Review History

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  • The initial submission of this article was received on June 14th, 2019 and was peer-reviewed by 2 reviewers and the Academic Editor.
  • The Academic Editor made their initial decision on July 15th, 2019.
  • The first revision was submitted on August 23rd, 2019 and was reviewed by the Academic Editor.
  • The article was Accepted by the Academic Editor on August 30th, 2019.

Version 0.2 (accepted)

· Aug 30, 2019 · Academic Editor


Thank you for your diligence in addressing the concerns of the reviewers. In particular, I found your rebuttal letter very clear and well-written, and I appreciated your explanations on several points. My only remaining suggestion for improvement is that you might consider including some of the explanatory text from the rebuttal letter into the manuscript -- areas that confused the reviewers may also confuse other readers. That said, I am satisfied with the revised manuscript, and I am happy to accept it for publication in PeerJ.

The decision of whether or not to publish the peer reviews alongside the paper is entirely yours, and will not affect how your paper is handled going forward. However, I encourage you to do so. Making the reviews public allows the reviewers to receive credit for their efforts, and also contributes to the emerging culture of fairness and transparency in editing and peer review.

[# PeerJ Staff Note - this decision was reviewed and approved by Laura Wilson, a PeerJ Section Editor covering this Section #]

Version 0.1 (original submission)

· Jul 15, 2019 · Academic Editor

Minor Revisions

Congratulations, both reviewers found your study interesting, novel, and solidly-constructed. They both recommended 'minor revisions', and I am happy to concur. Please be diligent in addressing all of the concerns that they raised, either in the revised manuscript or the rebuttal letter. I will look forward to seeing an improved version of this already strong work in the near future.

Reviewer 1 ·

Basic reporting

This is a well-researched study on the effects of rapid environmental change across the Paleocene-Eocene boundary on plants and plant-insect associations. Previous studies on the response of plants and insect herbivores during the PETM have mostly focused on the Bighorn Basin, Wyoming. This study focuses on floras from the Hanna Basin, Wyoming, which was likely wetter based on the abundance of coals. The data are analyzed in a variety of ways to look at how plant and insect damage type diversity changed before, during, and after the PETM, how community structure changed, and how this may have been affected by depositional environments. The study shows changes in plant communities during the late PETM, which did not return to pre-PETM composition after. Herbivore community structure, using insect damage as a proxy, also changed during the PETM but returned to pre-PETM structures afterwords. An unexpected finding was that the highest damage diversity occurred at sites with the lowest plant diversity.

Experimental design

The experimental design is appropriate for the questions posed.

Validity of the findings

The fossil localities in this study represent a variety of depositional environments. Are there differences in the quality of fossil plant preservation among the sites that could decrease the potential of damage being preserved at certain sites? I know that E was mentioned as having the best preservation.

The finding that insect damage diversity did not track plant diversity is interesting. In modern ecosystems, correlations between plant diversity and insect diversity has been suggested in multiple studies, and I think this discrepancy with findings in extant ecosystems should be should be discussed. Feeny's apparency hypothesis is mentioned as a possible explanation for the high damage diversity on Platanites raynoldsii at Level C (a level with low plant diversity). Is there a biological explanation for the low damage type diversity at sites with higher plant diversity or could this be a preservational issue? A recent paper that explores the correlation between plant and insect diversity is Schuldt et al. 2019. Multiple plant diversity components drive consumer communities across ecosystems. Nature Communications 10: 1460. A number of other relevant studies are cited in this paper.

Regarding changes in damage type diversity through the studied interval – Locality D was difficult to collect and therefore has a low sample size compared to the other sites. Therefore, the results from this site are considered more tentative in the manuscript. If locality D was removed from the analyses, would your interpretation of the results change in any way? For example, without D, damage type diversity appears to track changes in mean annual temperature. I’m not advocating removing locality D, just curious how this poorly sampled level could be affecting your interpretations of the responses of plants and plant-insect associations to environmental change.

Line 339: The line mentions that the described form of skeletonization is characterized by thickening at the ends of the secondary veins. Do you have any pictures that illustrate this or, if it is depicted in Figure 9, could you add an arrow to mark the position of this character? Also, the paragraph mentions that the veins of the leaf have been eaten, which was noted as atypical. What orders of venation were consumed? I can see at least some of the secondary and tertiary veins intact.

Figure 9 caption – “damage believed to be caused by extant beetle family”. Is this type of damage exclusively made by chrysomelids today?

Additional comments

Line 33: “insect herbivore diversity” – “insect herbivore damage diversity” is probably more accurate.

Line 90-92: “If Paleogene plant and insect communities had the same basic needs as modern ones, Hanna Basin plant and insect communities would not have
 been limited by water.” – Can you justify this statement more or add citations? Water limitations can vary a lot by species, so I was wondering if you were referring to plants and insects that are part of a particular biome type.

Line 219-220: “Herbivore damage was quantified on all identifiable leaves, and damage morphotypes (DTs) were documented using Labandeira et al. (2007).” – This could be more specific, because there are a bunch of different ways to quantify herbivory (DT system, surface area measurements, percent of leaves damaged, etc.). I now see that this is clarified later, but the sentence could be rephrased slightly to let readers know the general method of damage quantification before getting into the details in a later paragraph.

Figure 5. In Fig. 5A, “number of plant species” should be “number of plant morphotypes” or “morphospecies”. In 5B and 5C axes, what is “individuals” referring to? Number of leaves?

Typos etc.
Here are a few little errors I noticed when reading the paper:
Line 54 – missing period
Line 478 – missing the word “increase” somewhere I think
Carefully check citations – some have DOIs and some don’t, some titles are capitalized when they shouldn’t be (line 561 and 595, for example), missing publication info (line 578), etc.
Figure 9 caption – “Chrysomelid” should say “Chrysomelidae”; add space between “raynoldsii” and “with”.
Appendix A.1, A.2, D – The first cell in each of these files says “”.
Check spellings in Appendix B - For example, on the HB172 page, distinct and sharply; on HB178, symmetrical; HB183, Averrhoites; Platanites spelled wrong on Platanites page

Reviewer 2 ·

Basic reporting

This paper is very well written in clear, basic English. The structure conforms to normal scientific standard and the references cited are appropriate. The introduction and background information provide appropriate context. The figures are clear although there are perhaps more than necessary and few changes to improve the clarity of a couple of the figures are suggested in the general comments to the authors. Raw data is provided.

Experimental design

This paper documents original research, describing a new set of megafloral localities from the Hanna Basin of Wyoming. The authors construct the stratigraphic and depositional context of their localities and analyze floral composition as well as evidence of insect damage. The research question is stated in the first paragraph: to study how plant and insect herbivore communities change during times of disturbance. Their question is completely relevant to their samples, which span the Paleocene/Eocene Thermal Maximum (PETM), an interval of rapid global warming in deep time. The only other comparable terrestrial record of this interval is from a fluvial setting in the Bighorn Basin of Wyoming. This study complements similar previous studies of the Bighorn Basin plants and insect herbivores but in different (e.g., lacustrine) environments. The investigation is rigorous and the results documented and described in great detail. There are sufficient descriptions and data available to replicate the results.

Validity of the findings

The underlying data have been provided and are robust, although limited at the level of the greatest interest, the PETM. However, the authors are clear about the limitations of the sample at this level and the interpretation of results is tempered by the limitations. The main conclusions, as stated on lines 527-534, are appropriate with respect to the results described and link back to the original research question.

Additional comments

I greatly enjoyed reading this paper and was happy to see another terrestrial record of the Paleocene/Eocene boundary described. I appreciate the amount of work that went into this project and your clear description of methods. I have a few comments line-by-line and suggestions for simplicity and clarity, but no major changes seem warranted. Great work!

Lines 43-45. Need references to back up this statement.
Lines 45-48. The scale and magnitude of the PETM are not analogous to those of modern anthropogenic warming. Please be careful not to overstate the significance of this event for predicting change in our near future.
Lines 59-61. Need references to back up this statement.
Lines 61-66. You describe variation among regions after the bolide impact, but I do not see how this translates to instability across the Paleocene. Do we expect plant and insect diversity to always coincide? Apparently they don’t in this study.
Line 70. Energy “budge” – I assume you mean budget.
Line 79. Does the Hanna Basin really expand the geographic distribution of samples? Aren’t they all from this part of the country?
Lines 79-81. Not sure that you need a geologic map for figure 1a, which provides more detail than seems necessary. Might be better for context to make this part of the map a larger picture of western North America with the other PETM terrestrial sites located. This would demonstrate just how little is known about this interval and how much your study contributes to our understanding.
Lines 153-156. Can you put the radiometric ages onto figure 2 as they are described here? What is the significance, if any, for this study if the upper age limit is completely off? I don’t recall any other references to radiometric ages – perhaps the information about age calculations for the individual localities not relevant here?
Lines 167-213. I found it difficult to follow the localities and their placement with respect to the coal beds discussed here in figure 2. I’m also not sure that this detailed description is important. Could it be moved to the supplementary information and a briefer description of the sedimentology be provided?
Lines 193-203. This is a bit distressing. The most important of the samples for comparative purposes would be the D samples, as they are in the PETM. But they are the least well constrained stratigraphically and the least well preserved.
Lines 225-236. Is there any possibility of uneven sampling bias in the results of these equations? Please elaborate.
Lines 240-244. Why use two different diversity indices to assess the same influence? I found the discussion of the results of these a bit confusing and would suggest chosing one with a justification as to why it is the best.
Lines 245-246. Similarly, why use both Pielou’s J and rank-abundance curves?
Lines 264-266. Does this mean that some specialized herbivory is unrecognized, because it doesn’t look similar to what we know of modern specialized insect herbivory?
Lines 277-280. Please explain why LMAT appears to increase at level C before the PETM in your reconstructions in Table 1. This seems to me to be a major inconsistency with what is known of the interval.
Line 281. Not sure I understand this statement. It does seem the LMAT and MAP change considerably. Did you do an analysis of the statistical significance? Or do you mean that the errors overlap? How do your estimates compare with those for the Bighorn Basin? I think this should definitely be expanded.
Line 298. Floral “diversity richness” indices – do you mean one term or the other? I also assume you mean table 2 not table 1.
Lines 283-314. I found this discussion of results very confusing, constantly flipping between tables and back to figure 4. I would suggest simplifying this to describe each level in turn. I would also suggest using fewer indices, since it seems to me that you are basically describing floral richness and evenness. Jumping between levels and quarries using multiple indices that describe the same or similar aspects of the fauna and using multiple tables and figures makes this section needlessly complicated.
Lines 315-324. I don’t understand the difference between figures 5B, 5C and 6. Is figure 6 a subset of figure 5B? If so, why include figure 5B at all? I’m not sure what figure 6B demonstrates? I think figures 5 and 6 could be simplified and combined.
Lines 325-332. Just in terms of simplicity and spacing, it seems as though figures 7 and 8 could also be combined.
Lines 343-362. I find the legend in figure 10 confusing. I think you could simply have a green triangle indicating Paleocene, level A; a yellow triangle indicating Paleocene, level B; and so on. Somewhere, it needs to be clarified what these solid symbols mean. Are they the averages for each level? Maybe the x symbols could also be color-coded. Also, you explain in the text why some of the x symbols have labels but I would include this information in the figure caption. Those labels overlap and obscure many of the data points. I think it would be helpful to have a fuller description of what the axes mean.
Lines 446-448. I don’t see how the species:area relationship would add significantly to the depositional signal.
Lines 477-479. This sentence seems to be incomplete.

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