I Would Just Like To Say...

[Jesse]

that Helicoprion is one crazy animal with a very interesting history! 3 years of research and we are still learning something new about them all the time. It is interesting that for as little is known about them there are over 60 publications about the genus.

For your reading pleasure I present a story of research, madness, forced labor camps, and execution. All in the pursuit of this enigmatic shark!

http://www.g-to-g.co...ilter=repressed

Edited April 26, 2012 by Jesse

[Paleo sapiens]

That's one of my favorite paleo-topics. Weird sharks. And this one takes the proverbial cake.

The inexplicable swirl of teeth have been placed on the nose, dorsal, and lower lip to be used like a deadly, spring loaded chameleon tongue.

In my opinion, I like the mollusc crush hypothesis best. It seems a great way to crush nautiloid and ammonite shells.

[THobern]

It seems to make most sense as a radula-like structure.

[xonenine]

i have come across this site before while reading about Helicoprion, then lost it to my dismay - thanks a million!

[Jesse]

i have come across this site before while reading about Helicoprion, then lost it to my dismay - thanks a million!

Your welcome!

That's one of my favorite paleo-topics. Weird sharks. And this one takes the proverbial cake.

The inexplicable swirl of teeth have been placed on the nose, dorsal, and lower lip to be used like a deadly, spring loaded chameleon tongue.

In my opinion, I like the mollusc crush hypothesis best. It seems a great way to crush nautiloid and ammonite shells.

I can say with complete confidence that there is no way these sharks used their teeth for crushing nautiloid shells. There is absolutely no evidence of damage to any of the teeth I have looked at, and if they were used for crushing there would be considerable wear and damage to the teeth. Helicoprion teeth have only a single layer of enameloid in contrast to modern sharks which have 3 layers. The structure of the teeth are also wrong for crushing, they are long and quite narrow laterally, and they are heavily serrated.

I am open for discussion!

[Jesse]

For clarification of my point, would you use a steak knife or a hammer to crush a shell?

[Bill]

Do the teeth have nutrient grooves/holes?

[Jesse]

Yes, give me a few minutes and I will upload a cross section through one of the teeth.

[Jesse]

Here you go.

[Bill]

Thanks, though I was wondering if they had the same grooves as, for instance, a Striatolamia tooth, on the lingual side of the root.

[Jesse]

Ahh, yes, give me another few minutes I am scanning an old publication to pdf now and it has an image that will perfectly answer your question!

[Jesse]

From the original description of Helicoprion in 1898.

[Jesse]

Here is a legend: The areas in red are the nutrient tubes. area in green is the enameloid layer, yellow is the compound root.

[Jesse]

Do the teeth have nutrient grooves/holes?

Helicoprion had what is called a compound root, meaning all the teeth shared the same root. As a result the individual teeth don't come with it's own root and nutrient groove instead the nutrient tubes all run through the root and unto the teeth from the bottom.

[Auspex]

No doubt about it; this was one weird fish...

[Jesse]

And a lot shorter lived than previously thought. Google searches show that they died out around 225 MYA, but having compiled all the published papers on the shark the youngest confirmed finding is around 265 MYA. There is one specimen that was claimed to be from sediments from the Triassic, around 245 MYA, but it was not found in situ and has since been lost so who knows.

So they had a range from around 290-265 MYA, still a pretty good run!

[Al Dente]

I have wondered, do these tooth spirals have the same direction of tooth overlap? In other words is the overlap of individual teeth alway to the left when looking through the plane of the spiral or are there some spirals that go the opposite direction?

[Jesse]

The tooth in the posterior position overlaps the tooth directly in front of it on both sides evenly. So if you could see the side of the whorl not exposed in a concretion it would show the same overlapping pattern.

[Bill]

This has probably been thought of before but....what if we forget the classic shape of the shark's jaws, and think of them like a sperm whale? Streamline the whale's head but keep the long jaws

Add a cross-bar at the rear of the lower jaw, attach the root to it and the front of the jaw.

As with recent sharks, allow the top jaw to drop and move forward as it catches prey. Instead of teeth in the top jaw, have ribbed cartilage. As the mouth closes, the top jaw moves back into place, the ribbing drawing the prey over the teeth.

Lower jaw with teeth and x-bar, & upper ribbed jaw.

Consider the root as relatively lightly attached, and consisting of a different substance to other shark teeth roots, but formed in different layers.

When the shark dies, the 'weak' bond at each end of the root breaks down, releasing it. Now, the root might be 'built' in such a way that it contracts/shrinks. The tightly arranged teeth stop the top of the root shrinking as much as the rest. That would cause the root and teeth to form a whorl. The smaller teeth at the front would form a tighter whorl than the larger ones.

Edited above from 'same' to different

If plausible and new, remember,..............you heard it hear first.

Edited April 27, 2012 by Bill

[DeloiVarden]

This has probably been thought of before but....what if we forget the classic shape of the shark's jaws, and think of them like a sperm whale? Streamline the whale's head but keep the long jaws

Add a cross-bar at the rear of the lower jaw, attach the root to it and the front of the jaw.

As with recent sharks, allow the top jaw to drop and move forward as it catches prey. Instead of teeth in the top jaw, have ribbed cartilage. As the mouth closes, the top jaw moves back into place, the ribbing drawing the prey over the teeth.

Lower jaw with teeth and x-bar, & upper ribbed jaw.

Consider the root as relatively lightly attached, and consisting of a different substance to other shark teeth roots, but formed in different layers.

When the shark dies, the 'weak' bond at each end of the root breaks down, releasing it. Now, the root might be 'built' in such a way that it contracts/shrinks. The tightly arranged teeth stop the top of the root shrinking as much as the rest. That would cause the root and teeth to form a whorl. The smaller teeth at the front would form a tighter whorl than the larger ones.

Edited above from 'same' to different

If plausible and new, remember,..............you heard it hear first.

I must admit your theory is the best I have heard to date!

[Jesse]

Bill, I will give you credit for a unique hypothesis, I had a similar thought when I first started researching this beast. There are a few reasons for why this hypothesis wouldn't work however.

First, is while cartilage does curl upon decomposition, it would not form such a uniform spiral like we see with helicoprion. If your idea was correct we would expect to see some amount of translation of the spiral, meaning it would look more like a cone than a discus. In all of the specimens that have been described and that I have examined do not exhibit any translation, and I was looking for it from the start.

Second, the compound root rests upon a semi ossified band of cartilage that is very dense, almost like bone. This cartilage called the symphyseal crista was first described in 1966 and is present in all specimens found to date. This means that the root and teeth are partially supported by a very rigid cartilage that would be incapable of changing shape post mortem during decomposition.

Third is the way the teeth fit in position on the whorl. They fit very tight with no room for flexion and the roots of the teeth interact in such a way as to prevent compression during biting. If the jaw grew in a straight line it would not be possible for the row of teeth to roll in upon itself in such a uniform manner and keep the same spacing. I will attach a stylized drawing of the tooth whorl to better illustrate how the tooth roots interact.

Fourth, these whorls are found completely encased in cartilage that is presumed to be part of the lower jaw. The inner portion of the whorl shows evidence that it was encased in cartilage in life while the outer most portion was exposed for eating. This cartilage is not thought to be the lower jaw itself nor part of the skull.

[Bill]

Cheers Jesse.

Oh well, ...............

The ossified cartilage aside, (I know very little about these teeth whorls), my thoughts were that the root may consist of alternating layers, similar to plywood. I think in that case, the whorl would have formed in one plane, and not formed a cone.

[Jesse]

Trust me, I have had more ideas crushed by this shark than I care to admit, old saw jaw is a cruel mistress

Most people don't know about the internal structure of the whorl, the information was not easy to come by. It has taken almost 2 years to track down a copy of every publication for the shark, several of them are in foreign languages.

Add to that that much of the information readily available online is either completely wrong or unsubstantiated. So given that it really was a great idea, and I appreciate your sharing!

I would be more than happy to answer any and most questions about Helicoprion from anybody! All my friends are tired of hearing about it

[Bill]

Another thought, if they're found encased in cartilage, it must be different to the cartilage in the rest of the skeleton, surely. Especially considering the comparitive rarity of fossilized cartilage.

That also means the images of these sharks are all wrong. They all, to my knowledge, show bare teeth.

I can't image the whorl 'free floating' in the jaw, how did they attach?

Edited April 27, 2012 by Bill

[Jesse]

I was a bit misleading when I said encased, it is not completely encased there is a cutting surface exposed. And yes it is different than the rest of the cartilage of the skull, we have found cranial material for comparison, and yes all current images of Helicoprion are wrong.

You are right, the whorl does not free float. It is supported by a system of cartilages, can't go into to much detail here as this has not yet been published.

This image roughly shows where the cartilage would be covering the whorl, compare to the earlier whorl image.