprion.

Yet, even with the remaining mysteries, to see the new vision come out of the rock is a dream come true for Ray Troll. “It’s been a twenty year quest for me,” he says, which all started “when I first saw a whorl and became obsessed by it.” “I’ve drawn the animal so many hundreds of times. Literally hundreds.” And not only is Troll “thrilled” to see the new research, but the new identity of Helicoprion is a bit of a personal victory. Troll heads the wonderfully geeky band Ray Troll and the Ratfish Wranglers. For so long, it seemed that the object of his endless fascination was a shark, but now, Troll says, “It’s really cool to have [Helicoprion] circle back around” to the ratfish side of the family tree. “My two obsessions have all converged,” Troll enthuses, in a spectacular ratfish relative that has for so long challenged scientists to chase after its circuitous spiral trail.


Eastman, C. 1900. Karpinsky’s Genus Helicoprion. The American Naturalist, 34, 403: 579-582. 10.1086/277706

Lebedev, O. 2009. A new specimen of Helicoprion Karpinsky, 1899 from Kazakhstanian Cisurals and a new reconstruction of its tooth whorl position and function. Acta Zoologica, 90: 171-182. 10.1111/j.1463-6395.2008.00353.x

Tapanila, L., Pruitt, J., Pradel, A., Wilga, C., Ramsay, J., Schlader, R., Didier, D. 2013. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion. Biology Letters. 10.1098/rsbl.2013.0057

29 thoughts on “Buzzsaw Jaw Helicoprion Was a Freaky Ratfish

  1. Man, how cool is this? I’ve always loved Helicoprion, and nobody restores fish and “sharks” like Ray Troll. A wonderful marriage of science and art!

  2. A decade ago I was at the Utah Field House and they had a specimen of Helicoprion. Inside the tooth whorl were small denticals. To me that ment the whorl was covered in skin, just like Ray Troll illustrates.

  3. What to call members of the Edestidae,,, edestid “sharks” no…Edestid “ratfish”….no… Edestid holocephalians….no to wimpy; I’ll go with Edestid chondrosteans.

    What is the evidence for a lunate and not rat-like tail?

  4. Awesome! I have seen the images circulating for years and wondered. So cool to have the mystery solved. Thanks for a great post on a great story!

  5. Time for Troll et al. to get together with Wayne Itano, working on edestids. Look too at Helicoprion distribution in time and space – they often occur with huge fusulinids

  6. Hey Jim I can answer the tail question:

    Body fossils of close kin (Eugenodonts) to Helicoprion have been found and they all have the the lunate tail

  7. Classifying Helicoprion as a relative of modern ratfish would place it within the crown group Chondrichthyes. Unfortunately, we still don’t know whether it had the derived anatomical features of the crown group (yes it has tessellated cartilage, but that is a feature of the total group, not just the crown). Eugeneodont chondrichthyans have the “right” kind of teeth to place them within the crown chondrichthyans, so a relationship to chimaeroids is certainly one (of several) possibilities, but its relationships cannot yet be characterized as ‘solved’!

  8. I’m surprised that new teeth grew from the back of the jaw and not from the center of the spiral (Troll’s drawing). Do the inner teeth show evidence of resorption into the body?

  9. wow…’out of this world’ we always wonder what alien life would be like. we don’t have to go into space, we are in space…and we humans would look rather wierd in our own way

  10. Thanks for the post – it was extremely cool and interesting. Question though – how wide laterally are the teeth? I’m having toruble rectifying the pictured jasw and bilateral symetry…

  11. That painting/picture is bothersome, squid were not around 270M years ago.

    [Cephalophods that outwardly resembled modern squid – such as belemnoids – surely were. – BS]

  12. To charlie jones’s comment.

    I would assume that the spiral was NOT there at birth, and perhaps it formed over time. The tiny teeth could literally be it’s ‘baby teeth’ from when it was born and they just recycled around and around when new and bigger teeth came in as it grew!

    This is so exciting! I’ve been waiting for an answer to this mystery for the longest time!

  13. Like Charlie, I wonder about the large teeth growing in the mouth, and then getting smaller and smaller. This is unlike other whorls in nature.

  14. John: Are you saying that it’s not clear if eugeneodonts are holocephalians, or that holocephalians sensu lato are not monophyletic? Because as long as eugeneodonts are holocephalians, and Holocephali is monophyletic, that would mean *by definition* all holocephalians (fossil or extant) are crown-group chondrichthyans, because Chondrichthyes is the common ancestor of elasmobranchs and holocephalians, and all its descendants. Now, whether Helicoprion and its ilk are crown-group holocephalians is another matter entirely.

  15. Charlie and SDurnell: Once each tooth forms, it does not change size through time (except for minor wear and breakage). Its just that the teeth produced early on in the animal’s life (in the inside of the whorl) are smaller in size than those produced later in life.

  16. I would assume that the spiral was NOT there at birth, and perhaps it formed over time. The tiny teeth could literally be it’s ‘baby teeth’ from when it was born and they just recycled around and around when new and bigger teeth came in as it grew!

    That’s also what tuatara do, except in a straight line, not in a spiral: their teeth are fused to the jawbone, so they can’t be replaced, instead new teeth are added at the back. So, the baby teeth are near the tip (and eventually worn down to the bone), and the teeth get larger the farther back they are. Nothing moves, the jaw just grows at the rear end.

  17. I think that Helicoprion is not a crown holocephalan (holostylic euchondrocephalans), but a stem holocephalan, along with other autodiastylic euchondrocephalans, such as Debeerius. So, it is a crown chondrichthyan, as suggesting by teeth morphology.

  18. My reading of the journal article is that they are claiming Helicoprion is a Euchondrocephalan and stem-group holocephalan, not crown-group holocephalan. So calling Helicoprion a ratfish rather than some sort of a distant relation of a ratfish doesn’t seem quite right.

  19. Chase: Squid and octopus-like fossils have been found in Mazon Creek, which is Carboniferous. Permian squid are likely to have existed. Especially since Orthocone nautiloids had the same arrangement of tentacles as squid do (10). Just because we don’t have many fossils of Permian squid does not mean that they don’t exist, indeed, their completely soft bodies with minimal calcification would mean that, if they were present with Helicoprion, not much of them would fossilise, if any, seeing as Helicoprion’s cranial cartillage was so well hidden by the Rock. Modern Nautilus are far more ancient in lineage than orthocones, which is why they have so many tentacles, as would seem to be primitive for cephalopods. Orthocones were essentially squid like in most pysical aspects, minus suckers and plus the chambered shell, since the Silurian, and gave rise to the squids, belemnites, octopus, and ammonites. When this occured is left tantalisingly un-clear, but since primitive squid appear in the triassic, they must have been present at least in the permian.

  20. This is a splendid and entirely plausible interpretation of the Helicoprion feeding strategy. The hard-to-fossilize nature of its inferred prey suggests that we have much to learn about Late Paleozoic soft-bodied cephalopods.

  21. Ray Troll likely had a contagious fascination. Ever since I saw his exhibit at the Denver Museum of Nature and Science, I have been wondering if this puzzle got solved! Congrats to all! …. Best exhibit ever done at that museum.

  22. Is it possible it fed on shelled ammonoid cephalopods? The whorl seems to me to be precisely made as a can-opener for ammonites… :-)

  23. Perhaps the spiral jaw was also used as a nautiloid lure or for stealthier attack? The similarity to some ammonite shell fossils is uncanny.

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