After reviewing your manuscript "Use of Continuous Cranial Shape Variation in the Identification of Divergent Crocodile Species of the Genus Mecistops”, I feel that it covers a very interesting and important question. This manuscript quantifies the skull shape in a genus of crocodylians, which includes ecologically important and endangered species, and then attempts to identify the key features which can distinguish these species. This research presents important findings supporting the recent splitting of species based on population genetic evidence and would be useful in helping to identify illegal collection of endangered species in the field. I think that this manuscript addresses important morphological questions within a proper hypothesis driven framework (although not explicitly stated) and would be appreciated by readers of Journal of Morphology. However, it requires substantial revision in order for the results and conclusions to be well supported. I will briefly summarize the four major issues, but I have also attached my specific comments on the manuscript which provide more details.
First, a cross validation test should be performed in order to assess how reliably the features you’ve uncovered can distinguish individuals correctly. This can be done relatively easily using the Canonical Variates Analysis functions in the Morpho package in R and will allow a likelihood and success rate to be found for species identification. Combining this with a similar analysis for the allometric measures, particularly those which can be measured on live individuals, will make the conclusions stronger and much more applicable in the field.
Second, a greater consideration for how allometric ratios change across development and growth is needed throughout the manuscript. This includes both the introduction and discussion (see next point), but most importantly in the analyses performed. My recommendation would be to include additional juvenile and hatchling specimens (which are available in collections and existing publications, see my comments) and performing analyses to understand how shape and allometric ratios change relative to skull length and/or centroid size. However, I do appreciate that this would require devising new analyses and take considerable additional time. If this cannot be done, then at the very least additional sensitivity analyses must be undertaken in the allometric ratio analyses to determine whether: 1) adults and subadults differ in the allometric ratios and 2) whether ratios change relative to skull length or centroid size.
Third, the text in several parts of the manuscript, including the results and discussion, should be rewritten for greater clarity of communication and to more completely explain important factors that weigh on these analyses. Most importantly, the effect ontogeny has on snout shape and allometric ratios and how this affects the ability to use the features identified in this study needs to be more thoroughly discussed. The results section is also repetitive and unclear in many place, due in part to the structure. I have suggested a new organization which would simplify the presentation and greatly improve the clarity. Given that the data presented in this study are on the cranial bones themselves, the extent to which the measures can be transferred to live or wild harvested specimens which still have scales should be more thoroughly addressed (perhaps by showing specific measures that can be taken on images of live specimens). This is critical in order to achieve the major goal of this study.
Finally, the graphical abstract should be re-done as it is currently a copy of figure 3 and does not effectively summarize the major findings of the study. In my comments, I recommend a simple graphic which would be an effective way to redraft the graphical abstract. I also think that the figures could be improved and have provided recommendations for additional useful figures for explaining the results.
Overall, I think that this is an interesting study with important real world applications for morphology, but critical factors that affect the analyses have not been sufficiently assessed or addressed. If these major issues are resolved, then I would consider this study to be appropriate for publication. I am happy to answer any clarifying questions about my comments if needed.

After reviewing the revised manuscript “Use of Continuous Cranial Shape Variation in the Identification of Divergent Crocodile Species of the Genus Mecistops”, I am satisfied with the changes made. As in the original version, this manuscript identifies key features which can distinguish the ecologically important and endangered species of a genus of crocodylians.
I originally found four major issues, all of which have been satisfactorily met in the new revision. First, appropriate cross validation tests were performed and demonstrate the utility of the measures for species delimitation. Second, the discussion now very clearly explains the potential issues surrounding skull shape change across development and clearly states the focus of the current manuscript on mature individuals. Third, the additional analyses on measures that can be obtained on live animals and the revised organization of the manuscript make it clear which features can be most useful in the field for future researchers and conservation organizations. Finally, the figures are much clearer in the current draft.
This manuscript now presents its hypotheses effectively and the findings are discussed in an appropriate and compelling context that would interest the readers of the Journal of Morphology. As such, I think that this manuscript should be accepted with only a minor number of typographic corrections (see attached file).