Which Formation Do Summerville Megs Come From?

[Al Dente]

Seems like an argument based in semantics to me. I believe in the chrono-species reasoning. There was one big Carcharocles at any given time.

I too prefer to use the Chronospecies concept when discussing Carcharocles. It reduces arguments over which species a tooth belongs to when the age is known. But the question was when did megalodon first show up in the fossil record. Using the Chronospecies concept isn't going to answer this because it is an artificial method for identifying species. It cannot possibly answer a question about a speciation event.

[Al Dente]

Because there are well-known allometric form changes in the Carcharocles group of species, and because atypical specimens may occur in any species, an occasional tooth without lateral cusps should not make much of a ripple on the taxonomic pond.

I agree that calling a tooth a megalodon just because it lacks cusps isn't realistic due to the highly variable nature of Carcharocles teeth. If you look at the two known associated dentitions of C. chubutensis (aka C. subauriculatis) from the Lee Creek mine, both have lower teeth lacking cusps.

[cowsharks]

I agree that calling a tooth a megalodon just because it lacks cusps isn't realistic due to the highly variable nature of Carcharocles teeth. If you look at the two known associated dentitions of C. chubutensis (aka C. subauriculatis) from the Lee Creek mine, both have lower teeth lacking cusps.

Are these two known dentitions shown in Lee Creek Vol III? I don't have my copy handy to look at, and it takes too long to download on the computer.

Daryl S.

[Al Dente]

Are these two known dentitions shown in Lee Creek Vol III? I don't have my copy handy to look at, and it takes too long to download on the computer.

Daryl S.

Yes. They are the ones illustrated in Vol. III. Pete Harmatuk found both sets.

[Harry Pristis]

I too prefer to use the Chronospecies concept when discussing Carcharocles. It reduces arguments over which species a tooth belongs to when the age is known. But the question was when did megalodon first show up in the fossil record. Using the Chronospecies concept isn't going to answer this because it is an artificial method for identifying species. It cannot possibly answer a question about a speciation event.

Maybe this misconception is the result of the term "Megalodon" or "Meg" being adopted into the vernacular. The term now has broader application than just to the species, Carcharocles megalodon.

In science-speak, the species, C. megalodon, is limited to the mega-tooth sharks, with adult teeth typically without lateral cusps, for which there is abundant evidence from Middle Miocene to the Pliocene. (The short description for this argument.)

The vernacular "Megalodon" or "Meg" may refer to any individual mega-tooth shark tooth which has the morphological features of C. megalodon, but is not a tooth of a great white shark, Carcharodon carcharias.

"Megalodon" in this vernacular sense ignores allometric form changes and atypical tooth forms. It ignores geology and all the other measures that we apply to get a grasp on the (admittedly artificial) concept of species.

(I don't know what a "speciation event" is; is it like "Creation Week"?)

Allometric form change and mutations are real world phenonema. Organizing one's thinking about mega-tooth sharks around a morphospecies called "Meg" is naive in the scientific sense.

[Al Dente]

(I don't know what a "speciation event" is; is it like "Creation Week"?)

From Biology online website:

Speciation event

Definition

noun, plural: speciation events

A moment in which the evolutional lineage splits, starting history of a new species.

[non-remanié]

It does answer the question quite simply and elegantly if you subscribe to the fundamental philosophy of chronospecies in the case of the megalodon lineage. If there's just one mega-tooth shark that has evolved gradually over time, then no speciation event happened. For instance, chronospecies would imply that chubs and megs were never in direct competition as distinct species because they were always one and the same. Chronospecies is not simply a device to be used, if you adhere to its reasoning it has ramifications or else your logic becomes flawed. If anything morphospecies is the device to be used. The fact that we all still use morphospecies names by convention is really inconsistent with the basic chronospecies ideology, but we all do it, even those of us who wholeheartedly believe in the chronospecies argument. If you adhere to this chronospecies logic as I do, the basic question loses pretty much all of its real meaning, its just semantics based on convention to me. BUT even though it really doesn't matter to me and neither assertion is really the whole truth in my mind, it does seem that saying megalodon occurs in the Oligocene based on this line of evidence is highly deceptive and therefore, more wrong.

I too prefer to use the Chronospecies concept when discussing Carcharocles. It reduces arguments over which species a tooth belongs to when the age is known. But the question was when did megalodon first show up in the fossil record. Using the Chronospecies concept isn't going to answer this because it is an artificial method for identifying species. It cannot possibly answer a question about a speciation event.

[Al Dente]

It does answer the question quite simply and elegantly if you subscribe to the fundamental philosophy of chronospecies in the case of the megalodon lineage. If there's just one mega-tooth shark that has evolved gradually over time, then no speciation event happened. For instance, chronospecies would imply that chubs and megs were never in direct competition as distinct species because they were always one and the same. Chronospecies is not simply a device to be used, if you adhere to its reasoning it has ramifications or else your logic becomes flawed. If anything morphospecies is the device to be used. The fact that we all still use morphospecies names by convention is really inconsistent with the basic chronospecies ideology, but we all do it, even those of us who wholeheartedly believe in the chronospecies argument. If you adhere to this chronospecies logic as I do, the basic question loses pretty much all of its real meaning, its just semantics based on convention to me. BUT even though it really doesn't matter to me and neither assertion is really the whole truth in my mind, it does seem that saying megalodon occurs in the Oligocene based on this line of evidence is highly deceptive and therefore, more wrong.

Toothpuller-

Thank you for taking the time to explain this. When I first responded to this thread, it was because I took issue with the quote that Harry posted about most paleontologist agreeing that megalodon was a recent species. Not all of them do and I posted two examples that had some reference to this fact. The part of the quote that really bothered me was that most paleontologist believed that they disappeared suddenly about 1.6 million years ago. They don't. I have never seen paper published where a paleontologist makes this claim. I wanted to see if anyone had a reference to this part of the quote because I have never seen one and I am open to seeing evidence of this. Like I said in the first sentence of my response, I'm not a believer in an Oligocene age for megalodon but some paleontologists are.

Now to the chronospecies concept. It uses gradualism to explain evolution and after Eldredge and Gould's paper on Punctuated equilibrium in the 1970s many evolutionary biologists have abandoned the concept of gradual evolution or at least believe it is less a factor in evolution than punctuated equilibrium. It is the long periods of stasis that allow people to recognize different species in the fossil record instead of constant change. Some people still believe in gradualism as the main form of evolution. I don't.

Edited March 16, 2011 by Al Dente

[Auspex]

FWIW, IMHO, Gradualism and Punctuated Equilibrium are not mutually exclusive, but are two (of many) consequences of life. That which can persist, will.

[Harry Pristis]

I went back to elasmo-research.org and found this:

"Because the rate of evolutionary change in sharks is very slow and gradual, it can be frustratingly difficult to determine where one species stops and another begins. There is no evidence of punctuated equilibrium (sudden 'jumps' in form) in the shark fossil record. Without sharp discontinuities, boundaries between named species are often made rather arbitrarily along a continuum of variation. Thus distinctions among some fossil sharks may best be considered 'chronomorphs' (forms within an evolving lineage) rather than biologically discrete species."

In other words, no speciation events, no punctuated equilibrium, just change over time.

I did not find a citation for the 1.6 Ma extinction of C. megalodon. (The author(s) described this as "Plio-Pleistocene," though I would call that age Pleistocene:Calabrian.) There was a reference to the 1.6 Ma age being determined from radiometric data.

[siteseer]

I think any reference to a 1.6 million year extinction comes more from conversations than technical articles. I haven't seen a date given to that extinction in any article. In another thread I noted a publication that mentions a Late Pliocene occurrence in Australia and an informal report of an occurrence in southern California. There is also a formal report of a Late Pliocene occurrence of megalodon in northern Baja California, Mexico. Some paleontologists have questioned the occurrence but nothing has been put in print.

Here's a link to that previous thread:

http://www.thefossilforum.com/index.php/topic/771-mio-pliocene-fossils-of-northern-california/page__st__20

The part of the quote that really bothered me was that most paleontologist believed that they disappeared suddenly about 1.6 million years ago. They don't. I have never seen paper published where a paleontologist makes this claim. I wanted to see if anyone had a reference to this part of the quote because I have never seen one and I am open to seeing evidence of this.

Edited March 18, 2011 by siteseer

[Al Dente]

There is no evidence of punctuated equilibrium (sudden 'jumps' in form) in the shark fossil record. Without sharp discontinuities, boundaries between named species are often made rather arbitrarily along a continuum of variation. .

Lets start with defining Punctuated equilibrium and gradualism and then let's see which looks more like what we find in the fossil record for shark teeth.

From Wikipedia (I've edited to make it shorter):

Punctuated equilibrium is a theory in evolutionary biology which proposes that most sexually reproducing species will experience little net evolutionary change for most of their geological history, remaining in an extended state called stasis. Punctuated equilibrium also proposes that stasis is broken up by rare and rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which species split into two distinct species, rather than one species gradually transforming into another.^[1]

.Phyletic gradualism states that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (anagenesis). .

Lets take Cretalamna appendiculata which some people believe evolved into Otodus obliquus.

I'm not sure of the earliest record of C. appendiculata but it was definitely around during the Campanian some 83 million years ago. Still around largely unchanged in the Paleocene roughly 58 million years ago. Same species, little change for 25 million years. Sometime in the Paleocene Otodus obliquus pops up. Not just a new species but a new genus as well (sounds like a quick and rapid change to me). O. obliquus hangs around until the lutetian largely unchanged for roughly 15 million years. The two species hang around together during the Paleocene, not something that generally happens when one is slowly transforming into another.

I know I'm being a little facetious but the facts are that these species stay in stasis for long periods of time, not something that gradualism accounts for.

If you really want to see an excellent argument for gradualism in shark teeth, look up elasmo.com and look at Jim Bourdon's slide show called Segue: Otodus Carcharocles. He shows it as gradualism but I look at the same argument and see punctuated equilibrium in action. Either way it is truly an excellent piece of work by Jim Bourdon.

[Al Dente]

I think any reference to a 1.6 million year extinction comes more from conversations than technical articles. I haven't seen a date given to that extinction in any article. I noted a publication that mentions a Late Pliocene occurrence in Australia and an informal report of an occurrence in southern California. There is also a formal report of a Late Pliocene occurrence of megalodon in northern Baja California, Mexico. Some paleontologists have questioned the occurrence but nothing has been put in print.

Here's a link to that previous thread:

http://www.thefossil...ia/page__st__20

Thanks for the link for the Kemp reference. I had tried to locate this publication a few years ago but was unsuccessful. The Cameron Inlet Formation is shown in this paper from 2005 and it is described as early to late Pliocene. It does appear to be younger than the base of the Yorktown where megs are routinely found.

Memoirs of Museum Victoria 62(1): 67–89 (2005)

ISSN 1447-2546 (Print) 1447-2554 (On-line)

http://www.museum.vi...moirs/index.asp

Pliocene marine mammals from the Whalers Bluff Formation of Portland,

Victoria, Australia

[Paleoc]

One of the problems with defining a species by hard and fast lines is that those lines become very blurred when you look at any given animal. What do you call a meg some of whose lateral teeth have cusplets? Megalodon or chubutensis?

In South Carolina many of the megs which are found in the river, the lower teeth are very auriculatus like with narrow, thick rounded blades and large cusplets. The uppers are typical meg shaped.

Juveniles often have features of ancestral species. So if we find a 3 inch, chubutensis tooth, as an adult, it may completely lack cusplets completely. Is it a meg?

I have a juvenile Great White jaw. Most of the teeth have cusplets and some are only partially serrated. Isolated, those teeth would indicate a different species than the adult.

This where the concept of chronospecies come in. During X-time frame, most of the sharks of this type had X-type teeth. Some of the sharks had ancestral type teeth, some had more modern type teeth, some had a mixture of both. All the sharks can breed with each other so there is only 1 true species existing but for the sake of labeling them we will call them X-species.

Other side notes:

I have been to the Baja site. Much of the geology there is very confused and some of the formations highly inclined, indeed there are nearby volcanic cones. It appears that the meg teeth probably come from a Miocene deposit which is highly inclined but butts against a more shallow inclined Late Pliocene deposit, thus it would be easy to attribute the meg to the late Pliocene. In the late Pliocene formation, we came across several Parotodus teeth which typically are about 50 times less common than meg teeth and lots of Carcharodon teeth but not so much as a fragment of a meg. This is also the case in another late Pliocene deposit in Florida, where once again I found a Parotodus, several Carcharodon but not a single fragment of megalodon. If (and I think that it is a big if) megalodon survived until the latest Pliocene, I would think it would be in isolated areas and very rare.

Otodus. I have "Otodus" teeth from the late Maastrichtian which are essentially the same as or very similar to Paleocene Otodus teeth so Otodus goes back to the late Cretaceous. And since I know this is going to generate howls of outrage, here is a late Cretaceous tooth and a similar (not exactly the same tooth position) Paleocene tooth: (And yes, early Otodus have many Cretalamna type features).

Cretaceous:

Paleocene:

[tracer]

[non-remanié]

The megalodon lineage, a predator at the very top of the foodchain in a somewhat special case in my mind although I do agree with the current majority opinion on gradual vs punctuated equilibrium. The megalodon family tree has no branches, its a straight line through the various tooth-designs. With the evidence available, it is impossible to know if these were distinct species and unfortunately due to the nature of fossil deposits, we are unlikely to ever know more because all we have are isolated teeth and vertebral centra. But I do not believe this top predator ever had to compete with its sister species, because it was always one species. Its just a much simpler explantion than multiple top predator megatooth species swimming together at the same time. Sure there may have been a point in time where the teeth changed quicker and then a stasis resulted and that statis is mostly what we see in the fossil record, but I can't imagine that there were more than 1 megatoothed species at any given time. In the grand scheme, although we can clearly see differences in the shape of megs/chubs/etc I don't believe there can be much of a functional difference. Also clearly some tooth-deisgns are time transgressive such as in the case of juveniles. The evidence available at this point for the Oligocene species megalodon is no more than a drop in the bucket of random variation, which is not at all unexpected. Otherwise all we know is the straight line family tree through time. I would like to see a quote from a paleontologist who believes that megalodon, as a distinct species, began in the Oligocene and swam among a completely different species of megatooth shark for millions of years. I don't believe that is what the authors of the NZ article would claim, they are just reporting the details of one tooth and using the normal conventions. There are many other possible explanations for one singular occurrence...

Secondly, I would like more evidence than just the below quote from elasmo.com. I'm not convinced that quote isn't just a result of collectors there not really understanding the geology and believing megs to actually be from the Chandler Bridge fm, as we CLEARLY have evidence for through this entire thread. In "Late Oligocene sharks and rays from the Chandler Bridge Formation, Dorchester County, South Carolina, USA", Cicimurri and Knight make no reference to megalodon or uncusped megatooths in the Chandler Bridge fm. But even if it is true, which would not surprise me, it is not much in the way of solid evidence for the premise.

"C. megalodon, as suggested above, is the morphology where the lateral cusplets are absent. Upper teeth of Carcharocles from the Late Oligocene Chandler Bridge Fm. of South Carolina sometimes lack cusplets so technically must be called C. megalodon, however this trend is not normally seen until the Early Miocene." (elasmo)

In this entire thread we still have yet to get a complete answer to the original question from someone with a lot of firsthand experience and a solid geological background. I believe my and Paleoron's answers are pretty good, but obviously not many local collectors understand the issue any better at all because we still haven't really gotten a real answer out of the many low country fossil hunters. Yes, its probably a lag at the top of the Chandler Bridge. A lag of exactly what??? I would like to know the whole story.

And here is another quote from elasmo.com which elucidates the chronospecies argument better

"When carefully plotted (design-type/time) there is a gradual progression of the Carcharocles tooth-design from the Eocene to Pliocene — triangularization of the crown, standardization of serrations and disappearance of cusplets. When viewing this data it becomes apparent that the teeth of a single biological species are gradually evolving over time (most evident in the ontogentically adjusted loss of lateral cuslplets2.) This conclusion makes greater sense than the oceans swarming with various megatoothed sharks at any given point in time. However, from a paleontological perspective, there are characteristic-sets that transcend location and are clearly associated with a particular epoch/age. The 'chronospecies' serves that function for descriptive purposes -- a specific name ascribed for a particular characteristic-set. For purposes of this webpage we are including six broadly-defined chronospecies" (elasmo)

Toothpuller-

Thank you for taking the time to explain this. When I first responded to this thread, it was because I took issue with the quote that Harry posted about most paleontologist agreeing that megalodon was a recent species. Not all of them do and I posted two examples that had some reference to this fact. The part of the quote that really bothered me was that most paleontologist believed that they disappeared suddenly about 1.6 million years ago. They don't. I have never seen paper published where a paleontologist makes this claim. I wanted to see if anyone had a reference to this part of the quote because I have never seen one and I am open to seeing evidence of this. Like I said in the first sentence of my response, I'm not a believer in an Oligocene age for megalodon but some paleontologists are.

Now to the chronospecies concept. It uses gradualism to explain evolution and after Eldredge and Gould's paper on Punctuated equilibrium in the 1970s many evolutionary biologists have abandoned the concept of gradual evolution or at least believe it is less a factor in evolution than punctuated equilibrium. It is the long periods of stasis that allow people to recognize different species in the fossil record instead of constant change. Some people still believe in gradualism as the main form of evolution. I don't.

[non-remanié]

I believe this part is slightly incorrect. What we see in the case of the initial megatooth shark is, using your definition, cladogenesis, a definite branching from the Cretalamna line which continued on its own path. But starting with Otodus in the megatooth family tree we see slow evolution from one thing to another without any branching, a good choice for a chronospecies.

Lets take Cretalamna appendiculata which some people believe evolved into Otodus obliquus.

I'm not sure of the earliest record of C. appendiculata but it was definitely around during the Campanian some 83 million years ago. Still around largely unchanged in the Paleocene roughly 58 million years ago. Same species, little change for 25 million years. Sometime in the Paleocene Otodus obliquus pops up. Not just a new species but a new genus as well (sounds like a quick and rapid change to me). O. obliquus hangs around until the lutetian largely unchanged for roughly 15 million years. The two species hang around together during the Paleocene, not something that generally happens when one is slowly transforming into another.

[non-remanié]

Very elegantly stated, your explanation of the chronospecies usage. But since you knew it would create outrage, can we have some details on this late Maastrichtian Otodus? At least formation and state or country? There is definitely some funkiness with Cretalamna going on in that time period and I have been perplexed with the problem myself, but I'm not sure I am in the Cretaceous Otodus camp just yet. Cretalamna teeth tend to vary greatly over time and place and some at various times sure look like small Otodus.

One of the problems with defining a species by hard and fast lines is that those lines become very blurred when you look at any given animal. What do you call a meg some of whose lateral teeth have cusplets? Megalodon or chubutensis?

In South Carolina many of the megs which are found in the river, the lower teeth are very auriculatus like with narrow, thick rounded blades and large cusplets. The uppers are typical meg shaped.

Juveniles often have features of ancestral species. So if we find a 3 inch, chubutensis tooth, as an adult, it may completely lack cusplets completely. Is it a meg?

I have a juvenile Great White jaw. Most of the teeth have cusplets and some are only partially serrated. Isolated, those teeth would indicate a different species than the adult.

This where the concept of chronospecies come in. During X-time frame, most of the sharks of this type had X-type teeth. Some of the sharks had ancestral type teeth, some had more modern type teeth, some had a mixture of both. All the sharks can breed with each other so there is only 1 true species existing but for the sake of labeling them we will call them X-species.

Other side notes:

I have been to the Baja site. Much of the geology there is very confused and some of the formations highly inclined, indeed there are nearby volcanic cones. It appears that the meg teeth probably come from a Miocene deposit which is highly inclined but butts against a more shallow inclined Late Pliocene deposit, thus it would be easy to attribute the meg to the late Pliocene. In the late Pliocene formation, we came across several Parotodus teeth which typically are about 50 times less common than meg teeth and lots of Carcharodon teeth but not so much as a fragment of a meg. This is also the case in another late Pliocene deposit in Florida, where once again I found a Parotodus, several Carcharodon but not a single fragment of megalodon. If (and I think that it is a big if) megalodon survived until the latest Pliocene, I would think it would be in isolated areas and very rare.

Otodus. I have "Otodus" teeth from the late Maastrichtian which are essentially the same as or very similar to Paleocene Otodus teeth so Otodus goes back to the late Cretaceous. And since I know this is going to generate howls of outrage, here is a late Cretaceous tooth and a similar (not exactly the same tooth position) Paleocene tooth: (And yes, early Otodus have many Cretalamna type features).

Cretaceous:

Paleocene:

[Paleoc]

Very elegantly stated, your explanation of the chronospecies usage. But since you knew it would create outrage, can we have some details on this late Maastrichtian Otodus? At least formation and state or country? There is definitely some funkiness with Cretalamna going on in that time period and I have been perplexed with the problem myself, but I'm not sure I am in the Cretaceous Otodus camp just yet. Cretalamna teeth tend to vary greatly over time and place and some at various times sure look like small Otodus.

Near the bottom of the Severn formation, Prince Georges county, MD. A couple of feet above the contact with the Matawan formation.

Another specimen from the location, which at 2 inches is not a small tooth.

[Al Dente]

In this entire thread we still have yet to get a complete answer to the original question from someone with a lot of firsthand experience and a solid geological background. I believe my and Paleoron's answers are pretty good, but obviously not many local collectors understand the issue any better at all because we still haven't really gotten a real answer out of the many low country fossil hunters. Yes, its probably a lag at the top of the Chandler Bridge. A lag of exactly what??? I would like to know the whole story.

I don't know if there is a good answer for this. In North Carolina there is a pebbly lag deposit on top of many outcrops and quarries that contain a mixture of fossils from different epochs including fossils older than the formations found below them. When I look up descriptions of the strata in professional papers I get descriptions similar to the following:

Silverdale quarry- Good descriptions of the strata and then for the lag depost on top of quarry: "Lag deposit of pebbles, cobbles phosphatized bone and teeth."

Belgrade quarry similar description: "Discoidal pebble lag on Pliocene surface".

As far as labeling these teeth, I would just put "Lag deposit above Chandler Bridge Formation. Summerville, SC" .

[tracer]

you may have already read it, but i noted a discussion here that sounds like it would be of benefit to me were i to hunt fossils in the area in question.

[non-remanié]

I think these teeth have been included within Cretalamna appendiculata by those more knowledgable than myself. I'm not saying I know any better... I too might think the same as you and call them Otodus and this is part of the problem and confusing situation I referred to. Especially upper anteriors like this 2" tooth. I have seen similarly large specimens of especially upper C. appendiculata from the early Campanian or maybe Santonian. Morphology and definitely size seem to vary quite a bit within Cretalamna and is quite dependent on exact time and place it seems. Perhaps it is a critical part and essence of Cretalamna that led to its birth of the megatooth line, the variability and adaptability built into their DNA over time? Cretalamna has been described as eurytopic marine (able to live in a variety of marine habitats), but with a preference for deep water (Earl Manning pers comm). Perhaps their cosmopolitan nature and adaptability built up over time led to some that live primarily in shallow-waters and then others that prefered deeper water, but somehow did not differentiate into multiple species. Perhaps that is what we are seeing with the variability in size and morphology from different sites; those from shallow water faunas and those from sites with a more rare deeper water element? Just a small sample of what I'm talking about... C. appendiculata from the eocene Nanjemoy fm of Virginia are very similar in size and morphology to the late Campanian forms commonly found in NJ that never get very large. However, the paleocene Aquia fm. form is a little different with some tooth positions. And then some of those older early Campanian ones that approach sizes of 2" for anteriors. Perhaps this is more reason why they should all be included in the old name for the line; Otodus appendiculatus Agassiz, 1843.

Near the bottom of the Severn formation, Prince Georges county, MD. A couple of feet above the contact with the Matawan formation.

Another specimen from the location, which at 2 inches is not a small tooth.

[Auspex]

toothpuller, that's some good, well-reasoned thinking, and would form the basis for a good research paper (no matter where it lead).

[siteseer]

This is the other reference on a Late Pliocene occurrence of megalodon:

Ashby, J.R. and J.A. Minch. 1984.

The Upper Pliocene San Diego Formation and the Occurrence of Carcharodon megalodon at La Joya, Tijuana, Baja California, Mexico. In J.A. Minch and J.R. Ashby (eds.). 1984. Miocene and Cretaceous Depositional Environments, northwestern Baja California, Mexico. Pacific Section AAPG Volume 54.

As I noted above, some paleontologists question the age of the megalodon tooth, suggesting that it washed out of a Miocene formation. However, if so, other "Miocene-only" fossils should have been found also. The report does not mention any other finds unusual for the Late Pliocene.

Thanks for the link for the Kemp reference. I had tried to locate this publication a few years ago but was unsuccessful. The Cameron Inlet Formation is shown in this paper from 2005 and it is described as early to late Pliocene. It does appear to be younger than the base of the Yorktown where megs are routinely found.

Memoirs of Museum Victoria 62(1): 67–89 (2005)

ISSN 1447-2546 (Print) 1447-2554 (On-line)

http://www.museum.vi...moirs/index.asp

Pliocene marine mammals from the Whalers Bluff Formation of Portland,

Victoria, Australia

[Angus Stydens]

I am very late discovering this thread, but I thought I would put my two cent's worth in. I have been collecting the oligocene beds in Summerville since the mid 1960's, spending untold thousands of hours working the Chandler Bridge and Ashley formations. In all my years of digging in both, I have never, ever seen a single tooth that I would call a megalodon in these formations. By megalodons, I mean the standard shapes and configurations of such teeth as found in the rivers in coastal S.C. When the original poster asked where the megalodons are found in Summerville, I assume he is talking about the typical, run of the mill megs. I do think there are collectors who think they have found 5 or even 6 inch megs in the Chandler Bridge formation, but I would be willing to bet anything that they actually found them in the Wando formation, which is Pleistocene in age (130,000-70,000 ybp). There was a lot of reworking of fossils when the Wando was deposited, and I believe that the marine fossils found in this layer are partly those that were re-deposited when encroaching oceans scoured away Miocene (and possibly Pliocene) beds. I have not seen any publications to support it, but I also believe that some marine fossils found in the Wando are actually Pleistocene in age, too. Within the Wando, you will find angustidens and megalodons (reworked from oligocene and miocene/pliocene beds) mixed in with a huge number of terrestrial fossils, ranging from micro to megafauna species. The Wando formation is very commonly found directly overlying the Chandler Bridge, and to the casual collector, they look practically identical. If you did not see any Pleistocene fossils on the surface of the Wando, you could swear you were walking on the Chandler Bridge. Both formations are extremely similar in color and other than key fossils present, you can only tell the difference by examining the texture and clay content of the two layers. Because of this great similarity, it is very easy for a collector to "find a meg in the Chandler Bridge" when actually it is a reworked specimen in the Wando.

I collected with and talked to a geologist with the USGS for several years during the mid to late eighties when he and a crew worked in the N.Charleston, Summerville and outlying areas drilling core samples. His name is Rob Weems. He and his crew were trying to determine the location of the major fault(s)that was responsible for the major earthquake that hit Charleston in the 1880's. I asked him directly about the Hawthorne formation since I had heard so many collectors say that they found megs in this formation in Summerville. He told me that based on his core samples over the years that he had never seen any evidence of the Hawthorne in Summerville or in the immediately surrounding areas. He indicated that it was present mainly in Ga. and northern Fla. (if I recall correctly). He did not mention the record of invertebrates being found in this layer in Jasper County, S.C.

By the way, another formation where re-worked megs are found is in the Ten Mile Hill beds, which are dated at 240,000-200,000 ybp. Again, in these beds you will find a mixture of re-worked Miocene and Oligocene marine fossils, and Pleistocene terrestrial fossils. The descriptions of these and other Pleistocene beds can be found in a book authored by Albert E.Sanders from the Charleston, S.C. Museum. The book is entitled "Additions to the Pleistocene Mammal Faunas of South Caroline, North Carolina and Georgia".

Personally, if I had to guess why so many collectors think that the megs in Summerville are coming out of the Hawthorne formation is because the closest formation (in proximity to Summerville)with Miocene megs reported is the Hawthorne, even though these beds may be in southern Ga. or northern Fla. This is just my guess though, and I may be wrong.