Lower Eocene Footprints from Northwest Washington, USA. Part 1: Reptile Tracks

Round  1

Reviewer 1 Report

General comments: This paper describes exciting turtle and crocodylian tracks from Washington – a place where no crocodylian lives today. The paper has great merit and there are good interpretations, but the paper needs to be completely reorganized. I suggest a major revision given that the paper needs a complete reorganization and there are parts of the paper that need to be reframed or eliminated. Overall, the citations are good, but more citations can be added to back up statements about the modern reptile habits.

Major comments:

-Much of broader context and the importance of the paper need to be highlighted in the introduction. Currently, the introduction does not explain why this paper has an interesting result. Previous finds, ichnotaxomomy and other parts highlighted below can be added to the introduction so the reader know what to expect.

-The description of the tracks, interpretation of the track maker (identification), and the behavior interpreted from the tracks need to be put together. For example, start with the systematic assignments for the turtle, go through the description of the tracks (details), justify its assignment to a turtle and the ichnotaxon, and then write about the behavior of the tracks. Do the same for the crocodylian. Take the reader through the process – you can’t just call them turtle and crocodylian tracks immediately without going through the clear justification of the anatomy and then the identification.

-Finish the paper with the implications of the reptile tracks in this area (paleoenvironment). Please note that crocodylians are doing well in the tropics during the entire Cenozoic and that their range is decreasing as the tropic belts became narrower. Focus on the Cenozoic and remove references to the Mesozoic.

-Figures – a number of figures need revision and some of them are of poor to OK quality and may not be needed (13, 14). Please cite them more appropriately.

-The discussion needs to be reframed a bit, but this cannot be evaluated until the rest of the paper is reorganized. I would be happy to look at it then.

Specific comments:

Abstract

-crocodyle: change to ‘crocodylian’ (crown group) à change throughout manuscript

Introduction

-this need far more details about what has been done before. How is this area connected to other Eocene localities/formations in North America – start broader for context. I would like to know if anyone else has reported trace fossils.

            -move previous work section (starting on line 72) into the intro.

Line 50 – Can you put ‘Mount Baker foothills’ in a broader context? Where is this? County? Refer to figure 2 here.

-figure 2 comments. You refer to the localities as WWU-XXXXX but in the figure, the WWU is not included. Please make this clearer.

Table 1 – what datum are you using for your GPS point? WGS 84 (like Google Earth?). Please find out.

Line 87 – name the avocational paleontology enthusiasts or refer to the acknowledgments.

Figure 4 – need 1 in from of cm for the scale bar.

Line 99 – Use crocodylian, not crocodile

Line 104 - This association suggests that the turtle tracks were made by an animal that was crawling on wet riverbank sediment

            -what do you mean that the association of the animals suggests that that was crawling on wet riverbank sediment? Couldn’t you understand that from the sedimentology alone? How does having bird tracks there help interpret the original environment?

Turtle track section – this section need much better justification. Why are these interpreted as turtle tracks? What is the anatomy of the tracks? Please make comparisons with other turtle ichnofossils. Measurements and close-up figures would be helpful – like what is done for the crocodylian

Section 3.2 (starting at line 111) – this section can be better organized for the reader as you build your argument. Please organize it into a section describing the information directly from the tracks (number of digits, tail drag, manus vs pes morphology, size, stride) without assigning them to a specific track maker. Then, attribute the tracks to a crocodylian using comparison with your living crocodylian trackway and other trackways associated with extinct crocodylians. Answer: why is this not a big lizard (varanid)? Then, interpret the way the tracks were made by the animal. In sum, reorganize and build your case; you can’t just say they are crocodylian tracks.

Line 112 - Crocodylian trace fossils from the Chuckanut Formation have been observed on sandstone blocks were exposed by the 2003 Racehorse Creek landslide.

            -please correct the grammar in this sentence.

Figure 10. Where are these images from? Make sure to cite your sources.

Figure 11. What is the scale of these tracks (roughly)?

Figure 13. What is the source (not just the artist)?

Section 3

            I am not sure this entire section is needed for this paper. This is good background information for when this paper was written, but it can be condensed down to just saying that the methods of Vialov. I suggest cutting the entire section and summarizing in a line or two.

Line 181 ‘often been different’. How? Please cite the differences and explain your argument.

Section 4

            All of this great information needs to be sooner in sections 3.1. The separation is not necessary.

Line 292 – Italics for Anticusuchipes amnis

Section 5

            Lots of this information should be moved to the into and geological context. It is out of place here.

Line 321 – perissodactyl (spelling)

            -‘ This vegetation may have been an attractive for perrisodactyl mammals and giant’

                        -this is speculative and not grounded in evidence. Please be careful.

Figure 15.  It would be useful to show how these tracks are related to each other on an inset picture or drawing of the larger slab

Section 6 Discussion

            -reorganize and focus on what the reptile tracks tell us about environment of the area, and more broadly for crocodylian evolution in the Cenozoic (cut the Mesozoic part because it is not focused).

Line 333 – Crocodylians (crown group) only date back to the Cretaceous, not the Triassic (Crocodylomorpha). See work of Brochu.

Line 338 – Dinosaurs survived the end Cretaceous extinction as birds! You mean non-avian dinosaurs.

Line 349 – ‘Scarcity of Cenozoic crocodylian fossils is probably related to the worldwide decline in 349 temperatures that began in the late Eocene’

       -make sure to mention that this refers to North American and higher latitudes. Crocodylians were doing very well in the tropics during this time.

Author Response

I very much appreciate your detailed comments, and your constructive attitude. Submission of this manuscript was a bit hurried because I was trying to beat the 7/1/19 date when publication charges were being increased, so I was hoping for a chance to make improvements for the final draft. Your keen-eyed review is a major step int hat direction.I have made all of the minor changes that were suggested, and also adopted the major ones. Specifically, these are:

-Much of broader context and the importance of the paper need to be highlighted in the introduction. Currently, the introduction does not explain why this paper has an interesting result. Previous finds, ichnotaxomomy and other parts highlighted below can be added to the introduction so the reader know what to expect.

Response: I have extended the introduction to emphasize why the findings are significant. I have reduced the length of the discussion of ichnotaxonomy (as suggested), and include it as a separate section in the early part of the paper. The discussion of paleoclamate/palenvironment is now part of the "geologic setting" section, as you suggested.

-The description of the tracks, interpretation of the track maker (identification), and the behavior interpreted from the tracks need to be put together. For example, start with the systematic assignments for the turtle, go through the description of the tracks (details), justify its assignment to a turtle and the ichnotaxon, and then write about the behavior of the tracks. Do the same for the crocodylian. Take the reader through the process – you can’t just call them turtle and crocodylian tracks immediately without going through the clear justification of the anatomy and then the identification.

 Response: I have reorganized the paper based on this recommendation, the presentations for turtles and crocs are now clearly divided. I think the structure is much improved as a result of your advice.

-Finish the paper with the implications of the reptile tracks in this area (paleoenvironment). Please note that crocodylians are doing well in the tropics during the entire Cenozoic and that their range is decreasing as the tropic belts became narrower. Focus on the Cenozoic and remove references to the Mesozoic.

 Response: The paper concludes with a discussion of Cenozoic crocodylians and their ranges and I've added several additional references. Thanks for this suggestion.

-Figures – a number of figures need revision and some of them are of poor to OK quality and may not be needed (13, 14). Please cite them more appropriately.

 Response: I have made some improvements to the illustrations; the resolution of the figures in review version of the manuscript are lower than the original image files.Most of these figures are original creations, I have copyright permissions for other materials.

-The discussion needs to be reframed a bit, but this cannot be evaluated until the rest of the paper is reorganized. I would be happy to look at it then.

I welcome your suggestions for  improving the rewritten version.

Reviewer 2 Report

Well written and edited. The work is a pleasure to read. 

Few minor comments for the author to consider: 

Line 7: change from "and USA" to "USA"

Figure 2 has the tracksite locations discussed in the paper (i.e., KC-1, RCS-1), and also sites that are not referred to the body of work (i.e., RU-1, SM-series). "Locations are listed in Table 1" only includes the former and not the latter.

Incorrect figure references in lines: 307, 307, 372.

Preceding line 260 place "Ichnogenus: Anticusuchipes ichnogen. nov."

Line 261, include: Anticusuchipes amnis "ichnogen. nov. et ichnosp. nov."

Line 346: consider changing from "They [modern crocodylians] are endemic to southern Asia..." to "They are endemic to, not limited to southern Asia..." 

Please consider crediting photographers and artists for the following figures (unless the author is the respective photographer/artist): 3, 6B, 6C, 10, 14, 17.

Consider italics for line 292.

Double spacing occurs in lines: 31, 42, 44, 62, 75, 77, 92, 94, 140, 174, 180, 230, 259, 264, 301, 305, 342, 378, 390, 515.

No further comments. No reviewer file uploaded.

Author Response

Thanks for the very encouraging review. I have made all of the suggested changes. The organization of the paper has been improved as a result of the recommendations of the other reviewer, but the overall content remains much the same.

Round  2

Reviewer 1 Report

I went through the paper and noticed that the author did make lots of changes that I suggested. I made a few more suggestions (attached).

Comments for author File: Comments.pdf

Author Response

Thanks for the final check, I have incorporated your suggestions.