PreprintArticleVersion 1Preserved in Portico This version is not peer-reviewed
South East Asia’s Megalodon Shark First Record and Habitat Preference Modeling During Miocene Period (20 Ma) and Winter Monsoon Impacts in South Coast of West Java
Version 1
: Received: 21 January 2021 / Approved: 25 January 2021 / Online: 25 January 2021 (15:05:04 CET)
How to cite:
Wibowo, A. South East Asia’s Megalodon Shark First Record and Habitat Preference Modeling During Miocene Period (20 Ma) and Winter Monsoon Impacts in South Coast of West Java. Preprints2021, 2021010509. https://doi.org/10.20944/preprints202101.0509.v1
Wibowo, A. South East Asia’s Megalodon Shark First Record and Habitat Preference Modeling During Miocene Period (20 Ma) and Winter Monsoon Impacts in South Coast of West Java. Preprints 2021, 2021010509. https://doi.org/10.20944/preprints202101.0509.v1
Wibowo, A. South East Asia’s Megalodon Shark First Record and Habitat Preference Modeling During Miocene Period (20 Ma) and Winter Monsoon Impacts in South Coast of West Java. Preprints2021, 2021010509. https://doi.org/10.20944/preprints202101.0509.v1
APA Style
Wibowo, A. (2021). South East Asia’s Megalodon Shark First Record and Habitat Preference Modeling During Miocene Period (20 Ma) and Winter Monsoon Impacts in South Coast of West Java. Preprints. https://doi.org/10.20944/preprints202101.0509.v1
Chicago/Turabian Style
Wibowo, A. 2021 "South East Asia’s Megalodon Shark First Record and Habitat Preference Modeling During Miocene Period (20 Ma) and Winter Monsoon Impacts in South Coast of West Java" Preprints. https://doi.org/10.20944/preprints202101.0509.v1
Abstract
Otodus megalodon is known as the biggest shark ever alive and recent records show this species was only existed in America, Africa and Europe continents in the last Miocene period 20 million years ago (Ma). Recently, megalodon teeth have been discovered in South coast of West Java. Here this study aims to present and model the presence of O. megalodon. The length of the excavated tooth was ranging from 13 to 19 cm. The lithological analysis shows that the tooth was found in Miocene rock layers. Paleogeographic model shows that during Miocene southern parts of Java island were submerged including the recent locations where the megalodon tooth have been found. Half parts of the modeled West Java were an ocean with depth ranging from 0 to 200 m. High habitat use preferences by juvenile megalodon were estimated in the shelf (depth 0-40 m) with the size of 1365 km2 . Whereas habitat use preference by adult megalodon was low at this depth. Both juvenile and adult habitat use frequencies were low at a depth of between 80 m and 160 m. Habitat use preferences were increasing at a depth of > 200 m. After Miocene, the paleoclimate records show a decline in temperature and lead to the decline of whale population in ocean. The declining of megalodon’s prey explains the declining of this giant shark especially in post Miocene and early Pliocene periods.
Keywords
Habitat use; model; megalodon; Java; shark
Subject
Environmental and Earth Sciences, Atmospheric Science and Meteorology
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received:
29 January 2021
Commenter:
Jonathan M Werry
The commenter has declared there is no conflict of interests.
Comment:
Hi, I'm trying to follow through the logic of your megalodon juvenile vs adult historic habitat use based on present day white shark modeled habitat use...Any chance you can touch base via email to shed some light on my queries? best regards
Received:
9 March 2021
The commenter has declared there is no conflict of interests.
Comment:
Dear author,
Please find a review of this paper below. Firstly, I want to congratulate you on having written this paper and put it out there. I apologise in advance for the length of the review; but there was rather a lot to comment on (both praise and criticism). I provide an overview, some major comments by section, and some specific comments below as is typically written in an academic review. I hope this will be helpful to you in revising the manuscript before submitting it to a journal - as there is much potential here. However, please pay particular attention to my suggestions of calculating total length of the teeth you excavated, of discussing biotic hypotheses of megalodon's extinction, and especially regarding figure 2 - which is a stock photo from the internet of shark teeth apparently from Florida rather than South East Asia and its inclusion here is deeply worrying. I believe you could submit this paper to a peer-reviewed journal for publication, as it is expanding the fossil record of O. megalodon and data such as this is essential for science to advance. However, my concerns that I have pointed out in this review need to be addressed first, and especially with regards to what I've mentioned above (total length calculations, extinction hypotheses and figure 2). I wish you the best with revisions.
Overview:
This paper provides the first report of the iconic Otodus megalodon in Java Island, adding to the very limited fossil record for this species in South East Asia. I commend the author for this find and for expanding the geographic range of this extinct shark’s fossils.
The paper has potential, but it also needs a lot of work. There is good knowledge here for the key literature of O. megalodon, particularly regarding its distribution through time, and I think the bathymetry approach is solid, but there is some questionable scientific interpretation here – mostly due to a lack of communication as to how the science was actually done.
The paper states that it is using the methods of Cooper et al. (2020) to compare teeth and habitat use results, but that study covered neither teeth nor habitat and thus I do not understand what exactly was done here with regards to the teeth. It is not clear exactly how the fossils were measured, and I recommend using crown height to calculate the size of the shark – which would be far more informative to the bathymetry modelling than simply extrapolating from great white data (if that’s what’s been done, this isn’t clear either). Moreover, I do not understand where the data of juvenile and adult habitat occupation are coming from as it is not represented in the teeth found (13-19 cm teeth are adult O. megalodon teeth). If this data is taken from great whites, then it says nothing as to how O. megalodon used habitat in Java because the fossils themselves aren’t used.
Finally, despite being in the title, there is only a brief reference to Monsoon of the Miocene and I’m not convinced of its supposed impact on O. megalodon populations. This is because the study is using a very limited sample size of teeth (and even then the number of teeth is unclear) which cannot be representative of an entire population; and the monsoon occurred long before O. megalodon’s extinction. I don’t see how anybody can make interpretations about O. megalodon’s extinction from just a few teeth in one area. Moreover, the paper really hones in on the role of climate change in declining O. megalodon populations (and that of its prey), but doesn’t acknowledge any studies that argue to the contrary, which suggest that O. megalodon decline was almost certainly an entirely biotic mechanism, and probably came from declining coastal areas affecting prey, and/or nursery sites with competition exacerbating this and endothermic taxa like O. megalodon being particularly vulnerable to those declines. The exclusion of a decline in coastal areas as a theory to O. megalodon’s extinction is particularly surprising given that it is directly related to what is being reported here – O. megalodon teeth in a coastal area.
I am sorry I can’t be more positive. But the finding of O. megalodon in this new area is exciting and could fill in a paper by itself, so I hope the author will not be disheartened by my comments and instead can reformat the paper primarily around this novelty. The papers of Reolid & Molina (2015) and Trif et al. (2016), as well as Razak & Kocsis (2018) already cited in the paper, should provide a good template for this. I hope these comments are helpful to the author for their revisions.
Major comments:
=== Abstract ===
Some more detail on how you reached your conclusions is needed, especially with regards to juvenile use of habitat considering that the teeth discovered are all incredibly large, even for this species. Moreover, there is some background missing in this abstract that should be corrected. Finally, no mention is actually given to monsoons and their impacts, which really ought to be included given its presence in the paper’s title (but see Discussion comments below).
=== Introduction ===
In general, there’s some very nice background with regards to O. megalodon distribution and introducing the problem that only one study has been conducted on teeth in South East Asia. The section could do with some rewriting though. I hope my specific comments below will help.
Methods
One of my main concerns with this section is that I don’t really understand how you used Cooper et al. 2020 on the teeth since that study didn’t actually use any teeth, they simply used the total length of living sharks to get their relationships with specific body parts and extrapolated to O. megalodon. Furthermore, that study had nothing to do with habitat use, and was novel specifically because it used other analogue species as well as the great white shark. I think Razak & Kocsis 2018 is what you want to be using as your main comparison study here. I suggest also having a look at Diedrich 2013 for this purpose too.
There should also be a brief extra sub-section about the teeth themselves – how many did you find? Are they all dated to around the same time and if so, how did you date them? How did you measure the teeth – did you use total tooth height, crown height or crown width? My suggestion would be to include pictures of all individual teeth, with a scale bar (e.g. a ruler) next to them as a figure here and that you use equations from Shimada (2003; 2019) and Pimiento & Balk (2015) (specifically because this paper in particular uses averages where it’s difficult to determine lateral tooth position) to infer the total length of the sharks – those would be exciting results given the size of the teeth you report in the abstract and results and would help inform your habitat use modelling even further.
But perhaps my most major concern is that the left side of Figure 2 (the picture of the teeth) is a picture of shark teeth taken from Science Photo Library (specifically from this link here: https://www.sciencephoto.com/media/172184/view); despite the paper claiming that they are “the excavated megalodon teeth fossils” – this is misleading to readers and makes me question the science being reported here as it appears the excavated fossils are not being presented here. Without a figure displaying the teeth being excavated, the most vital data is missing from the paper. This needs to be rectified.
Results
I have some concerns with this section too. The results of the excavation itself seems to suggest that the paper only recorded a single tooth, yet somehow there’s also data for how many juveniles and adults were included at each depth from figure 8. I don’t understand where these data came from. Great whites are said to be used as references, but if that’s the case then all that’s been done here is stating the depths great whites would use as juveniles and adults and assuming O. megalodon did the same. I strongly recommend that you calculate total length of the O. megalodon sharks from the tooth or teeth excavated using Shimada (2003; 2019) to help inform your modelling, and that you show exactly where your juvenile and adult data came from – because if it’s from great whites then this isn’t actually adding anything to O. megalodon habitat use.
The bathymetry modelling looks fine to me (although this isn’t my area of expertise), but it’s how O. megalodon data is being considered within it that’s concerning me.
=== Discussion ===
This section needs rewriting as the theory of climate change affecting prey is repeated multiple times without expansion here.
Moreover, there is no consideration given to alternative theories of O. megalodon’s extinction, specifically a decline in coastal area (Pimiento et al. 2017) – which should be particularly relevant to this paper considering that it is focusing on a coastal area. The idea of climate change contributing to O. megalodon’s extinction is notably at odds with the findings of Pimiento & Ferron (also see Collareta et al. 2017 for expansion on role of prey declines, which they argue also favours a biotic mechanism), who have determined that climate had little to do with O. megalodon’s decline and that the shark was regionally endothermic. I strongly recommend revising the literature of O. megalodon extinction and physiology.
Finally, despite being in the title, there is only a brief mention of the monsoon 7-5.5 Ma and the paper does not convince me that it had anything to do with O. megalodon’s extinction (see specific comments) – I think this conclusion is a stretch at best considering that just one area, and possibly just one tooth (which isn’t included in any figure), are investigated here.
Conclusion
The conclusion seems fine based on the paper’s content, but since no mention is given to the monsoon, I don’t really see the need for its inclusion in the title. The monsoon discussion could be removed from the paper and little would change. I really think the paper should be focused only on the finding of the tooth (or teeth; again, this is impossible to tell because the figure used to show the teeth is a stock photo), body length calculations from said teeth, and using that size calculation to inform the bathymetry model and habitat use.
Specific comments:
=== Throughout: ===
Referencing is not always consistent – e.g. Cooper et al. 2020 is cited as “from (Cooper et al. 2020)” and “from Cooper et al. (2020)” at different points. Please check citations across the whole manuscript and fix. This inconsistency is also seen in the reference list so please go through them again. For example, “et al.” is used after naming 3 authors of the Cooper paper when there is just one additional author, whereas all authors are named in Boessenecker et al. 2019 and Pimiento et al. 2016.
Please also check throughout the manuscript and make sure megalodon is always named as “O. megalodon” after the first mention of its scientific name. This is not always done and should be fixed as this is basic scientific practise.
Abstract
Otodus megalodon is known as the biggest shark ever alive
Strange phrasing. An extinct shark is not exactly “alive” – I think the more general “Otodus megalodon is the biggest macropredatory shark that ever lived” is perfectly fine to use instead. Gets the same basic message across more coherently.
Recent records show this species was only existed in America, Africa and Europe continents in the last Miocene period 20 million years ago (Ma).
Not quite. There have been plenty of teeth found in South America, Japan & Australia as well, including from the Miocene. See Pimiento & Balk 2015 & Pimiento et al. 2016. I suggest perhaps instead stating that so far there has only been one single study that has described teeth found in South East Asia (Razak & Kocsis 2018), as you’re expanding that specific fossil record – this is where the novelty of this paper lies.
High habitat use preferences by juvenile megalodon were estimated in the shelf (depth 0-40 m) with the size of 1365 km2
Makes sense, but do you actually report any juvenile-sized megalodons? You state earlier that “tooth length” (unclear if this is total tooth height or crown height) is 13-19 cm. Those are very large teeth that almost certainly belong to adults. Based on the abstract, I don’t know how you reached this conclusion with such large teeth. I would also state how many teeth you found in the abstract.
After Miocene, the paleoclimate records show a decline in temperature and lead to the decline of whale population in ocean. The declining of megalodon’s prey explains the declining of this giant shark especially in post Miocene and early Pliocene periods.
This is certainly a theory that’s been seen in literature, but it’s now more widely thought that the decline in whale population was strongly linked to decreasing coastal area (see Pimiento et al. 2017), whereas climate is suggested to have had basically no role in megalodon’s decline in abundance & distribution (see Pimiento et al. 2016). I agree that declining prey almost certainly contributed to megalodon’s extinction, but I think climate shouldn’t be the only thing to consider with regards to megalodon and whales given that both were endothermic (see Ferron 2017) and could tolerate a wider range of temperatures.
Introduction
An extinct giant shark scientifically name Otodus megalodon (previously Charcarocles megalodon) is the last member of the predatory megatoothed lineage and is reported from Miocene (20 million years ago) to Pliocene periods from nearly all continents (Boessenecker et al. 2019).
There are references missing here – Boessenecker et al. (2019) is a good reference for when megalodon went extinct, but not so much for how the shark is named or its global distribution (the paper itself is mostly within western North America). I suggest seeing Pimiento et al. (2016) for global distribution and range, and Shimada et al. (2016) for why some call the shark Otodus rather than Carcharocles.
Based on fossil records, the global O. megalodon distributions including South America (Bahia Inglesa, Mina Fosforita, Punta la Gorda, Punta la Colorada,), Britain (Beaumaris), Australia (Batesford), North America (Tamiami, Gatun), Europe, Africa, and New Zealand (Wellington) (Keyes 1972, Pimiento et al. 2016).
Very good with naming the different records. But I fear this somewhat contradicts one of the statements from the abstract about megalodon teeth being limited to America, Europe and Africa – because this is clearly showing that they have a worldwide range. I’d also, where possible, include specific references to those formations (e.g. Pimiento et al. 2010 for Gatun).
Despite its globally distribution, reports of O. megalodon in Asia continents are still limited with the only report was from coast of Brunei (Kocsis & Razak 2018).
This is a great way to introduce the novelty of this paper, but I would make this “reports of O. megalodon in South East Asia are still limited” – since it’s this area you’re focusing on, and because you don’t want to get too broad with lumping all of Asia here as plenty of teeth have been found in other places in Asia, such as Japan (e.g. Uyeno et al. 1989; Gottfried et al. 1996).
Methods Study area
The two sites named in the results section really should be named here.
The excavated tooth was compared with results from Cooper et al. (2020) for identification purposes based on tooth shape and morphological characters.
There’s a couple of things here. Firstly, this gives me the impression that just one tooth was found. Is that the case? Because the results photo makes it look like more than 1 tooth was found and a range of 13-19 cm surely wouldn’t apply to just a single tooth? The fact that Figure 2’s left photo is a stock photograph found on the internet, and not a photo of the actual megalodon teeth (or tooth) found doesn’t help. Figure 2 needs to be picturing the actual teeth excavated and this needs to be fixed.
Moreover, it’s not clear what it is you actually did here. Cooper et al. (2020) didn’t use teeth in their study, and you should make reference to which morphological characters in the teeth you’re comparing – e.g. crown height or the presence of serrations.
The modeled Miocene ocean then used to estimate the habitat uses of extint megalodon
How were the megalodon fossils incorporated though? The best way to do this in my opinion would be to calculate total length.
Estimates of megalodon habitat uses follow method by (Cooper et al. 2020) by using the extant great white shark (Carcharodon carcharias) habitat uses as the only modern analogue.
It’s not clear how this was done. Cooper et al. (2020) had nothing to do with habitat use so I don’t see how any method from this paper would be appropriate. Moreover, this paper specifically used 4 other shark species as megalodon analogues in addition to the great white. I don’t think this paper is the right one to use and think something like Razak & Kocsis 2018 is a better study to use here.
Habitat modeling was made for juvenile and adult megalodon using the water depth as the function of habitat use preference.
Good, but you should describe how you did this. Was this done in any data analysis software like R (and if so, you should cite that software in your references) and how did you collect the data you used for this? The statistical results of that analysis should also be included as a key part of the results section. You state in the results that you used a bathymetry model – okay, that’s all good, but you should be stating this here in the methods and including all details of how it worked so that a reader could replicate your work if they wanted to.
Results
In South coast of West Java , there were 2 particular locations were megalodon tooth fossil can be founds. Those locations were Surade in west and Cimindi villages in east that were separated 200 km each other. Surade was located 5 km from the Indian ocean and 15 km for Cimindi.
This should be in the “study area” section of the Methods.
The megalodon tooth excavated was sizing 13-19 cm for its length and 14 for its base (Figure 2)
Okay, so just the one tooth was excavated? This should be stated in the abstract and methods, with the size of the tooth reported here. But how could just a single tooth range 13-19 cm – that’s a very big range. Plus, your figure caption states “megalodon teeth fossils”, implying multiple teeth. This should be fixed. I also don’t understand what you mean by “14 for its base.”
Finally, figure 2 is not very informative of what you’re describing here; and upon further investigation is a major concern because it is not representing what this paper is claiming to have excavated. You have multiple shark teeth included, almost all of which are not megalodon teeth. Furthermore, as stated above, this is a stock photo from an internet website, and was also used in a BBC article from this stock photo library 3 years ago. The use of this photo could arguably be seen as plagiarism since the original website is not credited. Finally, upon discovering this stock photograph, its caption claims the teeth were found in Florida, USA, rather than South East Asia as this paper is claiming. This is easily my biggest concern with the paper’s results, as it majorly lacks transparency; and is incredibly misleading to readers.
As I stated above, this figure should be a picture of just the tooth (or teeth) on its own with a scale bar like a ruler next to it (and of the teeth that were actually excavated). I also strongly suggest, as I did above, using the crown height of the tooth to calculate the total length of the shark – e.g. with Shimada 2019.
Based on lithological records, the soil and rock layers were from Miocene period (Figure 3)
Do you have any information as to a rough age range? That would be good to know if possible.
The submersion model then was developed up to 200 m depth referring to the depth of megalodon habitat.
The model itself looks fine in the figures, but how did you determine that 200 m depth is the depth of megalodon habitat? Did you use another paper as reference?
Figure 7. shows modeled habitat uses of megalodon estimated for juvenile and adult using extant Carcharodon carcharias as references. Juvenile was more common in coast at depth of 0-40 m in comparison to adult. Whereas habitat use preference by adult megalodon was low at this depth but increasing at depth of 40-80 m. Juvenile and adult habitat use frequencies were low at a depth of between 80 m and 160 m. Habitat use preferences were increasing at a depth of > 200 m (Figure 8).
Your results make sense to me, but it’s not clear how exactly you used the great whites as an analogue. Did you get depth data from them? Because if so, that’s not really answering your question of megalodon habitat use – it’s simply stating how great whites use depth. Sure, they’re an appropriate analogue, but it would be better to use the fossils you found and total length equations from those teeth (using Shimada 2003; 2019) to get an idea of the depth such sharks occupied and their habitat use, which is what Razak & Kocsis 2018 did. This uses great whites as a reference while also actually using the sizes of the megalodon sharks themselves.
I also don’t understand where you got all this juvenile data from. Your paper has given me the impression that just one tooth has been found, ranging from 13-19 cm in size. How can you possibly have juvenile data with those sizes reported? For reference, Shimada (2019) considers the biggest megalodon tooth in scientific literature to have a crown height of 12 cm, so it sounds like your tooth is possibly even bigger than this. This is another reason why including a proper figure of the fossils you actually found, and not a stock photograph, is so critically important for this study.
Figure 8. Habitat preference model of juvenile and adult megalodon in South coast of West Java during Miocene period (cross sectional view).
A nice figure, but again I don’t understand where you got the juvenile and adult data from. The bars representing each seem to show more adults in deeper waters and more juveniles in shallower waters – that makes sense, but in context of this figure, they don’t mean anything because they’re not showing exactly how many of each are in each section, or the proportions of sharks each life stage occupies. Without the actual numbers of these sharks included, I have no way of knowing where this data came from and how you came to these conclusions.
=== Discussion === Presences of megalodon in South coast of West Java represented by teeth fossils were comparable to other studies.
Which studies? Certainly not Cooper et al. 2020 (see above comments)
The soil and rock layers where the megalodon fossil was found was also comparable to the periods when megalodon exist as reported by other literatures that is from the Miocene to the Pliocene (23–2.6 Ma). Periods of soil layers in Surade and Cimindi were estimated from Miocene period
I suggest removing the first sentence. This is obvious because of how much we know of megalodon’s geological range. Instead, emphasise that this is the first study to recover and describe megalodon teeth from this area (Java) and the second for South East Asia – this is where the true novelty of this paper lies so it should be embraced.
As a comparison, extant great white shark has travelled over a long distance exceeding an estimated 1000 km in length (Bradford et al. 2020)
This isn’t really an appropriate comparison to megalodon going to >200 km depth waters. Nothing about the paper’s results or conclusions is suggestive of megalodon travelling across large ranges so be careful and stick primarily to the depth of the waters used. For reference sake too, great whites have also travelled far longer than 1000 km – for example, a single great white has been observed travelling across the entire Indian Ocean from South Africa to Australia and back (see Bonfil et al. 2005).
Based on observation of extant shark, Weng et al. (2007) have reported juvenile sharks have occasionally displayed deeper movements and vertical excursions reaching depth of 226 m.
This is a much more appropriate comparison to your results themselves.
Kocsis and Razak (2018) stated that megalodon juvenile prefers shallow marine coastal settings either looking for accessible food resource including smaller sharks, rays and bony fishes and avoiding larger predators including adult megalodon or toothed whales.
Yes, this is true. But this is also very characteristic of a nursery site – which juvenile sharks use for the exact purposes you state here. Please mention this and cite Pimiento et al. (2010) and Herraiz et al. (2020), which explore nursery sites of juvenile megalodon sharks.
Declining of megalodon population has been reported globally.
Please remove this. This is a strange sentence that implies the megalodon is still alive – which all evidence suggests it is not. The following sentence is a perfectly fine way to open up this paragraph.
Onset of megalodon population decline probably started in the late Miocene with a decrease in its global abundance and followed by a decline in its geographical range during the Pliocene. Population decline of megalodon has been attributed to intertwined of climate change and drop in the diversity of filter‐feeding whales as the primary factors (Pimiento et al. 2016) and the appearance of new competitors (large predatory whales and the great white shark) as secondary factors.
The first sentence is good; exactly what Pimiento et al. 2016 found. But that paper also found that climate actually played little to no role in megalodon’s decline given that megalodon occupied a wide range of temperature niches. Instead, the other factors you suggest (diversity decline of whales and new competitors) are currently considered the primary reasons for the shark’s decline. Please remove reference to climate change and also cite Boessenecker et al. 2019 here as that paper also looks into competition with the great white. Finally, you should also include a reference to decreasing sea levels and the decimation of coastal habitat areas as a reason for the decline of these whales and by extension megalodon (see Pimiento et al. 2017).
Megalodon population decline was an impact of declining prey caused by climate change. At the beginning of Miocene, diversity and abundance of marine mammals including small whales were high. Whereas, later during the Pliocene, there was a climate change in the form of drop in ocean temperatures that likely contributed to the declining of megalodon preys followed by megalodon populations.
This is all literally just the same thing you said earlier. Please remove.
Post middle Miocene oceanographic climate changes and cooling sea surface temperature may have resulted in megalodon range fragmentation and alongside competition with the newly evolved great white shark (Carcharodon carcharias) has also contributed to the megalodon population declines.
This is again repeating what you said earlier. Should cite Boessenecker et al. 2019 for reference to this theory.
Based on high-resolution benthic isotope record combined with paired mixed layer isotope and Mg/Ca-derived temperature data, a long term cooling trend synchronized with intensification of the Asian winter monsoon from 7 Ma until 5.5 Ma have been detected. Changes in the carbon cycle involving the terrestrial and deep ocean carbon reservoirs were determinant factors of Miocene climate cooling.
Okay, but you should cite where you got this information from and expand on it to apply it to megalodon populations. This is because, as of what’s written here, I struggle to see its relevance to megalodon extinction. Megalodon wasn’t extinct until 3.6 million years ago (Boessenecker et al. 2019), or possibly even as late as 2.6 million years ago (Pimiento & Clements 2014), long after the end of this monsoon period. Are you perhaps suggesting that megalodon was extinct from this area earlier than in other areas? If so, you should clearly state this and date the teeth you found to back up this claim. Based on the content of the paper, I don’t see any evidence connecting this monsoon and megalodon decline.
Moreover, megalodon had regional endothermy (see Ferron 2017; Pimiento et al. 2019) and thus could’ve tolerated a wide range of temperatures – hence why climate is thought to have had little role in its extinction (Pimiento et al. 2016). I suggest re-reading the above literature (and Pimiento et al. 2017) and thinking about how this incorporates into what you’re suggesting here.
Simply put, based on this current draft, I am not convinced that the monsoon had anything to do with extinction due to megalodon’s endothermy and the timing of its demise.
References
Boessenecker, R.W., Ehret, D.J., Long, D.J., Churchill, M., Martin, E. and Boessenecker, S.J., 2019. The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific. PeerJ, 7, e6088.
Bonfil, R., Meÿer, M., Scholl, M.C., Johnson, R., O'Brien, S., Oosthuizen, H., Swanson, S., Kotze, D. and Paterson, M., 2005. Transoceanic migration, spatial dynamics, and population linkages of white sharks. Science 310, 100-103.
Collareta, A., Lambert, O., Landini, W., Di Celma, C., Malinverno, E., Varas-Malca, R., Urbina, M. and Bianucci, G., 2017. Did the giant extinct shark Carcharocles megalodon target small prey? Bite marks on marine mammal remains from the late Miocene of Peru. Palaeogeography, Palaeoclimatology, Palaeoecology 469, 84-91.
Cooper, J.A., Pimiento, C., Ferrón, H.G. and Benton, M.J., 2020. Body dimensions of the extinct giant shark Otodus megalodon: a 2D reconstruction. Scientific reports 10, 14596.
Ferrón, H.G., 2017. Regional endothermy as a trigger for gigantism in some extinct macropredatory sharks. PloS One 12, e0185185.
Gottfried, M.D., Compagno L.J.V., and Bowman, S.C., 1996. Size and skeletal anatomy of the giant" megatooth" shark Carcharodon megalodon. In Great white sharks: the biology of Carcharodon carcharias (eds. Klimley, A.P. and Ainley, D.G.), pp.55-66, Academic Press, San Diego.
Herraiz, J.L., Ribé, J., Botella, H., Martínez-Pérez, C. and Ferrón, H.G., 2020. Use of nursery areas by the extinct megatooth shark Otodus megalodon (Chondrichthyes: Lamniformes). Biology letters 16, 20200746.
Pimiento, C. and Balk, M.A., 2015. Body-size trends of the extinct giant shark Carcharocles megalodon: a deep-time perspective on marine apex predators. Paleobiology 41, 479-490.
Pimiento, C., Cantalapiedra, J.L., Shimada, K., Field, D.J. and Smaers, J.B., 2019. Evolutionary pathways toward gigantism in sharks and rays. Evolution 73, 588-599.
Pimiento, C. and Clements, C.F., 2014. When did Carcharocles megalodon become extinct? A new analysis of the fossil record. PloS One 9, e111086.
Pimiento, C., Ehret, D.J., MacFadden, B.J. and Hubbell, G., 2010. Ancient nursery area for the extinct giant shark Megalodon from the Miocene of Panama. PLoS One 5, e10552.
Pimiento, C., Griffin, J.N., Clements, C.F., Silvestro, D., Varela, S., Uhen, M.D. and Jaramillo, C., 2017. The Pliocene marine megafauna extinction and its impact on functional diversity. Nature ecology & evolution 1, 1100-1106.
Pimiento, C., MacFadden, B.J., Clements, C.F., Varela, S., Jaramillo, C., Velez‐Juarbe, J. and Silliman, B.R., 2016. Geographical distribution patterns of Carcharocles megalodon over time reveal clues about extinction mechanisms. Journal of Biogeography 43, 1645-1655.
Razak, H. and Kocsis, L., 2018. Late Miocene Otodus (Megaselachus) megalodon from Brunei Darussalam: Body length estimation and habitat reconstruction. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 299-306.
Shimada, K., 2003. The relationship between the tooth size and total body length in the white shark. Journal of Fossil Research 35, 28-33.
Shimada, K., 2019. The size of the megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), revisited. Historical Biology 20, 1-8.
Shimada, K., Chandler, R.E., Lam, O.L.T., Tanaka, T. and Ward, D.J., 2016. A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the ‘megatoothed’ clade. Historical Biology 29, 704-714.
Uyeno, T., Sakamoto, O., and Sekine, H., 1989. Description of an almost complete tooth set of Carcharodon megalodon from a Middle Miocene bed in Saitama Prefecture, Japan. Bulletin of Saitama Museum of Natural History 7, 73-85.
Commenter: Jonathan M Werry
The commenter has declared there is no conflict of interests.
The commenter has declared there is no conflict of interests.
Please find a review of this paper below. Firstly, I want to congratulate you on having written this paper and put it out there. I apologise in advance for the length of the review; but there was rather a lot to comment on (both praise and criticism). I provide an overview, some major comments by section, and some specific comments below as is typically written in an academic review. I hope this will be helpful to you in revising the manuscript before submitting it to a journal - as there is much potential here. However, please pay particular attention to my suggestions of calculating total length of the teeth you excavated, of discussing biotic hypotheses of megalodon's extinction, and especially regarding figure 2 - which is a stock photo from the internet of shark teeth apparently from Florida rather than South East Asia and its inclusion here is deeply worrying. I believe you could submit this paper to a peer-reviewed journal for publication, as it is expanding the fossil record of O. megalodon and data such as this is essential for science to advance. However, my concerns that I have pointed out in this review need to be addressed first, and especially with regards to what I've mentioned above (total length calculations, extinction hypotheses and figure 2). I wish you the best with revisions.
Overview:
This paper provides the first report of the iconic Otodus megalodon in Java Island, adding to the very limited fossil record for this species in South East Asia. I commend the author for this find and for expanding the geographic range of this extinct shark’s fossils.The paper has potential, but it also needs a lot of work. There is good knowledge here for the key literature of O. megalodon, particularly regarding its distribution through time, and I think the bathymetry approach is solid, but there is some questionable scientific interpretation here – mostly due to a lack of communication as to how the science was actually done.
The paper states that it is using the methods of Cooper et al. (2020) to compare teeth and habitat use results, but that study covered neither teeth nor habitat and thus I do not understand what exactly was done here with regards to the teeth. It is not clear exactly how the fossils were measured, and I recommend using crown height to calculate the size of the shark – which would be far more informative to the bathymetry modelling than simply extrapolating from great white data (if that’s what’s been done, this isn’t clear either). Moreover, I do not understand where the data of juvenile and adult habitat occupation are coming from as it is not represented in the teeth found (13-19 cm teeth are adult O. megalodon teeth). If this data is taken from great whites, then it says nothing as to how O. megalodon used habitat in Java because the fossils themselves aren’t used.
Finally, despite being in the title, there is only a brief reference to Monsoon of the Miocene and I’m not convinced of its supposed impact on O. megalodon populations. This is because the study is using a very limited sample size of teeth (and even then the number of teeth is unclear) which cannot be representative of an entire population; and the monsoon occurred long before O. megalodon’s extinction. I don’t see how anybody can make interpretations about O. megalodon’s extinction from just a few teeth in one area. Moreover, the paper really hones in on the role of climate change in declining O. megalodon populations (and that of its prey), but doesn’t acknowledge any studies that argue to the contrary, which suggest that O. megalodon decline was almost certainly an entirely biotic mechanism, and probably came from declining coastal areas affecting prey, and/or nursery sites with competition exacerbating this and endothermic taxa like O. megalodon being particularly vulnerable to those declines. The exclusion of a decline in coastal areas as a theory to O. megalodon’s extinction is particularly surprising given that it is directly related to what is being reported here – O. megalodon teeth in a coastal area.
I am sorry I can’t be more positive. But the finding of O. megalodon in this new area is exciting and could fill in a paper by itself, so I hope the author will not be disheartened by my comments and instead can reformat the paper primarily around this novelty. The papers of Reolid & Molina (2015) and Trif et al. (2016), as well as Razak & Kocsis (2018) already cited in the paper, should provide a good template for this. I hope these comments are helpful to the author for their revisions.
Major comments:
=== Abstract ===Some more detail on how you reached your conclusions is needed, especially with regards to juvenile use of habitat considering that the teeth discovered are all incredibly large, even for this species. Moreover, there is some background missing in this abstract that should be corrected. Finally, no mention is actually given to monsoons and their impacts, which really ought to be included given its presence in the paper’s title (but see Discussion comments below).
=== Introduction ===
In general, there’s some very nice background with regards to O. megalodon distribution and introducing the problem that only one study has been conducted on teeth in South East Asia. The section could do with some rewriting though. I hope my specific comments below will help.
Methods
One of my main concerns with this section is that I don’t really understand how you used Cooper et al. 2020 on the teeth since that study didn’t actually use any teeth, they simply used the total length of living sharks to get their relationships with specific body parts and extrapolated to O. megalodon. Furthermore, that study had nothing to do with habitat use, and was novel specifically because it used other analogue species as well as the great white shark. I think Razak & Kocsis 2018 is what you want to be using as your main comparison study here. I suggest also having a look at Diedrich 2013 for this purpose too.
There should also be a brief extra sub-section about the teeth themselves – how many did you find? Are they all dated to around the same time and if so, how did you date them? How did you measure the teeth – did you use total tooth height, crown height or crown width? My suggestion would be to include pictures of all individual teeth, with a scale bar (e.g. a ruler) next to them as a figure here and that you use equations from Shimada (2003; 2019) and Pimiento & Balk (2015) (specifically because this paper in particular uses averages where it’s difficult to determine lateral tooth position) to infer the total length of the sharks – those would be exciting results given the size of the teeth you report in the abstract and results and would help inform your habitat use modelling even further.
But perhaps my most major concern is that the left side of Figure 2 (the picture of the teeth) is a picture of shark teeth taken from Science Photo Library (specifically from this link here: https://www.sciencephoto.com/media/172184/view); despite the paper claiming that they are “the excavated megalodon teeth fossils” – this is misleading to readers and makes me question the science being reported here as it appears the excavated fossils are not being presented here. Without a figure displaying the teeth being excavated, the most vital data is missing from the paper. This needs to be rectified.
Results
I have some concerns with this section too. The results of the excavation itself seems to suggest that the paper only recorded a single tooth, yet somehow there’s also data for how many juveniles and adults were included at each depth from figure 8. I don’t understand where these data came from. Great whites are said to be used as references, but if that’s the case then all that’s been done here is stating the depths great whites would use as juveniles and adults and assuming O. megalodon did the same. I strongly recommend that you calculate total length of the O. megalodon sharks from the tooth or teeth excavated using Shimada (2003; 2019) to help inform your modelling, and that you show exactly where your juvenile and adult data came from – because if it’s from great whites then this isn’t actually adding anything to O. megalodon habitat use.
The bathymetry modelling looks fine to me (although this isn’t my area of expertise), but it’s how O. megalodon data is being considered within it that’s concerning me.
=== Discussion ===
This section needs rewriting as the theory of climate change affecting prey is repeated multiple times without expansion here.
Moreover, there is no consideration given to alternative theories of O. megalodon’s extinction, specifically a decline in coastal area (Pimiento et al. 2017) – which should be particularly relevant to this paper considering that it is focusing on a coastal area. The idea of climate change contributing to O. megalodon’s extinction is notably at odds with the findings of Pimiento & Ferron (also see Collareta et al. 2017 for expansion on role of prey declines, which they argue also favours a biotic mechanism), who have determined that climate had little to do with O. megalodon’s decline and that the shark was regionally endothermic. I strongly recommend revising the literature of O. megalodon extinction and physiology.
Finally, despite being in the title, there is only a brief mention of the monsoon 7-5.5 Ma and the paper does not convince me that it had anything to do with O. megalodon’s extinction (see specific comments) – I think this conclusion is a stretch at best considering that just one area, and possibly just one tooth (which isn’t included in any figure), are investigated here.
Conclusion
The conclusion seems fine based on the paper’s content, but since no mention is given to the monsoon, I don’t really see the need for its inclusion in the title. The monsoon discussion could be removed from the paper and little would change. I really think the paper should be focused only on the finding of the tooth (or teeth; again, this is impossible to tell because the figure used to show the teeth is a stock photo), body length calculations from said teeth, and using that size calculation to inform the bathymetry model and habitat use.
Specific comments:
=== Throughout: === Referencing is not always consistent – e.g. Cooper et al. 2020 is cited as “from (Cooper et al. 2020)” and “from Cooper et al. (2020)” at different points. Please check citations across the whole manuscript and fix. This inconsistency is also seen in the reference list so please go through them again. For example, “et al.” is used after naming 3 authors of the Cooper paper when there is just one additional author, whereas all authors are named in Boessenecker et al. 2019 and Pimiento et al. 2016.Please also check throughout the manuscript and make sure megalodon is always named as “O. megalodon” after the first mention of its scientific name. This is not always done and should be fixed as this is basic scientific practise.
Abstract
Otodus megalodon is known as the biggest shark ever alive Strange phrasing. An extinct shark is not exactly “alive” – I think the more general “Otodus megalodon is the biggest macropredatory shark that ever lived” is perfectly fine to use instead. Gets the same basic message across more coherently.Recent records show this species was only existed in America, Africa and Europe continents in the last Miocene period 20 million years ago (Ma). Not quite. There have been plenty of teeth found in South America, Japan & Australia as well, including from the Miocene. See Pimiento & Balk 2015 & Pimiento et al. 2016. I suggest perhaps instead stating that so far there has only been one single study that has described teeth found in South East Asia (Razak & Kocsis 2018), as you’re expanding that specific fossil record – this is where the novelty of this paper lies.
High habitat use preferences by juvenile megalodon were estimated in the shelf (depth 0-40 m) with the size of 1365 km2 Makes sense, but do you actually report any juvenile-sized megalodons? You state earlier that “tooth length” (unclear if this is total tooth height or crown height) is 13-19 cm. Those are very large teeth that almost certainly belong to adults. Based on the abstract, I don’t know how you reached this conclusion with such large teeth. I would also state how many teeth you found in the abstract.
After Miocene, the paleoclimate records show a decline in temperature and lead to the decline of whale population in ocean. The declining of megalodon’s prey explains the declining of this giant shark especially in post Miocene and early Pliocene periods.
This is certainly a theory that’s been seen in literature, but it’s now more widely thought that the decline in whale population was strongly linked to decreasing coastal area (see Pimiento et al. 2017), whereas climate is suggested to have had basically no role in megalodon’s decline in abundance & distribution (see Pimiento et al. 2016). I agree that declining prey almost certainly contributed to megalodon’s extinction, but I think climate shouldn’t be the only thing to consider with regards to megalodon and whales given that both were endothermic (see Ferron 2017) and could tolerate a wider range of temperatures.
Introduction
An extinct giant shark scientifically name Otodus megalodon (previously Charcarocles megalodon) is the last member of the predatory megatoothed lineage and is reported from Miocene (20 million years ago) to Pliocene periods from nearly all continents (Boessenecker et al. 2019).There are references missing here – Boessenecker et al. (2019) is a good reference for when megalodon went extinct, but not so much for how the shark is named or its global distribution (the paper itself is mostly within western North America). I suggest seeing Pimiento et al. (2016) for global distribution and range, and Shimada et al. (2016) for why some call the shark Otodus rather than Carcharocles.
Based on fossil records, the global O. megalodon distributions including South America (Bahia Inglesa, Mina Fosforita, Punta la Gorda, Punta la Colorada,), Britain (Beaumaris), Australia (Batesford), North America (Tamiami, Gatun), Europe, Africa, and New Zealand (Wellington) (Keyes 1972, Pimiento et al. 2016). Very good with naming the different records. But I fear this somewhat contradicts one of the statements from the abstract about megalodon teeth being limited to America, Europe and Africa – because this is clearly showing that they have a worldwide range. I’d also, where possible, include specific references to those formations (e.g. Pimiento et al. 2010 for Gatun).
Despite its globally distribution, reports of O. megalodon in Asia continents are still limited with the only report was from coast of Brunei (Kocsis & Razak 2018). This is a great way to introduce the novelty of this paper, but I would make this “reports of O. megalodon in South East Asia are still limited” – since it’s this area you’re focusing on, and because you don’t want to get too broad with lumping all of Asia here as plenty of teeth have been found in other places in Asia, such as Japan (e.g. Uyeno et al. 1989; Gottfried et al. 1996).
Methods
Study area The two sites named in the results section really should be named here.
The excavated tooth was compared with results from Cooper et al. (2020) for identification purposes based on tooth shape and morphological characters. There’s a couple of things here. Firstly, this gives me the impression that just one tooth was found. Is that the case? Because the results photo makes it look like more than 1 tooth was found and a range of 13-19 cm surely wouldn’t apply to just a single tooth? The fact that Figure 2’s left photo is a stock photograph found on the internet, and not a photo of the actual megalodon teeth (or tooth) found doesn’t help. Figure 2 needs to be picturing the actual teeth excavated and this needs to be fixed.
Moreover, it’s not clear what it is you actually did here. Cooper et al. (2020) didn’t use teeth in their study, and you should make reference to which morphological characters in the teeth you’re comparing – e.g. crown height or the presence of serrations.
The modeled Miocene ocean then used to estimate the habitat uses of extint megalodon How were the megalodon fossils incorporated though? The best way to do this in my opinion would be to calculate total length.
Estimates of megalodon habitat uses follow method by (Cooper et al. 2020) by using the extant great white shark (Carcharodon carcharias) habitat uses as the only modern analogue. It’s not clear how this was done. Cooper et al. (2020) had nothing to do with habitat use so I don’t see how any method from this paper would be appropriate. Moreover, this paper specifically used 4 other shark species as megalodon analogues in addition to the great white. I don’t think this paper is the right one to use and think something like Razak & Kocsis 2018 is a better study to use here.
Habitat modeling was made for juvenile and adult megalodon using the water depth as the function of habitat use preference. Good, but you should describe how you did this. Was this done in any data analysis software like R (and if so, you should cite that software in your references) and how did you collect the data you used for this? The statistical results of that analysis should also be included as a key part of the results section. You state in the results that you used a bathymetry model – okay, that’s all good, but you should be stating this here in the methods and including all details of how it worked so that a reader could replicate your work if they wanted to.
Results
In South coast of West Java , there were 2 particular locations were megalodon tooth fossil can be founds. Those locations were Surade in west and Cimindi villages in east that were separated 200 km each other. Surade was located 5 km from the Indian ocean and 15 km for Cimindi. This should be in the “study area” section of the Methods.The megalodon tooth excavated was sizing 13-19 cm for its length and 14 for its base (Figure 2) Okay, so just the one tooth was excavated? This should be stated in the abstract and methods, with the size of the tooth reported here. But how could just a single tooth range 13-19 cm – that’s a very big range. Plus, your figure caption states “megalodon teeth fossils”, implying multiple teeth. This should be fixed. I also don’t understand what you mean by “14 for its base.”
Finally, figure 2 is not very informative of what you’re describing here; and upon further investigation is a major concern because it is not representing what this paper is claiming to have excavated. You have multiple shark teeth included, almost all of which are not megalodon teeth. Furthermore, as stated above, this is a stock photo from an internet website, and was also used in a BBC article from this stock photo library 3 years ago. The use of this photo could arguably be seen as plagiarism since the original website is not credited. Finally, upon discovering this stock photograph, its caption claims the teeth were found in Florida, USA, rather than South East Asia as this paper is claiming. This is easily my biggest concern with the paper’s results, as it majorly lacks transparency; and is incredibly misleading to readers.
As I stated above, this figure should be a picture of just the tooth (or teeth) on its own with a scale bar like a ruler next to it (and of the teeth that were actually excavated). I also strongly suggest, as I did above, using the crown height of the tooth to calculate the total length of the shark – e.g. with Shimada 2019.
Based on lithological records, the soil and rock layers were from Miocene period (Figure 3) Do you have any information as to a rough age range? That would be good to know if possible.
The submersion model then was developed up to 200 m depth referring to the depth of megalodon habitat. The model itself looks fine in the figures, but how did you determine that 200 m depth is the depth of megalodon habitat? Did you use another paper as reference?
Figure 7. shows modeled habitat uses of megalodon estimated for juvenile and adult using extant Carcharodon carcharias as references. Juvenile was more common in coast at depth of 0-40 m in comparison to adult. Whereas habitat use preference by adult megalodon was low at this depth but increasing at depth of 40-80 m. Juvenile and adult habitat use frequencies were low at a depth of between 80 m and 160 m. Habitat use preferences were increasing at a depth of > 200 m (Figure 8). Your results make sense to me, but it’s not clear how exactly you used the great whites as an analogue. Did you get depth data from them? Because if so, that’s not really answering your question of megalodon habitat use – it’s simply stating how great whites use depth. Sure, they’re an appropriate analogue, but it would be better to use the fossils you found and total length equations from those teeth (using Shimada 2003; 2019) to get an idea of the depth such sharks occupied and their habitat use, which is what Razak & Kocsis 2018 did. This uses great whites as a reference while also actually using the sizes of the megalodon sharks themselves.
I also don’t understand where you got all this juvenile data from. Your paper has given me the impression that just one tooth has been found, ranging from 13-19 cm in size. How can you possibly have juvenile data with those sizes reported? For reference, Shimada (2019) considers the biggest megalodon tooth in scientific literature to have a crown height of 12 cm, so it sounds like your tooth is possibly even bigger than this. This is another reason why including a proper figure of the fossils you actually found, and not a stock photograph, is so critically important for this study.
Figure 8. Habitat preference model of juvenile and adult megalodon in South coast of West Java during Miocene period (cross sectional view). A nice figure, but again I don’t understand where you got the juvenile and adult data from. The bars representing each seem to show more adults in deeper waters and more juveniles in shallower waters – that makes sense, but in context of this figure, they don’t mean anything because they’re not showing exactly how many of each are in each section, or the proportions of sharks each life stage occupies. Without the actual numbers of these sharks included, I have no way of knowing where this data came from and how you came to these conclusions.
=== Discussion ===
Presences of megalodon in South coast of West Java represented by teeth fossils were comparable to other studies. Which studies? Certainly not Cooper et al. 2020 (see above comments)
The soil and rock layers where the megalodon fossil was found was also comparable to the periods when megalodon exist as reported by other literatures that is from the Miocene to the Pliocene (23–2.6 Ma). Periods of soil layers in Surade and Cimindi were estimated from Miocene period I suggest removing the first sentence. This is obvious because of how much we know of megalodon’s geological range. Instead, emphasise that this is the first study to recover and describe megalodon teeth from this area (Java) and the second for South East Asia – this is where the true novelty of this paper lies so it should be embraced.
As a comparison, extant great white shark has travelled over a long distance exceeding an estimated 1000 km in length (Bradford et al. 2020) This isn’t really an appropriate comparison to megalodon going to >200 km depth waters. Nothing about the paper’s results or conclusions is suggestive of megalodon travelling across large ranges so be careful and stick primarily to the depth of the waters used. For reference sake too, great whites have also travelled far longer than 1000 km – for example, a single great white has been observed travelling across the entire Indian Ocean from South Africa to Australia and back (see Bonfil et al. 2005).
Based on observation of extant shark, Weng et al. (2007) have reported juvenile sharks have occasionally displayed deeper movements and vertical excursions reaching depth of 226 m.
This is a much more appropriate comparison to your results themselves.
Kocsis and Razak (2018) stated that megalodon juvenile prefers shallow marine coastal settings either looking for accessible food resource including smaller sharks, rays and bony fishes and avoiding larger predators including adult megalodon or toothed whales. Yes, this is true. But this is also very characteristic of a nursery site – which juvenile sharks use for the exact purposes you state here. Please mention this and cite Pimiento et al. (2010) and Herraiz et al. (2020), which explore nursery sites of juvenile megalodon sharks.
Declining of megalodon population has been reported globally. Please remove this. This is a strange sentence that implies the megalodon is still alive – which all evidence suggests it is not. The following sentence is a perfectly fine way to open up this paragraph.
Onset of megalodon population decline probably started in the late Miocene with a decrease in its global abundance and followed by a decline in its geographical range during the Pliocene. Population decline of megalodon has been attributed to intertwined of climate change and drop in the diversity of filter‐feeding whales as the primary factors (Pimiento et al. 2016) and the appearance of new competitors (large predatory whales and the great white shark) as secondary factors. The first sentence is good; exactly what Pimiento et al. 2016 found. But that paper also found that climate actually played little to no role in megalodon’s decline given that megalodon occupied a wide range of temperature niches. Instead, the other factors you suggest (diversity decline of whales and new competitors) are currently considered the primary reasons for the shark’s decline. Please remove reference to climate change and also cite Boessenecker et al. 2019 here as that paper also looks into competition with the great white. Finally, you should also include a reference to decreasing sea levels and the decimation of coastal habitat areas as a reason for the decline of these whales and by extension megalodon (see Pimiento et al. 2017).
Megalodon population decline was an impact of declining prey caused by climate change. At the beginning of Miocene, diversity and abundance of marine mammals including small whales were high. Whereas, later during the Pliocene, there was a climate change in the form of drop in ocean temperatures that likely contributed to the declining of megalodon preys followed by megalodon populations.
This is all literally just the same thing you said earlier. Please remove.
Post middle Miocene oceanographic climate changes and cooling sea surface temperature may have resulted in megalodon range fragmentation and alongside competition with the newly evolved great white shark (Carcharodon carcharias) has also contributed to the megalodon population declines.
This is again repeating what you said earlier. Should cite Boessenecker et al. 2019 for reference to this theory.
Based on high-resolution benthic isotope record combined with paired mixed layer isotope and Mg/Ca-derived temperature data, a long term cooling trend synchronized with intensification of the Asian winter monsoon from 7 Ma until 5.5 Ma have been detected. Changes in the carbon cycle involving the terrestrial and deep ocean carbon reservoirs were determinant factors of Miocene climate cooling.
Okay, but you should cite where you got this information from and expand on it to apply it to megalodon populations. This is because, as of what’s written here, I struggle to see its relevance to megalodon extinction. Megalodon wasn’t extinct until 3.6 million years ago (Boessenecker et al. 2019), or possibly even as late as 2.6 million years ago (Pimiento & Clements 2014), long after the end of this monsoon period. Are you perhaps suggesting that megalodon was extinct from this area earlier than in other areas? If so, you should clearly state this and date the teeth you found to back up this claim. Based on the content of the paper, I don’t see any evidence connecting this monsoon and megalodon decline.
Moreover, megalodon had regional endothermy (see Ferron 2017; Pimiento et al. 2019) and thus could’ve tolerated a wide range of temperatures – hence why climate is thought to have had little role in its extinction (Pimiento et al. 2016). I suggest re-reading the above literature (and Pimiento et al. 2017) and thinking about how this incorporates into what you’re suggesting here.
Simply put, based on this current draft, I am not convinced that the monsoon had anything to do with extinction due to megalodon’s endothermy and the timing of its demise.
References
Boessenecker, R.W., Ehret, D.J., Long, D.J., Churchill, M., Martin, E. and Boessenecker, S.J., 2019. The Early Pliocene extinction of the mega-toothed shark Otodus megalodon: a view from the eastern North Pacific. PeerJ, 7, e6088.
Bonfil, R., Meÿer, M., Scholl, M.C., Johnson, R., O'Brien, S., Oosthuizen, H., Swanson, S., Kotze, D. and Paterson, M., 2005. Transoceanic migration, spatial dynamics, and population linkages of white sharks. Science 310, 100-103.
Collareta, A., Lambert, O., Landini, W., Di Celma, C., Malinverno, E., Varas-Malca, R., Urbina, M. and Bianucci, G., 2017. Did the giant extinct shark Carcharocles megalodon target small prey? Bite marks on marine mammal remains from the late Miocene of Peru. Palaeogeography, Palaeoclimatology, Palaeoecology 469, 84-91.
Cooper, J.A., Pimiento, C., Ferrón, H.G. and Benton, M.J., 2020. Body dimensions of the extinct giant shark Otodus megalodon: a 2D reconstruction. Scientific reports 10, 14596.
Ferrón, H.G., 2017. Regional endothermy as a trigger for gigantism in some extinct macropredatory sharks. PloS One 12, e0185185.
Gottfried, M.D., Compagno L.J.V., and Bowman, S.C., 1996. Size and skeletal anatomy of the giant" megatooth" shark Carcharodon megalodon. In Great white sharks: the biology of Carcharodon carcharias (eds. Klimley, A.P. and Ainley, D.G.), pp.55-66, Academic Press, San Diego.
Herraiz, J.L., Ribé, J., Botella, H., Martínez-Pérez, C. and Ferrón, H.G., 2020. Use of nursery areas by the extinct megatooth shark Otodus megalodon (Chondrichthyes: Lamniformes). Biology letters 16, 20200746.
Pimiento, C. and Balk, M.A., 2015. Body-size trends of the extinct giant shark Carcharocles megalodon: a deep-time perspective on marine apex predators. Paleobiology 41, 479-490.
Pimiento, C., Cantalapiedra, J.L., Shimada, K., Field, D.J. and Smaers, J.B., 2019. Evolutionary pathways toward gigantism in sharks and rays. Evolution 73, 588-599.
Pimiento, C. and Clements, C.F., 2014. When did Carcharocles megalodon become extinct? A new analysis of the fossil record. PloS One 9, e111086.
Pimiento, C., Ehret, D.J., MacFadden, B.J. and Hubbell, G., 2010. Ancient nursery area for the extinct giant shark Megalodon from the Miocene of Panama. PLoS One 5, e10552.
Pimiento, C., Griffin, J.N., Clements, C.F., Silvestro, D., Varela, S., Uhen, M.D. and Jaramillo, C., 2017. The Pliocene marine megafauna extinction and its impact on functional diversity. Nature ecology & evolution 1, 1100-1106.
Pimiento, C., MacFadden, B.J., Clements, C.F., Varela, S., Jaramillo, C., Velez‐Juarbe, J. and Silliman, B.R., 2016. Geographical distribution patterns of Carcharocles megalodon over time reveal clues about extinction mechanisms. Journal of Biogeography 43, 1645-1655.
Razak, H. and Kocsis, L., 2018. Late Miocene Otodus (Megaselachus) megalodon from Brunei Darussalam: Body length estimation and habitat reconstruction. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen, 299-306.
Shimada, K., 2003. The relationship between the tooth size and total body length in the white shark. Journal of Fossil Research 35, 28-33.
Shimada, K., 2019. The size of the megatooth shark, Otodus megalodon (Lamniformes: Otodontidae), revisited. Historical Biology 20, 1-8.
Shimada, K., Chandler, R.E., Lam, O.L.T., Tanaka, T. and Ward, D.J., 2016. A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the ‘megatoothed’ clade. Historical Biology 29, 704-714.
Uyeno, T., Sakamoto, O., and Sekine, H., 1989. Description of an almost complete tooth set of Carcharodon megalodon from a Middle Miocene bed in Saitama Prefecture, Japan. Bulletin of Saitama Museum of Natural History 7, 73-85.