Lack Of Teeth?

[Raistlin]

I have been wondering something now that I have been hunting for fossils for a few months. It might be a stupid question but I just cannot figure it out without some expert help.

Why is there such a lack of teeth when hunting fossils? I of course do not mean in areas like STH or even at the beach but in other areas.

Let me explain a bit. I am hunting areas that are Ordovician to Mississippi I find tons of other marine animals. I know there were fish and sharks (yes I know they are fish also lol) but yet I do not find teeth. There are a few areas where I should find sharks teeth and really don't but what about fish teeth also?

It seems teeth are pretty hard and seem to stand up well in the earth (maybe it is the enamel). Should I not be seeing small fish teeth as well? Is there a lack of teeth or is it just my silly thoughts?

Any thoughts on this?

Thanks.

[ashcraft]

There are sharks teeth in the areas you are hunting, at least what is Mississippian in age. I have found a total of one that looks like the traditional sharks tooth. Other teeth are more common, the grinding type, which I have seen but haven't picked up.

Keep in mind that the "fish" that were in the ordovician were not the "fish" of today. Many lacked teeth and jaws entirely, and the apex predators were not fish in form at all, but rather cephalopods.

Modern toothy fish didn't become common until much later. It was a very different ocean back then.

Brent Ashcraft

[Raistlin]

Ahh OK so it is a lack of teeth because they had a lack of teeth. I did not realize this I somehow was getting time lines mixed or something.

I am interested in what the grinding teeth look like though. I might have seen one of these and not thought it to be a fossil.

Thanks for the explination.

[Boesse]

It's more a question of taphonomy and preservation - I spent three years researching marine vertebrate taphonomy for my master's thesis, and the single biggest control on the distribution and abundance of teeth and bones in marine rocks is deposition. Where the seafloor is being eroded, or where sediment is being 'bypassed' - these are the areas where vertebrate remains accumulate. In North America during the majority of the Paleozoic, the middle of the continent was covered up by an equatorial, tropical-subtropical sea that was dominated by carbonate (e.g. limestone) deposition. Carbonate systems are generally crappier at concentrating vertebrate remains, because sediment is generated more or less in situ rather than transported from elsewhere (e.g. sand from the Rockies and Appalachians). Carbonate rocks in general are more complete stratigraphically speaking (than siliciclastic rocks - sandstones, gravels, and shales) and have less ability to concentrate vertebrate skeletal elements into fossiliferous deposits.

It also depends upon the speed at which a basin subsides (and thus fills up with sediment): theoretically speaking, high-subsidence basins have the same number of fossils but spread through a larger volume of rock, and are thus less common and harder to discover. Low subsidence settings, on the other hand, will have the same number of fossils within a smaller volume of rock. Many many rock units on the west coast were deposited under conditions of rapid subsidence, and are often totally barren with respect to fossils; on the other hand, thin, time-rich strata on the east coast include numerous bonebeds and other sorts of time averaged deposits with abundantly preserved vertebrate fossils.

There are Silurian and Devonian bonebeds with abundant thelodont and placoderm bones in the US and elsewhere, but they are relatively uncommon. Sharks and many other fishy taxa are present in the Devonian - but conditions for preservation during the Paleozoic were a totally different animal than Mio-Pliocene preservation of sharks and whales on either coast.

Bobby

[Raistlin]

Well I can honestly say these are all things I have never considered.

Actually a good part of it I did not even know to consider. I just assumed that the teeth should show up more because I believed they could hold up to more than say a brachiopod. The other things mention so far never even came to mind.

[AgrilusHunter]

Nice explanation Bobby!

[ashcraft]

It's more a question of taphonomy and preservation - I spent three years researching marine vertebrate taphonomy for my master's thesis, and the single biggest control on the distribution and abundance of teeth and bones in marine rocks is deposition. Where the seafloor is being eroded, or where sediment is being 'bypassed' - these are the areas where vertebrate remains accumulate. In North America during the majority of the Paleozoic, the middle of the continent was covered up by an equatorial, tropical-subtropical sea that was dominated by carbonate (e.g. limestone) deposition. Carbonate systems are generally crappier at concentrating vertebrate remains, because sediment is generated more or less in situ rather than transported from elsewhere (e.g. sand from the Rockies and Appalachians). Carbonate rocks in general are more complete stratigraphically speaking (than siliciclastic rocks - sandstones, gravels, and shales) and have less ability to concentrate vertebrate skeletal elements into fossiliferous deposits.

It also depends upon the speed at which a basin subsides (and thus fills up with sediment): theoretically speaking, high-subsidence basins have the same number of fossils but spread through a larger volume of rock, and are thus less common and harder to discover. Low subsidence settings, on the other hand, will have the same number of fossils within a smaller volume of rock. Many many rock units on the west coast were deposited under conditions of rapid subsidence, and are often totally barren with respect to fossils; on the other hand, thin, time-rich strata on the east coast include numerous bonebeds and other sorts of time averaged deposits with abundantly preserved vertebrate fossils.

There are Silurian and Devonian bonebeds with abundant thelodont and placoderm bones in the US and elsewhere, but they are relatively uncommon. Sharks and many other fishy taxa are present in the Devonian - but conditions for preservation during the Paleozoic were a totally different animal than Mio-Pliocene preservation of sharks and whales on either coast.

Bobby

That explains the lack of teeth in our silurian/devonian beds, which are not particularly fossilferous to begin with, but there weren't many teeth to preserve during the Ordovician as I recall. Am I wrong on this?

Brent Ashcraft

[Boesse]

Nope, not wrong at all. I don't think there are any 'toothed' fish in the Ordovician, but there were some early vertebrates with dermal bones (Anaspids, thelodonts, maybe). Some of these dermal elements are similar in shape to low crowned teeth.

[Shellseeker]

Thanks Bobby,

I value TFF for a lot of reasons. One of those values are posts like yours that add detail and insight that I would have never figured out for myself. It is part of my education in a world of fossils.