NEWSLETTER 08/2014 08.09.2014

Rajella paucispinosa, holotype, ZMH 26000, almost adult male 471 mm TL fresh, off South Mozambique © Simon Weigmann, Hamburg

 

• Bizarre, Prehistoric Ratfish Chomped Prey with Buzzsaw Jaws

by Brian Switek

Helicoprion had saws for jaws. That’s really all there was to the 270 million year old ratfish’s dental cutlery. No upper teeth or anything else to slice against – just an ever-growing whorl of spiky teeth anchored to the lower jaw.

This new, definitive image of Helicoprion debuted last year thanks to the efforts of artist Ray Troll and a team of researchers led by Idaho State University paleontologist Leif Tapanila. A very special fossil – IMNH 37899 – preserved both the upper and lower jaws in a closed position, finally solving the mystery of what the ratfish’s head actually looked like. But determining the exact placement of that vexing spiral was just an initial step.

Paleontologists and artists had often supposed that Helicoprion had upper teeth to pierce slippery cephalopods and squirming fish, but the fossils Tapanila and colleagues examined showed that Helicoprion only had a buzzsaw embedded in the lower jaw. How did this long-lived and prolific genus of Permian fish eat with a saw for a jaw?

Part of the original Helicoprion project involved creating a virtual model of the fish’s skull from CT scans of IMNH 37899. Now, in a Journal of Morphology paper, University of Rhode Island biologist Jason Ramsay and the rest of the team from last year’s Helicoprion study have gone back to those models to outline how the freaky ratfish fed.

Helicoprion was a biter. The ratfish’s jaws were too narrow to suction feed, Ramsay and colleagues point out, and so old buzzsaw jaw had to actively chomp prey. And chomp it could. The researchers calculated that when IMNH 37899 opened wide and bit down hard, the points of highest bite force along the ratfish’s tooth row ranged between 267 and 538 pounds. Not the greatest bite force of all time, but not too shabby for a 20-foot-long carnivorous fish.

[A model of how Helicoprion bit into prey, on display in the Whorl Tooth Sharks of Idaho traveling exhibit.]

Despite such a powerful bite, though, Helicoprion probably didn’t eat highly-armored prey. The ratfish’s jaws were so slender that trying to balance hard-shelled brachiopods or bivalves in its mouth would have been an exercise in futility, and broken Helicoprion teeth are so rare that it seems the predaceous fish preferred soft fare.

Prehistoric cephalopods – the kin of today’s squid and octopus – were probably the main Helicoprion menu items. Some would have looked squid-like, albeit supported by robust hard parts inside, and been easy enough to snaffle up. Others, however, jetted around in coiled shells and would have presented Helicoprion with the challenge of drawing out the squishier parts from their protective casing. The unique bite of Helicoprion was able to do just that.

The Helicoprion buzzsaw didn’t only slice. It also conveyed food back into the mouth during the bite. The overall effect, Ramsay and colleagues conclude, was like a biological miter saw.

The process went something like this. Teeth at the front snagged the prey and, as the jaws closed, moved the flesh backward. Here, the middle teeth speared the food, securing it in the mouth, before the back teeth bit in and sent the morsel down the hatch.

If Helicoprion bit one of the coil-shelled ammonoids or nautiloids just right, this same process would have automatically shelled the cephalopod. In the case of a head-on bite, Ramsay and coauthors write, the back teeth ofHelicoprion could have gripped the cephalopod’s body while the front teeth pushed the shell out of the mouth. The overall effect, Ramsay and colleagues propose, “may have formed a novel mollusk shucking system.” Helicoprion – it slices, it dices, and makes Julienne ammonoids.

Reference:

Ramsay, J. Wilga, C., Tapanila, L., Pruitt, J., Pradel, A., Schlader, R., Didier, D. 2014. Eating with a saw for a jaw: Functional morphology of the jaws and tooth-whorl in Helicoprion davisii. Journal of Morphology. doi: 10.1002/jmor.20319

 

Author: Dr. Michelle Heupel

How are scientists helping to save sharks?

There is a lot of information on the internet about sharks and how to save them. Some of it is good, some of it is bad, some of it has a purpose, some of it has none. I’m starting to sound like Dr.Suess with all of this, but this is how things are in our world of increasing internet and social media. So there seems to be a lot happening and a lot of people involved in the cause. This is great because getting people to understand the problem is one way to create solutions, as long as what we tell them is correct.

So what is my role in all of the workings of shark (and ray!) conservation? My job is to create information. This is one of the best parts of my job – getting to learn things that maybe no one else in the world knows. What then? Then I need to get the information written up and published so others can use it and learn from it. This isn’t just about telling other scientists what I learned, this is also about making sure people who make decisions about management get the new information if they need it.

There are so many questions about sharks and rays. So many things we don’t know. For some species we don’t know how long they live, how many pups they have, how far they swim, and even how many are there. We need all of this information. People who decide if it is ok to fish sharks and rays, or whether we need to make a marine protected area, need this information. If they don’t know these answers they can’t make good decisions because sometimes they’ll have to guess what to do. My job is to give them the answers so they don’t have to guess (as often, we still have to guess sometimes). This same information is also used by conservation groups. If a manager makes a decision that doesn’t match the scientific information then the conservationists can use the information I provide to try to change the decision.

So, it seems like I sit outside of all the action doesn’t it? I don’t make the decisions and I usually don’t challenge the people who make the decisions. Those are other people’s jobs. My job is to get the information or ammunition needed to argue or make decisions. So, does someone like me ever really make a difference? You bet. Work I did to define what a shark nursery is has been used to save habitat for Endangered smalltooth sawfish. My science is listed in the Federal Register in the protections for sawfish, a real world result of my science! My data from studying mortality rates of blacktip sharks has been used to adjust the number of blacktip sharks caught in US fisheries. This was an unexpected outcome of one of my projects, but one that proved very useful to managers. These two examples are not the things my research is most known for, but they are some of the bits I am most proud of – times when science made a difference.

Times are complicated and our oceans are damaged, but with hard work and good science I hope to continue to make a difference where I can. We need more answers to save sharks and rays, and that means we need more science.