Allosaurus europaeus (Theropoda: Allosauroidea) Revisited and Taxonomy of the Genus

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Allosaurus europaeus is a species of predatory dinosaur based on a partial specimen from Portugal. This species has been considered by some authors as not valid, and its material has turned being included in the well-known Allosaurus fragilis.

The authors of this contribution re-describe in detail the Allosaurus europaeus material and re-diagnose it, suggesting its validity and distinction from other named Allosaurus species. They also review the European fossil record of Allosauridae.

The descriptive part is very informative and well-detailed. The authors are thanked for providing the first species-level analysis of the Allosaurus genus, yet the results of the phylogenetic analyses are not conclusive. I've re-run the analysis using the data set included in the manuscript and note that with just a very few data edits (in particular, setting a few multistate characters as ordered, so accounting for the implicit hierarchical relationships among the states so defined), the scenario suggested by the authors collapses and we cannot definitely assess any topology among the Allosaurus species.

I've also calculated the nodal support of the suggested topologies and obtained a very weak result: only the node Allosaurus is robust enough for not being considered merely due to sampling artifacts.

In summary, although the authors have provided a robust diagnosis for A. europaeus, their phylogenetic analysis is not robust enough for suggesting that such taxon is actually distinct from other Allosaurus taxa. This result is not surprising because a phylogenetic analysis based on shared derived apomorphies is not designed to spot all possible microevolutionary patterns leading to speciation (e.g., anagenetic transition from one ancestral to a descendant species without cladogenetic branching). For example, the topology preferred by the authors could be interpreted assuming that A. fragilis is the ancestor of A. europaeus, and that the latter represents a local speciation in the European part of the A. fragilis ancestral areale. Yet, such scenario requires a more detailed stratigraphic zonation of the different Allosaurus morphotypes (?species), not merely a phylogenetic analysis. A possible option is thus to improve the character and taxon sample of their phylogenetic analysis (adding more characters and including more Allosaurus specimens which could eventually support internal clusters in the sample). The authors are also invited to consider the application of specimen-level tip-dating Bayesian phylogenetics incorporating stratigraphic uncertainty, the most appropriate tool for addressing such questions.

Furthermore, I suggest to add a third outgroup, more complete than Neovenator, e.g., Acrocanthosaurus.

If the above suggestions are considered by the authors beyond the aims of their manuscript, I invite them to explicitly remark the weakness of their phylogenetic analysis, and - accordingly - to reduce the discussion about the palaeogeographic results. Yet, the discussion should focus much in depth on the features differentiating A. europeaus from A. fragilis: their mere mention (with no discussion of their possible biological meaning) does not explain why they cannot be considered just intraspecific variation.

Please, see in the attached pdf a series of comments on some parts of the manuscript.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English form of some sentences should be improved (see comments in the attached pdf).

Author Response

Response to Reviewer 1 Comments
1. Summary
Thank you very much for taking the time and effort to review this manuscript. Your comments and suggestions have been invaluable in enhancing the quality of the manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. If you have any further questions or require additional clarification regarding the revisions made, please do not hesitate to contact us. We are more than happy to provide any assistance necessary. Thank you once again for your contribution to the peer-review process.
2. Questions for General Evaluation	Reviewer’s Evaluation	Response and Revisions
Does the introduction provide sufficient background and include all relevant references?	Yes
Are all the cited references relevant to the research?	Yes
Is the research design appropriate?	Yes
Are the methods adequately described?	Yes
Are the results clearly presented?	Yes
Are the conclusions supported by the results?	Can be improved	Exceed the scope and timeframe of this work.
3. Point-by-point response to Comments and Suggestions for Authors
Comments 1: Allosaurus europaeus is a species of predatory dinosaur based on a partial specimen from Portugal. This species has been considered by some authors as not valid, and its material has turned being included in the well-known Allosaurus fragilis. The authors of this contribution re-describe in detail the Allosaurus europaeus material and re-diagnose it, suggesting its validity and distinction from other named Allosaurus species. They also review the European fossil record of Allosauridae. The descriptive part is very informative and well-detailed. The authors are thanked for providing the first species-level analysis of the Allosaurus genus, yet the results of the phylogenetic analyses are not conclusive. I've re-run the analysis using the data set included in the manuscript and note that with just a very few data edits (in particular, setting a few multistate characters as ordered, so accounting for the implicit hierarchical relationships among the states so defined), the scenario suggested by the authors collapses and we cannot definitely assess any topology among the Allosaurus species. I've also calculated the nodal support of the suggested topologies and obtained a very weak result: only the node Allosaurus is robust enough for not being considered merely due to sampling artifacts. In summary, although the authors have provided a robust diagnosis for A. europaeus, their phylogenetic analysis is not robust enough for suggesting that such taxon is actually distinct from other Allosaurus taxa. This result is not surprising because a phylogenetic analysis based on shared derived apomorphies is not designed to spot all possible microevolutionary patterns leading to speciation (e.g., anagenetic transition from one ancestral to a descendant species without cladogenetic branching). For example, the topology preferred by the authors could be interpreted assuming that A. fragilis is the ancestor of A. europaeus, and that the latter represents a local speciation in the European part of the A. fragilis ancestral areale. Yet, such scenario requires a more detailed stratigraphic zonation of the different Allosaurus morphotypes (?species), not merely a phylogenetic analysis. A possible option is thus to improve the character and taxon sample of their phylogenetic analysis (adding more characters and including more Allosaurus specimens which could eventually support internal clusters in the sample). The authors are also invited to consider the application of specimen-level tip-dating Bayesian phylogenetics incorporating stratigraphic uncertainty, the most appropriate tool for addressing such questions. Furthermore, I suggest to add a third outgroup, more complete than Neovenator, e.g., Acrocanthosaurus. If the above suggestions are considered by the authors beyond the aims of their manuscript, I invite them to explicitly remark the weakness of their phylogenetic analysis, and - accordingly - to reduce the discussion about the palaeogeographic results. Yet, the discussion should focus much in depth on the features differentiating A. europeaus from A. fragilis: their mere mention (with no discussion of their possible biological meaning) does not explain why they cannot be considered just intraspecific variation. Please, see in the attached pdf a series of comments on some parts of the manuscript.
Response 1: Thank you for pointing this out. We agree with this comment. However these suggestions require extensive additional analysis and data collection, which would exceed the scope and timeframe of the current study. Nevertheless, we addressed these weaknesses on to the manuscript in page 54, on eighth paragraph. Also, the addition of Acrocanthosaurus to the phylogeny were considered but we notice that by adding it would not alter the results, only increase uncertainty, so we think is not worth adding it.
Comments 2: The English form of some sentences should be improved (see comments in the attached pdf).
Response 2: Agree. We have rephrased some sentences accordingly and accept some suggestions that are highlighted in the manuscript.   Best Regards

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

 This review of the specimen ML 415 includes an adequate, in depth description of the specimen that has been needed within the theropod community for 18.  Sadly the paper lacks any real figures or evaluable assessments of other material from Portugal, and as such, this paper does not assess the diversity of allosaurid material from Portugal.  As a theropod worker, I was really looking forward to this when I agreed to review this paper.  Regardless, a strong, well-figured description is needed for ML 415 and Allosaurus europaeus, and with a complete rewrite this paper will be well-received and highly-cited for years.  The figures are very helpful and are the main strength of the paper.

I have attempted to edit the paper for clarity, grammar, punctuation and wording and I think the authors should go over the manuscript with more precision. 

There are some major revisions to the current version of the paper needed that would greatly improve the manuscript.  The Revised Diagnosis of A. europaeus is unclear and must be rewritten.  I recommend a Differentia section in which the differences between A. europaeus, A. jimmadseni, and A. fragilis are laid out.  I have edited some of the descriptive work and the authors should use these edited sections as templates along with previously described taxa (Chure and Loewen 2020) as a template for their description and comparison.  I edited the quadratojugal and postorbital and provide a template for the authors to revise the description.  If this happens, I am happy to look at the rest of the description again.  I feel that to further proceed with rewriting the description and providing comparisons is author level work.

There are also a few sections that are not original research by the authors, or necessary in the context of this description.  The review of the specimens historically attributed to genus Allosaurus, is largely identical to what is already described by Chure 2000; Loewen 2009; and Chure and Loewen 2020, who are not adequately cited.  The authors have not visited or studied the majority of this material.  While this section is likely appropriate in a dissertation chapter, this section should be removed, in that it even cites that the section is from the Paleobiology Database.  The authors should just refer to the PBD and only include their unique contributions to this discussion.  At most, this should be cited in the introduction and not a result.  This paper should not be published with this in the conclusions.

There are multiple issues with the phylogenetic analysis including the sources of scoring (often figures or photos rather than first-hand observations).  Many of the scorings I personally disagree with, based on firsthand observations of the specimens that are being scored.  There are also problems with selection of the character sets the analysis was created from (picking and choosing) and the taxon sampling (ignoring other specimens to save time).  A specimen-based analysis should include at least 3 specimens for A. fragilis and A. jimmadseni (totally easy to do) and then assess A. europaeus within that analysis. I can further dig into this analysis and am willing to, but it is unpublishable as is.  It is not informative other than to suggest that ML 415 is Allosaurus (partially due to the choice of characters and the choice of taxa to score).  I would recommend scoring A. jimmadseni and Ml 415 in Carrano et al 2012, but I also think that this is not going to be timely or especially informative.  The final conclusion, recovered in this matrix is the same stated in Chure and Loewen 2020 and is not novel.

The poorly supported phylogenetic section with speculation about North American Allosaurus species (that has been previously rejected) detracts from the excellent description of A. europaeus.  Alternately, the authors could join forces with authors who have seen the specimens in person (i.e. Evers or Carrano) to work on this phylogenetic section as a separate paper. I am happy to further review the rewritten descriptions and comparisons if another version of the paper comes along. A rewritten description and comparison of ML 415 would be a well-received paper.

I recommend major revisions to focus on the excellent descriptions of ML 415 and save the phylogenic analysis for a separate paper.  The potential strengths of this paper are the description, comparisons, and figures. 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

I think the authors should go over the manuscript with more precision. 

Reviewer 3 Report

Comments and Suggestions for Authors

Allosaurus is a famous theropod dinosaur holds significant paleogeographical importance due to its widespread distribution across North America and Iberian Peninsula during the Late Jurassic period,  For this reason, I have read with interest the manuscript on Allosaurus europaeus sent to Diversity. The manuscript is well-structured, with a accurate introduction. The data about Allosaurus from Portugal is presented accurately. The methods used are those common in dinosaur paleontology. The discussion and conclusions are adequately understood and justified. Therefore, this manuscript is suitable for Diversity. Only some small comments that this reviewer considers can improve the manuscript and that the authors should incorporate into the manuscript.

- In the abstract briefly explain that the Andrés specimen before citing it

- In Revised diagnosis it is not appropriate to start with Allosaurus. Because the concept of Allosaurus changes with the authors. The diagnosis only synapomorphies, apomorphies, combinations of characters etc., but not generic names.

- Please briefly describe the teeth. characters such as general shape, denticles, etc. In most sites only isolated teeth are found and being able to know information about the teeth of the holotype of Allosurus europaeus, however small it may be, is important.

 

 

Author Response

Response to Reviewer 2 Comments
1. Summary
Thank you very much for taking the time and effort to review this manuscript. Your comments and suggestions have been invaluable in enhancing the quality of the manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. If you have any further questions or require additional clarification regarding the revisions made, please do not hesitate to contact us. We are more than happy to provide any assistance necessary. Thank you once again for your contribution to the peer-review process.
2. Questions for General Evaluation	Reviewer’s Evaluation	Response and Revisions
Does the introduction provide sufficient background and include all relevant references?	Yes
Are all the cited references relevant to the research?	Yes
Is the research design appropriate?	Yes
Are the methods adequately described?	Yes
Are the results clearly presented?	Yes
Are the conclusions supported by the results?	Yes
3. Point-by-point response to Comments and Suggestions for Authors
Comments 1: In the abstract briefly explain that the Andrés specimen before citing it
Response 1: Thank you for pointing this out. However, we believe is not necessary to address this issue in the abstract, since Andrés specimen is the not the focus of this study.
Comments 2: In Revised diagnosis it is not appropriate to start with Allosaurus. Because the concept of Allosaurus changes with the authors. The diagnosis only synapomorphies, apomorphies, combinations of characters etc., but not generic names. Response 2: Agree. We have rephrased the sentence accordingly in page 7 in “revised diagnosis”.
Comments 3: Please briefly describe the teeth. characters such as general shape, denticles, etc. In most sites only isolated teeth are found and being able to know information about the teeth of the holotype of Allosurus europaeus, however small it may be, is important.
Response 2: We Agree. Regarding this matter, sadly we do not have sufficient data to clarify this topic. Since by addressing this issue would acquire to collect more data which is not feasible at this stage of this work.   Best Regards

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed all suggested edits and suggestions.

Reviewer 2 Report

Comments and Suggestions for Authors

Thanks for addressing my concerns.  I think you have a great paper here.

Comments on the Quality of English Language

Looking much better!