Overview

I have organized my comments by manuscript section with more thorough review provided for the figures. As this preprint has already gone through previous revision/review, my comments are fairly minor and I generally have no issues with any of the anatomical descriptions, functional interpretations, or taxonomic affiliations.

On a personal note, it is exciting to see a paper detailing isolated postcranial specimens for large bodied colobines as it will only improve functional interpretations of other specimens and provide a more nuanced picture of the anatomy of mixed substrate preferences. Such analyses are difficult without larger sample sizes of relevant elements and the assemblages presented here refine previously published, functional interpretations based on much more limited sample sizes.

Introduction

On line 137 to 138 the authors state that “P. mutiwa is currently known from only one single individual…” To stay consistent with later mention of a specific specimen number in the following sentence, I recommend providing the specimen number to which they are referring here as well.

Materials/Methods

On lines 269, 271, 273, and 278 (and possibly more) the authors begin their sentences with the genus abbreviations. It is generally recommended to start a sentence with the genus name written in full even when it has been defined earlier in the manuscript. I of course defer to the editors if this is an acceptable format for this publication.

Comparative Anatomy

On line 745 the authors describe a feature as being “extremely similar” I recommend removing the superlative.

Discussion

In lines 1481-1482 the authors state “…KNM-WT 16827, a partial skeleton attributed to P. mutiwa.” The fact that this specimen is attributed to P. mutiwa has been previously established in the paper so is redundant here. This occurs in subsequent discussion subsections as well. On lines 1483-1486 the authors use Roman numerals in their list of justifications. Unless this formatting is required by the journal, listing with numbers e.g. 1-4 would be simpler.

Figures

This isn’t a revision, but I wanted to compliment Figure 1 and Table 2 as they effectively convey a lot of important information very succinctly!

The functional rationales in Table 7 are a very nice touch.

The captions for Figs 2–4 seem redundant with information about the measurements already provided in Table 6. If the intention is to provided Table 6 in appendices, then they’re fine, but if all are intended to be a part of the main paper, I recommend shortening the captions. Figures 10 & 18 are very busy and although the scatterplots are straightforward, but the inclusion of the density estimates below makes the whole figure difficult to read.

In Figures 11, 14, 16, 19, 22 the individual taxa shapes within the violin plots are very small and difficult to tell apart. I also recommend making the font size smaller on the fossil taxa labels so they aren’t so crowded.

This could be a byproduct of uploading or the preprint viewing interface, but Table 12 has inconsistent font sizes and spacing. It’s also unclear why it’s split in two parts.

In footnote 3 for Table 16, “KNM-WT 1682” should be “KNM-WT 16827.”

Figures 20 & 21 are very dark making details of the specimens difficult to see. I recommend adjusting the saturation.

For Fig. 23 and its mentions in the main text, “estimated body masses” may be more accurate than “inferred body masses.” I also assume that the color coding on the individual points within the boxplot is based on taxon so a legend should be added for clarity.

Review of Postcranial anatomy of colobines (Mammalia, Primates) from the Plio-Pleistocene Omo Group deposits (Shungura Formation and Usno Formation, 1967-2018 field campaigns, Lower Omo Valley, Ethiopia)

First, let me commend the authors for all of the work that went into this MS….this is a lot of information and data and the basic descriptions and analyses all seem well done.  All of the figures, plots, and data are very nice and useful to have.  It is very nice to see this new monkey material be described and published, and I will look forward to its final publication.  My more detailed comments are provided in the annotated PDF, but I will summarize my main thoughts/suggestions here :

1)    My biggest criticism /concern with the current MS has to do with the organization.  As I mentioned above, the content is generally great, but the current organization is really hard to follow in a MS of this size.  To me, I think you need to describe all of the bones and interpret them within each taxonomic category rather than by anatomical element.  It is really hard to keep everything straight when you are discussing 5 different morphotypes element by element. Instead, it would be much easier for the reader and much clearer if you describe everything within the Sys Paleo section. For example, under the Pa. mutiwa heading, describe all of the elements you are assigning to this taxon, explain why you are assigning them to Pa. mutiwa, and provide a brief functional interpretation for this taxon.  Then move on to the next taxon.  Etc.  Right now, all of this information is in the MS to be sure, but it’s really difficult to put it all together because it’s spread out across all of the anatomical subheadings and then you start to put it together in the discussion.  This should all be synthesized in the Sys Paleo section and then the Discussion can focus more on the evolutionary implications and other things that you discuss on pages 96 onward.

2)    Somewhere up front, in the Introduction or Materials and Methods, you need some sort of discussion or justification as to how you came to decide that the specimens in this paper are all colobines rather than cercopithecines.  Because some of these colobines are large and overlap the size and morphological features of extant and fossil cercopithecines, the reader needs to know why these specimens are likely to be Pa. mutiwa rather than Soromandrillus or T. brumpti, for instance.  Or why the arboreal looking specimens must be colobine rather than Lophocebus cf. albigena.  What morphological criteria did you use to decide they are all colobines?  This needs to be addressed early in the paper.

3)    Along similar lines, I think there also needs to be some additional justifications in the Materials and Methods as to why the measurements were chosen and why the comparative sample was chosen.  The measurements chosen are fine (and are a nice set of indices), but why were these chosen?  Have they been used in past studies to assess various aspects of locomotor behavior?  In Table 7, it would be helpful to provide references to studies that have used these indices before to infer locomotor behavior.  It might also be worthwhile to look back at classic references like Fleagle (1976) and Harrison (1989) for additional features that have been definitively linked to differences in locomotor behavior in colobines and Old World monkeys more broadly.  Many of the  indices you have chosen have been used before and correlated to behaviors by studies in the field.  Where possible, you should cite these references rather than just make assumptions about the functional rationale for each of these measurements.  For any new index you are using, you could perhaps collect basic behavioral data from the literature and run correlations between these indices and the frequency of behaviors of interest to conclusively document the connection between these indices and certain behaviors.  See Arenson et al. (2020) paper for a recent example on extant monkeys and %terrestriality.  They were able to clearly demonstrate which indices were most highly correlated with %terrestriality data collected from field studies.  

The comparative sample of extant colobines seems reasonable….but why only Papio for comparison?  Is it because it is a large terrestrial monkey?  Is it because it is a large cercopithecine?  Or both?  And why not sample a more arboreal cercopithecine for comparison as well?  Throughout the plots, the sample is compared with extant colobines and Papio, which is fine, but in some cases you are possibly conflating taxonomic distinctions (colobines vs. Papio/cercopithecines) and locomotor distinctions (arboreal vs. terrestrial). 

Also, captive specimens are obviously not ideal for a study like this, but I understand that sometimes that’s the best you can do.  Can you at least confirm that they are non-pathological ?  Some comment on the criteria for inclusion in the study for the captive specimens is needed.   

And finally, there needs to be some comment on the adult/subadult status of the included specimens.  Are these all adults?  How was adult status determined (i.e., all epiphyses fused, all epiphyses fused with no lines, some epiphyses fused, M3/m3 eruption, ???).  If it is a mixed subadult/adult sample, this needs to be stated and identified in Table 3 with an additional column listing numbers of adult/subadult specimens or perhaps in an appendix somewhere.  

4)    Body mass estimation, GM, and sexual dimorphism- The section discussing body mass estimation and geometric means on pages 23-25 is unclear…I do not understand what is being calculated here.  Please clarify in greater detail.  

It would appear that a number of different Geometric means are being calculated for different anatomical elemetns from the data available, which is fine.  But each of the GMs needs to be calculated for as many of the extant taxa as possible as well so you can have some idea of how well they track dimorphism in extant taxa.  If these GM values lead to sexual dimorphism ratios similar to that seen from actual body mass data, then that’s great and they can assumed to be accurate, but this needs to be empirically demonstrated first.  A Male GM/Female GM for the humerus, femur, ulna, etc. cannot be assumed to track actual body size dimorphism well without comparing these GM dimorphism values to extant body mass dimorphism values through a regression.  This needs to be provided for all GM dimorphism indices.  There seems to be some attempt at this using Nasalis at the top of page 24 (again, it’s not entirely clear what was done), but for the comparison to be meaningful, the exact GMs that are used for the fossil taxa need to be applied to extant taxa, and not just Nasalis, but as many colobines as you have in your sample and definitely need to be done for some African colobines in addition to Nasalis.  

Similarly, in Fig. 24, I have no idea what is going on, in part because I don’t think these ratios are well explained in the Materials and Methods.  What is meant by a ‘male baseline’ in this Fig. 24?  What is being calculated as a GM ratio ?  It is unclear what is going on here.  I would think that a GM Sex dimophism ratio in any monkey should be greater than 1 if dividing male GM by female GM.  Please clarify what is going on in this plot and explain it up front in the Materials and Methods.  

5)    In some of the Figures (e.g., Fig. 10), regression statistics are provided between the variables being examined.  However, there seems to be some inconsistency as to what numbers are being reported.  What are the p-values of the regressions ?  In some cases, r-squared values are so low, that I have to wonder if they are even worth reporting if the relationship is really weak.  In any case, p-values should be provided.  

6)    The variable used for ulnar olecranon process height (e.g., see Fig. 14) seems to be capturing more of what I would argue is actually the relative LENGTH of the olecranon, not the HEIGHT, which is usually described in relation to its proximal extension.  You would expect colobines (and arboreal quadrupeds more generally) to have a more proximally extended or TALLER olecranon process above the sigmoid notch, even if Papio has a relatively long olecranon because it is retroflexed posteriorly.  So I would just change the terms here and it might be nice to add in a measure capturing the proximal extension of the olecranon above the sigmoid notch, i.e., olecranon HEIGHT.  The angulation measure is somewhat capturing this, but maybe a height linear measure in the proximal direction would be helpful as well ?

7)    Page 68 and onward, discussion of the extension of the articular surface onto the femoral neck- Some caution in the broad taxonomic and functional utilityof this feature is warranted and should be noted or cautioned in the text here.  It’s not unusual for many cercopithecines to have a bit of an extension onto the femoral neck, so I don’t know if this is a very good taxonomic indicator in terms of colobines vs. cercopithecines.  I would be very wary of assigning proximal femora to colobines on the basis of this feature.  For instance, Theropithecus often displays an extension of the articular surface onto the femoral neck.  Are the colobine specimens described here significantly smaller than T. brumpti and/or T. oswaldi of this time period ?  And/or to they display other distinctive features?  More broadly, this is why we need to have some additional justification as to why these specimens were determined to be colobines in the first place, as I have indicated in point #2 above.

8)    Discussion page 97- In the discussion regarding the interpretation of Pa. mutiwa’s locomotor adaptation, a number of features are noted as being suggestive of a more mixed climbing/arboreal component to this species’ repertoire than previously suggested.  Some of these features, such as a well-defined/deep sigmoid notch, have been associated with terrestrial quadrupedalism in that past.  Here, you are suggeting they indicate more climbing/arboreal behaviors instead.  Can you provide refernce to support this interpretation an provide an example of an extant species exhibiting these features that is more of a climber than a terrestrial quadruped?  Mandrills have many of these features and are quite terrestrial, for instance, so while it seems reasonable to point out that there might have been more climbing in the repertoire of Pa. mutiwa than previously appreciated, many of these features seem associated with more terrestrial behaviors.  If you have a reference for the deep sigmoid notch being indicative of climbing, please provide it.  But it has been noted previously to be associated with a stable elbow and terrestrial quadrupedalism.  And since Soromandrillus is also found in the Omo, can we be certain that these specimens belong to Pa. mutiwa rather than Soromandrillus?  Some comment on why they are likely to be mutiwa rather than Soromandrillus is needed somewhere in here.  Can T. brumpti be ruled out as well?  This is why it needs to be established why these specimens must be large colobines rather than large cercopithecines somewhere at the beginning of this paper.  The evolutionary interpretations depend heavily on making the correct assignments to subfamily and genus, so they need to be well-justified from the beginning.  To be clear, I’m not saying the assignments in this paper are unlikely to be correct, only that they need to be better justified from the beginning of the paper so we can be confident that they are all colobines.  

9)    Finally a few taxonomic notes- Cercopithecoides kimeui has been recently synonomized with C. coronatus (see Frost et al., 2022 colobine book chapter).   If you don’t agree, that is fine but you must state reasons why or I would suggest using the more currrent taxonomic arrangement.  Similarly, in the same book chapter, Frost et al. (2022) point out that the colobine at Laetoli is better referred to cf. Kuseracolobus rather than cf. Rhinocolobus based on the presence of a maxillary sinus, among other features, shared with Kuseracolobus and not found in Rhinocolobus.   This taxonomy should also be followed here, unless the authors want to argue more specifically otherwise. 

10) Appendices- During the re-organization of the paper, it seems to me that much of the descriptions in Appendix 1 should be moved to the main text in the Sys Paleo section.  

The Appendix 2 figure should incorporate the taxonomic changes I noted above in point #9.

Additional information regarding the sex and ontogenetic stage (adult, subadult, etc.) of each extant specimen and the numbers of males and females in each mixed sex samle should be given in the appendices.  

Other than that, my more detailed comments and suggested edits are in the attached annotated Word .docs.  I look forward to seeing the revised paper published sometime soon…