Extant Carcharhinus obscurus (Dusky Shark) jaw

[MarcoSr]

Here is a Carcharhinus obscurus (Dusky Shark) jaw that I recently acquired. The jaw is 17.5” wide and 9” inches high.

Here is the overall jaw:

To better see tooth details double clique the below pictures. If you mouse over the pictures you will see the file name which has additional positional information.

There are posts where unusual looking teeth get posted and identified as symphyseal teeth. Carcharhinus have both upper jaw and lower jaw symphyseal teeth. There is extreme variation in these symphyseal teeth and they are extremely difficult if not impossible to identify to a species.

Upper jaw symphysis with two files of symphyseal teeth (blue) and one file of medial teeth (red):

Lower jaw symphysis with one file of medial teeth:

Continued in the next reply:

Marco Sr.

Edited February 4, 2016 by MarcoSr

[MarcoSr]

Also extreme posterior teeth can widely vary and are extremely difficult if not impossible to identify to a species.

Upper jaw left and right side posterior teeth:

Lower jaw left and right side posterior teeth:

Here are the upper jaw A1 teeth left and right side:

Continued in the next reply:

Marco Sr.

.

Edited January 5, 2016 by MarcoSr

[MarcoSr]

Here are the lower jaw a1 teeth left and right side:

Here are some upper jaw lateral teeth left and right side:

Continued in the next reply:

Marco Sr.

Edited January 5, 2016 by MarcoSr

[MarcoSr]

Here are some lower jaw lateral teeth left and right side:

Here are pictures that show the number of rows of teeth in this jaw:

I can see at least 6 upper rows of teeth:

I can see 7 rows of lower teeth:

If you look closely at the tooth in the last row, you can see that it hasn't fully formed yet. (The root hasn't formed yet.)

The upper jaw has 15 tooth files left and 15 tooth files right of the symphyseal teeth.

The lower jaw has 16 tooth files left and 15 tooth files right of the medial tooth.

What makes individual tooth identification even more difficult is that there is a species variation which can make another Carcharhinus obscurus jaw and teeth slightly different because of shark age, gender, locality etc. To get a complete feel for Carcharhinus obscurus jaws and teeth you would really need to look at a lot of different jaws from different localities.

Marco Sr.

Edited January 5, 2016 by MarcoSr

[jcbshark]

Great pics as always It's pretty amazing how much teeth from the same shark can differ due to location.

[MarcoSr]

Great pics as always It's pretty amazing how much teeth from the same shark can differ due to location.

Jeff

I'm glad that the differences did show in the pictures that I posted because I wanted to show these differences so people can understand why it can be so difficult to identify an individual fossil tooth to a specific species. If I posted similar pictures for the other 30 or so Carcharhinus species it would show also how similar different species teeth can look. I really want to get a bull shark jaw next so I can see the differences first hand between bull and dusky teeth. I've always had problems telling them apart. However, seeing an entire jaw of teeth has helped me to see several tooth features that I hadn't really noticed before for dusky teeth.

Marco Sr.

[Doctor Mud]

Thanks for posting MarcoSr.

Seems like we are following a similar path, except you have many years experience on me in the fossil shark teeth department I believe :-)

The first jaw I decided I wanted to get was a Grey Nurse (Carcharias taurus) as I've acquired a bunch of fossil sand shark teeth from Morocco. In part thanks to sales and trades from TFF members (thanks guys!).

I've found that there are several species that are illegal to own remains from in Australia including Great White and Grey Nurse. There are replicas out there but not for the Grey Nurse :-( Not sure if this ban extends to the small toothed sand tiger (Ofontaspis ferox).

I totally understand and I'm supportive of the reasons for this by the way.

I guess you'd have to have a special permit for study to get these or visit a museum or institution for study.

Any problems like this in the states?

What jaws are you going to get next?

[isurus90064]

Hello MarcoSr, wonderful post, great photos and I could not agree more (looking at a lot of extant material really helps to understand), thank you!

[Coco]

Hi,

It is a great idea to do this topic. To understand the différences about teeth in a same jaw, it is very important to see a lot of recent jaws. It is why I have beginning to to a collection of them a lot of years ago...

I am very interesting in your next pics !

Coco

[MarcoSr]

Thanks for posting MarcoSr.

Seems like we are following a similar path, except you have many years experience on me in the fossil shark teeth department I believe :-)

The first jaw I decided I wanted to get was a Grey Nurse (Carcharias taurus) as I've acquired a bunch of fossil sand shark teeth from Morocco. In part thanks to sales and trades from TFF members (thanks guys!).

I've found that there are several species that are illegal to own remains from in Australia including Great White and Grey Nurse. There are replicas out there but not for the Grey Nurse :-( Not sure if this ban extends to the small toothed sand tiger (Ofontaspis ferox).

I totally understand and I'm supportive of the reasons for this by the way.

I guess you'd have to have a special permit for study to get these or visit a museum or institution for study.

Any problems like this in the states?

What jaws are you going to get next?

I won't buy any great white jaws or the very large tiger or mako jaws because they are a few of the sharks that are fished for to get the jaws for sale. The rest of the shark jaws come from the regular fishing industry where the sharks are caught for food (100 million per year). Great white jaws and grey nurse jaws are available for sale in the US on multiple websites. I thought the catching of great whites was banned worldwide but I see a lot of jaws coming out of Vietnam and China.

I already have another 17 jaws of different shark species and a wish list for another 28 species that I want to purchase. There are plenty of different shark species jaws on the market if you have the money. A bull shark jaw is what I want to purchase next.

Marco Sr.

[MarcoSr]

Hello MarcoSr, wonderful post, great photos and I could not agree more (looking at a lot of extant material really helps to understand), thank you!

Thank you. I have wanted to do this for a while and finally decided to do it.

Marco Sr.

[MarcoSr]

Hi,

It is a great idea to do this topic. To understand the différences about teeth in a same jaw, it is very important to see a lot of recent jaws. It is why I have beginning to to a collection of them a lot of years ago...

I am very interesting in your next pics !

Coco

Coco

I reached a point where reading books was no longer helping me to better id fossil shark teeth. Looking at the jaws I recently purchased has already helped a lot. I have a lot of different projects that I'm working on but hope to get some time to photograph the jaws each week.

Marco Sr.

[siteseer]

Hi MarcoSr,

Great thread. I think the most difficult thing to keep in mind for a fossil shark tooth collector, or even a fossil shark tooth researcher or two, is that modern sharks have not been (as a rule) officially named based on their teeth. In fact when you read general descriptions of shark species, very little is said about the teeth, and when they are mentioned, it's a quick sentence. On the other hand extinct sharks are defined in almost all cases by their teeth. Sometimes, teeth from the same locality that are very similar but with one form appearing a little larger/smaller or a little broader/narrower or with noticeably coarser/finer serrations are considered separate taxa. There never seems to be much leeway given in terms of intraspecific variation (in this case the range of tooth shapes within a species at a given jaw position). The localities that are rich in teeth offer an opportunity to see that variation within a few species.

It is only when we look at modern jaws, and if we're lucky, numerous jaws with great data and from reliable sources, that we get an idea of intraspecific variation. From that we get an idea of how narrowly we might have viewed extinct shark species.

Anyone interested in intraspecific variation but not sure if he/she is ready to invest in a lot of shark jaws should read an article with a title that focuses on a fossil shark tooth locality but also says at least one important thing about variation within a species. The article is:

Welton, B.J. and W.J. Zinmeister. 1980.

Eocene Neoselachians from the La Meseta Formation, Seymour Island, Antarctic Peninsula. Contributions in Science 329. Natural History Museum of Los Angeles County. 29 August 1980.

Within the discussion of myliobatoid teeth found at the site, the authors note that a preliminary analysis of over 300 modern Myliobatis californicus jaws (collected from two populations along the central and northern California coast) revealed that the arrangement of tooth rowgroups and the number and morphology of teeth in each row are highly variable. The range of variation transcends nearly all "genetically distinct dental patterns of other myliobatoids (including the lower but not the upper dentition of Aetobatus). Moreover, the sample includes examples of tooth variation that would also seem to cross generic boundaries even those of long-extinct forms (Igdabatis of the late Cretaceous of Niger; "Hypolophus"). Characters that had been considered to distinguish genera were found in the sample and may be more useful in separating male and female teeth or may only reflect the tooth production rate of a particular season.

While M. californicus is a ray and someone might say that its dentition might show more variation than is seen in any shark species, I think we can expect more variation in modern shark jaws of most species than is generally allowed for many named extinct species. In the 1800's and into the 1900's paleontologists gave names to partial teeth that would not hold up to later scrutiny and proposed multiple names to teeth that were later deemed all the same species. Starting with the work of Maurice Leriche in the early 1900's, shark researchers changed their focus from putting a name to isolated teeth to putting together dentitions, attempting to determine the variation within those dentitions. A lot of names have been synonymized but a lot of work remains to be done.

Years ago, I had the chance to talk to an ichthylogist about shark teeth. I asked him how many jaws he would like to have as a sample of a species in order to get an idea of tooth variation. He said it would have to be at least one hundred. I don't think the average natural history museum (even one near a coast) has near that many of any shark or ray. Maybe no museum does.

It will be interesting to see what you learn from the jaws you acquire. You might even think about buying damaged jaws. If you can get a decent quadrant out of a set, I would expect a dealer to be willing to work with you on price for a broken set he would have trouble selling to anyone else. You could soak out the teeth and display them to show the functional row and the individual tooth files which would also allow the roots to be seen (as discussed and figured in Cunningham, 1999 - http://www.elasmo.com/bin/sc_download.html.)

Jess

I really believe that to be able to successfully understand and identify fossil shark teeth you need to understand and be very familiar with extant shark teeth. As a result, I’m in the process of acquiring a good number of extant shark jaws which I intend to study and photograph. Here is a Carcharhinus obscurus (Dusky Shark) jaw that I recently acquired. The jaw is 17.5” wide and 9” inches high. I’m not trying to acquire the very large grade A type specimens (Wow they cost a lot) but study quality specimens (I can barely afford these).

There are posts where unusual looking teeth get posted and identified as symphyseal teeth. Carcharhinus have both upper jaw and lower jaw symphyseal teeth. There is extreme variation in these symphyseal teeth and they are extremely difficult if not impossible to identify to a species.

Edited December 16, 2015 by siteseer

[siteseer]

This topic has been brought up before. Check out this great thread:

http://www.thefossilforum.com/index.php?/topic/15407-let-me-see-your-recent-selachian-jaws/?hl=%22recent+jaws%22

Hi,

It is a great idea to do this topic. To understand the différences about teeth in a same jaw, it is very important to see a lot of recent jaws. It is why I have beginning to to a collection of them a lot of years ago...

I am very interesting in your next pics !

Coco

[MarcoSr]

Hi MarcoSr,

Great thread. I think the most difficult thing to keep in mind for a fossil shark tooth collector, or even a fossil shark tooth researcher or two, is that modern sharks have not been (as a rule) officially named based on their teeth. In fact when you read general descriptions of shark species, very little is said about the teeth, and when they are mentioned, it's a quick sentence. On the other hand extinct sharks are defined in almost all cases by their teeth. Sometimes, teeth from the same locality that are very similar but with one form appearing a little larger/smaller or a little broader/narrower or with noticeably coarser/finer serrations are considered separate taxa. There never seems to be much leeway given in terms of intraspecific variation (in this case the range of tooth shapes within a species at a given jaw position). The localities that are rich in teeth offer an opportunity to see that variation within a few species.

It is only when we look at modern jaws, and if we're lucky, numerous jaws with great data and from reliable sources, that we get an idea of intraspecific variation. From that we get an idea of how narrowly we might have viewed extinct shark species.

Anyone interested in intraspecific variation but not sure if he/she is ready to invest in a lot of shark jaws should read an article with a title that focuses on a fossil shark tooth locality but also says at least one important thing about variation within a species. The article is:

Welton, B.J. and W.J. Zinmeister. 1980.

Eocene Neoselachians from the La Meseta Formation, Seymour Island, Antarctic Peninsula. Contributions in Science 329. Natural History Museum of Los Angeles County. 29 August 1980.

Within the discussion of myliobatoid teeth found at the site, the authors note that a preliminary analysis of over 300 modern Myliobatis californicus jaws (collected from two populations along the central and northern California coast) revealed that the arrangement of tooth rowgroups and the number and morphology of teeth in each row are highly variable. The range of variation transcends nearly all "genetically distinct dental patterns of other myliobatoids (including the lower but not the upper dentition of Aetobatus). Moreover, the sample includes examples of tooth variation that would also seem to cross generic boundaries even those of long-extinct forms (Igdabatis of the late Cretaceous of Niger; "Hypolophus"). Characters that had been considered to distinguish genera were found in the sample and may be more useful in separating male and female teeth or may only reflect the tooth production rate of a particular season.

While M. californicus is a ray and someone might say that its dentition might show more variation than is seen in any shark species, I think we can expect more variation in modern shark jaws of most species than is generally allowed for many named extinct species. In the 1800's and into the 1900's paleontologists gave names to partial teeth that would not hold up to later scrutiny and proposed multiple names to teeth that were later deemed all the same species. Starting with the work of Maurice Leriche in the early 1900's, shark researchers changed their focus from putting a name to isolated teeth to putting together dentitions, attempting to determine the variation within those dentitions. A lot of names have been synonymized but a lot of work remains to be done.

Years ago, I had the chance to talk to an ichthylogist about shark teeth. I asked him how many jaws he would like to have as a sample of a species in order to get an idea of tooth variation. He said it would have to be at least one hundred. I don't think the average natural history museum (even one near a coast) has near that many of any shark or ray. Maybe no museum does.

It will be interesting to see what you learn from the jaws you acquire. You might even think about buying damaged jaws. If you can get a decent quadrant out of a set, I would expect a dealer to be willing to work with you on price for a broken set he would have trouble selling to anyone else. You could soak out the teeth and display them to show the functional row and the individual tooth files which would also allow the roots to be seen (as discussed and figured in Cunningham, 1999 - http://www.elasmo.com/bin/sc_download.html.)

Jess

Jess

I really had trouble initially understanding why so little research had been conducted or published on extant shark and ray dentitions/teeth. But you summarized this very well in your statement “I think the most difficult thing to keep in mind for a fossil shark tooth collector, or even a fossil shark tooth researcher or two, is that modern sharks have not been (as a rule) officially named based on their teeth.” Therefore the study of extant shark dentitions/teeth was not/is not required or a driving force for modern researchers in the naming of extant species.

I would like to make two points with respect to intraspecific variation. The first involves H. Cappetta. I have invested a lot of money in his books and articles and a lot of time reading them because I hold his opinions in highest regard. However it was a TFF post on a Myliobatis plate that really opened my eyes to the fact that even renowned researchers like Cappetta may not have fully studied the dentitions/jaws of the extant species of sharks and rays or be up to date in the latest published research on them. I made the comment in the post that Myliobatis had seven files, a median file and three lateral files on each side based upon Cappetta’s statements and pictures of specimens in his 2012 Handbook meaning that different numbers weren’t Myliobatis. Cappetta stated in his 2012 Handbook that “The dentition of Myliobatis includes seven dental files in each jaw” There were no qualifiers that this was the norm only or that other numbers of files occurred in extant Myliobatis. A TFF friend pointed me to the same research on the M. californicus. If memory serves me correctly, the study of the extant M. californicus found examples of plates with two to five lateral files and in some cases two median files with some plates having both single and double median files in different places in the same plate. Maybe I didn’t give due deference to Cappetta’s use of the word “includes” maybe meaning other possibilities were possible/likely. But in my opinion if that was his intention it should have been much more clearly stated. However, the M. californicus study gives tremendous insight into the possible plate variation of fossil Myliobatis.

The other point on intraspecific variation involves a longtime shark researcher from the Smithsonian, who would always preface a shark tooth id with a statement on how difficult an identification of an individual, isolated tooth was and that most individual, isolated teeth can’t be identified or shouldn’t be identified with 100% confidence to a specific species. He studied extant jaws for many years. He used to carry a little notebook with him and would record in it the teeth of each jaw that seemed out of place or whose features didn’t really fit the shark species for the jaw. Most of these teeth were not pathological in appearance. You would think that the more jaws that he studied the higher confidence he would have had in a tooth id. However, because of the large amount of intraspecific variation he saw in jaws over the years that wasn’t the case.

My first goal is to study at least a single jaw of as many different shark species as possible. My next goal would be to purchase damaged jaws as cheaply as possible so I could remove the teeth to take dentition pictures of the removed teeth like on J-elasmo. However I would also want to take pictures of each of the removed teeth in all of the classic views, something that J-elasmo hasn’t done. Finally I would like to look at a large sample size of selected species and add tooth variation by position to my pictures. However at my age and with my financial resources attaining my first goal will be challenging and the other two much less likely. Hopefully, these posts can inspire others to do so.

Marco Sr.

[MarcoSr]

This topic has been brought up before. Check out this great thread:

http://www.thefossilforum.com/index.php?/topic/15407-let-me-see-your-recent-selachian-jaws/?hl=%22recent+jaws%22

Jess

After reading Coco’s post years ago that you referenced, I became interested in extant shark and ray jaws to better understand fossil shark and ray teeth. From research that I did on-line I found the extant dentitions on http://elasmo.com/ to be useful. However there weren’t enough close-up pictures of the teeth in the jaws or pictures of individual teeth to satisfy all of my questions. J-elasmo, http://homepage2.nifty.com/megalodon/ , which showed dentitions of individual teeth removed from extant shark dentitions was very useful. However, I wanted to see more species and to see the variation in each tooth position within multiple jaws. There were other bits and pieces of nice extant jaws/teeth on different websites but nothing together that answered all of my questions. So I finally started purchasing extant shark jaws. I just wish I had done this 40 years ago.

Marco Sr.

[siteseer]

Marco Sr.,

I think a big roadblock to studies of modern shark teeth is the amount of study material. You would think museums would have numerous jaws of numerous species and some probably do but how many have all the collecting data per modern standards? I think at minimum the tag would have to have the total body size, weight, approximate age, gender, location caught, and approximate depth. I've noticed that when scientists want some specimens they go visit Dr. Gordon Hubbell and measure what he has because he has been meticulous about his collecting data. Museums might have a number of specimens but they were caught back in the days when scientists weren't as detail-oriented.

As you know, English is Henri Cappetta's second language. He writes very well in English but occasionally in his older papers he did not express a full thought as fluently. I have also noticed that when he has collaborated with another researcher, the quality of the article seems like an improvement over what the co-author might have done alone. In other words Cappetta's experience combined with another's plus the other's command of English has lead to some great work.

Yes, you would think that more experience with modern jaws would clarify the morphological range within a species. To great extent it is true because as a novice you might look at a blue shark tooth as an odd Hemipristis until you see blue shark teeth in a publication or someone points it out to you. We expect a scientist to be able to identify a tooth to species and we think if we read enough and acquire enough specimens, we will be able to as well, but nature is a moving target. Part of human nature is to put a quick label on everything and scientists took that further in classifying the natural world. For a time we thought every living thing was either a plant or an animal but that idea started to unravel when we realized that mushrooms were neither and the microscope revealed even more kingdoms.

The thing with shark teeth is that they have arrived at their forms as part of a whole animal which is only part of a larger experiment in survival (the species) within an environment that seems stable at the surface. The best shape for a tooth to be good at attacking another animal seems to be roughly triangular with a sharp tip. There are only so many variations of that general form (relative to the apparent number of genera/species that have ever lived) that appear to be very effective at gathering prey even when you consider that some tooth forms are better than others depending on the prey (long, fang-like teeth are better for catching fish or squid but large, serrated teeth are better for cutting through the flesh and bones of a sea lion). We can separate a pile of Carcharhinus upper teeth into broader-crowned and thinner-crowned, crown angles vs. crown curves, finely-serrated and coarsely serrated, but some teeth are weakly-serrated or not as curved or angled as others. And don't forget the lowers all look like variations of each other.

The reason Carcharhinus teeth are difficult to identify is that we happen to be living during a micro-thin slice of geologic time while Carcharhinus species are in the process of diverging from each other. It appears this diversification was triggered in the wake of the Middle Miocene - an interval that happened to be the second warmest time of the entire Cenozoic. Once the cooling trend that led to the Pleistocene ice ages started, oceanic environments diversified opening more potential niches for organisms. For whatever reason the base model of Carcharhinus was better at generating descendants capable of adapting to the changes and taking over more of those niches than other genera. Identifying Late Miocene-Recent Carcharhinus teeth can be hard enough. It would seem impossible to confidently put names to Oligocene teeth without jaws from that time or near that time to use as guides.

I think it's interesting that they find teeth very similar/identical to modern bull shark teeth even into the Middle Miocene (or further?)

Getting back to obscurus, I once found a tooth I identified as that in the Sharktooth Hill Bonebed but I haven't found another one. It stuck out because all the other Carcharhinus teeth I've collected from that are not near as broad-crowned. I checked with a friend who was digging the bonebed before I was born and he said that is a rare one and that he thought he found only one (maybe two) as well.

Yeah, shark jaws are expensive. Even a bunch of cheap ones adds up. I have some too but don't have some common ones like a mako or a bull shark. I once saw an Oxynotus for sale. That was cool. If you can make it, you should go to the Venice Shark Tooth Festival. Several shark jaw dealers go to that and you might be surprised what you can get for $20-50. I've seen some good stuff at the Tampa Fossil Fest too.

Jess

Jess

I really had trouble initially understanding why so little research had been conducted or published on extant shark and ray dentitions/teeth. But you summarized this very well in your statement “I think the most difficult thing to keep in mind for a fossil shark tooth collector, or even a fossil shark tooth researcher or two, is that modern sharks have not been (as a rule) officially named based on their teeth.” Therefore the study of extant shark dentitions/teeth was not/is not required or a driving force for modern researchers in the naming of extant species.

I would like to make two points with respect to intraspecific variation. The first involves H. Cappetta. I have invested a lot of money in his books and articles and a lot of time reading them because I hold his opinions in highest regard. However it was a TFF post on a Myliobatis plate that really opened my eyes to the fact that even renowned researchers like Cappetta may not have fully studied the dentitions/jaws of the extant species of sharks and rays or be up to date in the latest published research on them. I made the comment in the post that Myliobatis had seven files, a median file and three lateral files on each side based upon Cappetta’s statements and pictures of specimens in his 2012 Handbook meaning that different numbers weren’t Myliobatis. Cappetta stated in his 2012 Handbook that “The dentition of Myliobatis includes seven dental files in each jaw” There were no qualifiers that this was the norm only or that other numbers of files occurred in extant Myliobatis. A TFF friend pointed me to the same research on the M. californicus. If memory serves me correctly, the study of the extant M. californicus found examples of plates with two to five lateral files and in some cases two median files with some plates having both single and double median files in different places in the same plate. Maybe I didn’t give due deference to Cappetta’s use of the word “includes” maybe meaning other possibilities were possible/likely. But in my opinion if that was his intention it should have been much more clearly stated. However, the M. californicus study gives tremendous insight into the possible plate variation of fossil Myliobatis.

The other point on intraspecific variation involves a longtime shark researcher from the Smithsonian, who would always preface a shark tooth id with a statement on how difficult an identification of an individual, isolated tooth was and that most individual, isolated teeth can’t be identified or shouldn’t be identified with 100% confidence to a specific species. He studied extant jaws for many years. He used to carry a little notebook with him and would record in it the teeth of each jaw that seemed out of place or whose features didn’t really fit the shark species for the jaw. Most of these teeth were not pathological in appearance. You would think that the more jaws that he studied the higher confidence he would have had in a tooth id. However, because of the large amount of intraspecific variation he saw in jaws over the years that wasn’t the case.

My first goal is to study at least a single jaw of as many different shark species as possible. My next goal would be to purchase damaged jaws as cheaply as possible so I could remove the teeth to take dentition pictures of the removed teeth like on J-elasmo. However I would also want to take pictures of each of the removed teeth in all of the classic views, something that J-elasmo hasn’t done. Finally I would like to look at a large sample size of selected species and add tooth variation by position to my pictures. However at my age and with my financial resources attaining my first goal will be challenging and the other two much less likely. Hopefully, these posts can inspire others to do so.

Marco Sr.

Edited December 17, 2015 by siteseer

[MarcoSr]

Marco Sr.,

I think a big roadblock to studies of modern shark teeth is the amount of study material. You would think museums would have numerous jaws of numerous species and some probably do but how many have all the collecting data per modern standards? I think at minimum the tag would have to have the total body size, weight, approximate age, gender, location caught, and approximate depth. I've noticed that when scientists want some specimens they go visit Dr. Gordon Hubbell and measure what he has because he has been meticulous about his collecting data. Museums might have a number of specimens but they were caught back in the days when scientists weren't as detail-oriented.

As you know, English is Henri Cappetta's second language. He writes very well in English but occasionally in his older papers he did not express a full thought as fluently. I have also noticed that when he has collaborated with another researcher, the quality of the article seems like an improvement over what the co-author might have done alone. In other words Cappetta's experience combined with another's plus the other's command of English has lead to some great work.

Yes, you would think that more experience with modern jaws would clarify the morphological range within a species. To great extent it is true because as a novice you might look at a blue shark tooth as an odd Hemipristis until you see blue shark teeth in a publication or someone points it out to you. We expect a scientist to be able to identify a tooth to species and we think if we read enough and acquire enough specimens, we will be able to as well, but nature is a moving target. Part of human nature is to put a quick label on everything and scientists took that further in classifying the natural world. For a time we thought every living thing was either a plant or an animal but that idea started to unravel when we realized that mushrooms were neither and the microscope revealed even more kingdoms.

The thing with shark teeth is that they have arrived at their forms as part of a whole animal which is only part of a larger experiment in survival (the species) within an environment that seems stable at the surface. The best shape for a tooth to be good at attacking another animal seems to be roughly triangular with a sharp tip. There are only so many variations of that general form (relative to the apparent number of genera/species that have ever lived) that appear to be very effective at gathering prey even when you consider that some tooth forms are better than others depending on the prey (long, fang-like teeth are better for catching fish or squid but large, serrated teeth are better for cutting through the flesh and bones of a sea lion). We can separate a pile of Carcharhinus upper teeth into broader-crowned and thinner-crowned, crown angles vs. crown curves, finely-serrated and coarsely serrated, but some teeth are weakly-serrated or not as curved or angled as others. And don't forget the lowers all look like variations of each other.

The reason Carcharhinus teeth are difficult to identify is that we happen to be living during a micro-thin slice of geologic time while Carcharhinus species are in the process of diverging from each other. It appears this diversification was triggered in the wake of the Middle Miocene - an interval that happened to be the second warmest time of the entire Cenozoic. Once the cooling trend that led to the Pleistocene ice ages started, oceanic environments diversified opening more potential niches for organisms. For whatever reason the base model of Carcharhinus was better at generating descendants capable of adapting to the changes and taking over more of those niches than other genera. Identifying Late Miocene-Recent Carcharhinus teeth can be hard enough. It would seem impossible to confidently put names to Oligocene teeth without jaws from that time or near that time to use as guides.

I think it's interesting that they find teeth very similar/identical to modern bull shark teeth even into the Middle Miocene (or further?)

Getting back to obscurus, I once found a tooth I identified as that in the Sharktooth Hill Bonebed but I haven't found another one. It stuck out because all the other Carcharhinus teeth I've collected from that are not near as broad-crowned. I checked with a friend who was digging the bonebed before I was born and he said that is a rare one and that he thought he found only one (maybe two) as well.

Yeah, shark jaws are expensive. Even a bunch of cheap ones adds up. I have some too but don't have some common ones like a mako or a bull shark. I once saw an Oxynotus for sale. That was cool. If you can make it, you should go to the Venice Shark Tooth Festival. Several shark jaw dealers go to that and you might be surprised what you can get for $20-50. I've seen some good stuff at the Tampa Fossil Fest too.

Jess

Jess

Normally Cappetta's books are so well written in English that it is easy to forget English is not Cappetta's first language. Shark tooth features described in English are a major problem with tooth identification. Many terms used like thin, thick, narrow, broad, coarse, fine etc. are extremely variable in meaning to different people, I'm working with a small group of engineers who are developing software algorithms and models to define tooth features like serrations, root and crown shapes etc. in mathematical terms and using tooth dimensional relationships and shape factors etc. to create mathematical models for tooth species. Our goal is to remove as much subjective human decision making in the tooth id process as possible. Ultimately you can take high resolution pictures of a shark tooth and run the images through an image analysis algorithm which compares the tooth to these different models to get probabilities of which species the tooth might be, whether the tooth is an upper or lower, or position in the dentition. We are making great initial progress but this is a huge undertaking. Extant jaws as well as large samples of fossil teeth will be used to help create the models.

Getting any data on purchased shark jaws is almost impossible. For most the best you can get is sketchy data on where they are from like India, Taiwan, Philippines etc. I haven't found any supplier on the web that gives data on the individual shark like size, gender, age, exact location where caught etc. To do a scientific study of a species you would need that data and probably need to catch the sharks as part of that study or actually purchase the complete sharks or jaws from the fish markets before the sharks are cut up for sale.

With the number of sharks killed each year estimated at 100 million, soon there won't be readily available the different species that are available today. Many species' numbers are radically declining. Soon there may only be the small bottom dwelling sharks, the deep water sharks and a limited number of the typical shark species caught today.

Marco Sr.

[Coco]

I haven't found any supplier on the web that gives data on the individual shark like size, gender, age, exact location where caught etc. To do a scientific study of a species you would need that data and probably need to catch the sharks as part of that study or actually purchase the complete sharks or jaws from the fish markets before the sharks are cut up for sale.

For many of the ray jaws I preped, I raised the lenght and the gender because I obtained these rays of my fishmonger when he had removed wings to sell them. Thus I could measure them of the point of the nose at the end of the tail. But it is of the organization, it is necessary to put labels everywhere and to take time to make that. I have a scientific spirit, it is the reason why I had noted all this.

For me, it is more difficult to to the same think for sharks, because he cut head and tail... Very often I just obtain the heads...

Coco

[MarcoSr]

For many of the ray jaws I preped, I raised the lenght and the gender because I obtained these rays of my fishmonger when he had removed wings to sell them. Thus I could measure them of the point of the nose at the end of the tail. But it is of the organization, it is necessary to put labels everywhere and to take time to make that. I have a scientific spirit, it is the reason why I had noted all this.

For me, it is more difficult to to the same think for sharks, because he cut head and tail... Very often I just obtain the heads...

Coco

Coco

Your ray jaws are much more valuable because you do have data with them.

To get pictures of a shark, determine gender, and take dimensional data I would need to buy the entire shark right from the fishermen at the docks or from a commercial fish processor who would let me do that before the larger sharks are cut up and then sell me just the head. I need to investigate if there are any fish processors in the MD/VA area where I could do this. Although, I don't know if my wife would be happy with me bringing home quantities of shark heads or small sharks to remove and process the jaws. However, she did hang my recently purchased sharks jaws in my fossil room.

Marco Sr.

[Coco]

Marco, I have seen you put labels on the right or left side of the jaws. I always put mine on the right side to hold them on the right direction (because for certain species it is not easy to recognize the top of bottom when we don't know them).

Coco

[MarcoSr]

Marco, I have seen you put labels on the right or left side of the jaws. I always put mine on the right side to hold them on the right direction (because for certain species it is not easy to recognize the top of bottom when we don't know them).

Coco

Coco

I hadn't thought about that. Sharks with cutting and holding teeth can have for example in Carcharhinus the cutting teeth in the upper jaw and the holding teeth in the lower jaw while other genera like Hexanchus and Isistius have the cutting teeth in the lower jaw. Plus there are shark genera like Squatina where there is little difference between upper and lower teeth. The jaw structures don't always help either unless you are really familiar with them. I need to look at my tags.

Thank you.

Marco Sr.