-->PONE-D-26-04011-->-->Hyperelongate ornamental tail feathers in a new Early Cretaceous enantiornithine bird -->-->PLOS One

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Please revise ms following the reviewer's comments, especilly the places need to be clarified.

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Reviewers' comments:

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: N/A

Reviewer #2: N/A

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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-->5. Review Comments to the Author

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Reviewer #1: General Assessment

This manuscript represents a significant contribution to avian paleontology. The identification and detailed description of Plumadraco bankoorum and its unique Rachis-Dominated Feathers (RDFs) provide compelling evidence for complex sexual selection pressures in Early Cretaceous birds. Addressing the suggested revisions, particularly those concerning methodological clarity, nuanced interpretations of data, and consistent terminology, will further strengthen the manuscript and enhance its impact. I anticipate that these revisions will lead to an even more robust and influential publication.

Specific Recommendations for Clarification

Nesting Ecology and Morphology Correlations:

Clarification is needed regarding the inferences linking nesting ecology to tail morphology. Correlations should be treated with caution, as the specific ecology of this new taxon may differ from other fossils used for comparison. Please ensure that assumptions about nesting behavior do not overextend the available evidence.

Definition of Rachis-Dominated Feathers (RDFs):

The morphological definition of RDFs requires further illustration. Typically, "rachis-dominated" implies that the rachis comprises the major part of the feather structure; however, barbs are clearly observed in this specimen (particularly within the rackets). Please reconcile this terminology with the observed morphology to avoid confusion.

Phylogenetic Support Values:

Please provide support indices (e.g., bootstrap or jackknife values) for the TNT phylogenetic analysis. Including these statistical values will strengthen the robustness of the cladistic results.

Pygostyle Morphology and Display Mechanics:

Fan-shaped tail feathers and rectrices are generally understood to have evolved in Neornithines, often associated with a short pygostyle. However, in Enantiornithines, which possess an elongate pygostyle, the mechanical effect of this structure on tail feather display remains unclear. Please discuss how the long, shaped pygostyle might influence tail feather display mechanics compared to neornithines.

Reviewer #2: **Comments to the Author(s)**

This study describes a new enantiornithine bird and reports an unusual hyperelongate ornamental tail feather among early birds. Overall, this manuscript is well-written and the points are quite straightforward. I only have a few suggestions and recommendations that I believe might improve the quality of this manuscript:

1) Lines 21–22: In the abstract, I am not sure whether this comparison is appropriate — passerines today are considerably more diverse, clearly far exceeding the diversity level seen in enantiornithines.

2) Line 115: It is not very common to place the measurement table immediately here. Consider moving it to the location where measurements are first mentioned in the text.

3) Line 123: It would be more appropriate to refer to the holotype rather than simply the "fossil specimen" of Plumadraco.

4) Lines 145–154: In the Diagnosis section, it would be better to separate the characters that support referral to Enantiornithes from those that further support assignment to Bohaiornithidae. Additionally, many of the features used to assign this taxon to bohaiornithids — such as the furcula, coracoid, sternum, and sacral vertebrae — are indicated as crushed in the line drawing figure.

5) Line 153: Please indicate that this refers specifically to the lateral trabeculae of the sternum.

6) Lines 209–210: The rami in this new specimen are slightly bowed. Could this bowing account for the apparently narrow interclavicular angle, or might there be inconsistency in how this angle is measured across taxa?

7) Line 214: It is unclear whether "pterygoma" is the appropriate term for the coracoid body.

8) Lines 230–232: To me, the left trabecula appears more caudolaterally oriented rather than purely caudally oriented.

9) Line 266: Since the ungual phalanx of the minor digit is commonly very tiny and easily lost during preservation, it may be better not to place too much emphasis on the phalangeal formula being 2-3-1 here.

10) Lines 370–371: It is unclear how a precise 3D structure can be reconstructed from 2D observations alone.

11) Line 402: This should read "exceptional preservation of RDFs".

12) Lines 406–407: In Figure 6D, it would be helpful to indicate the exact location of the barbs within the tail feather of the modern bird-of-paradise.

13) Lines 426–429: The use of percentage values may be appropriate for Confuciusornis, given the large number of available specimens, but may not be applicable to enantiornithines, for which most taxa are represented by very few specimens.

14) Lines 453–454: The authors discuss differences in RDF morphology between STM11-4 and other fossil birds, yet only Orienantius is included in the comparison shown in Figure 7. It would be helpful to include additional enantiornithine tail feathers in this figure for a more comprehensive comparison.

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Reviewer #1: No

Reviewer #2: No

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Hyperelongate ornamental tail feathers in a new Early Cretaceous enantiornithine bird

PONE-D-26-04011R1

Dear Dr. Clark,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Jun Liu

Academic Editor

PLOS One

Additional Editor Comments (optional):

Did the last author really read this version? Zhonghe's affiliation should be changed as only "Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China"

Reviewers' comments: