Re-dating the extinction of Otodus/Carcharocles megalodon

[Boesse]

Hey all! This week my colleagues and I published a paper we spent most of the last decade sweating over. It is an exhaustive report of all known late Miocene-Pleistocene records of teeth of Otodus (aka Carcharocles) megalodon teeth from the west coast in an attempt to estimate the date at which O megalodon went extinct. Aside from some conspiracy theorists who will wait until they die and not see a live 'meg', we all know it's not living today as there is not a shred of positive evidence indicating its existence. We know it's around in the Miocene, and the early Pliocene. Did it survive into the Pleistocene? End of the Pliocene? or become extinct sometime earlier? These questions require serious thought because it has direct implications for whether or not O. megalodon went extinct at the same time as a bunch of weird marine mammals or if it was killed off by a supernova known to have occurred 2.6 Ma. An earlier study pooled fossil occurrences from around the globe and statistically reconstructed a mean extinction date of 2.5 Ma, with significant error (~3.6 Ma to 100ky in the future being the max and min extinction dates).

We found that in the California record, reliable occurrences are only found in early Pliocene rocks. All examples of late Pliocene or Pleistocene teeth were either poorly dated, reworked from Miocene rocks, had poor provenance, or are completely missing (and never photographed) and therefore the identification cannot be confirmed. We thus predicted a 3.6 Ma extinction date. To test this, we re-analyzed the dataset published in 2014 but chucked a bunch of bad data and exhaustively re-researched the stratigraphy of each locality and corrected about 3/4 of the dates in the remaining dataset, and added our new California records. When we analyzed this corrected dataset, our margin of error (the time between the max and min extinction dates) shrank from 3.6 million year long interval to 900,000 years; *probably* extinct by 3.6 Ma (mean extinction date), definitely by 3.2 Ma (min extinction date), and possibly as early as 4.1 Ma (max extinction date).

 

This extinction therefore precedes the 2.6 Ma supernova, as well as the Plio-Pleistocene marine mammal extinction (which in all likelihood was not a mass extinction or an extinction event, rather just a period of higher extinction/origination rate). About 4 Ma is when fully serrated Carcharodon carcharias teeth show up in the North Atlantic, indicating when the two overlapped, however briefly. We think this biotic event matches best - the mechanics of exactly how this was driven are to be figured out by someone else, but perhaps adult Carcharodon outcompeted juvenile O/C megalodon prior to becoming gigantic. Some analyses of Otodus lineage growth rate is going to be necessary.

 

Here's the open access paper here: https://peerj.com/articles/6088/

 

Here's a blog writeup I did for PeerJ here: https://peerj.com/blog/post/115284881293/early-pliocene-extinction-of-the-mega-toothed-shark-otodus-megalodon-boessenecker/

 

Excellent summary in Nat Geo: https://www.nationalgeographic.com/science/2019/02/megalodon-extinct-great-white-shark/

 

CNN: https://www.cnn.com/2019/02/14/us/megalodon-extinct-earlier-scli-intl/index.html

 

Fox News: https://www.foxnews.com/science/megalodon-shocker-huge-killer-shark-may-have-been-wiped-out-by-great-whites

 

Forbes: https://www.forbes.com/sites/melissacristinamarquez/2019/02/14/great-white-sharks-may-be-the-reason-why-giant-megalodon-shark-is-extinct/#6a06986a6486

 

Daily Mail: https://www.dailymail.co.uk/sciencetech/article-6700495/Giant-50-foot-long-predatory-shark-went-extinct-one-million-years-earlier-previously-thought.html

[ynot]

Nice job and a big help with dating megs.

[rebu]

What an amazing work. I am sure it wasn't easy to do all the research and must have been frustrating at times. Thanks to persistence and knowledge of people like you we will eventually get to find out the true story about our past. 

[Tidgy's Dad]

Excellent work. 

Several forum members have already excitedly posted about this, it's glad to hear it from the horse's mouth, so to speak.

[FossilsAnonymous]

Amazing work!

 

[DPS Ammonite]

Thanks Robert. We were waiting for you to announce your own paper. 

 

You are doing what others have done to figure out what happened during extinction events such as the Late Cretaceous event: reducing the range of errors of dates to figure out the sequence of events.

 

Maybe Megalodon which has been around for about 19 million years was replaced by new and improved models such as the Great White Shark that you mentioned. @Boesse Did Megalodon last longer than the average shark species? Somewhere I read that the average species (which species?) last about 3 million years. I suspect without good proof that sharks might last longer since their basic body plan has been around for a long time.

[Miocene_Mason]

1 hour ago, DPS Ammonite said:

Somewhere I read that the average species (which species?) last about 3 million years.

Methinks any attempt to quantify the time an average species lived for would be futile. The variables are so numerous, complex, and sometimes random that I don’t think there would be any meaningful pattern. We struggle to define where one species ends and another begins, which makes it hard to come up with a solid duration for even one.  Additionally, such variance exists for duration that even if one managed an average it would likely be useless, pushed and pulled by various outliers. 

[DeepTimeIsotopes]

Wow, nice job! Thanks for sharing it with us. 

[verydeadthings]

Congrats on the paper! I love to see the scientific community interact with non-professionals (who in many cases are experts in the field, regardless of affiliation). So does this rule out the extinction being related to the closing of the isthmus of panama? Could the extinction be related to changes in ocean circulation which reduced the availability of large prey?

[Boesse]

@verydeadthings In my opinion - and what we wrote in the paper - the isthmus of Panama closure was likely too localized, though that temporally does make some sense. I'm not convinced oceanographic changes from that closure would have affected C/O megalodon in places like the Indian Ocean and the Mediterranean.

 

[sharkdoctor]

great paper and interesting approach!

[DeepTimeIsotopes]

Saw this report on Scishow on Youtube

 

[Ludwigia]

What an enormous project! Can you estimate how many man-hours you guys put into it?

[The Amateur Paleontologist]

Good job! That's quite incredible

-Christian

[Monica]

I brought in a megalodon tooth to school yesterday to show my students (I bring a different fossil every Friday - we call it "Fossil Friday" and I'm pretty sure it's their favourite day of the week ), and I was able to give them this new information regarding the extinction date of the beast.  They were very impressed with both the tooth and the information given, so thanks for the science lesson! 

[siteseer]

Bobby,

 

I just read the paper.  As noted above, it was very thorough.  You and your colleagues addressed every question I had.  In fact I took out a piece of note paper to list my comments but I didn't end up writing much.  You took away all my "yeah, but..." responses.  For example, I always understood that the San Diego Formation was wholly late Pliocene in age so it seemed a megalodon tooth from it was all the evidence needed to establish a late Pliocene occurrence.  You addressed the occurrence listed by Kemp (1991).  I guess I never looked close enough at the specimen he noted.

 

You just touched on Parotodus benedeni though it's the same story.  It co-existed with megalodon (though followed a more pelagic and perhaps more specialist lifestyle) across the Miocene and also appears to have died out sometime in the Pliocene.  Parotodus is always rare to extremely rare except perhaps from the Tirabuzon Formation, but even in that, you couldn't call it common.  I think that's important - two large marine predators who happened to be closely-related dying out in about the same geologic instant.  And yes, it seems significant that the great white shark survived past whatever killed them off and even prospered.  The new model might have been somehow more energy-efficient than the old ones. 

 

The appearance of the killer whale might have had more significance.  The rare occurrences you noted (Japan, Italy) also indicate a distribution not reflected in the fossil record so far.  However, I do understand that a killer whale of the Pliocene might not have yet been the efficient pack predator it often is today.

 

It was also interesting to read about the current status of the Fernando Formation.  I started collecting fossils in the late 80's and it seemed a number of southern California collectors had shells and shark teeth from it (sites now gone due to land development).  I gathered from them that the Fernando was a name still used but it was from a previous generation of geologists none of whom formally defined it - something ripe for reinterpretation.  It was just understood.  It appears at least some of the old finds are now said to be from the Repetto.

 

Great paper.

 

Jess

[ashcraft]

Isn't it just as likely that great whites/orcas became more common because of the dwindling number of megs allowed a foothold into the niche, rather then causing the extinction?

 

Brent Ashcraft

[Scylla]

Thanks for the explanation and the paper. 

[Boesse]

Hey all, whoops! I didn't see any of these comments... the rest of spring semester was a particularly difficult one and I spent even less time on here than I have been. Trying to fix that this summer, though. Alright:

 

On 2/23/2019 at 2:34 AM, Ludwigia said:

What an enormous project! Can you estimate how many man-hours you guys put into it?

@Ludwigia I have no idea to be honest. Hundreds of hours of my own time spent writing, revising, rewriting, editing, and reading, and that doesn't include time spent by my colleagues, or the hours spent in museums or driving to/from museums. Total, I would wager somewhere in the 200-300 hour range.

 

On 2/23/2019 at 10:53 PM, ashcraft said:

Isn't it just as likely that great whites/orcas became more common because of the dwindling number of megs allowed a foothold into the niche, rather then causing the extinction?

 

Brent Ashcraft

@ashcraft For Carcharodon carcharias that's possible (time-wise) except then it requires a different biological trigger for C. megalodon extinction and is a more complicated (and in my opinion more unlikely) scenario. As far as orcas go, there are no records of killer whales that overlap with C. megalodon, and those that do occur in the late Pliocene are still small bodied with more numerous and smaller teeth (e.g. fish/squid eaters, not yet specialized for macrophagy).

 

On 2/23/2019 at 6:01 AM, Monica said:

I brought in a megalodon tooth to school yesterday to show my students (I bring a different fossil every Friday - we call it "Fossil Friday" and I'm pretty sure it's their favourite day of the week ), and I was able to give them this new information regarding the extinction date of the beast.  They were very impressed with both the tooth and the information given, so thanks for the science lesson! 

You're welcome! Glad it was useful!

 

On 2/23/2019 at 5:26 PM, siteseer said:

Bobby,

 

I just read the paper.  As noted above, it was very thorough.  You and your colleagues addressed every question I had.  In fact I took out a piece of note paper to list my comments but I didn't end up writing much.  You took away all my "yeah, but..." responses.  For example, I always understood that the San Diego Formation was wholly late Pliocene in age so it seemed a megalodon tooth from it was all the evidence needed to establish a late Pliocene occurrence.  You addressed the occurrence listed by Kemp (1991).  I guess I never looked close enough at the specimen he noted.

 

You just touched on Parotodus benedeni though it's the same story.  It co-existed with megalodon (though followed a more pelagic and perhaps more specialist lifestyle) across the Miocene and also appears to have died out sometime in the Pliocene.  Parotodus is always rare to extremely rare except perhaps from the Tirabuzon Formation, but even in that, you couldn't call it common.  I think that's important - two large marine predators who happened to be closely-related dying out in about the same geologic instant.  And yes, it seems significant that the great white shark survived past whatever killed them off and even prospered.  The new model might have been somehow more energy-efficient than the old ones. 

 

The appearance of the killer whale might have had more significance.  The rare occurrences you noted (Japan, Italy) also indicate a distribution not reflected in the fossil record so far.  However, I do understand that a killer whale of the Pliocene might not have yet been the efficient pack predator it often is today.

 

It was also interesting to read about the current status of the Fernando Formation.  I started collecting fossils in the late 80's and it seemed a number of southern California collectors had shells and shark teeth from it (sites now gone due to land development).  I gathered from them that the Fernando was a name still used but it was from a previous generation of geologists none of whom formally defined it - something ripe for reinterpretation.  It was just understood.  It appears at least some of the old finds are now said to be from the Repetto.

 

Great paper.

 

Jess

@siteseer The San Diego Formation was 'traditionally'' viewed as being late Pliocene but molluscan biostratigraphy and other new data indicate the base of the unit (which produced the Ashby and Minch La Joya specimen) is actually early Pliocene (there's a paper we cite on fossil chitons from the SDF that goes into all this).

 

Regarding Parotodus: Parotodus appears to have survived in the North Atlantic until the early Pleistocene, owing to apparently unreworked specimens from the Austin Sand Pit here in South Carolina. A detailed study of the extinction of Parotodus is still wanting, and I agree is critical. Many of these 'facts' about the timing and reasons for extinction are sort of colloquial and appear common sense but in actuality have rarely been critically assessed.

 

So the entire published fossil record of Orcinus consists of a tooth from Japan and the pilot whale sized, small-toothed, fish/squid eating Orcinus citoniensis from the late Pliocene of Italy. There are no late Miocene or early Pliocene records of any Orcinus. Orcinus that could have actually competed directly with C. megalodon apparently did not evolve until sometime in the Pleistocene, well after C. megalodon was no longer around. If we found abundant large teeth of Orcinus in the SDF and the Yorktown (and other units around the globe) then I would buy the idea of orcas outcompeting C. megalodon - but the available data suggest that even small bodied Orcinus completely post-dated C. megalodon and then passively reinvaded the vacant niche space sometime between the appearance of O. citoniensis and the modern O. orcinus (and that's keeping in mind that many if not most orcas feed on fish and sharks rather than marine mammals).

 

The Fernando formation is sort of a garbage can term and is defined chronologically - any "marine"-ish rocks in the LA basin and adjoining areas younger than early late Miocene and older than Pleistocene. It's not defined lithostratigraphically...