Otodus megalodon

[sharkdoctor]

Has anyone heard of Carcharodon megalodon categorized as "Otodus megalodon"?

 

I saw the following GSU abstract and related news articles:

https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/419391

https://eos.org/articles/extinct-megatoothed-shark-may-have-been-warm-blooded

https://www.foxnews.com/science/megalodon-may-have-gone-extinct-for-shocking-reason

 

The authors use “Otodus megalodon” to refer to Megs. Curious as to the source. I’ve not seen this convention. Is this emerging? Contested?

 

 

[Tidgy's Dad]

I think it's pretty much currently accepted that Otodus megalodon is correct. 

[Tidgy's Dad]

But you're right, the debate will continue................

[Miocene_Mason]

1 hour ago, Tidgy's Dad said:

I think it's pretty much currently accepted that Otodus megalodon is correct. 

Some very top scientists still reject this (I believe Bretton Kent does). It depends on what your positions on paraphyls are, or whether you are a lumper or splitter.

[Miocene_Mason]

Here’s the abstract of the paper that was placed Carcharocles in Otodus. I don’t believe it’s the first but the logic is quite convincing at least to me. It’s got some very reputable authors as well.

[Macrophyseter]

I find it extremely annoying how some people and the media have a tendency to depict ongoing arguments as official and final facts. 

 

But giving the "whys" regarding Otodus megalodon being the new possible scientific name, like Mason said, its notability mostly started from Shimada (2017) although having existed for a very long time. I don't know who first proposed it, but it argued that due to the existence of a paraphyly inside the Otodontidae, the genus Carcharocles, which is essentially a lone single-lineage offshoot from Otodus, should be moved into Otodus. However, they also proposed that to account for the clear differences between Otodus obliquus and megalodon, the taxon Otodus (Megaselachus) megalodon should be used. What Shimada (2017) simply did was add further evidence of a paraphyly inside the Otodontidae as well as arguing that the subgenus Megaselachus should be dropped. Now the big ticket here in the Carcharocles vs. Otodus debate is regarding the existence of paraphyletic taxons at the generic level. This has been an ongoing debate since the beginning of modern taxonomy- is it okay to grant a distinct genus every time some notable differences are found or are we to try to group species into existing genera as much as accuracy is possible? In the fossil community, we simply call it "lumpers vs. splitters".

 

Also, 'Carcharodon' megalodon has long been an invalidated taxon due to the overwhelming evidence that it is not familiarly related to the great white, much less generically.

 

3 hours ago, WhodamanHD said:

Some very top scientists still reject this (I believe Bretton Kent does)

Don't forget Mikael Siverson and some others!

 

[Brett Breakin' Rocks]

haha ----->This thread repeated Ad infinitum. 

 

Personally ... I find all of this makes everything suuuper easy for us to label our finds properly.  Or rather .. re-label .. them.   Oh wait ... darnit.   Again ?!

 

 

Ahhhh .. that makes me feel better. Kirk feels the pain too.

[Miocene_Mason]

2 hours ago, Macrophyseter said:

Don't forget Mikael Siverson and some others!

Yeah, all the major experts have their side. I wonder where Henri Cappetta stands now, I remember he supported Megaselachus at one point.

[Coco]

Hi,

 

I think Henri Cappetta is retired...

 

Coco

[Al Dente]

5 hours ago, WhodamanHD said:

Yeah, all the major experts have their side. I wonder where Henri Cappetta stands now, I remember he supported Megaselachus at one point.

Cappetta has used Otodus for these teeth at least since 2012 when his updated version of Handbook of Paleoichthyology came out. He was still calling auriculatus teeth “Otodus (Carcharocles) auriculatus” in a 2016 publication. Wasn’t Zhelezko using Otodus for auriculatus back in 1999?

[sharkdoctor]

Thanks for all of the thoughts.

@WhodamanHD For shark material, I've only ever worked with Brett Kent, which would explain why that convention is unfamiliar to me. I sent him a note after posting this thread and he agreed that Cappetta made an early proposal to use Otodus.

I have not finished understanding the new chapter that Brett wrote for the Calvert Volume ( https://opensi.si.edu/index.php/smithsonian/catalog/book/107 ), but at first blush, it doesn't seem that he feels the Otodus question is settled.

 

BTW, if you are interested in sharks from the Calvert Formation, the Calvert Volume chapter is a fascinating read.

[Miocene_Mason]

@sharkdoctor it is a bit wordy, and I haven’t really grasped it either. Overall it seems to me (though I could be wrong) Kent doesn’t believe the Otodus designation because it relies on anagenesis, IE the slow evolution with a direct ancestor to a direct successor, which would require all species in Carcharocles to be told apart. It’s not clear that their is a ancestor->predecessor progression, as some morphologies overlap and chronospecies can only really be told apart by age. Kent I believe thinks that it’s more cladogenetic, with say, C. angustidens and C. chubutensis having a common ancestor instead of angustidens being the direct ancestor to chubutensis. We can, however, tell apart Carcharocles from Otodus via serrations. I think it’s strange that it doesn’t mention Shimada et al 2017 (not sure if I cited that correctly, the paper I linked earlier in the thread) but perhaps they had already finished writing when it came out.

 

Or I could be understanding it completely incorrectly. 

 

Haven’t gotten a chance to read the Calvert section, will do!

[sharkdoctor]

@WhodamanHD Thanks for the thoughts and the reference. I've been plugging away on that Shimada paper for a bit. 

[britishcanuk]

I wonder when someone will propose dragging Otodus back to include their ancestors and lump Cretalamna in there, afterall they are about as closely related as their serrated-toothed descendants. As long as I have some idea of where they were found, their age and hopefully where they fit evolutionarily, I don’t get too caught up on the nomenclature, it’s all quite subjective and fluid. The irony of this debate is that the more gaps that are filled with fossil material, the more complex it becomes to stick labels on the evolutionary lineage. It’s easier to differentiate two sharks that look obviously different when there are no intermediates than it is to decide where and what to name when the entire lineage is complete and well understood.

[MikaelS]

I use Carcharocles, as I don't really have a problem with probable paraphyletic taxa as long as they are recognised as such. Its a practical way of recognising huge dental differences between end points of a perceived lineage. As someone implied in this thread if you refer megalodon to Otodus you could argue that all Cretalamna should be referred to Otodus as well and then you end up with a genus with a rather extreme morphological variability. So basically, Otodus is far from universally accepted as repository for megalodon by current palaeoichthyologists.

[MarcoSr]

10 hours ago, MikaelS said:

I use Carcharocles, as I don't really have a problem with probable paraphyletic taxa as long as they are recognised as such. Its a practical way of recognising huge dental differences between end points of a perceived lineage. As someone implied in this thread if you refer megalodon to Otodus you could argue that all Cretalamna should be referred to Otodus as well and then you end up with a genus with a rather extreme morphological variability. So basically, Otodus is far from universally accepted as repository for megalodon by current palaeoichthyologists.

 

I fully understand your reasoning and agree with it.  However, it is very confusing for amateurs when world renown shark researchers like yourself and Cappetta don't agree on the scientific name for a common fossil tooth species found worldwide like megalodon.  I guess we can use aka with different scientific names when we discuss megalodon.

 

Marco Sr.

[Miocene_Mason]

1 hour ago, MarcoSr said:

However, it is very confusing for amateurs when world renown shark researchers like yourself and Cappetta don't agree on the scientific name for a common fossil tooth species found worldwide like megalodon.

Confusing perhaps, but pretty common. It’s how science works, and I bet it will settle out eventually.

[britishcanuk]

On 1/3/2019 at 7:47 AM, MarcoSr said:

 

I fully understand your reasoning and agree with it.  However, it is very confusing for amateurs when world renown shark researchers like yourself and Cappetta don't agree on the scientific name for a common fossil tooth species found worldwide like megalodon.  I guess we can use aka with different scientific names when we discuss megalodon.

 

Marco Sr.

Hey Marco, we actually do use “aka” in scientific publications and such, except we call them synonyms or synonymous with. Here’s an example screen grabbed from shark-references.com (https://shark-references.com/species/view/Otodus-obliquus). As a botanist, we use the abbreviation for synonymous all of the time because plant taxonomy is never settled and makes shark taxonomy seem easy!

[MikaelS]

19 hours ago, MarcoSr said:

 

I fully understand your reasoning and agree with it.  However, it is very confusing for amateurs when world renown shark researchers like yourself and Cappetta don't agree on the scientific name for a common fossil tooth species found worldwide like megalodon.  I guess we can use aka with different scientific names when we discuss megalodon.

 

Marco Sr.

That's nothing compared with our disagreement on the spelling of Cretalamna/Cretolamna which has dragged on for nearly two decades now. You should see some of our correspondance where we use different ways of demonstrating our position but at the same time keeping it very civil (I think the most commonly used spelling we used was Cret(a/o)lamna or something similar. We both concluded that it is a very minor disagreement yet neither of us are yielding an inch. Two grown men arguing about a single letter....for decades.

[MarcoSr]

5 hours ago, MikaelS said:

That's nothing compared with our disagreement on the spelling of Cretalamna/Cretolamna which has dragged on for nearly two decades now. You should see some of our correspondance where we use different ways of demonstrating our position but at the same time keeping it very civil (I think the most commonly used spelling we used was Cret(a/o)lamna or something similar. We both concluded that it is a very minor disagreement yet neither of us are yielding an inch. Two grown men arguing about a single letter....for decades.

 

I'm aware of the Cretalamna/Cretolamna disagreement.  I have used both spellings.  Dr. Cappetta used a half page in his 2012 handbook to justify the Cretolamna spelling.   Dr. Michael Newbrey came to my house the end of October to personally pick up a large number of fossil shark, ray and bony fish vertebrae and other specimens for his studies.  After seeing some of my collection, he mentioned that you might be interested in some of my shark specimens.  Hopefully, I can help your research in the future.  If/when you begin work on Paleocene and Eocene Cretalamna species and want US specimens I have a decent number of great condition specimens (from your papers I know how important condition is) that I could donate and I also know a number of other collectors who would be willing to donate specimens as well.

 

Marco Sr.

[MarcoSr]

19 hours ago, britishcanuk said:

Hey Marco, we actually do use “aka” in scientific publications and such, except we call them synonyms or synonymous with. Here’s an example screen grabbed from shark-references.com (https://shark-references.com/species/view/Otodus-obliquus). As a botanist, we use the abbreviation for synonymous all of the time because plant taxonomy is never settled and makes shark taxonomy seem easy!

 

I spend a good amount of time studying extant shark jaws and teeth.  I see the myriad of scientific names that have been used for the same extant shark species.  When I'm trying to research a specific species it can be very difficult at times to find the relevant papers because of the different scientific names used.  Even when the scientific name is agreed upon there can be a myriad of common names for the extant species worldwide in common usage. Common names for extant sharks are much worse.  Researchers can use different common names than the general public (i.e. "white shark" versus "great white shark").  A number of common shark names correspond to different shark species worldwide.  All of this makes it very difficult at times for me to understand/know which specific species is really being discussed.  So I'm a very strong advocate of at least getting to a scientific name that everyone uses.  If future scientific research/data makes a name change appropriate, I understand that.  I also understand that the public common names will be whatever the public likes to use.

 

Marco Sr.

 

[KCMOfossil]

I know nothing about the specific issue being discussed here, but I appreciate the window this post provides on the process of fossil identification and classification.  Thank you, friends, for a fascinating and educational thread.

 

Russ

[siteseer]

On 12/12/2018 at 12:44 AM, Coco said:

Hi,

 

I think Henri Cappetta is retired...

 

Coco

 

 

Hi Coco,

 

I wrote to him in the 90's and he seemed like the kind of person who would never retire from studying sharks and rays.  It seems like retirement is when many paleontologists get back to writing up projects they started while in school.or in the early years after getting their degrees.

 

Happy New Year,

 

Jess

[siteseer]

On 12/12/2018 at 1:33 AM, Al Dente said:

Cappetta has used Otodus for these teeth at least since 2012 when his updated version of Handbook of Paleoichthyology came out. He was still calling auriculatus teeth “Otodus (Carcharocles) auriculatus” in a 2016 publication. Wasn’t Zhelezko using Otodus for auriculatus back in 1999?

 

 

Hi Al Dente,

 

As I recall, Cappetta was among the first, if not the first researcher to resurrect Carcharocles back in the 80's as listed in his Handbook of Paleoichthyology volume, Chondrichthyes II (1987).  Carcharocles was used in Jordan and Hannibal (1923).  I'd have to re-read it but I think Jordan and Hannibal assigned auriculatus to Carcharocles and therefore megalodon as well.  Of course, Cappetta knew this clashed with other names like Carcharodon and Procarcharodon (Casier's proposal for megalodon to separate it from Carcharodon) so he chose the genus that had priority as he understood ICZN rules then.  If he's changed his mind to Megaselachus and then to Otodus, I'd have to say that I still agree with his 1980's opinion.

 

To me (and as noted above) it's asking too much to put Otodus obliquus and Carcharocles megalodon in the same genus.  It runs against how shark fossils (mostly teeth) are classified.  Otodus obliquus is the apparent descendant of Cretalamna but no one is proposing Cretalamna megalodon and that would be the next step in logic if you're pushing Otodus megalodon as a name today.

 

Otodus arose at an interesting time, the early Paleocene, when the terrestrial and marine worlds were up for grabs again as they were in the Early Triassic, an interval after a mass extinction.  Sharks, rays, and fishes in general radiated with Otodus evolving into one of the top shark predators of the epoch.  Its teeth are like spikes with fine cutting edges.  They could grab and swallow medium-sized fishes and bite chunks out of larger fishes.

 

Some Otodus teeth show rippled or weakly-serrated edges in the late-early Eocene (sites in Maryland and eastern Europe) with fully-serrated teeth found all over the world by the mid-late Eocene.  A major development elsewhere among the vertebrates at this time was the evolution of whales and sirenians (sea cows).  These animals descended from four-legged forms but became not only fully-adapted to the sea by the late Eocene but also formidable competitors to even the larger predatory sharks of the time.  The transition to serrated teeth allowed Otodus-Carcharocles to deal with the tougher muscle and bones of large mammals (and the shells of sea turtles) in a way Paleocene Otodus teeth could not.  

 

Across the mid-late Eocene the world also transitioned from a largely-tropical one to a more temperate one, seasons more noticeable in the higher latitudes.  By the early Oligocene permanent ice became established at the poles and the drifting continents allowed for changes in ocean currents that led to now-isolated Antarctica to start to become covered in ice.  It was in the Oligocene that whales radiated after the older groups died out.  By the end of the epoch various toothed and baleen whales had appeared and Carcharocles increased in size as reflected in the size of the teeth found.  A large auriculatus teeth might be 3-4 inches but a late Oligocene angustidens tooth can be 5 inches or more.  The teeth subtly change in form across this time as well.  They broadened and slightly flattened as the lateral cusplets decreased in size.  Every once in a while a collector finds a Late Oligocene Carcharocles tooth without lateral cusplets or they are hardly noticeable. 

 

During the Early Miocene Carcharocles teeth are more often found with reduced cusplets, and by the Middle Miocene, it's a rarity to see one with even a barely noticeable cusplet.  These teeth without cusplets have the name, megalodon with some teeth reaching 6 inches or more.  By this time another group of marine mammals is evolving and diversifying, the pinnipeds (forms like seals, sea lions, walruses) and sirenians are at their peak in diversity.

 

From a climatic standpoint the world warmed in the early Miocene, the warmest time in the Cenozoic since the Early Eocene, with large areas of continents inundated by the sea, but then climates went back to the general cooling trend towards the end of the Miocene.  The ocean, like the organisms in it, evolves too.  The cooling climates and changing currents created more complex environments and even stratified the ocean, layers of cooler temperatures as depth increased.  Antarctica froze over completely.  At the end of the Miocene there was a drop in sea level as climates cooled sharply.  Organisms on land and sea that thrived in warm climates died out or retreated to lower latitudes.

 

Carcharocles survived into the Pliocene but collectors don't find as many in Early Pliocene layers and they do in Miocene ones though the largest teeth come from late Miocene-early Pliocene.  Only a few Carcharocles teeth are known from the late Pliocene and none are confirmed from Pleistocene sites.

 

What I'm saying (and took time setting up even if generally) is that the world of Otodus was completely different from that of megalodon.  Even if the argument is that obliquus-megalodon is essentially one shark moving through time so the genus should be the same, it is a lot to ask that the changes within that shark with all the changes in its environment along 45 million years were superficial enough (just the teeth?) not to warrant a separate genus along the way.  It's easiest to draw the line at the acquisition of serrations but there might have been significant changes in the lineage across an interval of distinct environmental shift, like the Oligocene.  The teeth changed so much and they likely changed slower than parts of the soft anatomy.  The fossil record doesn't allow us to see those changes and we might not see evidence of it even if the near-complete cartilaginous skeleton of a megalodon were ever found so the pro-Otodus people might be right but that seems like over-lumping to me and that's coming from someone who has been more lumper than splitter over the years. 

 

It's interesting that megalodon disappears from the fossil record at the same time, the late Pliocene, as its relative, Parotodus, and a once-large and diverse group of baleen whales known as cetotheres.  You get the idea that Carcharocles and Parotodus might have become specialized in preying on cetotheres and other Oligocene-Miocene marine mammals, so when those forms declined in number (sirenians also became less diverse with their populations more isolated), so did they.  They couldn't adapt to some combination of ever-cooling temperatures and the appearance/establishment of cool-adapted sharks and whales during the early Pliocene.

 

I started reading that recently-published Calvert Cliffs volume.  Bretton Kent talks about Otodus vs. Carcharocles as noted above.  Everyone interested in the topic should read that.

 

Jess