How Do Shark Teeth Grow?

[Jesse]

Hey all, I am continuing to work on the Helicoprion mystery and need to address a basic question. How do shark grow their teeth? I know that they form under the "gums" and progress posterior to anterior. What I am looking for is the actual formation of the tooth. I have been searching for a while and can find nothing definitive. Any literature on the subject wold be greatly appreciated.

I am trying to either support or dispute the thought that the whorl of the Helicoprion starts in the center with new teeth being formed and the teeth grow larger until they erupt and are eventually ejected. In other words, baby teeth in the middle, older teeth on the outside. My current hypothesis is that the baby teeth are on the outside and the oldest teeth are in the center. This is supported by wear on the inner teeth and little else.

Please Help!

[Paleoc]

Not only supported by wear on the teeth but as the shark grows and gets larger, the teeth get larger. In a modern dentition, each replacement tooth is slightly larger than the tooth it is replacing. But the individual tooth doesn't grow from a tiny bud (like a plant) and become larger. First a chalky enamel is formed, then the dentine inside the enamel gets filled in, the tooth enamel hardens and root forms but the enamel part of the tooth is always the same size as the tooth takes form.

Try this: http://www.elasmo.co...sc_ctaurus.html

Click on the links at the bottom of the page to see more.

Edited January 26, 2012 by Paleoc

[Boneman007]

Not only supported by wear on the teeth but as the shark grows and gets larger, the teeth get larger. In a modern dentition, each replacement tooth is slightly larger than the tooth it is replacing. But the individual tooth doesn't grow from a tiny bud (like a plant) and become larger. First a chalky enamel is formed, then the dentine inside the enamel gets filled in, the tooth enamel hardens and root forms but the enamel part of the tooth is always the same size as the tooth takes form.

Try this: http://www.elasmo.co...sc_ctaurus.html

Click on the links at the bottom of the page to see more.

I always though the enamel formed first and hardened then dentine infilled. I have found many cretaceous teeth that are just hollow enamel. We also find them as enamel with the detine infilled, but no roots.

Any ideas how this happens? acidic matrix that eats the dentine?

[Paleoc]

In most cases, the matrix destroys the roots. For example, in the South Carolina limestone quarries, small teeth are usually found rootless. Only after the tooth is about mako sized, do you find them with complete roots. However, one of the signs of an associated dentition is a bunch of teeth of the same species with some of them rootless and/or hollow.

Here is a single row of teeth from a mako. Note, the smallest blade is the first tooth (right), with each one after that, the blade is a hair larger than the one it replaces reflecting the growth of the shark.

Edited January 26, 2012 by Paleoc

[Jesse]

Paleoc, your awesome! That is exactly the information I was looking for!

I have been trying to convince 2 of the other members that the inner teeth of the tooth whorl are the oldest, but it is hard for some people to wrap their heads around a jaw that spirals in on itself. After reading your link, I went back and looked at some of the specimens and was able to see some evidence that the largest (newest) tooth on one of the whorls was still forming at the time the shark died.

Thank you!

[Boneman007]

In most cases, the matrix destroys the roots. For example, in the South Carolina limestone quarries, small teeth are usually found rootless. Only after the tooth is about mako sized, do you find them with complete roots. However, one of the signs of an associated dentition is a bunch of teeth of the same species with some of them rootless and/or hollow.

Here is a single row of teeth from a mako. Note, the smallest blade is the first tooth (right), with each one after that, the blade is a hair larger than the one it replaces reflecting the growth of the shark.

Is the first tooth on the left hollow?

[Paleoc]

If I were to break it open, it probably would be. Also the enamel is somewhat chalky.

[Paleoc]

Paleoc, your awesome! That is exactly the information I was looking for!

I have been trying to convince 2 of the other members that the inner teeth of the tooth whorl are the oldest, but it is hard for some people to wrap their heads around a jaw that spirals in on itself. After reading your link, I went back and looked at some of the specimens and was able to see some evidence that the largest (newest) tooth on one of the whorls was still forming at the time the shark died.

Thank you!

I don't see how the concept is that hard. Look at an ammonite. The oldest (and smallest) chambers are on the inside. I don't think the tooth whorl curls in on itself. I tend to think it grows outward in a spiral like an ammonite shell. The teeth in a modern shark would do the same thing if they didn't fall out. They would end up growing around and around each other in a whorl, with the oldest, smallest teeth in the middle and the newest, largest teeth on the outside. Which also sense in a evolutionary format. Helicoprion is growing teeth in the same manner as a modern shark, just not shedding them.

Edited January 28, 2012 by Paleoc

[Jesse]

I honestly don't know why it is so hard for people to accept it. I guess it is just because the Helicoprion looks so much different than his descendants.

When you say it grows outward in a spiral are you meaning that the whorl sits "outside" of the jaw?

[KGS]

This information is very interesting. I thought the new teeth would be real tiny and then slowly grow and get larger, but it looks like the new teeth are about the same size as the outermost fully formed teeth (crowns).

[jes4him]

This explains why I have a couple teeth without roots and inside the crown part is mostly hollow. They must have been teeth that weren't fully formed in the jaw when they got fossilzed.

[goroshkom]

The most profound in the web info on teeth growing seem to be here:

books.google.com/books?id=ON-sPP5rowwC

[THobern]

This explains why I have a couple teeth without roots and inside the crown part is mostly hollow. They must have been teeth that weren't fully formed in the jaw when they got fossilzed.

More likely a combination of poor fossilisation and weathering.

[Harry Pristis]

"Deposition of enamel generally begins soon after the beginning of dentine deposition.

...

"In contrast to dentine, the enamel layer... increases in thickness from the basal membrane outward: the last formed enamel layer lies outermost. The outer cover is formed by the enamel surface membrane (cuticula dentis, Nasmyth's membrane). It is important for the protection of the teeth because of its resistance to chemical agents, especially acids. ...

"Prior to the deposition of any hard substance, the mesodermal layer of odontoblasts [dentine-producing cells] and the ectodermal layer of ameloblasts [enamel-producing cells] are closely aligned on either side of the basal membrane. ...

"The formation of dentine precedes the precipitation of enamel. ...

"Dentine begins to form with the deposition by the odontoblasts of an organic ground substance along the inner surface of the basal membrane. Into this ground substance, which also contains fibrilles, carbonate salts are deposited. In this way a little tooth "shard" ("Zahnscherbchen") consisting only of dentine has arisen between the basal membrane and the surface of the tooth papilla.

"The cells of the tooth papilla, arranged in a cone and now enclosed beneath a coat of dentine, have become pulpa cells. New layers added to the inward face of the first formed dentine reduce the lumen of the originally very spacious pulp cavity. The dentine thus increases in thickness from the outside inward: the last formed dentine layer lies innermost.

"The formation of dentine is in many cases periodically interrupted by periods of quiescence. On sections this produces concentric growth lines."

From Comparative Odontology by Bernhard Peyer; 1968; University of Chicago Press.

[emphases added]