A New Rhynchosaur Taxon from the Popo Agie Formation, WY: Implications for a Northern Pangean Early-Late Triassic (Carnian) Fauna

Round 1

Reviewer 1 Report

The MS by Fitch et all describes an important set of rhynchosaur fossils, proposing a needed name to refer to the long known “Wyoming rhynchosaur”. I enjoyed reading the MS, given that the authors did an excellent job by documenting every relevant aspect related to the described fossils. I believe it is suitable to be published in Diversity, following the minor modifications requested below.

 

Main comments

I understand that the rather complex taxonomic issues concerning the definitions and use of Hyperodapedontinae, and Hyperodapedon were tackled in an adequate way. I would just like to remind that these definitions were proposed before the publication of the PhyloCode. Hence, they are not actually valid according to the rules of that code and we are still waiting for new/valid definitions. The authors could decide to propose them in this MS, following the regulation of the PhyloCode, by either keeping or changing those of Langer & Schultz (2000). Yet, if they decide not to do so, and given the high uncertainty in the relation within the “Hyperodapedon group”, I suggest that their strategy of using “old” genera names such as Paradapedon, Macrocephalosaurus, etc., (with which I agree) is deemed in the MS as more of an “utilitarian”/conservative way of fitting the names, rather than an actual attempt to formally resurrect those genera with new definitions. This can be done with a simple sentence explaining that, probably in the last paragraph of section 3.3.

In line 272-274, the authors say that “Following the topology of Sues et al. [16] and this work, the only non-H. gordoni species of Hyperodapedon would be the Zimbabwean hyperodapedontine”. Yet, this is correct only for Sues et al., because in Figure 5A H. gordoni and the “Zimbabwe form” are in a polytomy, and in figure 5B they are in separate clades.

The “4. Systematic Paleontology” section should be reorganized. The subheadings “4.1. USNM 494329”, “4.2. TMM 46035.1”, and “4.3. UWGM 7029” are unnecessary and should be deleted. The section should start straight with “Sauria McCartney, 1802 [74], sensu Gauthier et. al., 1988 [75] …”. The “Gen. et sp. indet.” of line 450 should be kept, but not that of line 488. Also, lines 445-449 and 483-487 should be deleted.

The morphological variations used to differentiate TMM 46035.1 and UWGM 7029 from Beesiiwo cooowuse could be instead regarded as variations within that species. Yet, this is not the interpretation of the authors, which must be put public to be scrutinized by following works. What I can suggest is that an additional phylogenetic analysis may be conducted with all Wyoming specimens lumped as a single OTU (with the variations scored as polymorphisms) to see what results from that as an alternative view.

 

Specific comments

Line 16: delete “instance of a”

Line 19: delete “the presence of”

Line 41: the use of “eponymous” here is a bit odd, as it seems to refer to the “Lossiemouth Formation”, what is not the case. I would delete it.

Lines 52-57: here I would mention that there are 12 new specimens, so it does not get confused with information in the following section.

Line 63: you say that “Five of the 12 specimens contain enough morphological information to allow diagnosis to generic or specific level”. Is USNM 494329 included in this count of 12, or are there 13 in total? I see that Hyperodapedontinae “Gen. et sp. indet.” are not included in this set of 5, so that I would rephrase that sentence for “Five of the 12 specimens contain enough morphological information to allow diagnosis to specific level”. These are the holotype and 4 specimens referred to Beesiiwo cooowuse.

Lines 64-66: why “UWGM 7033” is not mentioned here?

Lines 110-118: the “Geological Setting” is a bit long. Consider excluding parts such as the last portion of the second paragraph. But this is up to the authors, as no information is useless considering that this is an online publication.

Lines 171-176: this sentence came a bit odd; revise and consider dividing it in two.

Line 177: replace “morphology” by “of less inclusive groups”

Line 179: replace “fossil sites” by “fossils”.

Line 198: delete “and” before “was”.

Line 260 and 262: replace “monophyletic cladistic” by “phylogenetic”; all phylogenetic definitions are “monophyletic cladistic”, so using phylogenetic is enough.

Line 263: delete “the defined by” before “Langer”; also, it is “Langer & Schultz 2000” here, not “Langer”; see also that ref [58] is not Langer, but Langer et al.

Line 287: the term invalid does not really apply for nomina dubia, but for junior-synonyms instead. Here, perhaps change “also not considered valid” for “not employed here”.

Line 288: replace “nomen” by the plural “nomina”.

Lines 290-307: names in this paragraph are not properly italicized.

Line 296: include “hyperodapedontid” before “species”.

Line 323: put the “Referred specimens” section right after the “Holotype” section.

Line 340: missing “)” after “[17]”

Lines 356-357: why “UWGM 7033” is not mentioned here?

Line 360: replace “divided” by “separated”.

Line 361: replace “mesial” by “anterior”.

Lines 365-366: replace “The lateral and medial aspects of the maxilla, divided by the longitudinal groove, can be discerned from the trend of the respective face” by “The lateral and medial portions of the maxilla, divided by the longitudinal groove, can be differentiated by the shape of the respective margin”.

Line 368: replace “faces” by “margins”.

Line 372: you said “the area medial to the longitudinal groove is wider than the lateral area”, but isn’t it the contrary? i.e., the lateral area is wider?

Lines 384, 582, 584, 613: replace “dentition” by “teeth”.

Line 385: delete “horizontal”.

Line 427: replace “articulation” by “occlusion”.

Line 496: replace “dental row composition” by “traits”.

Line 501; replace “dentition on either side of the groove is” by “teeth on either side of the groove are”

Line 502: delete “meaning that the lateral dentition is subequal to the medial dentition”

Line 505: replace “second row of dentition is expressed” by “lateral row is exposed”.

Line 506: replace “greater” by “more”.

Lines 507-508: replace “rows of lateral dentition” by “lateral rows”.

Line 537: add “character” before “69”.

Lines 57-571 (and Fig. 5A): you said that “all three OTUs to represent hyperodapedontine”. This is correct based on the definition of Langer & Schultz (2000), but this is not the position in which Hyperodanpedoninae is placed in Figure 5A. Please, revise.

Line 571: replace “5” by “5A”.

Lines 586-587: delete “monophyletic”, all clades are monophyletic.

Line 600: replace “5” by “5B”.

Lines 601-609: these two sentences refer to relations also found in the first analysis (Fig. 5A), so it is best to mention them when you are discussing that first tree, and say here that this relation repeats in the second analysis.

Line 610: replace “form a sister taxa” by “have a sister taxon”

Line 611: delete “related” after “closer”

Fig. 5: Hyperodapedontinae is misplaced in both trees.

Fig. 5 (caption): in “Strict consensus of 100 MPTs (length=223). b. Strict consensus of 6 MPTs (length=223)”; the values do not match those mentioned in the text.

Line 623: the presence of “cosmopolitan hyperodapedontines” hangs in their differentiation from Beesiiwo cooowuse. If the authors choose to run an analysis with the Wyoming rhynchosaurs in a single OTU (see above), some comments should be added here.

Author Response

Please see attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript revisits the anatomy and taxonomy of the only hyperodapedontine rhynchosaur published so far from the Triassic of the USA. This specimen was originally identified as cf. Hyperodapedon sanjuanensis, an assignment that had implications for the Triassic global biostratigraphy. In the light of the amount of new information published about rhynchosaurs and Triassic tetrapod faunas as a whole in the last two decades, a revision of this American rhynchosaur was highly needed. As a result, the redescription and revised phylogenetic analysis of the putative cf. Hyperodapedon sanjuanensis from Wyoming is very welcomed.

The description and figures are well done, but I have found some major issues that should be addressed by the authors before the manuscript moves forward in the editorial process.  I discuss these issues as follows:

-  Diagnosis: the interpretation of USNM 494329 as the holotype of a new genus and species should be carefully rethink by the authors. The diagnosis of the new species is “1) maxilla with two lateral tooth rows and one medial tooth row; 2) crest-shaped areas respectively medial and lateral to a longitudinal groove on the occlusal surface of the maxilla; 3) dentary without a row of lingual teeth.” Character 1 occurs in Oryctorhynchus bairdi (Sues et al. 2020: JVP). Character 2 is ontogenetically variable, in which juvenile specimens change from crest-shaped tooth-bearing areas to cushion-shaped tooth bearing areas during life because of tooth plate wear (see H. sanjuanensis, H. mariensis intraspecific variability). Character 3 cannot be determined in USNM 494329 because lingual teeth occur distinctly more ventral than the occlusal dentition and this area is not preserved in the American specimen (see e.g. Hyperodapedon mariensis). As a result, I don’t see enough support for the erection of a new genus and species based on the information provided by the authors. Furthermore, USNM 494329 seems to be a juvenile because of the proportional size of the teeth, presence of crest-like tooth bearing areas, and distinct separation between each individual tooth.

-  Other rhynchosaur specimens from the Popo Agie Formation: the authors describe other hyperodapedontine specimens from the same unit, but they found differences with the holotype of the proposed new species. These differences rely on the number of tooth rows in the maxillary plate. However, the number of tooth rows increase during ontogeny (see e.g. Langer et al. 2000: Lethaia; Gentil and Ezcurra 2018: Historical Biology), as well as the morphology of the tooth-bearing area (cushion versus crest-shaped).

-  Maxillary lingual teeth: in figure 4b it seems that the specimen has lingual maxillary teeth. The authors should check this because it is an important taxonomic and phylogenetic feature for hyperodapedontine rhynchosaurs.

-  Phylogenetic nomenclature: the authors use a different phylogenetic nomenclature than that used by multiple, independent authors in the last 15 years. The proposal of the authors is justified based on the stem-based definition of Hyperodapedon sensu Langer y Schultz (2000: Palaeontology). However, the phylogenetic relationships of hyperodapedontine are extremely problematic and in continuous state of flux. As mentioned by the authors, a comprehensive revision of the phylogenetic relationships of Hyperodapedontinae goes beyond the scope of their manuscript, but I think that this is needed before proposing a change of phylogenetic nomenclature as that proposed by the authors in this manuscript. The latter proposal will generate taxonomic instability and confusion among researchers. As a result, I strongly suggest the authors to use the nomenclature followed by all the authors in the last 15 years.

-  Lines 464–649: the Sancruzodon AZ of Brazil is considered to be younger biostratigraphically than the Massetognathus-Chanaresuchus AZ of Argentina. The Dinodontosaurus AZ is interpreted as, at least partially, correlated with the Massetognathus-Chanaresuchus AZ of Argentina (see e.g. Novas et al. 2020: J South Am Earth Sciences). You should be careful with radioisotopic dates because they represent maximum depositional ages.

In conclusion, I think that the manuscript requires major modifications.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

This is an important contribution to our knowledge of the Late Triassic vertebrate fossil record of Wyoming. It merits publication after some revision based on the Comments below.

 

 

Comment 1 (line 19) Spielmann et al. 2013 (NMMNH Bulletin) reported an early Norian rhynchosaur from New Mexico—this should be mentioned.

 

Comment 2 (line 18) Carnian is not an epoch, it is an age. Late Triassic is an epoch.

 

Comment 3 (line 33) The authors are using the Long Norian timescale throughout. That should be mentioned as well as a detailed critique of the Long Norian by Lucas et al in ESR 2012.

 

Comment 4   (line 36)  ? nonmarine Carnian rocks are not rare in the northern hemisphere. There are plenty of them in the Keuper, Newark and Chinle sections, especially if the long Norian is not used.

 

Comment 5 (line 40) Where is this precise number from?

 

Comment 6 (line 41) and the rhynchosaur records from Texas --“Otischalkia, etc.?”

 

Comment 7 (Fig. 3) Why is “photo” present on some of the images?

 

Comment 8 (line 239) you should mention these are land-vertebrate faunachrons of Lucas

 

Comment 9 (line 239)  The discussion of the ages ignores: (1) capitosaur fossils from the Jelm Formation reported by Lucas 1994 that suggest a possible Anisian age; (2) various evidence that Popo Agie is Otischalkian; and (3) the substantial unconformity at the Popo Agie base.

 

Comment 10 (line 665).  This point should be made. The current cladistic taxonomy breaks up what was called Hyperodapedon into multiple genera, so of course the Hyperodapedon biochron survives but using the subfamily to correlate. Correlations are the same, taxonomy differs.

 

Common 11 (line 693) See Comment 4 above. There is a Ladinian gap, but there are Carnian rocks in the lower Chinle Group.

Comments for author File: Comments.pdf

Author Response

Please see attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

To the editor and authors,

I have gone through the revised version of the manuscript and I am not completely happy how my previous comments were addressed by the authors, in particular those related to the phylogenetic nomenclature and the absence of lingual teeth in the dentary. The ontogenetic and morphofunctional variability of the rhynchosaur maxillary tooth plates is more complex than recognized by the authors, but this complexity is well documented only in the abundant rhynchosaur samples from India, Brazil and Argentina, which is mostly still unpublished. So, I can't ask the authors to study and re-consider it because it goes beyond the scope of their project.

As I said, I don't agree with the phylogenetic nomenclature section but the authors have support on Articles of the ICZN and PhyloCode for this. However, it is extremely likely that the phylogenetic interrelationships among rhynchosaurs will change in the near-future. The authors said that all phylogenetic hypotheses change, it is true, but the hyperodapedontine relationships are particularly unstable and it is one of the main regions of uncertainty in the archosauromorph tree.

Regarding the absence of lingual teeth, I have studied several maxillary tooth plates preserving the main blade of the dentary in occlusion and it is not possible to determine the absence of lingual teeth because they should have been positioned considerably more ventral to the dentary occlusal blade than it is preserved in the Popo Agie specimen. I strongly recommend the authors to report uncertainty regarding the absence/presence of lingual dentary teeth in the American rhynchosaur specimen.

Although I consider that the manuscript still has issues that should be corrected, the revision of the enigmatic Wyoming Hyperodapedon was strongly needed and I am happy that it was finally conducted. As a result, I think that the manuscript can be accepted for its publication but I urge the authors to re-think (mainly) about the absence of dentary lingual teeth.