The specimen described here is sure to be of interest to many experts on Triassic terrestrial faunal assemblages. As currently written, the manuscript contains a nice, cohesive project, and many of the essential pieces of a thorough paper are here. However, I would recommend reorganization of the text, addition of a few other pieces of background information, and some revision of the figures, in order to maximize the readability and usability of the manuscript. Specific points are outlined in detail below.
Full disclosure: I am a volunteer editor for PeerJ, and also am co-presenting a paper for an upcoming scientific meeting with the senior author.
SPECIFIC COMMENTS:
The specimen described here is sure to be of interest to many experts on Triassic terrestrial faunal assemblages. As currently written, the manuscript contains a nice, cohesive project, and many of the essential pieces of a thorough paper are here. However, I would recommend reorganization of the text, addition of a few other pieces of background information, and some revision of the figures, in order to maximize the readability and usability of the manuscript. Specific points are outlined in detail below.
- I would strongly advise reworking the abstract; there is lots of summary about Crosbysaurus, but very little on the specimen itself. You should include basic locality information, how it is referred to the taxon, etc. As it stands, the abstract is not particularly effective in summarizing the unique results of this study.
- The introduction might be restructured to improve readability and accessibility to most readers. I would start with a brief discussion of Crosbysaurus and the problems of Triassic "ornithischian" teeth, and perhaps include the current first paragraph somewhere in the middle, or else move it to the methods. The discovery narrative is good to include, but could perhaps be condensed a little.
- Where are the various institutions located? Cities, states, and countries should be included in the abbreviations list.
- Please include a basic geological background for the locality, in a concise paragraph or two. How old is the locality? What other fauna are known? What was the basic lithology? Where does it sit in section?
- I strongly recommend framing the description in a conventional "systematic paleontology" format. See, for example, https://peerj.com/articles/182/#results -- the standardized layout can make it easier for the typical paleontologist reader to navigate the paper and find the relevant information.
- How were measurements taken? Sliding calipers? Digital measurement? On what equipment were photos taken?
- In referring the tooth to Crosbysaurus, you should also mention why you do not refer it to similar tooth taxa. How is it different from Revueltosaurus, Tecovasaurus, etc.? A stronger differential diagnosis must be included.
- Conclusions: "Cosmopolitan" can be taken to mean spanning many countries, but Crosbysaurus is only found in the United States. Maybe use the term "widespread" instead?
- Acknowledgments should be under a separate heading.
- Because geographic range is such a big part of this paper's conclusions, I would include a figure (or modify Figure 1) showing the new find relative to other localities with Crosbysaurus.
- In Figure 2, the letters / lines added on the photo are hard to see in places. I would use light-colored drop lines/drop letters to help them stand out.
- Figure 3 should be redone; part 1 is quite blurry, and part 2 is not entirely in focus either. I might recommend coating the specimens for photography (e.g., ammonium chloride or a similar removable powder); color can obscure important morphology on teeth, and for this paper it is essential to have high-quality photographs. The lettering is really big relative to the teeth itself; I would scale the text on the figure down, to improve aesthetics. If possible, get a photo showing a close-up of the denticles drawn in Figure 5. This is a pretty key piece of anatomy and should be as well-illustrated as possible. Consider moving Figure 4 into part of Figure 3, so that it is alongside Figure 3C. This too would improve usability by the reader and ease comparisons between figures.
