A Meg with character

[Shellseeker]

I went out today in the forecast of Hurricane ETA.

It was better than I anticipated.  Less windy, less rain.  The sun was out about half the day just North of Wauchula, Florida.

I did not have a lot of success most of the morning,  small shark teeth, 70% broken.  My find of the day was a tiny broken dolphin tooth.  Early afternoon, my luck changed.  I found some gravel 3-4 inches deep with clay at the bottom. The small teeth were mostly whole and a little more colorful,  then I found a broken Meg,  then my find of the day (below) a Meg just under 2.5 inches. It is always better to be lucky.

 

Character!!! Great Serrations/Tip,  some curious color patterns, 

 

So, why put this in fossil ID.  I had questions and thought it a good way to attract those who have a greater understanding of Megs than I do.

 

Are those rock boring (baby) clam marks?

Look are the indentations at the edges where the blade meets the root.  Are there cusps there?  I have Megs that do not have those indentations.  Are they a common feature...

 

Those are sort of preamble questions.

 

Here is the one I really wanted to know.  I have a number of Megs which, just like this Meg , is missing all the detail around the Bourlette. Was it dissolved by some chemical process? If so, why would the bourlette dissolve, but not the root material?  This Meg came out of the clay... the enamel is in fantastic shape. This does not seem like water wear. 

 

I always think of questions on my finds,  I do not always get answers.

[jcbshark]

Beautiful tooth for sure Jack   Could it be that the tooth wasn’t fully formed as in not the last file? Perhaps the bourlette hasn’t  finished forming..... just a guess on my part but I have some teeth just like that

[thelivingdead531]

I don’t have any answers, as usual, but I wanted to say that tooth is marvelous! 

[Plax]

Sea level was a couple hundred feet lower just thousands of years ago. Your tooth would have been leaching in a well drained upland at that time. This repeated many times during the years since the shark shed this tooth. Of course it may have been buried deeper through much of this time. Also shark teeth abundances are usually lag deposits which are aquifers. All that water coursing through the sediment would selectively dissolve the less mineralized portions of the teeth. I have seen lags with just hollow enamel representing the shark teeth. Those are indeed gastrochaenid mollusk borings in my opinion. Rock boring mollusks.

[Shellseeker]

Plax, 

THANKS for your response.  I appreciate the fact that you are willing to speculate on some answers that are difficult to prove. I have some other details that may or may not apply to this discussion.  I found this tooth (as indicated above) north of Wauchula.  The last time there was sufficient salt water to support large sharks in the higher inlands of south central Florida was approximately 3 million years ago in the Pliocene and prior to that around 12 million years ago in the Miocene.

Also, this specific tooth was found encased in bluish clay.  I have occasionally wondered if that clay was part of the ocean bottom when the tooth was dropped.

 

 

So, Sea level rises and falls based on how much of it is locked in the polar ice caps. and we know that we came to the ending of an ice age some 15-20 thousand years ago.  I had added this chart to some previous threads...

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Sea level was a couple hundred feet lower just thousands of years ago. Your tooth would have been leaching in a well drained upland at that time. This repeated many times during the years since the shark shed this tooth.

Agree, I think your basic premise on sea level works, but the tooth was dropped some 2-3 MYA and the vast majority of that time , there was little or no sea water above it.  At some point, it did get into the clay ( the clay is about 6-7 inches thick where I dug),  and I believe it entered the clay after the rock boring mollusks had performed their work and markings on the tooth).. I am assuming that "rock boring mollusks" were saltwater based.

Supposedly , Megs went extinct 2 MYA,  I have a paper that implies the last time Salt water covered Fort Meade , Florida was about 3 MYA.  and I have this Meg stuck in Clay. I must admit I know little or nothing on how clay forms. I have seen ocean bottom clay in 30-40 foot holes near the Gulf of Mexico... It tends to be lime green and somewhat slimey. There was bedrock below the clay.

 

 

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Of course it may have been buried deeper through much of this time.

Plax, I am parsing this... We have relatively simple processes in Florida.

If buried deeper , I am not sure that I understand, what geologic process 1st buried the tooth in clay, sand, mud, gravel , and then uncovered enough of that to be accessible to me in rivers or creeks. The water obviously is obviously capable of "digging" a canyon between the banks , but no deeper than the distance between the top of the bank and gravel on the river bottom.

 

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All that water coursing through the sediment would selectively dissolve the less mineralized portions of the teeth. I have seen lags with just hollow enamel representing the shark teeth.

All the above is preamble.  Your point here is the key.  I also have seen teeth that are ONLY the enamel.  So I agree that this can happen... But what about the root versus the bourlette ?

Are both not made of the same material?   Look at the fine lines on the non_bourlette root material.  Seems not to be water worn which might remove/polish all those little lines.  So is the wearing process chemical?  I have seen mud molds of seashells where the shell have been completely dissolved  !!!!! Is the Bourlette being dissolved?    Once again, Thanks for answering and listening to my ramblings.   Jack

[Shellseeker]

Plax, Starting the search... How does Florida Clay Form ?

Clay minerals typically form over long periods as a result of the gradual chemical weathering of rocks, usually silicate-bearing, by low concentrations of carbonic acid and other diluted solvents. These solvents, usually acidic, migrate through the weathering rock after leaching through upper weathered layers.

 

So there is salt water, maybe over a layer of shell,  on top of sand, on top of Bedrock eventually...  There may be some rock in that sand, but certainly enough silica in the sand.

 

I am still somewhat confused by the clay.. It is lore and actual experience that Megs are generally found in the top couple of inches of the clay.  Why are the Megs not underneath the Clay....

[Mahnmut]

Hello Shellseeker,

I do not have specific answers to your questions, but maybe some insights to offer:

- talking about  cartilage, there is not simply a binary distinction between bone and cartilage, there may be fine gradients. I think tooth and enamel are relatively clearly distinct, but inside the cartilage you can have mineral concentrations (mostly calcium phosphate) from close to zero up to fully mineralized bone, depending on the hardness needed in the respective organ, but also the age (lifetime) of the animal in question, maybe also health issues...

I do not know the details for sharks, but it would make sense if the (bio-) mineralization got stronger towards the tooth, making the further parts more easy to erode, chemically or mechanically.

 

-I am not sure, because English is not my first language, but I think "clay" is a term that is used in a broad laymans sense and a specific geologists sense.

Clay minerals in the specific sense are phyllosilicates  often produced by the chemical weathering of other silicate rocks.

In the broader sense I believe many forms of sticky, dense mud ( often containing clay minerals among others) are called clay colloquially.

I am not sure about the conditions in Florida, but I could imagine that something like that could also be deposited during the drying up of a shallow sea?

There will be members here who know more about that.

 

Best Regards

J

[Plax]

Your bluish clay looks like weathered (rotten) limestone if we're talking about the screen pic. We get this in our local eocene. I also see pebbles in your screen. This is typical of lag concentrations of shark teeth. Shark teeth are no different than quartz pebbles in that they're resistant clasts. A meg tooth being a large resistant clast survives many erosion and depositional sequences. It could have been bored shortly dropping out of the sharks mouth or any time afterward that it was exposed on the sea floor. The abundant meg teeth off our NC coast at "meg ledge" are a prime example. The last warm interglacial saw sea level 30 or 40 feet higher than now but during the late Pliocene (post meg time) it was much higher. The depth post deposition of the original tooth is more relevant to its dissolution during low stands which dominated during the Pleistocene. Between 300 and 400 feet lower depending on which paper you refer to. Your tooth was in an upland no doubt during those times with the usual dissolution of limestones from rain and ground water acidity.

[Bradley Flynn]

What a tooth

[jeannie55]

While I am far from able to contribute to this conversation, I have learned a lot from your post and the replies from our forum members. Nice teeth!

[Shellseeker]

I am very pleased with the detailed responses from @Plax and @Mahnmut.  It gives me something to parse, analyze, and learn.

I am interested in taking what I have learned from field experience over the last 13 years and match it to facts and science, to the extent tht is possible.

I had thought that the 'clays" I found were linked to sea bottom , because 95% of the time Megs were laying on top , not in like this one, or underneath.

I have little time to address this morning, but will come back after I think more..

 

In the meantime, a description of the geology of some of my hunting grounds.

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Hawthorn Group, Peace River Formation

The Peace River Formation crops out or is beneath a thin overburden on the southern part of the Ocala Platform extending into the Okeechobee Basin. These sediments were mapped from Hillsborough County southward to Charlotte County. Within this area, the Peace River Formation is composed of interbedded sands, clays and carbonates. The sands are generally light gray to olive gray, poorly consolidated, clayey, variably dolomitic, very fine to medium grained and phosphatic. The clays are yellowish gray to olive gray, poorly to moderately consolidated, sandy, silty, phosphatic and dolomitic. The carbonates are usually dolostone in the outcrop area. The dolostones are light gray to yellowish gray, poorly to well indurated, variably sandy and clayey, and phosphatic. Opaline chert is often found in these sediments. The phosphate content of the Peace River Formation sands is frequently high enough to be economically mined. Fossil mollusks occur as reworked casts, molds, and limited original shell material. Silicified corals and wood, and vertebrate fossils are also present. The Peace River Formation is widespread in southern Florida. It is part of the intermediate confining unit/aquifer system.

 

[Plax]

3 hours ago, jeannie55 said:

While I am far from able to contribute to this conversation, I have learned a lot from your post and the replies from our forum members. Nice teeth!

I like your opuntia flower!

[Shellseeker]

Some context:  Megs lived for 20+ million years, approximately 23 to 3.6 million years ago (mya), during the Early Miocene to the Pliocene. Their teeth needed to drop to the ocean floor during that time period.

Here is a picture of Florida during that time period. Note that Tampa and my current hunting area (red) is beach front just below Fort Meade, Florida. Fort Meade is 140 feet above sea level today.

So I needed about 150 feet (50 m) of sea water for a Megalodon to swim over Fort Meade. When is the last time that happened? About 3 mya (Pliocene) and previous to that, about 12 mya (Miocene).

I agree with Plax that rock boring mollusks did their damage soon after the tooth was shed onto the ocean bottom.

I have been forces to adjust the idea that the clay preceded the dropping of the tooth.  I have become very excited finding clay on the creek/river bed. To me Clay means pristine Megs a high % of the time and in the vast majority of cases, the Meg lays on top of the clay, so I have learned to scrape my flat pointed shovel across the top of the clay. I do not have a good theory on why the Megs are mostly on top , rather than under or in the clay.

As Mahnmut indicates, there are lots of clay variations and I have seen many of them. This is not the clay like mud that sucks my boot in, or the grayish broken clay like pebble rock that can be a couple of feet in layers over shell or bedrock. It is the pure white, lime green or blue clay 3-15 inches in depth,  laying just above limestone bedrock, that is almost pure clay like the stuff you might buy for molding in an Arts & Crafts store.

High Quality teeth come out.... protected for 3 million years in a wrapping of clay and sand.

 

My expectations were very high when I saw the point of this latest Meg sticking out of the blue clay. I considered the possibility that damage to the bourlette happened before the Meg was buried in the clay. That would be an alternative path to water coursing through the sediment would selectively dissolve the less mineralized portions of the teeth.  Both were likely . I value this tooth both for the damage to the bourlette and pristine nature of the enamel.  The tooth is trying to tell its story, I just have not yet learned how to translate.

 

There is no one correct answer.  I enjoy the conversations because it leads to new understandings on my part and new questions to be answered in a future discussion.   Thank for the help,  Jack

 

[Al Dente]

4 hours ago, Shellseeker said:

To me Clay means pristine Megs a high % of the time and in the vast majority of cases, the Meg lays on top of the clay, so I have learned to scrape my flat pointed shovel across the top of the clay. I do not have a good theory on why the Megs are mostly on top , rather than under or in the clay.

The river concentrates the Meg teeth and other large dense clasts beneath the sand and gravel (therefore on top of the clay). Sand and gravel constantly move downstream, mostly during higher flows when the current is stronger. Dense objects like teeth are more resistant to this movement so they accumulate on the bottom. The dense clay doesn’t move downstream because it is more cohesive but can be slowly eroded by the movement of the sand, releasing more teeth.

 

Teeth locked in the clay aren’t exposed to the constant abrasion of the moving sand and gravel. That is one reason the are more pristine than ones found within or just beneath the sand and gravel.

[Shellseeker]

On 11/10/2020 at 11:56 AM, thelivingdead531 said:

I don’t have any answers, as usual, but I wanted to say that tooth is marvelous! 

 

On 11/11/2020 at 9:17 AM, Bradley Flynn said:

What a tooth

 

On 11/11/2020 at 9:24 AM, jeannie55 said:

While I am far from able to contribute to this conversation, I have learned a lot from your post and the replies from our forum members. Nice teeth!

 

When I first retired to South Florida,  I had no concept or understanding of the richness of the fossil layers in Florida. I had a lot of time on my hands. and I am a very curious person, wanting to know all that I can about the fossils I find.

My basic secret to success is bulldog persistence. I invest huge amounts of time and effort into a hobby I love, and occasionally I find these clay layers on the bottom of the river.  Thanks for the comments.   Jack

 

[Shellseeker]

5 hours ago, Al Dente said:

Dense objects like teeth are more resistant to this movement so they accumulate on the bottom. The dense clay doesn’t move downstream because it is more cohesive but can be slowly eroded by the movement of the sand, releasing more teeth.

 

This is insightful.  Megs in the current get broken by turbulence rolling downstream. Fossils on the surface of the river bottom get sandblasted.  Years back, a friend showed me a 2.5 foot section of Mastodon tusk that had evidently been laying in the sand, in the current. It only had 50% left having been eroded and polished length wise.

Megs find it difficult to intrude into the dense clay,  leaving impressions like cookie cutters when pried out. In order to stay pristine, they need to be protected by layers of sand and gravel from water erosion over time.

So, when I find a Meg in this environment, packed in dense clay under layers of sand and gravel, that has significant damage,  I wonder why.

On 11/11/2020 at 9:07 AM, Plax said:

A meg tooth being a large resistant clast survives many erosion and depositional sequences.

This one might have had a previous unprotected existence, and then landed on the clay layer....

 

Thanks to all for the responses.