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3/30/2013
Sharp science: Whorl-tooth mystery solved

By SCOTT BOWLEN

Daily News Staff Writer

Not every college road trip helps to solve a 270-million-year-old mystery.

Then again, Jesse Pruitt, an Idaho State University undergraduate, was packing some unusual cargo when he hit the highway for Texas in 2011.

Pruitt knew the fossilized sets of buzzsaw-like teeth were of Helicoprion, a large, shark-like fish that lived in the Paleozoic era. But these spiral whorls embedded in limestone dug from Idaho mines had yielded only vague clues about the entire structure of the fish.

That’s because Helicoprion skeletons were mostly cartilage. The cartilage disintegrated over time, leaving only the toothy whorls behind in the fossil record.

Pruitt was trying to figure out where the whorls — which can be two feet in diameter — were located in or on Helicoprion

Alexander Karpinsky, the Russian geologist who first studied a Helicoprion fossil in 1899, thought the whorls might be part of the tail or dorsal fin, or, more likely, an extension of the snout.

Subsequent study suggested that the whorl was part of Helicoprion’s lower jaw. That was the presumed whorl location in 1993, when Ketchikan artist Ray Troll first noticed a Helicoprion fossil in a museum basement.

Intrigued by the weird spirals and the questions they raised, Troll dug deep into the available research and drawn many renditions of the animal through the years while working on other projects.

Then, about four years ago, Troll got a call from Pruitt. The undergrad was studying Helicoprion. What did Troll know about them?

More than enough, it turned out, to set Pruitt on scientific journey that led to the road trip in 2011, when Pruitt ferried three Helicoprion whorls from Idaho to the University of Texas High Resolution X-Ray CT Facility in Austin, Texas.

"I got some pretty weird looks when I put those things on the cart and was trying to roll them up to my hotel room down there," Pruitt said. "Big chunks of rock."

Big chunks of rock: That was the key. Until then, researchers had studied just the visible surface of whorls embedded in limestone. No one had looked within the rock. And now you could, with a CT scanner.

"We really didn't know what to expect would be inside the rock," Pruitt said.

***

Data from within the rock ultimately proved the whorls’ exact location on Helicoprion’s anatomy, opening new avenues of study and understanding about these massive fish that could grow to at least 25 feet in length.

That wasn’t all. Researchers discovered a key structure indicating Helicoprion wasn’t a shark. It was a predecessor of the modern-day ratfish. Not only was that fun news for Troll, a ratfish aficionado who actually has a species of ratfish — Hydrolagus trolli — named after him, it’s prompted some redrawing of the evolutionary family tree for ancient fishes.

***

Fossilized whorls of Helicoprion should have a warning tag: "Danger! Can cause obsession."

Dr. Leif Tapanila understands this.

Tapanila is a palaeologist who’s an associate professor at Idaho State University and the research curator at the Idaho Museum of Natural History. Tapanila got involved in the research after Pruitt first started asking questions about the 30 or so Helicoprion fossils in the museum collection and became the principal investigator for the research paper on Helicoprion that was published by the Royal Society journal "Biology Letters" in February.

"Once you get into working on the spirals — Rays’s probably mentioned this — it becomes a bit of an obsession," Tapanila said. "It’s no joke, this is the sort of thing you wake up at 3 in the morning dreaming about."

As noted above, Troll first noticed the whorl spirals at a museum in 1993. He began reading the available science on Helicoprion, including Karpinsky’s early work from 1899 and the work of paleontologist Dr. Rainer Zangerl, who had written about ancient sharks.

Troll is well known for his art that often blend scientifically accurate depictions of fish in fun, fanciful situations. His interest in depicting the fish — including prehistoric animals — as correctly as possible has earned Troll a strong and appreciative following in the fish-science community.

But, what exactly did a Helicoprion look like?

"This was a whole new world of sharks to me," Troll said. "I was blown away. I'd never seen anybody do these drawings of these things."

As Troll set out to draw Helicoprion himself, he contacted Zangerl for advice. Their collaboration resulted in Troll’s first rendition of Helicoprion, which appeared in the 1994 book "Planet Ocean" by Troll and Brad Matsen.

Zangerl told Troll that the scientist who had done the most work on Helicoprion was a Dane by the name of Svend Erik Bendix-Almgreen. Bendix-Almgreen had published a paper in 1966 from research he’d conducted on the Helicoprion fossils at the Idaho museum, drawing most of his data from one particular fossil — Idaho Number 4.

"(Bendix-Almgreen) was the last guy to actually do any sort of extensive paper on Helicoprion," said Troll of the now-deceased scientist.

Troll continued to draw Helicoprion, incorporating Bendix-Almgreen’s information for the Helicoprion in his book "Sharkabet." However, without new science to further describe the sharky creature’s actual structure, Troll eventually set it aside.

Until he heard from Jesse Pruitt.

Pruitt is a Marine Corps veteran who had gone back to school at Idaho State University and was working in the museum’s paleontology department when he noticed the fossil tooth whorls.

"Like anybody that sees that fossil for the first time — you're kind of filled with questions more than anything else — (Pruitt) started asking all of these questions about this fossil," Tapanila said.

Pruitt decided to pursue Helicoprion as a research project, looking at why the fossilized toothy whorls were in a spiral, and whether they were a different configuration when the animal was alive.

"I thought I’d work on this and see what I could figure out," Pruitt said.

"The project started with Jesse Pruitt," said Tapanila, who helped put together the grant proposal that funded the initial project. "It wasn't too long after he got me involved that Jesse contacted Ray (Troll), and Ray has been just amazing to work with. The guy, he's passionate about this animal, and has been following it almost 20 years."

"It was really Ray that pushed me to dig a little deeper into this," Pruitt said. "He and I had some early conversations, and bounced some ideas back and forth. He set me straight on a couple of things, helped me figure out ... what kind of research had been done in the past."

Troll told Pruitt about Almgreen’s 1966 paper — and about Idaho Number 4.

"I said, ‘Go back to the back rooms and see if you can find this specimen, Number 4,’" Troll said.

Pruitt and Tapanila’s early study showed the whorls had formed as spirals in the living animal, rather than curling up after the animal died.

"About that time, we noticed there was a special type of cartilage that encases the whorls, that wouldn’t be present if they were straight," Pruitt said.

Unlike the regular type of cartilage that completely disappears from the fossil record, the cartilage around the teeth was calcified, leaving evidence of its original presence in the living fish.

"We looked at the rock and you could see, sure enough, in addition to the usual spiral of teeth and roots, you could see other parts of the skeleton associated with that spiral," Tapanila said.

Which meant that the portions of the fossil encased in the rock might yield further clues.

Troll suggested using a CT scanner to peer into the rock. With assistance from Dr. Dominique Didier, a ratfish researcher and assistant curator of ichthyology at the Academy of Natural Sciences in Philadelphia, funding was cobbled together for Pruitt to take Idaho Number 4 and two other Helicoprion fossils to the specialized CT scanning facility at the University of Texas.

The CT scans of Idaho Number 4 were a revelation.

"At that point, we got excited, because Leif and I didn't know what it was, but we knew it was something that had never been seen before," Pruitt said.

Dr. Alan Pradel of the American Museum of Natural History, a specialist in reconstructing fossil material from CT scan data, was involved in interpreting the Helicoprion CT information.

"For the first time, we could see that the spiral of teeth was located within the upper and lower jaw," Tapanila said. "What this allows us to do — really for the first time in the 120-year history of study of this animal — is say this spiral belongs inside the head of the animal. And furthermore, it was located in the lower jaw."

And it wasn’t dangling out at the end of a long lower jaw. Instead, the chop-saw whorl filled a short lower jaw. In addition, only 15 or so of the sharp, serrated teeth were exposed along the jaw’s centerline.

"Because we have this curved series of teeth, only the 15 last teeth to be made are actually exposed and used for chomping," Tapanila said. "All of the other teeth are in the lower jaw or concealed under the next whorl and completely contained."

So how did it form?

The team learned that the teeth formed in the back of the jaw near the throat. New teeth pushed forward in a conveyer-belt like system to the front of lower jaw, but then, instead of the teeth shedding off the animal as they do in sharks, the teeth curled back into the jaw itself and were covered by the above-mentioned cartilage to form the continously expanding spiral whorl within the jaw.

The oldest teeth were in the center of the whorl. The upper jaw contained no teeth whatsoever.

The Idaho Virtualization Lab at Idaho State University, including lab Manager Robert Schlader, created 3-D virtual reconstructions of the whorl and jaw from the CT scans, which allowed the team to obtain further information from the fossils.

Troll had heard about shark-jaw mechanics research being done at the University of Rhode Island, led by Dr. Cheryl Wilga, a Native Alaskan originally from Kenai.

"I just cold-called her and I said, ‘Cheryl, I bet this really weird old shark would be cool if we could get your input on how this thing worked, and what it was cutting," Troll said.

Wilga and one of her graduate students, Jason Ramsey, became involved in the project. Using what they know about how muscles connect on the skeletons of sharks and rays, Wilga and Ramsey deduced three major muscles between the lower and upper jaws of Helicoprion.

As the whorl of Helicoprion swung up in a bite, the teeth would rotate about a quarter turn along with the chomp to create a true chop-saw effect.

"With the tooth whorl in the middle, their jaw sort of worked like a radial-arm saw, only in reverse," Wilga said.

Helicoprion teeth show very little wear, suggesting that Helicoprion dined mostly on soft critters.

"This animal wasn't eating heavily armored fish or thickly shelled animals," Tapanila said. "It was going after (prey) almost certainly that were relatively soft and meaty.... The lack of teeth breakage, and just how this mouth is going to rotate back and slice — it's really a good steak cutter, but not a good bone cutter."

Unique sets of cartilage held the whorl in its vertical orientation, and the jaws have bumps that inhibited the jaws from closing too much, preventing the whorl from slicing up into the creature’s cranium.

"These little knobs basically keep the whorl from continuing up and cutting its brain in two," Troll said.

The jaws’ orientation relative to the cranium was the landmark indication that Helicoprion was in the evolutionary line of chimera-ratfish rather than sharks.

Sharks have upper jaws that aren’t fused to the cranium. The Helicoprion fossil showed a couple of connection points where the upper jaw was beginning to fuse with the skull — a major piece of information.

"In looking at the joints of the upper jaw, we could tell it had this particular type of (suspension of) the jaws from the cranium that was closer to chimera than sharks," Wilga said. "I think the biggest thing is, we changed its position from being more shark-like to more chimera-like."

That wasn’t huge surprise, said Tapanila, because people had suggested that Helicoprion belonged to the side of the family tree that includes chimeras and ratfish.

"But their agreements were based largely on teeth, and the best indication of ancestry really comes down to that upper jaw attachment," Tapanila said. "So now that we have this additional line of evidence, it pretty much seals the deal when looking at (Helicoprion’s) heredity."

The results of the research made news internationally when published last month in "BiologyLetters."

The research solved two of the fundamental questions about Helicoprion — how the whorl spiral fits in the animal, and how it grows.

"Until you ... have some level of closure on that, you really can't go anywhere else with this fossil," Tapanila said. "And that's sort of been the stopping point for almost all of the research during the past 100 years on this animal."

Now, the research into other aspects of Helicoprion continues, with more papers about various aspects of the animal currently in the works

"Like in most scientific studies, one solution usually raises 10 questions," Tapanila said. "It's the kind of project that can last quite a while because there are so many things about the animal that are strange. But now I think we have enough good information to start from and to build on. ... We can make predictions now and test those predictions. It's a lot of fun."

Pruitt, who is now a scanning technician at the Idaho Virtualization Lab, is continuing his education with the goal of staying in the paleontology field while working with CT scanning and post (scan) processing.

"That’s what I’m trying to structure my education toward now," Pruitt said.

***

Although Troll wasn’t an author on the research paper, his artwork that depicts the current hypothesis of Helicoprion’s appearance accompanied the paper’s publication. The recent advances are huge, but until an entire Helicoprion fossil is found, "all we can do is make educated guesses," he said.

Still, "I feel ... great that my images are out there with the shark and this whole thing that I've put so much time into," said Troll, adding that he experienced a "big sort of letting-go process" when the scientific paper was published.

That Helicoprion now is understood to be part of the "ratfish clan" has brought some resolution for Troll.

"It’s totally weird, like these two major drivers, obsessions, in my life kind-of converging," Troll said with a smile. "All the questions aren’t answered by any means, but I am trying to bring some resolution, trying to wrap this chapter of my life up."

Troll will be involved in a Helicoprion exhibit that’s tentatively scheduled to open June 21 at Idaho State University.

Part of the exhibit will feature the debut of documentary about Helicoprion that’s being produced by Marc Osborne Jr. of Ketchikan. A teaser for the film, "Tease of the Buzzsaw Sharks of Idaho" has been posted on Youtube already.

"Marc is directing that, and shooting it, and editing it,"?Troll said. "He's doing a terrific, awesome job."

The film will feature music from Ketchikan locals Don Kenoyer, The Amish Robots, and perhaps Troll’s own group, the Ratfish Wranglers.

A Troll-penned tune, "The Whorl-Tooth Sharks of Idaho," has been recorded for the film by the Kansas-based country band, 3 Trails West.