Mosasaur Feeding Ecology from the Campanian Bearpaw Formation, Alberta, Canada: A Preliminary Multi-Proxy Approach
Emily Bamforth
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsI believe this is a well-researched and well-laid out paper, with important implications for understanding niche-partitioning in Cretaceous mosasaurs of the Bearpaw Formation. In particular, the multi-disciplinary nature of this research, combining microwear analysis, EDX, and tooth bending strength, contributes significantly to our understanding of several large-bodied predators could coexist in a shallow continental sea.
I have included an annotated PDF of the manuscript suggesting some considerations and edits. Below, I have also outlined a few points that I believe would clarify and improve the manuscript.
1. In the Methods and Materials Section, there is no to how many specimens were included in the study, where they came from geographically, if they were isolated teeth or skulls, or their completeness. I understand that some of this information is included in the supplementary data, but I suggest including, at the least, a count of how many specimens were included of each taxon, the type of specimen they were (isolated teeth vs. skull, original vs. cast), and the locality the specimens were collected from. This will improve the reproducibility of the study.
2. Although it is included in the supplementary data, I suggest including sample size numbers in Figures 2 though 5.
3. For a more initiative presentation of the Energy-dispersive X-ray Spectroscopy results, I suggest presenting the data in table format (please see notes in annotated manuscript), as it is difficult to follow all the different taxa and their suggested prey species through the text.
4. I believe more discussion is warranted on the suggestion that Tylosaurus had a similar dietary niche to Cretaceous plesiosaurs. Although I understand this study is limited to Albertan specimens, there are some examples of Tylosaurus gut contents from elsewhere to suggest these animals were higher-level predators. Everet (2004; see reference below) described a Tylosaurus from the Niobrara Formation of Western Kansas with plesiosaur remains in its gut. Although not referenced in the paper describing the species, the type of Tylosaurus saskatchewanensis had a 3m-long 𝘗𝘭𝘪𝘰𝘱𝘭𝘢𝘵𝘦𝘤𝘢𝘳𝘱𝘶𝘴 in its gut contents. More information on this specimen can be obtained through the Royal Saskatchewan Museum.
a. Everhart, M. J. "Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas." The Mosasaur 7, no. 4 (2004).
5. I feel more discussion could be included in the Discussion section as to how this study influences the broader view of Cretaceous marine food webs and ecosystems. For example, do/could shallow or continental seas today host the same diversity of large-bodied predators? If not, was it likely just dietary niche partitioning that allowed these large animals to co-exist? Could these mosasaur species have partitioned their niches in other ways, such as being diurnal vs. nocturnal, or possibly have migrated? There has also been some suggestion recently that Cretaceous marine foodwebs may have supported higher trophic levels that today’s marine systems (see Cortez et al., 2024, reference below). Could the same be true of the Bearpaw ecosystem?
a. Cortés, D., & Larsson, H. C. (2024). Top of the food chains: an ecological network of the marine Paja Formation biota from the Early Cretaceous of Colombia reveals the highest trophic levels ever estimated. Zoological Journal of the Linnean Society, 202(1), zlad092.
Comments for author File: 
Comments.pdf
Author Response
Reviewer 1: I believe this is a well-researched and well-laid out paper, with important implications for understanding niche-partitioning in Cretaceous mosasaurs of the Bearpaw Formation. In particular, the multi-disciplinary nature of this research, combining microwear analysis, EDX, and tooth bending strength, contributes significantly to our understanding of several large-bodied predators could coexist in a shallow continental sea.I have included an annotated PDF of the manuscript suggesting some considerations and edits. Below, I have also outlined a few points that I believe would clarify and improve the manuscript.
Response: Dear reviewer 1, thank you for your thorough check of this manuscript. It is really appreciated! Below responses to your comments and suggestions. The other comments from the pdf I mostly weaved into the text, see resubmission file. Kind regards, Femke Holwerda.
Comments 1. In the Methods and Materials Section, there is no to how many specimens were included in the study, where they came from geographically, if they were isolated teeth or skulls, or their completeness. I understand that some of this information is included in the supplementary data, but I suggest including, at the least, a count of how many specimens were included of each taxon, the type of specimen they were (isolated teeth vs. skull, original vs. cast), and the locality the specimens were collected from. This will improve the reproducibility of the study.
Response 1. Thanks for pointing this out, I have included a table listing all these things.
|
Taxon |
Mosasaurus |
Prognathodon |
Tylosaurus |
Plioplatecarpus |
Elasmosaur |
Sawfish |
Shark |
|
Type |
Skull & teeth |
Skull & teeth |
Teeth |
Teeth |
Teeth |
Teeth |
Teeth |
|
Locality |
Lethbridge |
Lethbridge |
Manyberries |
Lethbridge |
DPP |
Iddlesleigh |
Iddlesleigh |
|
Formation |
Bearpaw |
Bearpaw |
Bearpaw |
Bearpaw |
Bearpaw |
Bearpaw |
Bearpaw |
|
N Microwear |
10 |
5 |
2 |
3 |
- |
- |
- |
|
N EDX |
16 |
16 |
9 |
7 |
5 |
4 |
15 |
|
N Tooth Bending Strength |
30 |
28 |
- |
5 |
- |
- |
- |
Comment 2. Although it is included in the supplementary data, I suggest including sample size numbers in Figures 2 though 5.
Reply 2. We have added sample sizes in the figures
Comment 3. For a more initiative presentation of the Energy-dispersive X-ray Spectroscopy results, I suggest presenting the data in table format (please see notes in annotated manuscript), as it is difficult to follow all the different taxa and their suggested prey species through the text.
Reply 3. We have added a table with an overview of ‘who likely ate what’ based on our analyses, and have included this in the Discussion section, where similarly the PCA diagram of all EDX data gives an overview of how closely overlapping the different vertebrates were.
|
Taxon |
Mosasaurus |
Prognathodon |
Tylosaurus |
Plioplatecarpus |
|
Sr/Ca range |
0,12 – 0,73 |
0,11 – 0,57 |
0,31 – 0,77 |
0,17 – 0,71 |
|
Ba/Ca range |
0,06 – 0,33 |
0,03 – 0,33 |
0,13 – 0,21 |
0,03 – 0,11 |
|
Dominant microwear |
Fine scratches |
Pits |
Gouges |
Fine scratches |
|
Likely prey |
Large range of vertebrate prey items Large range of invertebrate prey items |
Harder vertebrate prey items (turtles, large fish) Harder invertebrate prey items (shellfish, ammonites) |
Fish and larger vertebrates
|
Softer prey items (squid and fish) Harder prey items (large fish, ammonites) |
Comment 4. I believe more discussion is warranted on the suggestion that Tylosaurus had a similar dietary niche to Cretaceous plesiosaurs. Although I understand this study is limited to Albertan specimens, there are some examples of Tylosaurus gut contents from elsewhere to suggest these animals were higher-level predators. Everet (2004; see reference below) described a Tylosaurus from the Niobrara Formation of Western Kansas with plesiosaur remains in its gut. Although not referenced in the paper describing the species, the type of Tylosaurus saskatchewanensis had a 3m-long ??????????????? in its gut contents. More information on this specimen can be obtained through the Royal Saskatchewan Museum.
Everhart, M. J. "Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas." The Mosasaur 7, no. 4 (2004).
Reply 4. We are grateful for this information on Tylosaurus saskatchewanensis! I have been trying to see the specimen during my time in Canada, but sadly did not manage. Thanks also for the predation on plesiosaur reference. We have included the possibility that, by following the range of the elasmosaurs in terms of EDX results, but with a higher trophic level as evidenced by its Sr range, Tylosaurs were in fact predating elasmosaurs, instead of simply occupying a similar dietary niche (which is fish, and benthic prey).
Comment 5. I feel more discussion could be included in the Discussion section as to how this study influences the broader view of Cretaceous marine food webs and ecosystems. For example, do/could shallow or continental seas today host the same diversity of large-bodied predators? If not, was it likely just dietary niche partitioning that allowed these large animals to co-exist? Could these mosasaur species have partitioned their niches in other ways, such as being diurnal vs. nocturnal, or possibly have migrated? There has also been some suggestion recently that Cretaceous marine foodwebs may have supported higher trophic levels that today’s marine systems (see Cortez et al., 2024, reference below). Could the same be true of the Bearpaw ecosystem?
- Cortés, D., & Larsson, H. C. (2024). Top of the food chains: an ecological network of the marine Paja Formation biota from the Early Cretaceous of Colombia reveals the highest trophic levels ever estimated. Zoological Journal of the Linnean Society, 202(1), zlad092.
Reply 5. We do concur that the Cretaceous sea was more productive than modern seas. Higher sea level equals more shallow seas, with high primary productivity working its way up the foodchain.We have added a line about this citing Cortes&Larsson in the Discussion. A broader discussion on this topic (similarly, adding your comment from the Introduction on regional WIS differences) will be added to a follow-up paper from this – where Sr, C and O isotopes have been measured on a sleuth of Bearpaw marine vertebrates (and a DMTA study on the Bearpaw mosasaurs is in the works, when FH can find an appropriate machine for the analysis).
It is really hard, however, to measure diurnal vs nocturnal hunting behaviour, or even seasonality in deeptime remains. Similarly, scavenging behaviour is hard to determine via this type of analysis. After a very interesting discussion with Mike Polcyn, during his PhD defense here in Utrecht, I do have some lines to add regarding Plioplatecarpus’ possible ‘enigmatic’ feeding ecology, and we also have added a line about the broader implications for marine Cretaceous ecosystems.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsIntroduction
Polcyn et al., 2014, is not in the references, on the other hand it is suggested to cite references in addition to those of Polcyn et al 2014:
Bardet, N., Falconnet, J., Fischer, V., Houssaye, A., Jouve, S., Pereda Suber-biola, X., Perez-Garcia, A., Rage, J.C., Vincent, P., 2014. Mesozoic marine palaeobiogeography in response to drifting plate. Gondwana Research 26, 869e887.
Fernández Marta S. & Talevi Marianella. 2015. An halisaurine (Squamata: Mosasauridae) from the Late Cretaceous of Patagonia, with a preserved tympanic disc: insights into mosasaur middle ear. Comptes rendus Palevol14: 483–493.
Fernandez, M.S., Martin, J.E., Casadío, S., 2008. Mosasaurs (Reptilia) from the late Maastrichtian (Late Cretaceous) of northern Patagonia (Río Negro, Argentina). Journal of South American Earth Sciences 25, 176e186.
Gallagher, W.B., 2005. Recent mosasaur discoveries from New Jersey and Delaware, USA: stratigraphy, taphonomy and implications for mosasaur extinction. Netherlands Journal of Geosciences 84, 241e245.
P. González Ruiz, M. Férnandez, M. Talevi, J. Leardi, M. Reguero.2019. A new Plotosaurini mosasaur skull from the upper Maastrichtian of Antarctica. Plotosaurini paleogeographic occurrences. Cretaceous Research 100, 104166-10417. https://doi.org/10.1016/j.cretres.2019.06.012
Kiernan, C.R., 2002. Stratigraphic distribution and habitat segregation of mosasaurs in the Upper Cretaceous of western and central Alabama, with an [sic] historical review of Alabama mosasaur discoveries. Journal of Vertebrate Paleontology 22,9e103.
Mil
an, J., Jagt, J.W., Lindgren, J., Schulp, A.S., 2017. First record of Carinodens (Squamata, Mosasauridae) from the uppermost Maastrichtian of Stevns Klint, Denmark. Alcheringa. An Australasian Journal of Palaeontology 1e6.
Mulder, E.W.A., Jagt, J.W.M., Kuypers, M.M.M., Peeters, H.H.G., Rompen, P., 1998. Preliminary observations on the stratigraphic distribution of Late Cretaceous marine and terrestrial reptiles from the Maastrichtian type area (SE Netherlands, NE Belgium). Oryctos 1, 55e64.
Materials and methods: photographs of the teeth analyzed should be added
Figure 1 could be improved, it seems like a rudimentary diagram
Results
Assemble figures showing what is described, not just statistical graphs.
For example in 3.1 Microwear show pits, fine scratches, etc.
Add photographs of the teeth where you can see what is shown in figure 3
Figure 6, Plioplatcarpus teeth are not identified? Are there no premaxilla, maxilla and dentary teeth classified?
I have not checked all the references but the authors should do so since the first citation that appears in the text does not appear in the reference list
Author Response
Reviewer comment 1:
Polcyn et al., 2014, is not in the references, on the other hand it is suggested to cite references in addition to those of Polcyn et al 2014:
Bardet, N., Falconnet, J., Fischer, V., Houssaye, A., Jouve, S., Pereda Suber-biola, X., Perez-Garcia, A., Rage, J.C., Vincent, P., 2014. Mesozoic marine palaeobiogeography in response to drifting plate. Gondwana Research 26, 869e887.
Fernández Marta S. & Talevi Marianella. 2015. An halisaurine (Squamata: Mosasauridae) from the Late Cretaceous of Patagonia, with a preserved tympanic disc: insights into mosasaur middle ear. Comptes rendus Palevol14: 483–493.
Fernandez, M.S., Martin, J.E., Casadío, S., 2008. Mosasaurs (Reptilia) from the late Maastrichtian (Late Cretaceous) of northern Patagonia (Río Negro, Argentina). Journal of South American Earth Sciences 25, 176e186.
Gallagher, W.B., 2005. Recent mosasaur discoveries from New Jersey and Delaware, USA: stratigraphy, taphonomy and implications for mosasaur extinction. Netherlands Journal of Geosciences 84, 241e245.
- González Ruiz, M. Férnandez, M. Talevi, J. Leardi, M. Reguero.2019. A new Plotosaurini mosasaur skull from the upper Maastrichtian of Antarctica. Plotosaurini paleogeographic occurrences. Cretaceous Research 100, 104166-10417. https://doi.org/10.1016/j.cretres.2019.06.012
Kiernan, C.R., 2002. Stratigraphic distribution and habitat segregation of mosasaurs in the Upper Cretaceous of western and central Alabama, with an [sic] historical review of Alabama mosasaur discoveries. Journal of Vertebrate Paleontology 22,9e103.
Milan, J., Jagt, J.W., Lindgren, J., Schulp, A.S., 2017. First record of Carinodens (Squamata, Mosasauridae) from the uppermost Maastrichtian of Stevns Klint, Denmark. Alcheringa. An Australasian Journal of Palaeontology 1e6.
Mulder, E.W.A., Jagt, J.W.M., Kuypers, M.M.M., Peeters, H.H.G., Rompen, P., 1998. Preliminary observations on the stratigraphic distribution of Late Cretaceous marine and terrestrial reptiles from the Maastrichtian type area (SE Netherlands, NE Belgium). Oryctos 1, 55e64.
Reply 1: Thank you for providing these additional citations. I have included a different citation from (the now newly minted) Dr Polcyn, as he and I had a very fruitful conversation about the specific plioplatecarpid skull curiosity (in relation to diving behaviour) during his PhD defense (coincidence or not; I was part of the exam committee). Kiernan 2002 is already included, and the other citations, though very interesting, I do not immediately see relevant for this particular study, but rather, if you permit me, they would be very useful for a paper on type-Maastrichtian mosasaur microwear that myself and colleagues should be submitting somewhere in the coming year.
Reviewer comment 2:
Materials and methods: photographs of the teeth analyzed should be added
Reply 2: Sadly, it wasn’t possible to photograph all teeth. A more comprehensive catalogue is available on the emuseum page of the Royal Tyrrell Museum of Palaeontology; https://rtmp.emuseum.com/objects/list
Reviewer comment 3:
Figure 1 could be improved, it seems like a rudimentary diagram
Reply 3: we’ve added the skull of the Tyrrell Prognathodon this figure was inspired by, to better highlight what we’re measuring for the tooth bending strength
Reviewer comment 4: Results
Assemble figures showing what is described, not just statistical graphs.
For example in 3.1 Microwear show pits, fine scratches, etc.
Add photographs of the teeth where you can see what is shown in figure 3
Reply 4: We’ve added schematics of what microwear we’ve been counting, with an SEM image included for Figure 1 (materials and methods)
Reviewer comment 5:
Figure 6, Plioplatcarpus teeth are not identified? Are there no premaxilla, maxilla and dentary teeth classified?
Reply 5: Unfortunately, this was not possible with the isolated teeth of the Plioplatecarpus specimens used here for microwear and EDX
Reviewer comment 6: I have not checked all the references but the authors should do so since the first citation that appears in the text does not appear in the reference list
Reply 6: We have checked the references and all should be there now, thanks for notifying us! We have also added all CC licenses to the images used from Phylopic.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Comments and Suggestions for Authors...............
