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Thank you again for submitting your manuscript to PeerJ. I am pleased to tell that the revised manuscript has been accepted for publication in PeerJ.
[# PeerJ Staff Note - this decision was reviewed and approved by Kenneth De Baets, a PeerJ Section Editor covering this Section #]
Thank you for submitting your manuscript to PeerJ. I have now received reports from reviewers and, after careful consideration, I have decided to invite a minor revision of the manuscript. Reviewer 1 suggest revisions on some words and sentences. Please provide a point-by-point response to these comments along with your revision.
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I had the opportunity to review this manuscript previously and report on the findings. I suggest only a few very minor comments in the attached PDF file.
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Just a minor comment. When referring to "femoral nutrient foramina," they are small openings in the "mid-shaft" region of the bones. Openings in other regions (e.g., in the epiphyseal regions) are not nutrient foramina. Rather, they could be epiphyseal foramina.
The manuscript improved largely after authors performed requested modifications. In my view it can considered as accepted
The methods and results sections are now more complete and clear after authors performed requested modifications.
The discussion section improved after modifications. Authors should check for incomplete sentences, grammar, and typos.
Thank you for submitting your manuscript to PeerJ. I have now received reports from four reviewers and, after careful consideration, I have decided to invite a major revision of the manuscript. Collectively, all Reviewers think this paper is interesting and should be published in PeerJ. The study provides new insights for the paleobiology of the xenarthran clade.
As you will see from the reports copied below, the reviewers raise important concerns. The current database still needs to be properly expanded. The method used in this paper is a bit outdated and should be updated with a new method suggested by the reviewer. Also the description of the method is not careful enough and additional information is needed. In addition, some literature needs to be added, such as the literature on body size. The language of the article needs to be further refined by a native speaker.
If you feel that you are able to comprehensively address the reviewers’ concerns, please provide a point-by-point response to these comments along with your revision. If you are unable to address specific reviewer requests or find any points invalid, please explain why in the point-by-point response.
The paper is solid and well-written. Even if the manuscript is clearly understandable, a detailed language revision from a fluent English speaker is strongly suggested. The research is adequately contextualized, well-structured, and presents relevant, novel insights for the paleobiology of the xenarthran clade.
The statistics are correctly used, as the analyses are controlled for phylogeny and body size. However, the paper would strongly benefit from the inclusion in the dataset of other taxa and the evaluation of alternative topologies. Ideally, the second genus of extant sloths, Choloepus, should be included. This peculiar taxon, considered convergent to Bradypus in many biological aspects related to metabolism and extremely slow suspensory locomotion, would reinforce (or modify) the evolutionary reconstructions of MMR for sloths. Moreover, the authors only investigated the topology that resulted from the recent molecular studies on xenarthrans. Proper evaluation of model fitting should also consider the topology based on the morphological evidence, analyzing additional, alternative phylogenetic relationships. In any case, the results presented here are relevant as they investigated MMR at the xenarthran level, constituting a first approximation of the knowledge of metabolic needs for some extinct lineages. This task is sometimes challenging to study due to the lack of more data.
This paper represents an essential contribution to studying metabolism in extinct xenarthrans, shedding light on an obscure aspect for paleontologists. It provides novel insights and confirms several previous observations, further resuming all the contributions on this aspect that have been published so far. For all these reasons, the research is of great value and will represent a milestone for future research on this subject.
Minor comments are provided in the attached pdf file.
The manuscript is clear, with excellent English, the references well-complete, and figures that harmonize well with the text.
The investigation proposed by Carela and colleagues correspond perfectly with the journal’s aims. Their methodology is well-presented and applied, and the relevance is clear.
The investigation is robust and will interest not just xenarthran specialists. The conclusions are interesting and well-supported.
See editor’s letter
In general, the language is clear. However, some statement lack citations, especially in Discussion. Figures and figure legends are not professional and clear enough. More comments are shown in the PDF file.
This study used a method which was described 11 years ago (Seymour et al., 2012). The method can be improved, as more recently studies have standardised and improved the method. Additionally, the method section lacks detailed information. For example, the author does not include body mass references, and there is no explanation as to why only the largest foramen was measured when there were more than one foramina on the femur shaft.
Although the findings and results seem interesting, there is a lack of data and statistics results in the Results and Discussion sections. The discussion reads more like a literature review, and it does not offer potential explanations for why different selected mammalian groups exhibited different blood flow rates.
The submitted manuscript is an excellent piece of research on xenarthran paleobiology. Histological aspects are frequently overlooked in mammalian paleobiology, so in this regard, the manuscript makes an outstanding contribution to the discipline. Indeed, results obtained indicating that extinct large and giant xenarthrans could have a higher metabolism than expected based on extant relatives are a major contribution.
The referenced literature is mostly correct. Since I'm not a fluent English speaker, I can't provide a comprehensive grammar correction, although so far I understand the writing is correct, clear, and concise. Sometimes, there are some repetitions of words along the same sentence, that can improve by using synonyms. Also, I would recommend using "extant" instead of "living".
Figures are well made, clear, and sufficient to convey the results. I was expecting some tables with values and statistics, but their only mention is for Supplementary Files, which I couldn't reach. I encourage authors to include tables in the main paper corpus.
I don't have any major concerns about the data analysis and interpretation. Among other minor issues, the authors seem to have overlooked the work by Toledo et al. 2017 on the evolution of body size in extant and extinct sloths and anteaters, referenced only in the introduction. In this work, the authors addressed most of the topics related to this manuscript, including metabolism, diet, and locomotion. I strongly recommend the authors read that work and discuss its proposals in light of the new findings. Also, there is a recently published work by Barbosa et al. 2023 on the body size estimations of Brasil Quaternary xenarthrans and a work by Zack et al. 2023 about the relationship between body size and trabecular bone in extant xenarthrans that the authors will find interesting to reference.
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