Review Reports - The Controversial Origin of Ferruginous “Coprolites”

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This article does an excellent job of documenting these objects, which I believe are all or mostly all concretions not coprolites. The main weakness of the article is that it fails to demonstrate (or argue) that they are likely not coprolites, which should be the conclusion.

Late in the paper the characteristics of coprolites (a few) are discussed. There needs to be a section up front that tells the reader how to evaluate whether or not these objects are coprolites. What are characteristic features of coprolites that these objects might show? What if any bona fide coprolites do they resemble? Etc.

I will say that they are almost all not smooth or striated, and there seem to be no recurring morphotypes beyond a few very very broad categories. Those are features that argue against a coprolite origin.

My other comments/suggestions are:

Lines 117-119 As noted in a 2014 paper published in Volumina Jurassica, almost all so-called Morrison coprolites are not that (Hunt & Lucas, 2014).

Lines 563-564 In my experience, when describing assemblages of coprolites they can be organized into discrete often recurring morphotypes. See for examplea recent paper published (Zahir et al in Palaios) on a rather extensive assemblage of coprolites from the Triassic of Morocco.

Inclusions can also be important indicators that the structure is likely a coprolite.

Lines 564, 571 Figure 37 must be a typo; isn’t Figure 39 being referred to here?

Lines 687, 859—Hirabromus not Hydrobromus

Note that the specimens Hunt et al described as Hirabromus do look like coprolites, unlike most of the rubbly, irregularly shaped botryoidal objects illustrated in this paper. My default would be that these are concretions.

Line 893 so what are typical coprolite features, none of which are visible here?

Lines 923-927—The “agnostic” conclusion that these things might be bromalites/coprolites is not well supported. Instead, I would argue these things are concretions for the most part and only those with definite features characteristic of coprolites could be coprolites. I think an abiotic origin fits the data best.

Comments for author File: Comments.pdf

Author Response

I have changed the wording to say that the new evidence suggests that Salmon Creek specimens are of abiogenic origin. However, a single depositional model cannot be applied to all ferruginous "coprolite" localities. I see my work is being a lesson in the kind of detailed geologic observation and laboratory analysis that can be applied by future investigators, not a situation where I should declare universal conclusions.

I have added a description of characteristics, as you have suggested.

I agree

My other comments/suggestions are:

Lines 117-119 As noted in a 2014 paper published in Volumina Jurassica, almost all so-called Morrison coprolites are not that (Hunt & Lucas, 2014).

Thanks, I have added that reference

I am familiar with the Morocco paper, but I did not cite it because it makes no reference to ferruginous "coprolites". I agree with your views about discrete recurring morphotypes, but there have been authors who claim that both Salmon Creek and Whitemud Formation specimens can be divided into morphotypes. I decided to provide figures that show the diversity of specimens from these and other localities, which to me support the absence of recurring morphotypes. I trust readers to come to their own conclusions. A major point in the manuscript is that some investigators have based their observations on an inadequate number of specimens, and/or specimens that came from biased collecting.

Inclusions can also be important indicators that the structure is likely a coprolite.

Yes, I discuss that issue

Lines 564, 571 Figure 37 must be a typo; isn’t Figure 39 being referred to here?

Yes, the reference is to Figure 39, I have made the correction

Lines 687, 859—Hirabromus not Hydrobromus

Thanks for noticing this typo.

I discuss the Hirabromus ichnotaxonomy in regard to the the inconsistent illustration of the holotype. Otherwise, I do not want to take a position on this published report. I have focused on ferruginous "bromalites" only where I have been able to study the actual specimens.

Line 893 so what are typical coprolite features, none of which are visible here?

I have expanded the text in regard to typical coprolite features

As I noted in an above comment, I prefer to take an "agnostic" position. In the past, there have been too many papers where authors have cited purportedly "compelling" evidence to support both biologic and abiotic origins for these ferruginous masses, some of the researchers using selective evidence to support a preconceived conclusion. I believe that my paper will have stronger influence if I refrain taking that kind of position, Instead, I offer guidelines that can be used to make objective interpretations. In particular, I see a critical need for detailed information on the geologic setting and specimen mineralogy.

GENERAL REPLY:

Thanks for the careful review, which is very helpful. I have altered the introduction to provide more clarity in regard to the project goals, and I added a brief description on coprolite characteristics, versus characteristics of ferruginous specimens.

I added the suggested reference to the 2014 Morrison Formation "coprolites", though it refers to siliceous specimens. But I appreciate its comment about the vast quantities quartz and agate specimens that are advertised as dinosaur coprolites, similar to way that every rounded rock is labelled as a gastrolith.

The morphotype situation is interesting. Several authors have claimed that the Whitemud and Salmon Creek "coprolites" can be divided into morphotype categories. My position is that morphotyping has been clouded by biased collecting, and I have described that issue at length.

I have tried to clarify my "agnostic" position. I don't want to make any general statement that these objects are all pseudocoprolites. The literature already has too many ferruginous "coprolite" reports where researchers claim to have arrived at a compelling conclusion. Instead, I want to report some analytical protocols that can be used to make valid interpretations, in lieu of the researchers who have based their declarations on the "I know poop when I see it" preconception.

Thanks for catching some typos and other small errors. I appreciate your keen eye, and I have made all of those changes. Thanks again for the encouraging review; my manuscript is better because of it.

Reviewer 2 Report

Comments and Suggestions for Authors

This contribution is an interesting and detailed study of enigmatic ferruginous objects found from several geological formation and deposit of different time period (Permian, Cretaceous, Miocene, Pleistocene). The goal is to discuss the interpretation of these objects as coprolites, which remains largely controversial, and which here remains (even if widely discussed) uncertain and unresolved. The aim of the contribution to resolve this debate is therefore not achieved.

It is an impressive paper of 47 pages, including 44 figures, 3 tables and 65 bibliographic references. The structure of it is peculiar with 6 chapters: 1) Introduction: 5 p. and 5 fig; 2) Material and methods: 1 paragraph and 2 sentences (only methods); 3) Salmon Creek: 15-16p. and 23 fig with 8 paragraphs; 4) Mineralogy: 13-14p. and 10 fig., with 7 paragraphs; 5) Discussion: 7.5p. and 6 fig. with no less than 9 paragraphs; and finally 6) summary of 1 p. (plus 3p. of bibliography). The figures are plethoric and constitute paragraph with very few comments/sentences. Globally speaking, the contribution need probably to be re-organized (contents; simple copy and paste will improve the facts and assumptions. (?)) and reduced (some put in annex or SI)…to be more ‘readable’. (funny the wat that author quote himself in the text ; ‘Mustoe say…’). In Hunt et al. 2012, the correct term is Bromalite instead of Bromolite sometimes used here (see also Mondini 2023)

The introduction is may be too long, and indeed it is good to how that coprolites are not only found in Quaternary deposits (ie; Buckland who coined the term), and to emphasize about their importance for paleoenvironmental studies, as well as the morphological and morphometrical (figs. 18-19) features of these ‘copro’ objects (and what’s about morphometry?). A very positive point here, is the presentation of the geological context which is not so often provided for this kind of studies. The list given p.2 could be reported in the discussion. The descriptions of the samples would have been better placed in the materials section of the materials and methods (but as mentioned, only the methods are in the very short chapter 2, while the 'Materials' are presented in chapter 3).

The study material comes from specimens from Salmon Creeks (Washington) dated of late Miocene, with some data from other localities (Madagascar), bibliography or recent material (ex. fig. 43, 44).

Association found with burnt vegetal (wood) (p.20-21 &3.8) is interesting and probably should deserves to be developed further. Analytical approaches (chapter Mineralogy) seems essential to precise the nature s.l. of these ‘copro’ and they bring significant information’s. T

Other commetns : text and figures up to 4.4. X-Ray Diffraction included are descriptions. From 4.5. Siderite Geochemistry, it is discussion and hypotheses. Highlight these two parts. Were the samples observed under the SEM 'metalized'? How were the samples prepared to release the pollen and other micro 'samples'?

The chapter discussion is well conducted and useful, as many speculative and fancifully explanation has need proposed

In the end, we are left somewhat unsatisfied regarding the origin of these objects, and would have liked a bit more interpretation to understand the origin and ‘convoluted’, sinuous, nature of such ’concretions’, nodules, pseudomorphs…. It would be relevant to have more confidence and may be to take a stand to finally answering to the scientific question exposed in the introduction, and goal of the paper after all (at least for the Salmon Creek specimens) …event if it ‘remains unprovable’ (line 888)! However, we understand that this is a complex matter, as there are many examples of these ferruginous (rusty – sic) objects in a wide space-time context: that is why the last chapter (Summary) fits well with this contribution and is quite honest, stating that no final conclusion is reached.

This contribution about enigmatic presupposed copro is very interisting and it deserves to be published, with some reorganization of chapters.

Line 46 : decomposed and not composed

Line 248: precise in fig. 12 the beds yielding “copro”

Author Response

I have clarified the statement of my goals. My aim was never to end the debate by making a "right answer" declaration.

I did some organization rearrangement in the hope of improving presentation clarity . I changed references to "Mustoe" and "we" to "I". The original plural format came because I had invited Whitman College Professor Pat Spencer to be a coauthor, but he soon dropped out, saying that he lacked the time to participate .

I divided the Introduction into two parts, the second now a new section headed "Global Occurrences". I have expanded the methods section to provide more details.

The study material comes from specimens from Salmon Creeks (Washington) dated of late Miocene, with some data from other localities (Madagascar), bibliography or recent material (ex. fig. 43, 44).

The association of "coprolites" and ancient wood is an important feature at Salmon Creek, first reported by Pat Spencer and Ted Danner, but ignored by other investigators who based their observations on specimens that they obtained from other collectors. I would like to do more detailed on the wood relationship, and the study of ancient wood has long been my main research interest. However, site access at Salmon Creek is presently very limited because of private property restrictions.

I have added a description of the SEM sample preparation, which included sputter coating of specimens with Pd to provide electrical conductivity. The pollen preparation method is described in the Mustoe & Leopold paper, which is cited as a reference. The petrographic thin sections were made using standard methods, nothing special. If desired, I can provide details in the methods section.

The chapter discussion is well conducted and useful, as many speculative and fancifully explanation has need proposed

I have changed the statement to say that the new data suggest the possibility that Salmon Creek "coprolites" are of abiogenic origin, but I don't believe that a single depositional model can be applied to all localities. My hope is that my presentation can be used to provide a foundation for improving the quality of future investigations, and to provide a lens for viewing past research. I want to avoid providing and "final answer". There is much work yet to be done.

This contribution about enigmatic presupposed copro is very interesting and it deserves to be published, with some reorganization of chapters.

Thanks, I appreciate your encouraging response.

Line 46 : decomposed and not composed

Thanks, I have made the change.

Line 248: precise in fig. 12 the beds yielding “copro”

Thanks, I added an arrow to show the "coprolite" stratum

GENERAL REPLY

Thanks for the careful review, and for your useful suggestions.

I have done some reorganization, one change being to divide the long introduction into two sections, adding a Global Occurrences section. I have also written a clearer statement in regard to research goals. It has never been my intent to make a general statement in regard to the biogenic/abiogenic controversy, though I believe that the evidence from Salmon Creek supports the abiogenic origin, and I have included that statement in the conclusions. However, my main goal is to describe types of data that can be used to make valid interpretations, in lieu of the past reports where researchers have based their conclusions on the "I know poop when I see it" preconception.

Thanks for catching a variety of small errors. I have made those adjustments. I appreciate your efforts to improve the manuscript; it is an example of the positive values of peer review.