How wear, age, and sex relate to enamel chipping in Cayo Santiago rhesus macaques (Macaca mulatta)

Debbie Guatelli-Steinberg; Luke D. Fannin; Qian Wang

doi:10.1371/journal.pone.0337554

Peer Review History

Original SubmissionJuly 2, 2025
15 Aug 2025 Decision Letter - James Cray, Editor Dear Dr. Guatelli-Steinberg, Please submit your revised manuscript by Sep 29 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols . We look forward to receiving your revised manuscript. Kind regards, James J Cray Jr., Ph.D. Academic Editor PLOS ONE Journal requirements: When submitting your revision, we need you to address these additional requirements. 1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf 2. Please include a complete copy of PLOS’ questionnaire on inclusivity in global research in your revised manuscript. Our policy for research in this area aims to improve transparency in the reporting of research performed outside of researchers’ own country or community. The policy applies to researchers who have travelled to a different country to conduct research, research with Indigenous populations or their lands, and research on cultural artefacts. The questionnaire can also be requested at the journal’s discretion for any other submissions, even if these conditions are not met. Please find more information on the policy and a link to download a blank copy of the questionnaire here: https://journals.plos.org/plosone/s/best-practices-in-research-reporting. Please upload a completed version of your questionnaire as Supporting Information when you resubmit your manuscript. 3. PLOS requires an ORCID iD for the corresponding author in Editorial Manager on papers submitted after December 6th, 2016. Please ensure that you have an ORCID iD and that it is validated in Editorial Manager. To do this, go to ‘Update my Information’ (in the upper left-hand corner of the main menu), and click on the Fetch/Validate link next to the ORCID field. This will take you to the ORCID site and allow you to create a new iD or authenticate a pre-existing iD in Editorial Manager. 4. If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. Additional Editor Comments (if provided): [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. Is the manuscript technically sound, and do the data support the conclusions? Reviewer #1: Partly Reviewer #2: Yes ******** 2. Has the statistical analysis been performed appropriately and rigorously? -->?> Reviewer #1: No Reviewer #2: Yes ****** 3. Have the authors made all data underlying the findings in their manuscript fully available??> The PLOS Data policy Reviewer #1: Yes Reviewer #2: Yes ****** 4. Is the manuscript presented in an intelligible fashion and written in standard English??> Reviewer #1: Yes Reviewer #2: Yes ******** Reviewer #1: This manuscript presents a study of enamel chipping as it relates to wear, age, and sex in the Cayo Santiago rhesus macaque population. The article is well-written and the question is important for understanding dietary estimation in fossil taxa, and even for understanding the factors that might impact the evolution of tooth shape and enamel thickness among primates. That being said, the use of a large number of statistical analyses and inconsistent use of a Bonferroni-corrected significance threshold limit the utility of the findings. Please find my recommendations below: Introduction • Introduction doesn’t discuss the potential impact of enamel thickness on both wear and chipping, and how that might influence diet-wear-chipping relationships o How does rhesus macaque enamel thickness vary and how might that influence the application of this study to other taxa? o I appreciate that this is mentioned in the discussion, but incorporating some mention into the introduction would be helpful for understanding how macaques compare to the fossil primates we are hoping to better understand through this study of macaques • The logic of lines 122-127 is unclear. Males have more missing/broken teeth in this population, but is that related to age or tooth wear? Why would that lead you to hypothesize that males will have more chipping than females even when wear is accounted for? Are there any specific feeding behaviors observed in males that would indicate a higher likelihood for chipping independently from wear and aging? o Similarly, the next paragraph is a bit confusing. It is stated that there aren’t sex differences in food material properties, but then stated that females consume more soil than males. I would consider increased geophagy to be a sex difference in food material properties, but perhaps that’s not accurate? • Line 139: Typo, “in in” • Line 149: “Varying loads on brittle materials” seems to be missing a word. • Line 177: “adaption” should be “adaptation” Methods • Line 178: “excel” should be capitalized • It’s unclear why the multiple observations of tooth wear was described for these individuals since only the postmortem tooth wear seems to be used throughout the analyses… is this accurate? • From my understanding of lines 211-222, it seems as though only half of the teeth were scored for wear (left or right), but chipping was scored on all teeth (left and right). Is that accurate? If so, that’s a big issue and if not, that should be clarified in the text. • Lines 221-222: Blinding to age and sex makes sense, but it seems that by looking at the teeth the observed would be “unblinded” to wear, perhaps this could just be excluded? • Line 241: “areas of were” may not need the “of”, or a word is missing • Line 244: Why Spearman’s rank (rather than Pearson’s) unless variables are nonparametric? Normality test results could be reported if normality is a concern. • Rather than running so many logistic regressions with Bonferroni, the authors should seriously consider using a GLMM with individual and tooth position as crossed random effects. Including all of the molars in one analysis would probably provide quite a bit more power. o Both age and dental wear could also be included in a GLMM without running the Spearman’s rank assessment because imperfect collinearity does not violate the GLM’s assumptions o This approach would seem to better address the question since the authors are not explicitly interested in tooth position, but in the frequency of chipping across the molar row o This would also reduce the need for the Proc Mixed model between sexes… essentially you can just put all of the data into a single Proc Mixed model (or a series of models with model selection as described) Results • Unclear why maxillary and mandibular data are pooled for Mean Age at Death in Table 2 when the other variables are separated by tooth position, if the goal is just to demonstrate that females are older on average than males then why separate uppers and lowers? • Reporting results as significant at two levels (with or without Bonferroni correction) somewhat defeats the purpose of the Bonferroni correction o One of the benefits of the GLMM approach that I recommend is that Bonferroni correction would not be necessary • Lines 366-367: Recommend specifying the variables (chip sizes) rather than saying, “In this table”, because what’s important is the finding rather than the table. Discussion • Line 376: This topic of crack formation independent of enamel chipping could be mentioned in the introduction since “crack” is used frequently to describe the formation of chips in the introduction of this paper • Lines 399-401: Setting up the time in Sabana Seca as a natural experiment of the role of geophagy on enamel chipping is really clever and could be introduced in the introduction more clearly. • Lines 409-412: The sex difference in age at death is not statistically significant (I’m pretty sure this wasn’t tested, but it doesn’t seem to be significant based on the SDs for the means), so this discussion of the impact of age differences by sex is probably overstating the impact of this difference, though the logic that this refutes the hypothesis that geophagy is contributing to higher rates of enamel chipping is still well-founded • Lines 427-432: How would increased area of the tooth relate to scaling of the cusps and regions where chips are likely to form based on the mechanics of enamel fracturing? This could merit more discussion. • Could the sex differences in chipping be related to different metabolic requirements in males and females? Are males simply chewing more than females? There is considerable focus on the finding of sex differences in chipping frequency, and it may be worth mentioning that male and female rhesus macaques are more sexually dimorphic than many fossil primates to which we might be interested in applying these results o The differences between the sexes could even be thought to invalidate the 15% and 25% thresholds for hard object feeding since these males and females have such similar diets and fall into different categories. Perhaps these thresholds need to better account for not only sex but look at species-specific patterns of chipping? Reviewer #2: This manuscript reports on a study of the relationship of molar wear, age and sex to enamel chipping in a sample of rhesus macaques of known age from Cayo Santiago. The authors discuss the importance of this relationship for diet and food ecology of fossil primates. The authors extrapolate these results to the broader considerations of dental tissue growth and development and reproductive investment. The paper is well written and well organized. The literature review is good and appropriate, and the specific aims are clearly stated. Methods are clear and appropriate, as are the results. The discussion clearly presents the results as they relate to the specific aims and the application of these results to the study of fossil primates. Figures and tables are clearly presented. I have minor revisions to suggest. I do not need to review this manuscript again unless requested by the corresponding editor: Abstract Line 39: The Bonferroni level of significance is unclear. Making this clearer where the report is of one tooth (with P = 0.05) and multiple teeth (with the Bonferroni level of significance) would be helpful Methods Table 1: Should the P-value for each of the results should be indicated as < 0.001? It seems unlikely that they are all equal to 0.001. lines 285-286: Clarify that this is a regression, not a mixed-model ANOVA. Results line 307: should the second use of “chipping” be removed? Table 3: Table legend should include an indication of * and *. You also might consider using something other than “” and “*” since the is used in Table 5 for another meaning. This could simplify the presentation for other readers. Discussion 1st paragraph (lines 374-379). This is a lot of information in 2 sentences. The first sentence could be broken up to present the results more clearly. Figure 2 legend – The wording is awkward. Is a word missing? This is more clearly stated on line 205. ******** what does this mean? ). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy Reviewer #1: No Reviewer #2: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org . Please note that Supporting Information files do not need this step. https://doi.org/10.1371/journal.pone.0337554.r001
Revision 1
22 Sep 2025 Author Response Response to Reviewers We thank the reviewers for the effort and thoughtful comments and suggestions, which we respond to below. Reviewer #1: This manuscript presents a study of enamel chipping as it relates to wear, age, and sex in the Cayo Santiago rhesus macaque population. The article is well-written and the question is important for understanding dietary estimation in fossil taxa, and even for understanding the factors that might impact the evolution of tooth shape and enamel thickness among primates. That being said, the use of a large number of statistical analyses and inconsistent use of a Bonferroni-corrected significance threshold limit the utility of the findings. Please find my recommendations below: Response: As we explain in detail below, based on Reviewer 1’s recommendation, we replaced the original set of by-tooth logistic regression analyses in the main text (Table 3) with a new repeated measures GLMM analysis in which values of variables for each tooth type are treated as repeated measures for each individual. Importantly, the new results from this GLMM are consistent with our original analyses, namely in finding statistically significant effects on chipping frequencies for both wear and sex. As noted by Reviewer 1, the advantage of the new analysis is that it has higher power than our previous analyses. We include the original analyses in the Supplementary Information because it allows us to: (1) provide a “by-tooth” assessment of the effects of predictors that might be of interest to other researchers, and (2) simultaneously eliminate any concerns regarding the collinearity of wear and age. Schielzeth et al. (2020) [Schielzeth, H., Dingemanse, N.J., Nakagawa, S., Westneat, D.F., Allegue, H., Teplitsky, C., Réale, D., Dochtermann, N.A., Garamszegi, L.Z. and Araya‐Ajoy, Y.G., 2020. Robustness of linear mixed‐effects models to violations of distributional assumptions. Methods in Ecology and Evolution, 11(9), pp.1141-1152] explain that, as Reviewer 1 pointed out, linear mixed models are robust to collinear predictors. The authors of this paper found that weak to moderate correlations had little effect on the precision of GLMM estimates but that there were large effects on the precision of estimates for predictors with correlations as high as 0.8. Correlations for wear and age do not reach this level in our data but for some tooth types, they are close (Table 2, main text). Thus, as noted above, we include our original analysis in the SI, in part because it eliminates any concern regarding collinearity of these variables. Although Reviewer 1 found our use of Bonferroni correction to be inconsistent, we believe that we used the correction consistently but reported the traditional level of statistical significance as well. We did this because there is longstanding and continuing controversy over when and how to use the Bonferroni correction and other multiple correction methods. Some researchers, including statisticians, find the Bonferroni correction to be overly conservative and even question whether corrections for multiple testing are necessary (e.g., Cabin, R.J. and Mitchell, R.J., 2000. To Bonferroni or not to Bonferroni: when and how are the questions. Bulletin of the Ecological Society of America, 81(3), pp.246-248.201]; Streiner, D.L. and Norman, G.R., 2011 Correction for multiple testing: is there a resolution? Chest, 140(1), pp.16-18]; and Armstrong, R.A., 2014. When to use the Bonferroni correction. Ophthalmic and Physiological Optics, 34(5), pp.502-508). Armstrong (2014) does not recommend the use of the Bonferroni correction except for situations in which it is “imperative to avoid Type I error” and when “…a large number of tests are carried out without preplanned hypotheses in an attempt to establish any results that may be significant” (Armstrong 2014:505). In further considering the need for a Bonferroni or other multiple testing correction in our supplementary analysis, we realize that our study does not satisfy either of Armstrong’s (2014) conditions. We now include this reasoning in the Supplementary Information document labelled “Supplementary Information: Analysis by Tooth Type.” Reviewer #1: Introduction doesn’t discuss the potential impact of enamel thickness on both wear and chipping, and how that might influence diet-wear-chipping relationships o How does rhesus macaque enamel thickness vary and how might that influence the application of this study to other taxa? o I appreciate that this is mentioned in the discussion, but incorporating some mention into the introduction would be helpful for understanding how macaques compare to the fossil primates we are hoping to better understand through this study of macaques. Response: We appreciate this suggestion. We now include a new paragraph in the introduction of the revised MS discussing macaques as a model for understanding how “non-food” factors --such as dental wear, age, and sex-- might affect enamel chipping frequencies in fossil primates (including hominins). This paragraph includes an evaluation of rhesus macaque enamel thickness and molar sexual dimorphism. Reviewer #1: The logic of lines 122-127 is unclear. Males have more missing/broken teeth in this population, but is that related to age or tooth wear? Why would that lead you to hypothesize that males will have more chipping than females even when wear is accounted for? Are there any specific feeding behaviors observed in males that would indicate a higher likelihood for chipping independently from wear and aging? Response: We appreciate the reviewer’s point about the unclear logic linking broken teeth (in this case canines) to molar enamel chipping. However, we also mentioned that in humans there is a tendency for males to have higher frequencies of chipping. That was actually the second “empirical finding” that influenced our thinking. We have rephrased our expectation of higher frequencies of chipping in Cayo Santiago males, basing it solely on the finding that in humans, when sex differences in chipping have been found, males generally have higher chipping frequencies than females. It is not clear why this is the case, though it could have to do with sex differences in bite force, tooth grinding, quantity of food ingested, the material properties of foods, and/or sex differences in enamel thickness. We also removed the words “when age and wear were accounted for” since it is not clear why, in humans, males tend to have greater frequencies of chipping than females do. Finally, we do not know of any specific feeding behaviors that Cayo Santiago rhesus males engage in that would indicate a higher likelihood of chipping. Reviewer #1: Similarly, the next paragraph is a bit confusing. It is stated that there aren’t sex differences in food material properties, but then stated that females consume more soil than males. I would consider increased geophagy to be a sex difference in food material properties, but perhaps that’s not accurate? Response: We see Reviewer #1’s point, but it isn’t clear to us that soil is always a “food.” Primates seem to consume soil for a variety of reasons, including as a method of self-medication (Krishnamani and Mahaney, 2000: Krishnamani, Ramanathan, and William C. Mahaney. "Geophagy among primates: adaptive significance and ecological consequences." Animal Behaviour 59, no. 5 (2000): 899-915). For this reason, we prefer not to presume that soil is eaten as a food (i.e., similar to monkey chow or other substance consumed for nourishment). Reviewer #1: Corrections • Line 139: Typo, “in in” • Line 149: “Varying loads on brittle materials” seems to be missing a word. • Line 177: “adaption” should be “adaptation” Methods • Line 178: “excel” should be capitalized Response: These errors have been corrected. Reviewer #1: It’s unclear why the multiple observations of tooth wear was described for these individuals since only the postmortem tooth wear seems to be used throughout the analyses… is this accurate? Response: Sorry for our lack of clarity. We have rewritten this sentence to be clear that we used the postmortem tooth wear measurements: “The sample and dental wear measurements made on the deceased monkeys that were used for that study are the same as those used here. “ Reviewer #1: From my understanding of lines 211-222, it seems as though only half of the teeth were scored for wear (left or right), but chipping was scored on all teeth (left and right). Is that accurate? If so, that’s a big issue and if not, that should be clarified in the text. Response: Again, sorry for our lack of clarity. All teeth were originally scored for both wear and chipping. Then, the most-well oriented antimere was used in our analysis for both wear and chipping. We have clarified this in the text: “For our analyses, for each antimeric pair, we used the most-well oriented antimere for both wear and chipping.” Reviewer #1: • Lines 221-222: Blinding to age and sex makes sense, but it seems that by looking at the teeth the observed would be “unblinded” to wear, perhaps this could just be excluded? Response: That is a good point: we have removed this sentence. Reviewer #1: Line 241: “areas of were” may not need the “of”, or a word is missing Response: Corrected: removed word “of” Reviewer #1: Line 244: Why Spearman’s rank (rather than Pearson’s) unless variables are nonparametric? Normality test results could be reported if normality is a concern. Response: We had indeed conducted normality tests but did not include them. We do so now in the Materials and Methods section. We used Spearman’s rank rather than Pearson because Shapiro-Wilk tests revealed that the variable “wear” was not normal for any of the six tooth types. Reviewer #1: Rather than running so many logistic regressions with Bonferroni, the authors should seriously consider using a GLMM with individual and tooth position as crossed random effects. Including all of the molars in one analysis would probably provide quite a bit more power. o Both age and dental wear could also be included in a GLMM without running the Spearman’s rank assessment because imperfect collinearity does not violate the GLM’s assumptions o This approach would seem to better address the question since the authors are not explicitly interested in tooth position, but in the frequency of chipping across the molar row o This would also reduce the need for the Proc Mixed model between sexes… essentially you can just put all of the data into a single Proc Mixed model (or a series of models with model selection as described) Response: We recognize that imperfect collinearity does not violate GLMM assumptions as explained by: Schielzeth, H., Dingemanse, N.J., Nakagawa, S., Westneat, D.F., Allegue, H., Teplitsky, C., Réale, D., Dochtermann, N.A., Garamszegi, L.Z. and Araya‐Ajoy, Y.G., 2020. Robustness of linear mixed‐effects models to violations of distributional assumptions. Methods in Ecology and Evolution, 11(9), pp.1141-1152. The authors of this paper found that weak to moderate correlations had little effect on the precisions of GLMM estimates but that there were large effects on the precision of estimates for predictors with correlations as high as 0.8. Correlations for wear and age in our data set do not reach this level but for some tooth types, they are close. As noted above, our original analysis, now included in the SI, eliminates any concern regarding collinearity of these variables, simultaneously providing analyses by tooth type. Our original analysis is consistent with our new GLMM analysis in finding significant effects for wear and age. In our original analysis, wear and sex were the most frequent statistically significant predictors across tooth types. In our new analysis, wear and age are the only statistically significant predictors. In our GLMM, we designated “individual” as random but tooth type as a fixed effect. We believe that tooth type may have a consistent effect on the likelihood of chipping, as for example, third molars erupt later than second molars and tend to have thicker enamel than first and second molars, at least in humans (Smith, T.M., Olejniczak, A.J., Reid, D.J., Ferrell, R.J. and Hublin, J.J., 2006. Modern human molar enamel thickness and enamel–dentine junction shape. Archives of Oral Biology, 51(11), pp.974-995.) Both of these factors would tend to result in systematically lower frequencies of chipping in third molars. These two factors could explain why the three tooth types in our sample with the lowest frequencies of chipping were all third molars (although our GLMM ultimately did not reveal significant effects by tooth type). Our new GLMM analysis is fully described on page in the statistical methods section of the revised manuscript. Our results are incorporated into a new Table, labeled Table 3 of the revised manuscript. Reviewer 1: Results: Unclear why maxillary and mandibular data are pooled for Mean Age at Death in Table 2 when the other variables are separated by tooth position, if the goal is just to demonstrate that females are older on average than males then why separate uppers and lowers? Response: We have revised the Table (which is now Table 1) to report the age of individuals rather than separating by upper and lower dentitions. Reviewer 1: Reporting results as significant at two levels (with or without Bonferroni correction) somewhat defeats the purpose of the Bonferroni correction Response: Please see our response above re: Bonferroni correction and why we no longer apply it. Reviewer 1: One of the benefits of the GLMM approach that I recommend is that Bonferroni correction would not be necessary Response: Yes—this was a much-appreciated suggestion. Please see our response above for how we carried out our GLMM analysis. Reviewer 1: Lines 366-367: Recommend specifying the variables (chip sizes) rather than saying, “In this table”, because what’s important is the finding rather than the table. Response: Corrected. Reviewer 1: Discussion: Line 376: This topic of crack formation independent of enamel chipping could be mentioned in the introduction since “crack” is used frequently to describe the formation of chips in the introduction of this paper Response: To be more clear ( hopefully) when we first use the word “crack” in the introduction we added the words “in some instance” before “creating a chip,” as follows: “Biting objects with the force necessary to fracture them can cause enamel, a brittle material, to crack, in some instances creating a chip (or more precisely a chipping scar) on the enamel surface [1].” In in our second use of the word “crack” in the introduction, we now include in parentheses, after the word crack: “i.e., fractures within the enamel.” Reviewer 1: Lines 399-401: Setting up the time in Sabana Seca as a natural experiment of the role of geophagy on enamel chipping is really clever and could be introduced in the introduction more clearly. Response: We thank Reviewer 1 for this excellent suggestion. We now include expectations regarding the role of geophagy (and the comparison between free-ranging and captive conditions) on enamel chipping in the introduction. Reviewer 1: Lines 409-412: The sex difference in age at death is not statistically significant (I’m pretty sure this wasn’t tested, but it doesn’t seem to be significant based on the SDs for the means), so this discussion of the impact of age differences by sex is probably overstating the impact of this difference, though the logic that this refutes the hypothesis that geophagy is contributing to higher rates of enamel chipping is still well-founded Response: We softened the language here, in attempt not to overstate this point, now stated as “Also evident from Table 2, males in this sample were three years younger than females, on average. If the sex effect were solely dependent on age, then males would not have been expected to have higher chipping frequencies than females.” Reviewer 1: Lines 427-432: How would increased area of the tooth relate to scaling of the cusps and regions where chips are likely to form based on the mechanics of enamel fracturing? This could merit more discussion. Response: Agreed, but we do not know how cusps and regions where chip Attachments Attachment Submitted filename: Response to reviewers.docx https://doi.org/10.1371/journal.pone.0337554.r002
4 Nov 2025 Decision Letter - James Cray, Editor Dear Dr. Guatelli-Steinberg, Please submit your revised manuscript by Dec 19 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols . We look forward to receiving your revised manuscript. Kind regards, James J Cray Jr., Ph.D. Academic Editor PLOS ONE Journal Requirements: If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. Additional Editor Comments: There are two very minor issues to be addressed prior to acceptance. [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author Reviewer #1: (No Response) Reviewer #2: (No Response) ******** 2. Is the manuscript technically sound, and do the data support the conclusions??> Reviewer #1: Yes Reviewer #2: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? -->?> Reviewer #1: Yes Reviewer #2: Yes ****** 4. Have the authors made all data underlying the findings in their manuscript fully available??> The PLOS Data policy Reviewer #1: Yes Reviewer #2: Yes ****** 5. Is the manuscript presented in an intelligible fashion and written in standard English??> Reviewer #1: Yes Reviewer #2: Yes ****** Reviewer #1: The authors have done an excellent job of addressing my concerns. I have only a small number of minor notes on this version of the manuscript: Page 12, line 257: “chip occlusal areas of” seems to have an unnecessary “of” Page 14, line 294: “are” should be “as” in this line Page 18: p-values throughout are listed as “p < number” when they may be better listed as “p = number” Page 25, lines 471-473: This sentence seems to have a misplaced comma Reviewer #2: This paper is well written, and the authors have incorporated the reviewers’ comments thoroughly. The revised analyses and results are explained in a clear manner. I appreciate that the authors included the original results in the supplemental material for those interested in the analysis of individual teeth. My original comments were well addressed. I have only two minor comments, both related to figure legends. Figure 1 legend: the c figure is included twice. Should these descriptions be combined? Also, the colors used in the figure are quite similar. Perhaps either colors that contrasting more, or include one of the colors by dotted lines for individuals with color blindness. Figure 2 legend – The first part of this figure legend is awkward. It seems that there is either a word missing, or extra words. ****** what does this mean? ). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy Reviewer #1: No Reviewer #2: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] To ensure your figures meet our technical requirements, please review our figure guidelines: https://journals.plos.org/plosone/s/figures You may also use PLOS’s free figure tool, NAAS, to help you prepare publication quality figures: https://journals.plos.org/plosone/s/figures#loc-tools-for-figure-preparation. NAAS will assess whether your figures meet our technical requirements by comparing each figure against our figure specifications. https://doi.org/10.1371/journal.pone.0337554.r003
Revision 2
5 Nov 2025 Author Response Response to Editor Thank you for your careful review of our paper. Reviewers had minor revisions, which we have addressed in the revised MS. Below, we detail the changes that were made in this version of our MS. REVIEWER 1: The authors have done an excellent job of addressing my concerns. I have only a small number of minor notes on this version of the manuscript: Page 12, line 257: “chip occlusal areas of” seems to have an unnecessary “of” Page 14, line 294: “are” should be “as” in this line RESPONSE: These two items have been corrected REVIEWER 1: Page 18: p-values throughout are listed as “p < number” when they may be better listed as “p = number” RESPONSE: We originally reported p-values with “=” signs as they are exact p-values. Reviewer 2 suggested we change them to inequalities. Reviewer 1 (as noted above), however, states that these should be listed as “p=number” (which is what we thought originally). We have looked further into this issue, and it seems Reviewer 1 is correct: these should be reported as exact p-values with an equal sign. We have made this change throughout the MS. RESPONSE: These two items have been corrected REVIEWER 1: Page 25, lines 471-473: This sentence seems to have a misplaced comma RESPONSE: Corrected. REVIEWER #2: This paper is well written, and the authors have incorporated the reviewers’ comments thoroughly. The revised analyses and results are explained in a clear manner. I appreciate that the authors included the original results in the supplemental material for those interested in the analysis of individual teeth. My original comments were well addressed. I have only two minor comments, both related to figure legends. Figure 1 legend: the c figure is included twice. Should these descriptions be combined? Also, the colors used in the figure are quite similar. Perhaps either colors that contrasting more, or include one of the colors by dotted lines for individuals with color blindness. RESPONSE: We are showing something different in “c” so we prefer to leave “c” as it is. We agree that the green and blue in this figure would be problematic for individuals with blue-yellow color blindness. We have changed the colors in Figure 1 to blue/red. REVIEWER #2: Figure 2 legend – The first part of this figure legend is awkward. It seems that there is either a word missing, or extra words. RESPONSE: Sorry, we are not seeing where the reviewer finds the wording to be awkward. For this reason, we have not changed this figure legend. Many thanks for your time and for helping us improve this MS. Best wishes, Debbie Guatelli-Steinberg and co-authors Attachments Attachment Submitted filename: Letter to Editor.docx https://doi.org/10.1371/journal.pone.0337554.r004
11 Nov 2025 Decision Letter - James Cray, Editor <p>How wear, age, and sex relate to enamel chipping in Cayo Santiago rhesus macaques (Macaca mulatta) PONE-D-25-35913R2 Dear Dr. Guatelli-Steinberg, We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication. An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. For questions related to billing, please contact billing support . If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. Kind regards, James J Cray Jr., Ph.D. Academic Editor PLOS ONE Additional Editor Comments (optional): Reviewers' comments: https://doi.org/10.1371/journal.pone.0337554.r005
Formally Accepted
Acceptance Letter - James Cray, Editor PONE-D-25-35913R2 PLOS ONE Dear Dr. Guatelli-Steinberg, I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team. At this stage, our production department will prepare your paper for publication. This includes ensuring the following: * All references, tables, and figures are properly cited * All relevant supporting information is included in the manuscript submission, * There are no issues that prevent the paper from being properly typeset You will receive further instructions from the production team, including instructions on how to review your proof when it is ready. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few days to review your paper and let you know the next and final steps. Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. You will receive an invoice from PLOS for your publication fee after your manuscript has reached the completed accept phase. If you receive an email requesting payment before acceptance or for any other service, this may be a phishing scheme. Learn how to identify phishing emails and protect your accounts at https://explore.plos.org/phishing. If we can help with anything else, please email us at customercare@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. James J Cray Jr. Academic Editor PLOS ONE https://doi.org/10.1371/journal.pone.0337554.r006

Open letter on the publication of peer review reports

PLOS recognizes the benefits of transparency in the peer review process. Therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. Reviewers remain anonymous, unless they choose to reveal their names.

We encourage other journals to join us in this initiative. We hope that our action inspires the community, including researchers, research funders, and research institutions, to recognize the benefits of published peer review reports for all parts of the research system.

Learn more at ASAPbio .