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[# PeerJ Staff Note - this decision was reviewed and approved by Virginia Abdala, a 'PeerJ Computer Science' Section Editor covering this Section #]
Although there are a large number of points raised by the two referees, these are all very minor in nature and so not represent any substantive problems and should be relatively easy to deal with. I look forwards to seeing a revised version of this MS soon.
[# PeerJ Staff Note: It is PeerJ policy that additional references suggested during the peer-review process should *only* be included if the authors are in agreement that they are relevant and useful #]
The paper is well written, clear, and thoroughly cited. The figures are useful and all justified. I suggest including the two figures in the supplementary material as figures in the main paper.
This is a spectacular specimen in an unusually good state of preservation and completeness, so it is well worthy of description. The description is satisfactory, if a little brief in places, but it lacks measurements, so these should be added. Perhaps a table of measurements is in order. The order of the description should also be slightly reordered, and I suggest several minor corrections/edits (see additional comments).
The methods and analysis are clearly explained.
Given the disarticulated nature of the cranial bones, an illustrated reconstruction of the cranium would be very useful. This would help to demonstrate the overall morphology and proportions of the skull, to allow comparison with reconstructions of the skulls of closely related Toarcian species by Grossman and others. I wouldn’t say this is essential, but it is possible, and I would personally add one.
The authors make a convincing case for the referral of the specimen to P. wildi and justify their broader conclusions.
The following is an itemised list of minor corrections, suggestions, and comments (sorry, italics are missing). I do not wish to remain anonymous and if the authors have any follow-up questions I would be happy for them to contact me directly at [email protected]. Adam S. Smith
Page 7, line 68. Delete “dire”, it’s a bit hand-wavy.
Page 8, line 74 (and other citation and reference in list). “Bailey” should be “Baily”. I could be responsible for this because I cited it wrong in my thesis and paper on Rhomaleosaurus cramptoni.
Page 8, line 78. “longirostrus” should be “longirostis”.
Page 9, line 97. Change “…(Sachs et al., 2016a). Indicating…” to “…(Sachs et al., 2016a), indicating…”
Page 10, line 139. “…reconstructed with synthetic resin or with shale matrix.” Mark these on the figures.
Page 12, line 164. “BMNH”. This is outdated, the correct 5-digit MDA Code is “NHMUK”. See: https://collectionstrust.org.uk/mdacodes/
Page 14, line 219. I think “2B” should be “2A”?
Page 15, line 233. “later” should be “latter”.
Page 15, line 250. Change “…can be seen as…” to “…is…”
Page 15, line 255. Delete the superfluous “and”.
Page 16, line 260. I thought the description of the braincase elements was missing earlier in the paper, but found it here. It should be moved up to the end of the description of the cranium.
Page 20, line 355. I think it would be simpler to include Supplementary Fig. 1 as a figure in the main paper, it’s just as relevant as the other vertebrae figures. I presume this shows the reverse (‘dorsal’ left lateral) side of the specimen MH7, in which case it would be worth clarifying this in the description and figure caption, because it wasn’t immediately obvious – I wondered if it might be a different specimen.
Page 20, line 359. A count (or estimate) of the total number of rows of gastralia would be useful here. Likewise the number of overlapping lateral elements in each row. And do the posterior-most gastralia articulate with the pubis?
Page 20, line 366. “Narrow anterolateral and lateral processes…” They don’t look narrow to me, maybe better described as triangular?
Page 21, Line 378. Change “The facet for the coracoid and the humerus is approximately equal in width” to “The facets for the coracoid and the humerus are approximately equal in width”.
Page 21, line 386. “The pubis forms a smoothly convex anterior margin”. A large part of it looks flat to me, unless the margin is hidden by the gastralia?
Page 21, line 390. Can you annotate the reconstructed resin part on the figure?
Page 22, line 394. Delete “in profile”.
Page 22, line 403. “A tubercule is located on the posterior surface.” Annotate this on the figure.
Page 22, line 409. “knee”. I suppose it should be “elbow” in the forelimb, although this terminology is rarely used in the literature for plesiosaurs. It may be better to avoid it completely, and replace with something like “the anterodistal end of the humerus is unexpanded”
Page 23, line 421. To clarify, is the arrangement of the bones in the right forelimb at least partially unnatural (i.e. distorted by taphonomic processes)? The ulna and ulnare, for example, appear to be out of position.
Page 23, line 426. “the femur is shorter proximodistally”. They look subequal in the figures (accounting for the breaks in the middle of both femora), so again, a table of measurements would be useful to quantify statements like this.
Page 25, line 479. I think this would be fine as a main figure rather than supplementary material. Note the typo “ptergoids” in the figure caption for Supp. Fig 2.
Page 26, line 485. “later” should be “latter”.
Page 27, line 517. OUM J.28585 was tentatively referred to Eurycleidus by Cruickshank (1994), a referral followed by O’Keefe and others, but it actually differs from the type material of Eurycleidus, so the specimen does not really represent Eurycleidus. As such, it is better to give only the specimen number so as not to perpetuate this erroneous referral. i.e., change “similar to T. hawkinsii and Eurycleidus Andrews, 1922 (OUM J.28585)” to “similar to T. hawkinsii and OUM J.28585”. See Smith (2015): https://palaeo-electronica.org/content/2015/1146-plesiosaurus-megacephalus
Page 29, line 567. “A keel on the lateral surface of the cervical vertebrae may be present in two anterior cervical vertebrae, but it is not present throughout much of cervical column, as in M. homalospondylus (Owen, 1865), M. tournemirensis (Bardet, Godefroit, and Sciau, 1999).” This wording is unclear, I suggest rewriting as: “A keel on the lateral surface of the cervical vertebrae may be present in two anterior cervical vertebrae. However, unlike the condition in M. homalospondylus (Owen, 1865) and M. tournemirensis (Bardet, Godefroit, and Sciau, 1999), this character is absent from the rest of the cervical column.”
Page 30, line 591. Change to “F. brevispnius” to “F. brevispinus”.
Page, 31, line 595. Delete superfluous “convex”.
Page 33, line 648. Delete “from the palate and pectoral girdle”.
Page 36, line 727. Change “R. zeatlandicus” to “R. zetlandicus”
Figure 11 Caption. Specify the specimen number for P. wildi and explain it is a comparison figure.
Thank you for the opportunity to review the article by Miguel Marx and colleagues describing a new specimen of Plesiopterys. I need to emphasize that I was aware of the preparation of this article and have discussed the phylogenetic aspects of the study with the authors before. I also need to emphasize that I frequently cooperate or have previously cooperated with some of the authors.
The article is quite well written and mostly clear. The figures are informative. There are some minor issues with descriptions of the methods that I discuss below.
The article includes sufficient introduction and background. Relevant prior literature is referenced.
The article includes all data necessary to replicate the results.
Below, I discuss some minor issues I've found (or, I didn't understand). I look very much forward to seeing the article published after, what I believe, will be minor revisions.
The study represents original primary research, the research question is well-defined. The methods are described with sufficient detail though there are some parts that should be reworded and corrected. For example:
line 144: "unweighted parsimony analyses"
- parsimony analysis using equal weights (please, change that throughout the MS).
lines 145, 146: "which is an iteration of multiple previous studies derived from the parent matrix"
- I don't understand what this means. This version is significantly different (with respect to taxon sampling) than the original matrix of Benson and Druckenmiller (2014) but only slighly different than the version by Sachs, Eggmaier, and Madzia (2024).
lines 147, 148: "Characters 25, 138, 139, 153, and 248 have been modified and thus differ from those provided by Benson and Druckenmiller (2014)."
- This part reads like the authors speak about new modifications. I would modify the sentence to make clear that these changes have been actually compiled by Madzia and Cau (2020) based on previously published studies.
line 149: "67 character states are ordered as per Madzia and Cau (2020)."
- In fact, these characters were first ordered by Madzia et al. (2019): https://doi.org/10.1017/S0016756818000523
Descriptions of the results are also slightly unclear. For example:
lines 612-614 (and also 633): "MH 7 was scored for 135 characters out of 270 used by Sachs, Eggmaier, and Madzia (2024). The first 200,000 trees were saved to RAM (hold 200000;) then a New Technology search with 1000 addition sequences"
- By typing "hold 200000;" you just made space for 200k trees. Nothing was saved before the analyses. Could you please reword it (also on line 633)?
All underlying data have been provided and conclusions are well stated. Here are some comments on particular parts:
Stratigraphic setting of MH 7.
- According to the authors, MH 7 originates from "εII6c (Harpoceras serpentinum zone)". It seems that the most relevant current source would be Maisch (2021). The layer εII6 is assigned to H. falciferum zone, H. exaratum subzone. Please, check your stratigraphic sections and modify accordingly.
lines 31, 32: "MH 7 is a derived non-microcleidid plesiosaur that forms a paraphyletic grade with Franconiasaurus brevispinus and other more derived cryptoclidian plesiosaurs."
- This is somewhat awkwardly phrased. MH 7 is simply an early-diverging plesiosauroid (no need to emphasize it's not a microcleidid) that is inferred as a sister taxon to Franconiasaurus + Cryptoclidia. I don't think it makes any sense to speak about paraphyly here.
lines 32, 33: "Our results demonstrate a stepwise diversification of the ancestral cryptoclidians during the Early Jurassic."
- Again, please, rephrase. MH 7 and F. brevispinus are not ancestral cryptoclidians. They are simply close to the origin of Cryptoclidia. I am also not sure what you mean here by "stepwise diversification". The two are just successively more closely related to Cryptoclidia.
lines 46-48: "The Lower Jurassic fossil record of plesiosaurians is especially diverse, incorporating both long necked 'plesiosauromorphs' and short necked 'pliosauromorphs'"
- Please, consider removing the terms 'plesiosauromorphs' and 'pliosauromorphs' with proper taxon names. It is correct that plesiosaurs were diverse in the Early Jurassic and that all three major clades (pliosaurids, rhomaleosaurids, and plesiosauroids) have already existed but they were quite similar by the time - essentially all quite "long-necked"...
line 63: "A phylogenetic analysis by Benson et al. (2014) recovered P. wildi [...]"
- Did you mean Benson and Druckenmiller (2014)?
lines 101-103: "This discrepancy could possibly be related to taxonomic over-splitting among plesiosaurs rather than preferential segregation within separate basins."
- I don't understand. No evidence has been provided suggesting that European plesiosaurs have been over-splitted. In fact, those that have been reassessed in recent years have shown to be diagnosable. So, the diversity is indeed high (though I would say the disparity is quite low). I am also not sure comparing the plesiosaur diversity and paleobiogeography with that of ichthyosaurs is relevant or correct. Early Jurassic plesiosaurs from the Siberian deposits are quite similar to the European taxa. But, they are usually too incomplete to be assigned more precisely.
lines 191-201: "Revised diagnosis. A plesiosauroid plesiosaurian [...]"
- Owing to the fact that the type specimen needs redescription, it would be very useful to say if this is based on your restudy of the type only or also on the referred specimen. And if also on the referred specimen, indicate which characters are derived from each specimen.
line 619: "[...] form a paraphyletic grade to more derived long-necked plesiosaurs."
- I would write they are reconstructed successively closer to cryptoclidians (I probably wouldn't specify that they are "long-necked"; some are clearly not, right? :)). More importantly, speaking of paraphyly here is misleading. Since you consider MH 7 conspecific with the type of Plesiopterys you probably don't think the topology represents an actual evolutionary sequence. Rather, It is due to the type being immature. F. brevispinus is quite different and simply later-diverging.
lines 702, 703: "In addition, the topology (Fig. 12) demonstrates a paraphyletic diversity of basally diverging plesiosauroids"
- I don't understand. There doesn't seem to be anything surprising about the placement of the taxa you included.
lines 710, 711: "Moreover, these results retain a high plesiosauroid diversity and possible endemism for the Toarcian Posidonienschiefer Formation"
- I am afraid I can't see the relevance of this part or the other parts in which the potential endemism is discussed.
Some additional minor comments:
lines 96, 97: "[...] were reported also in Fennoscandian deposits (Sachs et al., 2016a). Indicating the dispersal of these genera from [...]"
- change to "[...] deposits (Sachs et al., 2016a), indicating the [...]".
line 110: "[...] near Holzmaden, Germany was [...]"
- change to "[...] near Holzmaden, Germany, was [...]"
line 185: "[...] Lower Toarcian [...]"
- change to "[...] lower Toarcian [...]"
line 257: "[...] small ridges [...]"
- Could you please reword it? I am not sure I understand what "small ridges" mean.
line 591: "brevispnius"
- brevispinus
line 620: "[...] built-in calculator [...]"
- implemented script.
line 624: "[...] position between F. brevispinus and Microcleididae. [...]"
- reverse because microcleidids are earlier-diverging.
line 638: "[...] returned as a non-microcleidid plesiosaurian [...]"
- "non-microcleidid" is redundant here. I would just write "an early-diverging plesiosauroid".
Figures
Fig. 12 - Microcleididae is incorrectly indicated. In A, it shouldn't cover Seeleyosaurus (it's part of the trichotomy, not the clade), and in B-D, it should also cover Eretmosaurus and Westphaliasaurus. Note also that you haven't reconstructed Pliosauroidea (Pliosauridae + Rhomaleosauridae) in any of your analyses so you should replace the name on the trees with Pliosauridae (Rhomaleosauridae was inferred as the earliest-diverging branch of Plesiosauria).
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