Sharktooth Hill weirdness - oddball shark tooth

[siteseer]

This tooth was collected in the Sharktooth Hill Bonebed by Bob Ernst back around 1994-1995.  At the time he and I thought it was a weird Parotodus because it appears to have a bourlette.   The form wasn't really a good match otherwise.  It's just over 1 7/8 inches along the slant and about 3/8 inches in labiolingual thickness.  The cutting edges are underrated with no hint of lateral cusplets  The tip is chipped but it doesn't appear to have been damaged when it was collected.

 

Now, I think it's the giant thresher, Alopias grandis, but seems irregular for that as it basal outline of the root isn't a broader U-shape - maybe a jaw position variation or a regional variation.  The apparent bourlette could be just the way some of the enameloid wore off.  I don't think I've seen another tooth like this one from the STH Bonebed - thought the forum might want to see something oddball.  I was inspired by that weird spiny thing that Marco posted a photo of.

 

Jess

[ynot]

Nice tooth Jess.

Wish I could help, but I know nothing.

 

[sixgill pete]

Jess, I can see how you would think it could be either of those. But other than that, I cannot offer any help.

[siteseer]

Tony and Don,

 

It's weird.  I've been meaning to get photos of it for years.  I actually have one with a few other teeth but it's part of an old group shot - attached.

 

The tooth on the top row in the middle is the largest STH Parotodus I have and the C. hastalis tooth on the end is the largest "caramel-tipped" one I have (Northern Shark has an even bigger one).  The  first tooth on the bottom is one of the largest hastalis I have found (two uppers and one lower at 2 5/8 inches).  The tooth in the middle is a bit of a mystery too because I think it's a Parotodus but the root lobes don't seem bulky enough.  The tooth on the end is another oddball that makes me wonder if it's an upper intermediate of a Parotodus.

 

Jess 

[Al Dente]

I think the tooth has more features in common with Alopias grandis than with Parotodus.

[MarcoSr]

2 hours ago, Al Dente said:

I think the tooth has more features in common with Alopias grandis than with Parotodus.

 

I agree with Eric.  It looks more like an Alopias grandis to me also.

 

Marco Sr.

[Troodon]

Very nice and cool tooth with features of both species.  Not seeing an A. grandis with that well formed bourlette and looks natural.  This along with the root shape and thickness leans me more toward parotodus.

[Boesse]

The root is very otodontid like with a lingual torus, and the dental band seals the deal for me. I think this is an unusual Parotodus.

[Northern Sharks]

Right off the bat, the first tooth looks like A.grandis, but the more you look at the details.........?

Love the Parotodus in the group shot too

[siteseer]

Now, you all know why I call it "weirdness."

[sagacious]

Jess,

 

Thanks for posting these photos. Alopias teeth are of interest to me, and this is an interesting tooth. However, I think it fits into the natural range of crown and root variation of Alopias grandis very well.

 

A lateral view photo would likely help settle this, but I don't see the pronounced lingual torus characteristic of P benedeni. I do see what is likely abrasive wear on the lingual surface, at the central margin of the root and crown, which leads to what resembles a chevron-shaped dental ligament scar, or bourlette. Wear at this same location is common on A grandis teeth subjected to wave wear, and images of A grandis teeth with such wear can be found with a web search. The significance of this specific issue cannot be overstated, and a conservative and cautious point of view may be beneficial here, because the appearance of a bourlette on this tooth is exceedingly prejudicial with respect to this tooth's identity. I agree with your assessment that the "apparent bourlette" may simply reflect wear to the enameloid.

 

Has this tooth been dipped in a consolidant? Would it be possible to see a lateral and/or basal photo?

 

If the 'bourlette' is seen to be enameloid wear, and the height of the lingual torus is shown to be uncharacteristic of P benedeni, then the identity of this tooth would be uncontroversial: A grandis. I agree with the ID assessments of Al Dente and Marco Sr.

 

Better photos would be helpful, but I agree with your suspicion that the smaller tooth with the compressed U-shaped root may be a P benedeni intermediate.

 

Regards,

Eric

[powelli1]

Well the more I look at it the more it looks like a 5th or 6th upper right lateral tooth from Parotodus benedeni to me. I have five Parotodus teeth from the Lee Creek Mine in Aurora, NC and from other places that look just like this tooth and the size it right also. I have collected around 150 Parotodus teeth over the last 30 years and 114 of those are from an associated dentition I collected from the Lee Creek Mine. The last few lateral teeth tends to thin out unlike the first few anterior & lateral upper & lower that are very robust teeth, the lower teeth of most Parotodus are even more robust across the jaw and as in most Sharks the upper teeth are thinner for cutting and the lowers to grasp & hold on to the prey. So for the last few upper lateral and posterior they get thinner with the teeth that I have seen and collected. Jess I hope this helps some. George 

[MarcoSr]

9 hours ago, powelli1 said:

Well the more I look at it the more it looks like a 5th or 6th upper right lateral tooth from Parotodus benedeni to me. I have five Parotodus teeth from the Lee Creek Mine in Aurora, NC and from other places that look just like this tooth and the size it right also. I have collected around 150 Parotodus teeth over the last 30 years and 114 of those are from an associated dentition I collected from the Lee Creek Mine. The last few lateral teeth tends to thin out unlike the first few anterior & lateral upper & lower that are very robust teeth, the lower teeth of most Parotodus are even more robust across the jaw and as in most Sharks the upper teeth are thinner for cutting and the lowers to grasp & hold on to the prey. So for the last few upper lateral and posterior they get thinner with the teeth that I have seen and collected. Jess I hope this helps some. George 

 

You definitely have to trust George's opinion.  He has collected personally more Parotodus by far than anyone else that I'm aware of.

 

I sent a link to this post to researcher Bretton Kent who published a paper with George on George's associated Parotodus dentition.  Brett also believes the tooth is a Parotodus.  He also stated in his e-mail " I certainly think it's possible the giant threshers were in the Pacific, but haven't seen one yet."   So if anyone does have a giant thresher from the West Coast, please let me know.

 

Marco Sr.

 

[siteseer]

On 4/29/2017 at 4:42 PM, sagacious said:

Jess,

 

Thanks for posting these photos. Alopias teeth are of interest to me, and this is an interesting tooth. However, I think it fits into the natural range of crown and root variation of Alopias grandis very well.

 

A lateral view photo would likely help settle this, but I don't see the pronounced lingual torus characteristic of P benedeni. I do see what is likely abrasive wear on the lingual surface, at the central margin of the root and crown, which leads to what resembles a chevron-shaped dental ligament scar, or bourlette. Wear at this same location is common on A grandis teeth subjected to wave wear, and images of A grandis teeth with such wear can be found with a web search. The significance of this specific issue cannot be overstated, and a conservative and cautious point of view may be beneficial here, because the appearance of a bourlette on this tooth is exceedingly prejudicial with respect to this tooth's identity. I agree with your assessment that the "apparent bourlette" may simply reflect wear to the enameloid.

 

Has this tooth been dipped in a consolidant? Would it be possible to see a lateral and/or basal photo?

 

If the 'bourlette' is seen to be enameloid wear, and the height of the lingual torus is shown to be uncharacteristic of P benedeni, then the identity of this tooth would be uncontroversial: A grandis. I agree with the ID assessments of Al Dente and Marco Sr.

 

Better photos would be helpful, but I agree with your suspicion that the smaller tooth with the compressed U-shaped root may be a P benedeni intermediate.

 

Regards,

Eric

 

Hi Eric,

 

I don't have the profile shot but at its greatest thickness, it's 3/8 inches so that is not much of a lingual protuberance.  So many terms synonymous with "bourlette," the one I was taught in the late 80's though the technical term in English at the time was "neck," I believe.  I saw "dental band" in the 90's.  Anyway, I think it is unusual wear rather than a bourlette but it sure looks original.

 

Yes, Bob Ernst liked to use glyptol as a consolidant.  It worked but it also made the specimen more yellow-to-green than it was.  I should clean it off and use Paraloid.

 

Yeah, when I saw that smaller tooth and its root, I knew it couldn't be a posterior but could be the intermediate position you never get a good view of.  That's another tooth that should be photographed.

 

Thanks for commenting.

 

Jess

 

 

 

 

 

 

[siteseer]

On May 1, 2017 at 6:32 PM, MarcoSr said:

 

You definitely have to trust George's opinion.  He has collected personally more Parotodus by far than anyone else that I'm aware of.

 

I sent a link to this post to researcher Bretton Kent who published a paper with George on George's associated Parotodus dentition.  Brett also believes the tooth is a Parotodus.  He also stated in his e-mail " I certainly think it's possible the giant threshers were in the Pacific, but haven't seen one yet."   So if anyone does have a giant thresher from the West Coast, please let me know.

 

Marco Sr.

 

 

 

Marco Sr.,

 

Yes, wow, it's great to get George's and Dr. Kent's opinion.  George with his almost unmatched experience with Parotodus and Bretton Kent who might be the one person matching that experience along with his general shark and biomechanics angle.  I have that paper - part of an interesting volume to have.  

 

It's tough, though.  I have conflicting opinions from people I respect including those who don't think they were helping.

 

Jess  

 

[sagacious]

14 hours ago, siteseer said:

 

Hi Eric,

 

I don't have the profile shot but at its greatest thickness, it's 3/8 inches so that is not much of a lingual protuberance.  So many terms synonymous with "bourlette," the one I was taught in the late 80's though the technical term in English at the time was "neck," I believe.  I saw "dental band" in the 90's.  Anyway, I think it is unusual wear rather than a bourlette but it sure looks original.

 

Yes, Bob Ernst liked to use glyptol as a consolidant.  It worked but it also made the specimen more yellow-to-green than it was.  I should clean it off and use Paraloid.

 

Yeah, when I saw that smaller tooth and its root, I knew it couldn't be a posterior but could be the intermediate position you never get a good view of.  That's another tooth that should be photographed.

 

Thanks for commenting.

 

Jess

 

Hey Jess,

 

Thanks for the reply.  It's always interesting how each tooth in a collection has something interesting to say.

 

The modern anatomical terms used to describe shark teeth is also an interesting subject to me, in that it reflects a bit of the history of the study of fossil shark teeth, which is (still) somewhat separate from other paleontological studies.  I'm not sure who first applied the term 'bourlette' to shark teeth, but it may possibly have been Louis Agassiz, in his early-mid 1800's Recherches sur les poissons fossils.

 

For those unfamiliar, "bourrelet" is a French term, long applied to the forward bearing surface or rotating band on an artillery projectile.  A quick look at a diagram of an artillery shell will show immediately the similarity of placement and appearance of this rotating band, and the bourlette on a shark tooth.  Shark teeth are often projectile-shaped, for example, hastalis means "like a spear," so the connection is a natural one.  "Bourrelet" was at some point Americanized to "bourlette," and presto, we have a French-American anatomical term of reference that has tenaciously resisted the practice of using Greek or Latin for modern anatomical terminology.

 

"Neck" seems slightly ambiguous, and leaves room for confusion, since "neck" also describes a general area of the tooth, so it seems like another term is needed for specific anatomical elements at that location.  "Dental band" is likewise nonspecific.  Neither term describes precisely the location, function, and relevance of the thing we're trying to name.  A bourlette is actually the scar from the periodontal ligament that helps hold the shark tooth in place. 

 

Periodontal (or dental, for short) ligament scar seems to describe this better than anything else, and leaves zero room for ambiguity.  If Louis Agassiz were around today, no doubt he'd find all this STH weirdness très intéressant!

 

Eric

[MarcoSr]

26 minutes ago, siteseer said:

 

 

Marco Sr.,

 

Yes, wow, it's great to get George's and Dr. Kent's opinion.  George with his almost unmatched experience with Parotodus and Bretton Kent who might be the one person matching that experience along with his general shark and biomechanics angle.  I have that paper - part of an interesting volume to have.  

 

It's tough, though.  I have conflicting opinions from people I respect including those who don't think they were helping.

 

Jess  

 

 

Jess

 

I totally respect George and Dr. Bretton Kent.  I've been looking at a lot of different extant shark jaws over the last two years and have purchased a good number of them.  I have been struck by the wide variation of tooth features of a species not only between tooth features in different jaws of the same species but also by variation of tooth features even in individual jaws themselves.  And I'm not talking about pathological differences caused by injury.  So I'm not surprised at all when fossil tooth features are confusing and seem to differ from the norm for a species.  I guess you really need to look at the most likely possibility for this tooth.  Even though it could be an unusual giant thresher (which I still lean to in my heart based upon the labial view of your tooth), giant threshers are not reported from the fauna or anywhere else in the Pacific that I'm aware of.  And although Parotodus are pretty rare from the fauna, they are reported from it.  So there is a much higher probability of an unusual Parotodus being collected from the fauna than an unusual giant thresher.  Also tooth position variation in tooth features like root thickness as George stated in his post or time period variation of the Miocene versus Pliocene tooth features like root thickness as Brett explained to me for Parotodus can explain the less than expected root thickness.

 

Marco Sr. 

[siteseer]

On 5/4/2017 at 6:49 PM, sagacious said:

 

Hey Jess,

 

Thanks for the reply.  It's always interesting how each tooth in a collection has something interesting to say.

 

The modern anatomical terms used to describe shark teeth is also an interesting subject to me, in that it reflects a bit of the history of the study of fossil shark teeth, which is (still) somewhat separate from other paleontological studies.  I'm not sure who first applied the term 'bourlette' to shark teeth, but it may possibly have been Louis Agassiz, in his early-mid 1800's Recherches sur les poissons fossils.

 

For those unfamiliar, "bourrelet" is a French term, long applied to the forward bearing surface or rotating band on an artillery projectile.  A quick look at a diagram of an artillery shell will show immediately the similarity of placement and appearance of this rotating band, and the bourlette on a shark tooth.  Shark teeth are often projectile-shaped, for example, hastalis means "like a spear," so the connection is a natural one.  "Bourrelet" was at some point Americanized to "bourlette," and presto, we have a French-American anatomical term of reference that has tenaciously resisted the practice of using Greek or Latin for modern anatomical terminology.

 

"Neck" seems slightly ambiguous, and leaves room for confusion, since "neck" also describes a general area of the tooth, so it seems like another term is needed for specific anatomical elements at that location.  "Dental band" is likewise nonspecific.  Neither term describes precisely the location, function, and relevance of the thing we're trying to name.  A bourlette is actually the scar from the periodontal ligament that helps hold the shark tooth in place. 

 

Periodontal (or dental, for short) ligament scar seems to describe this better than anything else, and leaves zero room for ambiguity.  If Louis Agassiz were around today, no doubt he'd find all this STH weirdness très intéressant!

 

Eric

 

 

Eric,

 

I have been looking for where I had the "bourlette conversation" before.  Years ago, someone asked about the origin of the word and we talked about it.  I don't think it was here.  "Bourrelet" also has similar translations as a "cushion" or "pad" with my understanding being that it refers to a buffer zone of sorts as the bourlette visually separates the crown from the root on the lingual face.  Google Translator came up with "bead:" which does not make sense.  Yes, it is interesting to try tracking how anatomical terms have changed and why no standard has ever been agreed upon in English at least.  There just seems to be this understanding that there are at least two different words at any one time for a tooth feature. 

 

Some terms are from the French. perhaps influenced by researchers/collectors who have read Leriche's work from the first half of the 20th century.  A popular shark tooth ID guide of the 1960's was "Kelley's Guide to Shark Teeth" and the author seemed to base names on Leriche (1942), a review of fish fossils from the Atlantic Coastal Plain and Gulf Coast of North America, in particular.  For instance, I have seen references to the posteriormost tooth in the jaws as the" commissural tooth" which is from the French "commissure," the corner of the mouth.  In English we talk about the "heels" of the crown (lateral extensions of the main cusp) and that is a direct translation of "talons" in French.  Some researchers call the heels "blades" though I think this is also from old usage.

 

And then there's the use of "principal" teeth, meaning the uppers.  I'm not sure where that came from but that goes back to at least the 60's as well.  Collectors did use the term "lowers" at the time.  I thought "principal" could have been a mistranslation of "superieur."  Another level of confusion can be reached when you see an Ebay auction for a "principle" tooth.

 

I think "neck" is also from French ("cou") but I can't find a reference with that term.  I have seen French/Belgian authors use "sillon linguale," or lingual groove or "lunule" referring to the crescent moon-like shape.

 

The bourlette seems to be tooth character in larger shark teeth.  It makes sense a stronger ligament might be necessary to help strengthen the connection between a larger, bulkier tooth, as in Carcharocles or Parotodus, and the jaw.  A stronger ligament would leave a mark, but then, why wouldn't there one on Carcharodon hastalis or C. carcharias teeth or Isurus oxyrinchus, some teeth of which did get rather chunky relative to their length?  I have seen somewhere in the past that a researcher referred to the bourlette as a ligament scar.

 

It's weird that scientists would allow this level of imprecision in terminology across time but even long-dead sharks can present a moving target as people try to identify their teeth with some level of confidence. 

 

Jess

 

 

 

 

 

[siteseer]

On 5/4/2017 at 7:55 PM, MarcoSr said:

 

Jess

 

I totally respect George and Dr. Bretton Kent.  I've been looking at a lot of different extant shark jaws over the last two years and have purchased a good number of them.  I have been struck by the wide variation of tooth features of a species not only between tooth features in different jaws of the same species but also by variation of tooth features even in individual jaws themselves.  And I'm not talking about pathological differences caused by injury.  So I'm not surprised at all when fossil tooth features are confusing and seem to differ from the norm for a species.  I guess you really need to look at the most likely possibility for this tooth.  Even though it could be an unusual giant thresher (which I still lean to in my heart based upon the labial view of your tooth), giant threshers are not reported from the fauna or anywhere else in the Pacific that I'm aware of.  And although Parotodus are pretty rare from the fauna, they are reported from it.  So there is a much higher probability of an unusual Parotodus being collected from the fauna than an unusual giant thresher.  Also tooth position variation in tooth features like root thickness as George stated in his post or time period variation of the Miocene versus Pliocene tooth features like root thickness as Brett explained to me for Parotodus can explain the less than expected root thickness.

 

Marco Sr. 

 

 

 

Hi Marco Sr.,

 

Yes, I was thinking about you today when I saw that new post about a newly-published article on identifying Carcharhinus teeth (which also reminded me of Naylor and Marcus, 1994).  Of all people you would know how shark tooth morphologies can converge on the most efficient form for processing particular prey within the limits of basic tooth structure and that means unrelated forms can approach each other in tooth shape and character details just as closely-related forms might not distinguish themselves consistently.  We all operate under the assumption that sharks can almost always be identified by their teeth even as we understand that the teeth may be the slowest part of the body to change over time.  The teeth in any file in a shark's jaws are not going to be identical, and like you said, even when there is no pathology.  It's why paleontologists, some at least, try to restrain themselves from naming a new taxon based on one or a few teeth when the specimens exhibit some character that varies a little from the norm.

 

Actually, the serrated thresher is present in the Sharktooth Hill Bonebed.  It's just present at a level of rarity beyond Parotodus.  Elasmo.com has a pretty good scale of rarity (see the Aquia Formation under Faunas) with "Rare" being one or two specimens found per year by all collectors.  An even higher level might be "Exceptionally Rare," reserved for taxa of which one or two specimens might be found in a lifetime of collecting.  I think this has been discussed on the forum before but Bob Ernst found one in the 80's or early 90's.  Another collector I know found one in the 60's.  It's quite possible that other collectors have been equally lucky and the teeth were considered  just "weird-looking" megs.  The fact that other specimens haven't shown up at shows tells me that they have been exceptionally rare finds. 

 

I get the feeling that the serrated thresher at least only rarely visited coastal areas of the Pacific.

 

Is the serrated thresher found in the same bed with A. grandis on the east coast?  I was always under the assumption that grandis was an Early Miocene form and the serrated one was younger but perhaps not reaching the Late Miocene.

 

Jess

 

 

[sagacious]

3 hours ago, siteseer said:

Eric,

 

I have been looking for where I had the "bourlette conversation" before.  Years ago, someone asked about the origin of the word and we talked about it.  I don't think it was here.  "Bourrelet" also has similar translations as a "cushion" or "pad" with my understanding being that it refers to a buffer zone of sorts as the bourlette visually separates the crown from the root on the lingual face.  Google Translator came up with "bead:" which does not make sense.  Yes, it is interesting to try tracking how anatomical terms have changed and why no standard has ever been agreed upon in English at least.  There just seems to be this understanding that there are at least two different words at any one time for a tooth feature. 

 

Some terms are from the French. perhaps influenced by researchers/collectors who have read Leriche's work from the first half of the 20th century.  A popular shark tooth ID guide of the 1960's was "Kelley's Guide to Shark Teeth" and the author seemed to base names on Leriche (1942), a review of fish fossils from the Atlantic Coastal Plain and Gulf Coast of North America, in particular.  For instance, I have seen references to the posteriormost tooth in the jaws as the" commissural tooth" which is from the French "commissure," the corner of the mouth.  In English we talk about the "heels" of the crown (lateral extensions of the main cusp) and that is a direct translation of "talons" in French.  Some researchers call the heels "blades" though I think this is also from old usage.

 

And then there's the use of "principal" teeth, meaning the uppers.  I'm not sure where that came from but that goes back to at least the 60's as well.  Collectors did use the term "lowers" at the time.  I thought "principal" could have been a mistranslation of "superieur."  Another level of confusion can be reached when you see an Ebay auction for a "principle" tooth.

 

I think "neck" is also from French ("cou") but I can't find a reference with that term.  I have seen French/Belgian authors use "sillon linguale," or lingual groove or "lunule" referring to the crescent moon-like shape.

 

The bourlette seems to be tooth character in larger shark teeth.  It makes sense a stronger ligament might be necessary to help strengthen the connection between a larger, bulkier tooth, as in Carcharocles or Parotodus, and the jaw.  A stronger ligament would leave a mark, but then, why wouldn't there one on Carcharodon hastalis or C. carcharias teeth or Isurus oxyrinchus, some teeth of which did get rather chunky relative to their length?  I have seen somewhere in the past that a researcher referred to the bourlette as a ligament scar.

 

It's weird that scientists would allow this level of imprecision in terminology across time but even long-dead sharks can present a moving target as people try to identify their teeth with some level of confidence. 

 

Jess

 

Jess,

 

Thanks very much for that backstory and insights.  I reckon you're right that English-speaking fossil shark researchers, in using borrowed terminology, have left us with a variety of sometimes confusing terms for the same structures.  I'm sure this multiplicity of terms presents quite a bit of ambiguity to those new to fossil shark tooth collecting, while researching and trying to better understand their finds.

 

Google translate is often sort of ambiguous as well. In the case of bourrelet, I think "pad" is possibly more synonymous with "bearing surface," and "bead" is synonymous with "strip or stripe," as in a bead of caulking.  That may shed better light on any possible connections there.

 

Most of the great white shark teeth I have don't show a very distinct dental ligament scar, and those that are wave-worn often show no hint of one -- like we get from the deposits here on the West Coast some places.  In comparison with Carcharocles teeth, the Carcharodon ligament scar is much reduced and may/may not be present as an enameloid marking, and even on a pristine tooth, it's often hard to see without using a hand lens.  The dental ligament scar may, possibly, also be eroded by tannic river acidity while the root of the tooth weathers, and this may explain why one often hears that white shark teeth have no bourlette. 

 

For those who mostly recover their Carcharodon teeth waveworn, I've included a photo below with the bourlette/dental ligament scar shown.  The tooth is C hubbelli, with the ligament scar fairly distinct as a uniform-width non-enameloid strip between the crown and root.  The same can be seen on Isurus, but since the ligament scar doesn't intrude onto the crown as an enameloid chevron as in Parotodus or Carcharocles, it's best seen on a large, pristine tooth -- and with magnification.

 

Thanks as well for the reference to Kelley's Guide to Shark Teeth.  I'll see if I can find a copy somewhere.

 

Eric

[MarcoSr]

14 hours ago, siteseer said:

 

 

 

Hi Marco Sr.,

 

Yes, I was thinking about you today when I saw that new post about a newly-published article on identifying Carcharhinus teeth (which also reminded me of Naylor and Marcus, 1994).  Of all people you would know how shark tooth morphologies can converge on the most efficient form for processing particular prey within the limits of basic tooth structure and that means unrelated forms can approach each other in tooth shape and character details just as closely-related forms might not distinguish themselves consistently.  We all operate under the assumption that sharks can almost always be identified by their teeth even as we understand that the teeth may be the slowest part of the body to change over time.  The teeth in any file in a shark's jaws are not going to be identical, and like you said, even when there is no pathology.  It's why paleontologists, some at least, try to restrain themselves from naming a new taxon based on one or a few teeth when the specimens exhibit some character that varies a little from the norm.

 

Actually, the serrated thresher is present in the Sharktooth Hill Bonebed.  It's just present at a level of rarity beyond Parotodus.  Elasmo.com has a pretty good scale of rarity (see the Aquia Formation under Faunas) with "Rare" being one or two specimens found per year by all collectors.  An even higher level might be "Exceptionally Rare," reserved for taxa of which one or two specimens might be found in a lifetime of collecting.  I think this has been discussed on the forum before but Bob Ernst found one in the 80's or early 90's.  Another collector I know found one in the 60's.  It's quite possible that other collectors have been equally lucky and the teeth were considered  just "weird-looking" megs.  The fact that other specimens haven't shown up at shows tells me that they have been exceptionally rare finds. 

 

I get the feeling that the serrated thresher at least only rarely visited coastal areas of the Pacific.

 

Is the serrated thresher found in the same bed with A. grandis on the east coast?  I was always under the assumption that grandis was an Early Miocene form and the serrated one was younger but perhaps not reaching the Late Miocene.

 

Jess

 

 

 

Jess

 

There is a huge disconnect in how extant and fossil sharks are/were named.  Fossil sharks are/were named almost exclusively based upon tooth features because not much else was found in association.  Associated dentitions and vertebrae in some cases have helped.  Extant sharks are/were named based upon physical characteristics with tooth features in a lot of cases not even described.  There are a number of DNA studies being conducted on extant sharks.  I haven't really had the time to try to understand the impact of what has been published to date but fully expect major taxonomy revisions.

 

With respect to giant threshers, my sons and I have personally found 50+ from multiple sites in MD, VA, and NC.  At Plum Point in MD, you can find both serrate and non serrate giant threshers.  I used to believe years ago non serrate giant threshers appeared in zone 10 of the Calvert Formation and evolved into serrated giant threshers appearing in zone 11 and disappearing by zone 12.  However now we also find both serrate and non serrate nice condition giant threshers along the Potomac River at sites where you only have zones 14 and 15 of the Calvert Formation exposed.  The condition of the teeth implies that they are coming out of the exposures of zones 14 and 15 and not reworked from older zones.  My son Mel recently found a serrate excellent condition giant thresher tooth in situ from zone 14 of the Calvert Formation on the Pamunkey River in VA which was verified by testing of formation found around a cetacean specimen found in the same layer.  I used to believe the non serrate giant thresher evolved into the serrated giant thresher which then went extinct.  However now, I'm pretty convinced the non serrate giant thresher appeared first, evolved into the serrate giant thresher, but populations of non serrate giant threshers remained also.  Both populations seem to have become extinct by zone 15 of the Calvert Formation in MD and VA.  I have also found a non serrate giant thresher in the Lee Creek mine which came out of the Pungo River Formation (It is that funky green color like a lot of chubs from the Pungo River Formation) which equates to zones 3 or 4 of the Calvert Formation.  This could show non serrate giant threshers really appeared earlier in NC than MD. 

 

Bretton Kent is studying giant threshers and hopefully he will publish a paper that deals with both the time period and geographic range of both the serrate and non serrate giant thresher.  If you can PM me with contact information of the collectors with serrate giant threshers from STH I'll pass that on to Brett.

 

Marco Sr.

[Al Dente]

5 minutes ago, MarcoSr said:

 

 I used to believe years ago non serrate giant threshers appeared in zone 10 of the Calvert Formation and evolved into serrated giant threshers appearing in zone 11 and disappearing by zone 12.  However now we also find both serrate and non serrate nice condition giant threshers along the Potomac River at sites where you only have zones 14 and 15 of the Calvert Formation exposed.  The condition of the teeth implies that they are coming out of the exposures of zones 14 and 15 and not reworked from older zones.  My son Mel recently found a serrate excellent condition giant thresher tooth in situ from zone 14 of the Calvert Formation on the Pamunkey River in VA which was verified by testing of formation found around a cetacean specimen found in the same layer.  I used to believe the non serrate giant thresher evolved into the serrated giant thresher which then went extinct.  However now, I'm pretty convinced the non serrate giant thresher appeared first, evolved into the serrate giant thresher, but populations of non serrate giant threshers remained also.  Both populations seem to have become extinct by zone 15 of the Calvert Formation in MD and VA. 

 

This makes me wonder if serrated and non-serrated are from the same species. Some modern sharks have teeth that become serrated as the shark ages. Modern Hammerheads do this. I have also found modern Rhizoprionodon with serrated teeth even though most have non-serrated teeth.

[MarcoSr]

3 hours ago, Al Dente said:

 

This makes me wonder if serrated and non-serrated are from the same species. Some modern sharks have teeth that become serrated as the shark ages. Modern Hammerheads do this. I have also found modern Rhizoprionodon with serrated teeth even though most have non-serrated teeth.

 

Eric

 

Some, not all, young modern great whites have teeth that are only partially serrated with side cusplets.  I see this in some of the smaller great white jaws.  The cusplets disappear and the teeth fully serrate as the shark ages.

 

That is a very interesting possibility for the giant threshers.  Both the non serrated and serrated seem to have disappeared from the MD and VA faunas around the same time.  The non serrated seem to have appeared in the MD faunas earlier but the evolution could have been for the teeth to serrate as the shark aged rather than all ages having serrated teeth.  There are a number of shark fossil species where the young show ancestral traits which the adults loose.

 

Marco Sr.

[siteseer]

On 4/29/2017 at 4:42 PM, sagacious said:

Jess,

 

Thanks for posting these photos. Alopias teeth are of interest to me, and this is an interesting tooth. However, I think it fits into the natural range of crown and root variation of Alopias grandis very well.

 

A lateral view photo would likely help settle this, but I don't see the pronounced lingual torus characteristic of P benedeni. I do see what is likely abrasive wear on the lingual surface, at the central margin of the root and crown, which leads to what resembles a chevron-shaped dental ligament scar, or bourlette. Wear at this same location is common on A grandis teeth subjected to wave wear, and images of A grandis teeth with such wear can be found with a web search. The significance of this specific issue cannot be overstated, and a conservative and cautious point of view may be beneficial here, because the appearance of a bourlette on this tooth is exceedingly prejudicial with respect to this tooth's identity. I agree with your assessment that the "apparent bourlette" may simply reflect wear to the enameloid.

 

Has this tooth been dipped in a consolidant? Would it be possible to see a lateral and/or basal photo?

 

If the 'bourlette' is seen to be enameloid wear, and the height of the lingual torus is shown to be uncharacteristic of P benedeni, then the identity of this tooth would be uncontroversial: A grandis. I agree with the ID assessments of Al Dente and Marco Sr.

 

Better photos would be helpful, but I agree with your suspicion that the smaller tooth with the compressed U-shaped root may be a P benedeni intermediate.

 

Regards,

Eric

 

Hi Eric,

 

My brother recently took some photos for me - attached are profile views:

 

Jess

 

[Al Dente]

The side views make me think this is too thin to be Parotodus.