PONE-D-22-00629The appendicular myology of Stegoceras validum (Ornithischia: Pachycephalosauridae) and implications for the head-butting hypothesisPLOS ONE

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4. We note that you have referenced (Fechner R. Morphofunctional evolution of the pelvic girdle and hindlimb of Dinosauromorpha on the lineage to Sauropoda. 197 pp. Unpublished Ph. D. dissertation, Fakultät für Geowissenschaften, Ludwig-Maximilians-Universität, Munich. 2009.) which has currently not yet been accepted for publication. Please remove this from your References and amend this to state in the body of your manuscript: (Fechner R. Morphofunctional evolution of the pelvic girdle and hindlimb of Dinosauromorpha on the lineage to Sauropoda. 197 pp. Unpublished Ph. D. dissertation, Fakultät für Geowissenschaften, Ludwig-Maximilians-Universität, Munich. 2009. [Unpublished] as detailed online in our guide for authors

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Additional Editor Comments:

Reviewers make some questions about your work, which is why I have decided to request minor revisions. Basically, I ask you to pay attention to the following criticisms from reviewer 1. The main questions of this reviewer are about the organization in the discussion and conclusions sections.

Reviewers 1 and 2 emphasize the need to increase comparisons as much as possible. If you are not in a position to do so or disagree, please justify it in your response to this editor.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: N/A

Reviewer #2: N/A

Reviewer #3: N/A

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This manuscript is thorough and detailed. The authors have included numerous muscles, each described in detail. I appreciate that the Results section is clearly written in plain English with citations presented for readers who are looking for the EPB specifics. There is no excessive jargon nor overly-complicated sentence structures. I also like that the authors are looking for functional meaning in the reconstructed myology.

However, I found the Discussion and Conclusion sections difficult to follow. These sections would benefit from further description of (1) the authors’ thought processes and (2) the meaning/significance of the topics chosen for discussion. The Discussion paragraph from lines 1267-1284 presents well-constructed arguments and supporting facts in an easy to follow, logical structure; I therefore believe the writing style of this paragraph would serve as a good template for reformatting the rest of the Discussion. Also, although several of the specific myological arrangements highlighted by the authors in the Discussion could have arisen via selection for intra-specific competition, they would also simply add stability to a biped during locomotion and may have arisen via selection for this ‘benefit’. Such viable alternatives weaken their potential lines of support for inferring head butting behavior in Stegoceras. Thus, my main request of the authors is for them to compare their findings to those from additional other ornithischians and, especially, bipedal nonavian dinosaurs. If the authors can convincingly show that the skeletal and myological features highlighted in their Discussion list are unique specializations seen only in pachycephalosaurs (i.e., they are not also seen in other bipedal nonavian dinosaurs or in ornithischians more broadly), then their conclusions concerning potential head-butting behavior would be better supported.

The authors consistently compare to numerous sauropod and theropod taxa in the Results section, but the addition of consistently comparing to a few ornithischians would go a long way toward strengthening their arguments about the uniqueness of Stegoceras. I recognize not all myological descriptions are conducted in the same format and that it can sometimes be difficult to draw meaningful comparisons, but a plethora of prior publications exist to potentially compare against. The authors already cite a few prior studies, such as those by Dilkes 1999, Langer et al. 2007, and Maidment and Barrett 2011, but they draw few comparisons to the myology of the taxa presented in those studies. Other myology studies the authors could potentially compare against which could strengthen their manuscript might include Fearon and Varricchio 2016 (on Oryctodromeus) and Andrei and Solomon 2013 (on Zalmoxes shquiperorum). The authors do not necessarily need to add more comparisons to all of these taxa, but rather more comparisons in general (against whichever taxa they see as ‘best’/most appropriate) with language to highlight how the myology of S. validum is similar to or differs from the “norm” or “standard” myology of ornithischians as currently understood.

Beyond my two primary concerns summarized above, the following minor concerns are listed below:

At numerous points in the manuscript the authors us the term ‘reptiles’ to discuss a group of organisms in a phylogenetic context. As reptiles are a paraphyletic clade and the context is related to a phylogenetic discussion, it would be better to more specifically list the group/groups the authors are implying. For example: Line 98, Line 698, and Line 1048.

Additionally the authors could improve clarity at a few locations in the Results section:

Hind limb is two words

Lines 345-347 Please make it clear if you are reconstructing with conservative morphology. It seems like it but best to be clear and direct.

Line 406 Does "one" mean they have a tendinous insertion?

Lines 499-500 As written, this is easy to misread or become confused by showing absence. Consider rewriting.

Lines 581-582 Which is "this muscle"? The anconeus or the extensor carpi ulnaris?

Line 598 So is only the origin reconstructed? Unclear.

Lines 716-718 I feel like this statement is correct but inaccurate evolutionary phrasing in the technical sense.

Line 851 What are “these” features?

Line 857 Do you mean the reconstructions are inconsistent or there is disagreement on the EPB attachment locations and divisions? Not clear as written.

Line 1006 Please specify the bone referred to as "its" for clarity.

Lines 1028-1030 Same being that the PIFE 3 in crocs attaches where the ISTR does in birds? Please make clear.

Lines 1342-1344 Better developed in pachycephalosaurs than who?

Also, it should be discussed how stability is more important for any biped than a quadruped and why the morphology of S. validum specifically supports headbutting and not just bipedality. Instances to consider adding/expanding this discussion include:

Lines 33-36 If the pelvic muscles are enlarged to balance reduced pubic muscles, would they still have a benefit to head-butting beyond a balanced condition?

Lines 1333-1335 And added to stability for life as a biped correct?

Lines 1336-1339 Wouldn't this also help in general with being bipedal?

Lines 1359-1365 So your list above summarizes, in general, how more stable Stegocerus is, correct? And then here you are saying that stability is related to or useful for headbutting? Please make sure the text is clear here to help your readers make the connections you are describing.

Other comments:

Line 27 Are the attachments sites enlarge or how did you estimate the size of the muscles?

Line 97 Add (non-avian dinosaurs) after birds for explicit clarity.

Lines 104-111 Are there other specimens of S. validum that preserve postcranium material or not? Is this the best preserved postcranium of all pachycephalsaurs? If these answers are what I suspect they might be, they will add importance to your manuscript.

Lines 118-123 Many of your muscles are missing osteological correlates or the bones to insert on. What do you do about them in blender?

Lines 135-142 Move this paragraph to the methods.

Line 200 Are there osteological correlates on the cervical or dorsal vertebrae or is this reconstruction a prime level of inference? It should be stated either way.

Lines 271-272 If it is some myological reconstructions then Jasinoski citation needs and e.g. but if it is only Jasinoski, then drop the “some”.

Lines 328-329 Saying it is found in both and that it is unequivocal is redundant.

Lines 393-394 Needs to be more like "Though lack of an osteological correlate does not rule out attachment of the SC at the subacromial depression, we reconstruct this muscle as attaching to the scapula along the scapulocoracoid suture ..."

Lines 495-498 Why do the origin and insertion have to move together? Why does a crocodilian origin imply a crocodilian insertion? Please cite literature supporting this idea or instances where origins and insertions have migrated together.

Lines 637-639 Please add something about how there is a general rugose area at this location in S. validum and that makes an independent osteological correlate indistinguishable.

Lines 662-664 Since the bones aren't preserved you don't know where the insertion was and are predicting/hypothesizing where it would have been. Please change the language here to reflect that.

Lines 727-728 Are osteological correlates present?

Lines 742-743 Rewrite this sentence. I agree with the logic but as written it implies that either another muscle was used or not as much flexion of the digits occurs in birds rather than that less muscle force/mucle body was needed to produce the same motion due to the reduction of digits.

Lines 773-780 This reads like discussion

Lines 903-910 I feel like this description of this unknown muscle scar should be its own paragraph not intermixed with a muscle you are not assigning there unless you are trying to say it is an extension of the ILT, but if so this is not clear as written.

Lines 992-1002 If the foot was planted the caudofemoralis would "wag" the tail.

Lines 1021-1024 Please expand this discussion of the differences in attachment sites to clarify how S. validum is similar to Piechowski and Talanda yet different from Maidment and Barrett. It is difficult to follow as written.

Line 1027 Please rewrite so it is clear where the ISTR is in birds. The lateral surface or specifically lateral surface of the shaft.

Lines 1223-1225 This paragraph belongs in the methods

Line 1248 Would “conservative methodologies” or something similar be a better phrase than “caveats used”?

Lines 1248-1250 Does “muscles predicted by the EPB)” and “null hypothesis” mean unequivocal muscles?

Lines 1257-1259 I don't understand how this sentence fits in with the rest of the paragraph.

List that starts on Line 1290 I suggest considering splitting this into two lists. One that is anatomical features not related to myology and one that lists features related to myology. I think more space should be devoted to the second list than the first list as it is directly relevant to your data.

Lines 1318-1320 Is it possible that the transition from quadrapedality to bipedality could cause an increase in stress and result in this morphology?

Line 1360 It isn't really that they need to be explained but that they support that hypothesis.

Lines 1372-1375 Lack of evidence is not evidence so it is possible not definitive.

Lines 1407-1419 Paragraph 2 of the conclusion is all new information which traditionally gets included before the conclusion and the conclusion is more of a summary of the work. Your conclusion could benefit from more of a summary.

Table 1

- You have room to add the abbreviation here too under muscle name. This would be helpful to readers.

- DSC Insertion missing Level of Inference

- SC Origin Levels of Inference flipped for the 2 insertions (always on coracoid, sometimes on the scapula)

- BB Insertion should include the equivocal ulna insertion

- BR Insertion should include the equivocal ulna insertion

Table 2

- EDL should be later distal condyle of femur or anterior cnemial crest, not and

- EDB only shows up in this table, nowhere else in the manuscript

- FDL origin does not match the text description

- TA Insertion missing Level of Inference

- ADF2 missing from table

Figure 1

- Reconstructions are C and D. Scans are A and B

Figure 2

- Reconstructions are C and D. Scans are A and B

Figure 3

- Reconstructions are C and D. Scans are A and B

- If you are splitting the supracoracoideus here, then split it into brevis and longus in Table 1.

Figure 4

- Reconstructions are C and D. Scans are A and B

Figure 5

- Reconstructions are C and D. Scans are A and B

Figure 6

- Reconstructions are C and D. Scans are A and B

Figure 7

- Reconstructions are C and D. Scans are A and B

Figure 8

- Reconstructions are C and D. Scans are A and B

- Part D missing the “e” in “ILFE”

- ED longus or brevis? If ED is meant to represent both than make the name plural in the caption.

Figure 9

- Reconstructions are C and D. Scans are A and B

- ED longus or brevis? If ED is meant to represent both than make the name plural in the caption.

- FMT lateralis or medialis? If FMT is meant to represent both than make the name plural in the caption.

Figure 10

- Reconstructions are C and D. Scans are A and B

- FB in Table 2 and Figure 13. Here it is FBB and FBL which are briefly talked about in the text. Make consistent across manuscript

Figure 11

- Reconstructions are C and D. Scans are A and B

- GSC lateralis or medialis? If GSC is meant to represent both than make the name plural in the caption.

Figure 12

- Specify this is a reconstruction of the pelvic and hind limb musculature

- Why are fewer muscles reconstructed here than in the individual bone figures?

- FDL superficialis or profundus? If FDL is meant to represent both than make the name plural in the caption.

Figure 13

- Specify this is a reconstruction of the pelvic and hind limb musculature

- Why are fewer muscles reconstructed here than in the individual bone figures?

- ED longus or brevis? If ED is meant to represent both than make the name plural in the caption.

- GSC lateralis or medialis? If GSC is meant to represent both than make the name plural in the caption.

- FMT lateralis or medialis? If FMT is meant to represent both than make the name plural in the caption.

Reviewer #2: This is an extremely well-written, well-organised and coherent paper. I have only the most minor of comments. Firstly, for reasons nobody knows, hind limbs is two words, while forelimbs is one word. Please correct throughout! On the review PDF the figures were low resolution and the labels unreadable. I suspect this is a conversion problem, but I would urge you to unbold any labels and check proofs when you get them very carefully. I've previously found figure reproduction in PLoS One to be pretty poor and low resolution, so do check. I have a couple of very very minor comments on the attached. My only other comment, and I hate doing this, because it is obviously the worst kind of review, is that I'm feeling rather hard done by that you haven't cited my 2012 Proc B paper at all. In it (mostly in the supplement), I provided full pectoral and pelvic muscle reconstructions of all major groups of ornithischian dinosaurs, including discussion about how changes in features such as the deltopectoral crest and acromial process affect lines of action and thus function of muscles. You haven't cited that paper AT ALL. I think it is directly relevant to your discussion, as well as to various places where you talk about what previous work has inferred and why. I realise it was in the supplement to the main paper, but I don't think you can ignore it - and the findings of the main paper are relevant too. Please have a look at this paper because while I don't think it'll change any conclusions, I do think it may strengthen arguments - at it's really the only other work on ornithischians.

Susannah Maidment

susannah.maidment@nhm.ac.uk

Reviewer #3: The science is sound throughout the manuscript and it is quite straightforward to read. Citations supporting muscle reconstructions and the methodology are supplied in each section and the limitations of the work are properly addressed in the beginning and end. Additionally, implications beyond head-butting (e.g., carnivory) are addressed which is wonderful to see.

Attached is a word document containing some minor revisions on a line-by-line basis. Most of these pertain to formatting/references, and so nothing that will be majorly time-consuming. Though not required by any means, I do wonder if the authors will consider uploading 3D files of bones/muscles they used onto an online database.

In any case, this was a fascinating work and I am eager to see follow-up research on other pachycephalosaur skeletal material in the future.

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Reviewer #1: Yes: Kristyn K. Voegele

Reviewer #2: Yes: Dr Susannah Maidment

Reviewer #3: Yes: Andre J. Rowe

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The appendicular myology of Stegoceras validum (Ornithischia: Pachycephalosauridae) and implications for the head-butting hypothesis

PONE-D-22-00629R1

Dear Dr. %Bryan Robert Schjerning Moore%,

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.

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Kind regards,

Claudia Patricia Tambussi, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Thank you for considered the feedback by the three reviewers. The main questions raised by the them, especially reviewer 1, have been satisfactorily considered in this new version of the manuscript.

Please, consider at a later stage in the editorial process: add a reference on lines 161-162; delete the double parentheses in table 1, Latissimus dorsi ((LD); please check that “unparsimonious” be a correct word (line 2637)