First Evidence of Reproductive Strategies in Cephalopods Preserved in Phosphate and Siderite Nodules from the Devonian of Uruguay

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The work intituled 'First evidence of reproductive trategies in cephalopods preserved in phosphate and siderite nodules from the Devonian of Uruguay' is a very good contribution to the knowedge of ancient ammonoids reproductive strategy, as well as a geological contribution to the San Gregorio Formation (age and deposition).

I think this work is suitable for the journal Fossil Studies with only very minor revisions. I have highlighted some very minor typographic errors to be found directly in the attached pdf.

The main problem lies in the confusion between chronostratigraphy and geochronology in some parts of the manuscript. Please consider the use of Lower/Upper for chronostratigraphic purpose (boddy of rocks) and Early/Late for geochronologic purpose (time event). I have corrected these issues directly in the attached pdf.

Another remark: please, at first mention of a taxon add the name of the author(s) and the year of introduction.

Last proposition: I think the discovery of this new Lagerstätte raises important issues in terms of geoheritage, maybe this point desserve to be developed in the manuscript.

Comments for author File: Comments.pdf

Author Response

Comments for the Editor

 

We have considered all the reviewers questions and concerns, as you will see from the text below, where we responded to all the sentences. Also, all the suggested changes when corresponding were included in the manuscript template. We added a NEW Figure 1 which was improved as Reviewer 2 requested. Also, Table 1 was modified to add the size for the ammonitella stage. The English language was improved as the reviewers suggested and new references were added to the list. The changes that need to be done in the References section in order to follow the journal guides will be completed if our manuscript arrives at the final steps of the peer-review process.  

We hope that the revised version of our manuscript suits you and the reviewers and the article can be finally accepted for publication in Fossil Studies. Since now, we are indebted to you and the reviewers for the kindly and constructive revision of our work.

Yours sincerely,

 

Graciela Piñeiro (on behalf of my coauthors)

 

The work intituled 'First evidence of reproductive trategies in cephalopods preserved in phosphate and siderite nodules from the Devonian of Uruguay' is a very good contribution to the knowedge of ancient ammonoids reproductive strategy, as well as a geological contribution to the San Gregorio Formation (age and deposition).

I think this work is suitable for the journal Fossil Studies with only very minor revisions. I have highlighted some very minor typographic errors to be found directly in the attached pdf.

Thank you very much for your review report, we accepted all the suggested changes.

The main problem lies in the confusion between chronostratigraphy and geochronology in some parts of the manuscript. Please consider the use of Lower/Upper for chronostratigraphic purpose (boddy of rocks) and Early/Late for geochronologic purpose (time event). I have corrected these issues directly in the attached pdf.

Yes, we agree, and all these terms were revised to make them consistent.

Another remark: please, at first mention of a taxon add the name of the author(s) and the year of introduction.

Done

Last proposition: I think the discovery of this new Lagerstätte raises important issues in terms of geoheritage, maybe this point desserve to be developed in the manuscript.

Many thanks for this suggestion, which of course, we will follow. Indeed, the discovery of this large number of nodules and the unexpected so amazing results that we had after their study, has promoted the creation of the new Museo de las Bochas in the San Gregorio city, supported by the Municipality of the Tacuarembó Department and the annual financial support from Facultad de Ciencias to the senior author. In that way, we are collaborating in the preservation of this rich cultural heritage for a local population of my country and for the overall paleontological record.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper provides new information about the Devonian fossil assemblages preserved in the redeposited phosphorite concretion, and new hypotheses about ammonite reproductive strategies. This information is interesting and new, but it is not presented in the right way, and the evidence for either the age of the assemblage or the reproductive habitats of the ammonoids is very weak. In my opinion, this paper should be rejected, but can be resubmitted after significant improvement. References also should be rearranged following the journal rules.

I think it should focus on two key points:

1) Evidence for the age of fossil assemblages preserved in redeposited nodules. Now the evidence is mainly indirect and based on palaeoclimatic interpretation of fossils, with very few determinations even at the genus level (except for inarticulate brachiopods). This line of evidence should be strengthened by more determinations of corals and cephalopods, and by comparison with contemporaneous fossil assemblages from nearby regions. It should be noted that the determination of the studied ammonoids as Glaphyrites (Carboniferous-Early Permian genus) is in complete contradiction with the proposed age of their host assemblage (Devonian)! Preservation of ammonoids is relatively poor, while their shell outline shared features common in many Paleozoic lineages. In the opinion of the reviewer, an analysis of this assemblage can be provided at the beginning of the article, after Introduction and Geological setting;

2) Taphonomy of juvenile ammonoid accumulations and their interpretation. All figured specimen from such clusters represented by juveniles much older if compared with ammonitellae (the latter composed from protoconch and first whorl). Taking into account published data about ammonitellae accumulations of the different age, as well as strong re-organization of shell wall at the end of ammonitella stage (nepionic constriction), associated with ammonoid hatching, long existence of newly hatched ammonites within the gelatinous-like masses covered eggs seem to be impossible. Taking into account small size of ammonite eggs and small amount of yolk, newly hatched tiny ammonoids should be active hunters on small-sized prey. Difference in phosphatic nodule chemical composition near to juvenile ammonite accumulations and outside, can be explained by the influence of organic matter decay in such accumulations or by further diagenetic changes.

Here is a list of suggested corrections and comments:

Lines 12-24: such long introduction in abstract describing geological details is unnecessary; instead, here you can rather focused on re-interpretation of the age of phosphorite or siderite nodules

Lines 26-27: “diminutive copies of adult ammonoids also found within the nodules” - these are not copies, because significant changes in septal suture and shell form occurs through ammonoid ontogeny

Line 33: “progenitors” should be replaced by “parents”

Lines 35-36: “suggests the presence of a new ammonoid species for the Uruguayan record” – there are no evidence for such a species

Fig. 1(map): please add also the map in other scale, showing position of this one in South America, and show rather studied localities instead the areas

Line 68: “led to the description of the” – rather “were referred to as new species”

Line 69: “Orthoceratid” – “orthoceratid”

Lines 76-77: “but direct comparisons with the previously reported Glaphyrites type specimen” – unclear; please specify

Line 142: Drushchit should be replaced by Drushchits

Line 152: ammonitella should be ammonitellae (plural)

Lines 203-204: “phosphate and siderite nodules” - can you add here some refs or analyses supporting chemical composition of these nodules?

Line 223: “gelatinous substance that feed them” – such a mass can be protective, but the only food source for ammonites within the eggs is yolk

Line 264-265: “measurements of diameters of the ammonitella stage were taken following” – here diameter of juveniles is measured, while diameter of ammonitellae is much smaller

Line 224: “The ammonitella average diameter at this stage is near 0,2 mm” – rather 2 mm

Lines 278-280: “The embryonic shell (ammonitella) includes a semicircular to elliptical initial chamber in transverse cross section (Figs. 6-7), which is not easily distinguishable from the first whorl, and three additional whorls” - this is nonsense; ammonitellae always has only one whorl and no chambers except protoconch and body chamber

Lines 283-284: “retains an organic wall” - why? protoconch was aragonitic, not organic

Lines 291-294: “the phragmocone could be at the second stage of mineralization; however, the external wall of the first whorl is covered by a single crystalline layer while the region near the umbilical area remains unmineralized.” - rather, original aragonitic layer was replaced by apatite during the diagenesis, this is a common type of ammonite preservation in phosphorite concretions

Lines 232-236: without any doubts, siphuncle here is outside the former ammonitella

Line 355: “the globular morphology of the caecum” - it is common in ammonoids

Lines 507-508: “similar, although no fossiliferous nodules” - phosphorite nodules of the different age are similar to each other

Line 510: “diagenetic red trilobite” - what does it mean? Can you determine these trilobites?

Lines 531-532: “which represent a group more frequently described as to be a component of Silurian and Devonian faunas (Dzik, 1984)” - orthoceratids in some cases are common in assemblages of latest Paleozoic and even Triassic

Lines 586-587: “perhaps during the reproductive seasons” – this is definitely not the case of studied juvenile accumulations

Lines 602-603: “The fact that any of the clusters herein described contain ammonitella” - there are no ammonitellae in these clusters, only older ammonoids

Line 641 and below: all refs should be re-arranged in order of their appearance in the text and cited as [1, 2]

Lines 693-694: please cite instead the translated version of this article, http://mmtk.ginras.ru/pdf/Drushchits%20et%20al.,1977)Ammonitella_en.pdf

Please refer also Lehmann et al. 2014 (https://link.springer.com/article/10.1007/s12542-013-0219-8) who discussed ammonite specimens with jaws preserved, studied by Closs

Comments on the Quality of English Language

Some points remain unclear, and a minor English edition is desirable.

Author Response

This paper provides new information about the Devonian fossil assemblages preserved in the redeposited phosphorite concretion, and new hypotheses about ammonite reproductive strategies. This information is interesting and new, but it is not presented in the right way, and the evidence for either the age of the assemblage or the reproductive habitats of the ammonoids is very weak. In my opinion, this paper should be rejected, but can be resubmitted after significant improvement. References also should be rearranged following the journal rules.

With all our respect for the reviewer, we consider that we have provided fundamental evidence to prove both the Devonian age of the nodules and the description of new and, until now unique information about early ammonoid reproductive traits. Of course, the hypotheses in paleontology are discussable and authors have the opportunity of generate alternative interpretations and also detailed criticism on particular conclusions, by discussing them in their own papers.  

I think it should focus on two key points:

• Evidence for the age of fossil assemblages preserved in redeposited nodules. Now the evidence is mainly indirect and based on palaeoclimatic interpretation of fossils, with very few determinations even at the genus level (except for inarticulate brachiopods).

We did not base the Devonian age only in paleoclimatic interpretation, which indeed is very often used as a complementary proof for paleoecological reconstructions and age interpretations, but we also presented paleobiogeographical and biostratigraphic evidence, including taxonomic determinations, for groups such as the brachiopods that are considered as valuable indexes for stablishing age correlations in Paleozoic sequences. We also explained that more inclusive taxonomical identification for the ammonoids preserved in the nodules will require the loan of the Uruguayan specimens assigned to Glaphyrites that were found a long time ago preserved in similar concretions. These specimens were translated for study to other countries and so, they were housed in foreign collections. Even though, we made a morphological comparison between the ammonitella stage of the shells in the clusters and that of specimens assigned to Glaphyrites sp. from the United States. We have to say that we could not obtain relevant information to stablish definitive conclusions. The description of new ammonoid species in this paper is not possible or recommendable without analyzing in deep the morphology of the specimens previously described; doing so, we could turn more complex the study of these fossils.  Concerning the taxonomy of other taxa, such as the building organisms, their presence in the Uruguayan nodules would have important paleogeographical implications that will be described in detail in a forthcoming paper. However, the recognition of their presence in the assemblage preserved by the nodules is important to be mentioned in this article, because it helps in the interpretation of the preferred reproductive habitat of the described ammonoid clusters.  

• A) This line of evidence should be strengthened by more determinations of corals and cephalopods, and by comparison with contemporaneous fossil assemblages from nearby regions.

We already responded to part of these concerns in the previous paragraph- Thus, we will respond to other requests of the reviewer in the following lines.

1. B) It should be noted that the determination of the studied ammonoids as Glaphyrites (Carboniferous-Early Permian genus) is in complete contradiction with the proposed age of their host assemblage (Devonian)! Preservation of ammonoids is relatively poor, while their shell outline shared features common in many Paleozoic lineages. In the opinion of the reviewer, an analysis of this assemblage can be provided at the beginning of the article, after Introduction and Geological setting;

The comparison with the ammonitella stage of Glaphyrites was not contradictory but needed because this is the only ammonoid taxon described for Uruguay and the specimens, which unfortunately are not in our collections, were found in similar nodules! although they were collected from other outcrops of the San Gregorio Formation and the specific geographic location was not very well defined. The hatchlings that we describe herein are part of a Devonian fossil assemblage, as we are proposing in this article and it is interesting to reveal the anatomy of the ammonitella stage for these shells .- Therefore, taking into account the generated issue we could suggest at least three hypotheses, a) there is more than one species preserved in the reworked nodules of the San Gregorio Formation; b) the assignation to Glaphyrites of the previously described Uruguayan ammonoid specimens is wrong, and c) If there is only one species and the taxonomic assignation to Glaphyrites is correct, it can be suggested that the biochron of this taxon extends back to Devonian. All hypotheses will be analyzed and possible solved in other pendent second paper on the taxonomy of the Uruguayan ammonoids. (see pag. 10 y 11)

1. a) Taphonomy of juvenile ammonoid accumulations and their interpretation. All figured specimen from such clusters represented by juveniles much older if compared with ammonitellae (the latter composed from protoconch and first whorl). Taking into account published data about ammonitellae accumulations of the different age, as well as strong re-organization of shell wall at the end of ammonitella stage (nepionic constriction), associated with ammonoid hatching, long existence of newly hatched ammonites within the gelatinous-like masses covered eggs seem to be impossible.

We would think in a similar way than the reviewer if we only would find one cluster, but we now have more than 40 clusters and we are sure that we will find yet more when the remaining nodules will be open. As you said, the previously found accumulations of ammonoid shells represent a mixture of individuals preserved in different ontogenetic stages, so, evidence as that we are describing herein has not been found previously. For that reason, it is difficult to us interpret our finding taking into account previous records. We revised literature on reproductive strategies in fossil and particularly in recent cephalopods and we realized the poor knowledge that we have of most species, mainly in those living in deep-depth environments. Even though, we found some interesting information that was included in the manuscript, concerning the function of the gelatinous envelope that the females deposit over the eggs in each batch. Indeed, when responding your questions and concerns we are realizing that we can suggest that the reproduction in these ammonoids may have included the spawning of eggs in one single reproductive season.

We proposed the hypothesis that the reproductive strategy in our ammonoids is that they hatch at a juvenile stage, where the hatchlings are large and well-developed and morphologically similar to the adults and that they may have lived together with their parents at the same habitat (as described in a very recent paper by Vidal and Shea, 2023 for extant cephalopod species). For to support such a hypothesis we presented SEM photographic material that show the ammonitella stage morphology without or with only minor marked changes showing the passage to the hatchling or early juvenile stage. In general, all or almost all the clusters contain juvenile shells bearing the initial chamber plus three whorls, a clear fact indicating that there is not a coincidence but evidence that these clusters are part of an ammonoid multiple spawn. The fact that is seen as problematic to many colleagues is that there are not ammonitellae in these clusters, as expected. The fact is, as we explained in our manuscript, that there is no evidence of ammonitellae masses completely proven, and we think very interesting that none of our clusters contains such expected ammonitellae.

According to some authors in some species of extant cuttlefishes, living in warm to template climates can produce masses of few large eggs and also masses containing a larger number of small eggs, something that could be related with some of our findings; we observed some clusters having a different number of shells and those containing only a few, are larger. However these large shells consist of the initial chamber and three whorls, following the morphological plan observed in the smaller ones.  Our hypothesis may seem unlikely, but it is even more improbable to think that the clusters correspond to clouds or sets of juvenile ammonoids that hatched in the open sea and were deposited by chance on a coral reef in a shallow sea, forming individual masses that do not contain other taxa or sediments.  (see some arrangements at pag. 10, 11 y 15)

Taking into account small size of ammonite eggs and small amount of yolk, newly hatched tiny ammonoids should be active hunters on small-sized prey.

Yes, but we have not tiny ammonitellae close to hatch to become active predators, also we do not have masses of confidently identified ammonitellae that can be interpreted as yet no hatching embryos. As explained above, and considering our interpretation of the shells in the clusters as hatchling ammonoids, they would have been very close to transform in active predators. We have presented references of the feeding function of the gelatinous envelope that may have been complementary of the yolk for guarantee the continuity of the embryo’s growth until the hatching is produced. The size of the ammonoid eggs predicted by the size of the ammonitellae should have been small but there is no direct evidence of that yet. Surely, the reproductive strategies of ammonoids during the Paleozoic were highly variable and that could explain that some hatch as ammonitellae and others as juveniles similar to their parents.    

Difference in phosphatic nodule chemical composition near to juvenile ammonite accumulations and outside, can be explained by the influence of organic matter decay in such accumulations or by further diagenetic changes.

Yes, you are right, but in our case the influence of the organic matter decay is only detected in the way of tubules and fibrous deposits ONLY at the nodules containing the hatchling clusters. Although there are other fossils preserving delicate organic structures, the tubules were not detected around them. Therefore, we prefer to keep our interpretation because it is consistent with other of the characteristics that we described for the clusters.   

Here is a list of suggested corrections and comments:

Lines 12-24: such long introduction in abstract describing geological details is unnecessary; instead, here you can rather focused on re-interpretation of the age of phosphorite or siderite nodules.

Okay, done. (see the new abstract at pag. 1)

Lines 26-27: “diminutive copies of adult ammonoids also found within the nodules” - these are not copies, because significant changes in septal suture and shell form occurs through ammonoid ontogeny.

Agree, it will be changed as corresponds. (Pag. 10 and 11)

Line 33: “progenitors” should be replaced by “parents”

Done! Thanks!

Lines 35-36: “suggests the presence of a new ammonoid species for the Uruguayan record” – there are no evidence for such a species

As explained, we will not describe a new species at this time, but we reformulated the paragraph. (Pag. 15)

Fig. 1(map): please add also the map in other scale, showing position of this one in South America, and show rather studied localities instead the areas.

The map was improved. (Pag. 2)

Line 68: “led to the description of the” – rather “were referred to as new species”

The paragraph was modified. (Pag. 11 and 15)

Line 69: “Orthoceratid” – “orthoceratid”

Done! (Pag. 2)

Lines 76-77: “but direct comparisons with the previously reported Glaphyrites type specimen” – unclear; please specify

The text was improved. (Pag. 3)

Line 142: Drushchit should be replaced by Drushchits

Done! Thanks!

Line 152: ammonitella should be ammonitellae (plural)

Okay, done!

Lines 203-204: “phosphate and siderite nodules” - can you add here some refs or analyses supporting chemical composition of these nodules?

This evidence was already shown in figure 5. (Pag. 9)

Line 223: “gelatinous substance that feed them” – such a mass can be protective, but the only food source for ammonites within the eggs is yolk.

Yes, but as we explained above, the gelatinous mass can feed the embryos until hatching, as a complement of the yolk. We added more information for this, but you can check at:

https://poseidonsweb.com/squid-eggs/. https://www.tandfonline.com/doi/epdf/10.1080/07924259.1993.9672291?needAccess=true

and see also Vidal and Haimovici (1998).

Line 264-265: “measurements of diameters of the ammonitella stage were taken following” – here diameter of juveniles is measured, while diameter of ammonitellae is much smaller.

Yes, we included the measurements for the ammonitellae stage in Table 1 part B. (Pag. 10)

Line 224: “The ammonitella average diameter at this stage is near 0,2 mm” – rather 2 mm

Right! It was fixed. Thanks! (Pag. 11)

Lines 278-280: “The embryonic shell (ammonitella) includes a semicircular to elliptical initial chamber in transverse cross section (Figs. 6-7), which is not easily distinguishable from the first whorl, and three additional whorls” - this is nonsense; ammonitellae always has only one whorl and no chambers except protoconch and body chamber.

You are right, it was a mistake and the text was changed. (Pag. 10-11)

Lines 283-284: “retains an organic wall” - why? protoconch was aragonitic, not organic

Because the SEM-EDS marked that was only phosphatic, but as you well marked that may be a taphonomic condition. It was fixed accordingly. (Pag. 11)

Lines 291-294: “the phragmocone could be at the second stage of mineralization; however, the external wall of the first whorl is covered by a single crystalline layer while the region near the umbilical area remains unmineralized.” - rather, original aragonitic layer was replaced by apatite during the diagenesis, this is a common type of ammonite preservation in phosphorite concretions.

Okay, it was modified accordingly. Thanks! (Pag. 11)

Lines 232-236: without any doubts, siphuncle here is outside the former ammonitella

But there is a prosiphon that is continuous with the caecum. (Pag. 12)

Line 355: “the globular morphology of the caecum” - it is common in ammonoids

Okay, it was noted. (Pag. 10-11)

Lines 507-508: “similar, although no fossiliferous nodules” - phosphorite nodules of the different age are similar to each other

Yes, okay. The reference was only descriptive

Line 510: “diagenetic red trilobite” - what does it mean? Can you determine these trilobites?

Although it would be part of other study, we can say that many fossils preserved in the nodules are dyed with different colors denoting the presence of diagenetic impregnation with minerals. Trilobites are dyed red probably by the presence of iron minerals in the sedimentary layers where the decay of organic matter started. But for avoid wrong interpretations we removed the terms.

 Lines 531-532: “which represent a group more frequently described as to be a component of Silurian and Devonian faunas (Dzik, 1984)” - orthoceratids in some cases are common in assemblages of latest Paleozoic and even Triassic

Yes, they can be, but it is not the most common for this ancient group. It is true that they had a very long biochron, which extends for more than 400 million years, but their climax was in the Ordovician to Devonian assemblages. On the other hand, we have added other important evidence that do not support a Permian or Triassic age for the community in the nodules.

Lines 586-587: “perhaps during the reproductive seasons” – this is definitely not the case of studied juvenile accumulations

Okay, we removed such idea. (Pag. 16)

Lines 602-603: “The fact that any of the clusters herein described contain ammonitella” - there are no ammonitellae in these clusters, only older ammonoids

Yes, and it is the most intriguing feature of these findings. We fixed the sentence because indeed we had no ammonitellae in the more than 40 clusters, only hatchlings. (Pag. 17)

Line 641 and below: all refs should be re-arranged in order of their appearance in the text and cited as [1, 2]

We asked to present the references as they are now and it was allowed. We will modify them at the last revision round.

Lines 693-694: please cite instead the translated version of this article, http://mmtk.ginras.ru/pdf/Drushchits%20et%20al.,1977)Ammonitella_en.pdf

Okay, done.

Please refer also Lehmann et al. 2014 (https://link.springer.com/article/10.1007/s12542-013-0219-8) who discussed ammonite specimens with jaws preserved, studied by Closs

We could not find Lehmann et al., 2014. The last paper of Lehmann that I have is from 1990:

Lehmann, U., Kulicki, C., 1990. Double function of aptychus (Ammonoidea) as jaw elements and opercula. Lethaia 23, 325–331. The fossils that you are referred are from Uruguay! Closs studied them and leave them at Germany.

 

Comments on the Quality of English Language

Some points remain unclear, and a minor English edition is desirable.

We did such a revision.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Comments are provided in the attached .doc file

Comments for author File: Comments.pdf

Author Response

 

NEW RESPONSES TO THE REVIEWER ARE IN BLUE

First Evidence of Reproductive Strategies in Cephalopods Preserved in Phosphate and Siderite Nodules from the Devonian of Uruguay

Piñeiro et al., 2024

Fossil Studies, review round 2

After corrections made by the authors, this MS looks much better compared to its early version, but still needs some improvement. Two key issues remained: 1) the age of the assemblage studied is insufficiently proven; 2) other explanations for accumulation of juvenile ammonoids should also be considered (see references below).

With all our respect for the reviewer, we consider that we have provided fundamental evidence to prove both the Devonian age

Such evidence is still lacking. The only Devonian species mentioned in this article is an inarticulate brachiopod (belonging to a long-ranged genus, the species of which show a little differences between each other), all other taxa are identified as "rugosa", "tabulata", "trilobite" and cannot be used as evidence for an age other than Palaeozoic. No comparison with Devonian assemblages of nearby areas is given, so this conclusion can only be considered as preliminary.

Again with all respect, we are not describing corals in this article, they are new findings for our country and we will describe them with colleagues that are specialists in the matter. We are only describing the possible first evidence of reproductive traits in ammonites based on materials that never were found before. The evidence of a Devonian age is clear for us, considering multidisciplinary information (e.g., stratigraphy, biostratigraphy, paleoenvironmental and paleoclimatic evidence. Regarding that information we consider a possible general age for the complete assemblage. Indeed, we do include comparisons with Devonian assemblages of nearby areas (e.g., Carrera et al., 2013, Page 21; Ianuzzi et al., 2023, Page 21, who assigned a Lower Carboniferous age to the San Gregorio Formation, and remember that this is a unit deposited in glacial environments that are not consistent with a reefal assemblage). As you say below, the concretions can contain biota from little different ages, and for that reason we did not assigned a more precise age than Devonian to the studied assemblage. Thus, in this regard we consider that we do not need to add more information, but we will specify that we are assigned a preliminary Devonian age to the nodule formation, which will be definitively confirmed in a forthcoming paper on the Stratigraphy of the the Devonian Durazno Group from Uruguay.   

Therefore, taking into account the generated issue we could suggest at least three hypotheses, a) there is more than one species preserved in the reworked nodules of the San Gregorio Formation; b) the assignation to Glaphyrites of the previously described Uruguayan ammonoid specimens is wrong, and c) If there is only one species and the taxonomic assignation to Glaphyrites is correct, it can be suggested that the biochron of this taxon extends back to Devonian. All hypotheses will be analyzed and possible solved in other pendent second paper on the taxonomy of the Uruguayan ammonoids. (see pag. 10 y 11)

The preservation of the studied specimens is poor, and hypotheses A and B seem possible. In my opinion, the preservation of the studied ammonoids prevents their determination even at the family level, and these specimens should only be classified as indeterminable goniatitids. Their determination as "Glaphyrites" lacks any solid evidence.

Well, we will have into account the expert opinion of the reviewer once we describe these materials in a forthcoming paper. But we need to revise the type specimens that were described by Closs and also the paratypes. We will try to recover them to our collections.   

We would think in a similar way than the reviewer if we only would find one cluster, but we now have more than 40 clusters and we are sure that we will find yet more when the remaining nodules will be open. As you said, the previously found accumulations of ammonoid shells represent a mixture of individuals preserved in different ontogenetic stages, so, evidence as that we are describing herein has not been found previously. For that reason, it is difficult to us interpret our finding taking into account previous records.

In fact, accumulations of juvenile ammonite specimens are described from different regions and ages, and mainly referred to mass mortality of juveniles, see for example https://www.sciencedirect.com/science/article/pii/S0031018216302127 and https://www.sciencedirect.com/science/article/pii/S0016699511000957 (and refs. herein)

Thus, you don’t need to propose a new explanation for specimens recorded

We thank very much to the reviewer for provide us with so interesting papers, mainly because they reinforce our conclusions and interpretations about the specimens described in this article. So please, see that in the paper of Stinessbeck et al., (2016) the accumulations are very different to those described by us, mainly because they contain more than one taxon. However, authors discuss that hatchlings are the earliest ontogenetic stage that is found in the ammonoid fossil record because eggs and embryonic stages have not the enough fossilization potential. According to these authors “hatchling is where the fossil record begins” (page 191 at the end). We will add this interesting discussion in the revised version of the manuscript to be resubmitted.

We proposed the hypothesis that the reproductive strategy in our ammonoids is that they hatch at a juvenile stage

All ammonoids hatched at the ammonitella stage, their hatching is marked by significant changes in shell structure (appearance of a new layer after nepionic constriction), while all specimens figured in the discussed article represents juveniles at much later stages of ontogeny.

Unfortunately, we do not know how old the hatchlings that we describe in this article are, and there are not undisputable proofs that ALL ammonoids hatch at the ammonitella stage.   

Their feeding on the former egg mass cover is possible but difficult to prove.

Not as difficult if we consider data from extant cephalopods combined with the fact that we have more than forty clusters of hatchling ammonoids attached to a mass that can be a gelatinous, protective and nutricional substance (as Mapes and Nützel (2009) proposed that should be).

 The origin of the studied juvenile accumulation after mass mortality, independent of either reproduction or feeding strategies, should also be discussed in this article.

Mass mortality in cephalopod early stages is common. In the case of our clusters we do not have much taphonomic information about the cause of mortality because they were preserved in nodules, meaning that we don’t have the original taphocenosis. But included this and other hypotheses in the manuscript. 

In general, all or almost all the clusters contain juvenile shells bearing the initial chamber plus three whorls, a clear fact indicating that there is not a coincidence but evidence that these clusters are part of an ammonoid multiple spawn.

No, such an accumulation can be explained by mass mortality of juveniles of a single age class, e.g. a few months after hatching, due to drastic oxygen depletion in the water column (caused by algal blooms or improved stratification due to freshwater influx) or other causes.

We don’t have any evidence to prove such kind of interpretations. Again, we remind to the reviewer that there are no other “accumulations” in the literature like those we are present herein. We can interpret them as reproductive mass mortality (possibly semelparity), a hypothesis also considered by Stephen et al. (2012), which by the way is a very interesting paper, they found accumulations of early juvenile ammonoids, but associated to juvenile and adults of several other taxa. For that reason, they would not have the same origin as our clusters. Indeed, semelparity type of reproduction produces large offspring, but with high risks of mortality. The conditions of the bottom where the clusters fossilized after death are difficult to infer given that the original deposits where the nodules formed, were eroded by the glaciers. However, we added some hypotheses into the revised manuscript.

According to some authors in some species of extant cuttlefishes, living in warm to template climates can produce masses of few large eggs and also masses containing a larger number of small eggs, something that could be related with some of our findings; we observed some clusters having a different number of shells and those containing only a few, are larger.

Ammonoid reproductive strategies differ significantly from those of coleoid cephalopods. Almost all ammonoids have very small eggs and hatchlings, whereas coleoids explore a range of different reproductive traits.

Yes, it is possible, but ammonite eggs are not found yet, and calculating the size of the eggs from the size of the ammonitellae is not assured, because ammonitella is an embryonic stage, thus it should be yet inside the egg. We do not know when and how they hatch. We added information from extant cephalopods for explain what represent the clusters that we are describing because there are not confident evidence from the fossils.

However these large shells consist of the initial chamber and three whorls, following the morphological plan observed in the smaller ones.  Our hypothesis may seem unlikely, but it is even more improbable to think that the clusters correspond to clouds or sets of juvenile ammonoids that hatched in the open sea and were deposited by chance on a coral reef in a shallow sea, forming individual masses that do not contain other taxa or sediments.  (see some arrangements at pag. 10, 11 y 15)

You have figured a single colonial coral, this is definitely not a ‘coral reef’. Also, phosphorite concretions can contain a mix of fossils from different ages and environments, and corals can be from facies other than ammonoid clusters.

No, ammonoids are preserved in association with the corals (see please figure 11B). The coral remains preserved in the nodules are as we already explained to you, more than 80% of the samples studied. For that reason we interpret with strong evidence that what we have preserved is a reefal environment in the nodules.

We could not find Lehmann et al., 2014. The last paper of Lehmann that I have is from 1990:

I referred here to the article by Jens Lehmann et al. with proper hyperlink, but not to Ulrich Lehmann. These are different persons )))

https://link.springer.com/article/10.1007/s12542-013-0219-8 

Ok, reference included.

Some additional corrections are needed:

 

“post-ammonitella clusters” in the fig. 3-4 captions rather should be replaced by “clusters of juvenile ammonoids”

Done.

Lines 491-492, “Ornamentation of the external surface of the ammonitella stage in individual shells from clusters of the Devonian of Uruguay” – please indicate ammonitella and post-ammonitella stages in figure; here fig. A shows both ammonitella and post-ammonitella stages

Done.

Author Response File: Author Response.pdf