An unusual bird (Theropoda, Avialae) from the Early Cretaceous of Japan suggests complex evolutionary history of basal birds

The Early Cretaceous basal birds were known largely from just two-dimensionally preserved specimens from north-eastern China (Jehol Biota), which has hindered our understanding of the early evolution of birds. Here, we present a three-dimensionally-preserved skeleton (FPDM-V-9769) of a basal bird from the Early Cretaceous of Fukui, central Japan. Unique features in the pygostyle and humerus allow the assignment of FPDM-V-9769 to a new taxon, Fukuipteryx prima. FPDM-V-9769 exhibits a set of features comparable to that of other basalmost birds including Archaeopteryx. Osteohistological analyses indicate that FPDM-V-9769 is subadult. Phylogenetic analyses resolve F. prima as a non-ornithothoracine avialan basal to Jeholornis and outgroup of the Pygostylia. This phylogenetic result may imply a complex evolutionary history of basal birds. To our knowledge, FPDM-V-9769 represents the first record of the Early Cretaceous non-ornithothoracine avialan outside of the Jehol Biota and increases our understanding of their diversity and distribution during the time.

1. The anatomical descriptions are perfect, but I recommend expanding a little bit the universe of comparisons, including other basal birds (particularly pygostilians). Thus, the paper requires more explanations to justify why Fukuipteryx falls outside Ornithothoraces, instead of being a basal member of Pygostilia.
2. The ms begins with a conclusion: convergence was a common topic among basal birds, and Fukuipteryx represents one of these cases. I am not saying that convergence was not presence in this part of the tree of life, but I believe the allocation of Fukuiteryx outside Pygostilia seems counterintuitive. It it hard to believe that such a "modern" kind of pygostile present in Fukuiteryx results case of convergence with that of derived pygostilians (e.g., enantiornithes).
3. Although I guess that Fukuiteryx is a pygostilian, I agree with the authors that it does not associate immediately with any of the currently recognized basal pygostilian clades (i.e., Confuciusornithidae, Sapeornithididae, Enantiornithes). Thus, this is the reason I encourage the authors to review their original interpretations, but also considering the possibility that Fukuipteryx represents a pygostilian not particularly related with any of the currently recognized clades.
Particular observations on the ms are as follows: ABSTRACT I recommend modifying the text, by almost repeating what it is said in the main text about that early Cretaceous birds "are currently known from the two-dimensionally-preserved specimens from north-eastern China, Las Hoyas (Spain), and Araripe (NE Brazil)". Current knowledge on basal birds does not restrict to China alone. DIAGNOSIS With the aim to quickly realize the size of the specimen, I suggest comparison with a living bird. For example: "A non-ornithothoracine bird the size of a sparrow/chicken/turkey..." (choose the correct one). Lines 122-123 -Authors cite Anchiornis as a "non-avian theropod". However, different recent papers (Agnolín and Novas, 2013;Agnolín et al., 2019;Pei et al. 2018) demonstrated the avian affiliation of Anchiornis, as originally proposed by Xu (2011). Lines 137-138 -Authors say that dorsal centrum of Fukuipteryx bears large and deep, suboval lateral excavations, as in Confuciusornis, but not in more stemward avialans such as Jeholornis and Archaeopteryx. Important is to also include that enantiornithes also bear such large excavation on dorsal centra. Lines 152-155 -Please, insert information about the number of free caudals in enantiornithes and basal ornithurines. Lines 152-155 -Why do you assume Fukuipteryx had more than five free caudals? Lines 176 -178 -Similarities that Fukuipteryx shares with some enantiornithes in the particular shape of pygostile, can be used in support that Fukuipteryx is a bird related with enantiornithes, rather than consider these features as convergent acquisitions. Lines 183-184 -Authors say "Thus, such feature may have been already present in basalmost birds with pygostyle as suggested in that of F. prima". I suggest to change this phrase for "Thus, such feature may have been already present in basalmost pygostilians as suggested in that of F.prima".

DISCUSSION
Ideas developed in present "Discussion" are based on the assumption that Fukuipteryx is an avialan less derived than Jeholornis. However, Fukuipteryx exhibits several enantiornithine/ornithotoracine features suggesting a higher position among birds. Line 292 -Authors say "The following morphological features indicate Fukuipteryx prima is an avialan". However, Fukuipteryx exhibits features that are clearly MORE DERIVED than basal avialans (e.g., Archaeopteryx, Jeholornis, Rahonavis). Lines 296-297 -Authors say "Furthermore, F. prima exhibits numerous primitive features comparable to non-ornithothoracine birds". Please, list these features. Lines 308-309 -Authors say that Fukuipteryx "exhibits several primitive features that cannot be explained solely by ontogeny. For example, the pygostyle is large, robust and well-fused". Nevertheless, this kind of pygostile gathers a set of clearly derived features, being morphologically far from a primitive condition, as represented by Sapeornithidae and Confuciusornithidae. Line 314 -Another feature considered by authors as "primitive" for Fukuipteryx is pelvic elements unfused each other. But this is an ontogeny-dependent feature, and cannot be taken as indicative for a basal position of Fukuipteryx among Avialae. Lines 325-327 -The strict consensus tree supports the basal position of Fukuipteryx prima within Avialae and outside of Ornithothoraces. I highly respect authors for cladistics analysis they did, but the placement of Fukuipteryx as a bird less-derived than Jeholornis seems counterintuitive. General aspect of each of the available bones of Fukuipteryx (particularly the complex shape of the pygostile) suggests it as a pygostilian bird. I recommend to discuss this point, as well as to make some comments if it is closer to Enantiornithes or Jinguofortisidae. Lines 341-343 -Authors state that "skeletal features of F. prima demonstrate that the shortening and fusion of caudal vertebrae are not necessarily associated with the flight adaptations". Authors are right about that the origin of a pygostile does not necessarily had an univocal relation with flying capabilities. However, and regarding Fukuipteryx, I am unable to recognize which are those "skeletal features" which are not related with flight. On the contrary, all the wing bones of Fukuipteryx closely resemble those of a flying bird. Line 348 -Authors defend that the pygostile evolved independently from flight capabilities. However, the kind of pygostile present in Fukuipteryx seems more derived than that of Confuciusornis, resembling that of enantiornithes. A "pygostile" (that is: fusion of distal caudals) evolved in oviraptorosaurs and pygostilian birds, and may have evolved many times among basal birds. However, a pygostile with the system of crests and grooves present in Fukuipteryx gathers much more characteristics than "fused vertebrae" alone. I am unable to say that such a complex pygostile IS NOT related with flight control. Lines 352-353 -Authors refer about that "The discovery of Fukuipteryx prima further increases the geological distribution of non-ornithothoracine birds." But if Fukuiraptor, instead, is a basal pygostilian, then this paleobiogeographic conclusion could be incorrect. Accepting Fukuipteryx as a member either of Enanthiornithes or Ornithothoraces, then the paleobiogegraphic conclusion results more congruent with already known pygostilian/ornitothoracine temporal and paleobiogeographic distributions.

ILLUSTRATIONS
The illustrations of the present ms are excellent and I hope they become fully published. I have inserted some observations close to some of the illustrated bones. By observing them, it seems clear that Fukuipteryx (even accepting it is a pygostilian), it does not comfortably fit among enantiornithes, for example. Thus, although I do not share author´s results depicting Fukuipteryx as a non-ornithothoracine bird, I agree with them in viewing Fukuipteryx as a bizarre pygostilian! Notes on the figures are as follows: Figure 3b. The well-developed latero-dorsal crests conform a derived character, absent in basal pygostilians, but present in enantiornithines. This view is almost identical to Mirarce (Atterholt et al., 2018). Figure 4b. The furcula is robust, but different from enantiornithes in lacking a hypocleidium. Figure 4c. The acromial process of coracoid does not surpass the cranial level of coracoid, similar to basal birds and different from derived ornithothoracines. Figure 4c. The coracoid exhibits a modern aspect in being strut-like, different from most basal birds. Thus, it fits well among derived pygostilians. However, it differs from enantiornithines in the following features: 1) proximal end is robust, apparently different from more slender one of enantiornithes; 2) the glenoid is CONCAVE, different from the flat or convex one of enantiornithes; 3) the dorsal surface of coracoid seems devoid of the typical excavation of enantiornithes. Figure 5a. The hole present on the proximo-medial corner of humerus, is it an artifact of preservation? How it relates with the broken proximal half of deltopectoral crest? Figure 5b. This extensive and rectangular deltopectoral crest is also present among enantiornithes. Figure 5c. Could you offer information if an interosseous groove -a characteristic of many enantiornithes-is present or not on the radius? Figure 5d. The abbreviation "imt" is not explained in figure text. Figure 5. A reconstruction of the entire manus will be welcome! Figure 6a. The proximal end of femur remembers me that of El Brete (Argentina) enantiornithes.

Reviewer #1 (Remarks to the Author):
This study reports a new taxon of Early Cretaceous avialan (hereafter 'basal bird', following the authors' usage) from Japan.
The skeleton is reasonably complete, although the images suggest that the specimen is not very well preserved and is in some ways difficult to interpret. It has been subjected to CT scanning so the skeletal elements are figured and described individually, although the resultant volumes are somewhat low resolution and not particularly straightforward to interpret.
We consider that the preservation of the specimen is reasonably good, as noted by Reviewer 2. While the specimen does not preserve the entire skeleton, it is one of few examples of the Early Cretaceous birds that preserves substantial amount of bones three-dimensionally. We replaced some volumes with higher-resolution images. The images in the original manuscript was in low resolution for initial submission purpose. We are prepared to provide high-quality images upon request.
Perhaps most significantly, the specimen represents the first basal bird from the Early Cretaceous of Japan, and the first such discovery from outside of China, Korea, or Germany.
The description of the skeletal material is relatively thorough, although it would be helpful for more information about how certain elements were identified. For example, what makes the authors sure that the putative surangular is in fact a surangular? The volume presented is difficult for me to assess. We provided additional notes on the identification of the surangular and comparison with that of confuciusornithids (Lines 124-126).
The authors perform a phylogenetic analysis, although due to missing data support values for the topology are weak, and there is uncertainty as to whether some of the osteological interpretation is confounded by the skeleton deriving from a subadult animal, as suggested by an osteohistological assessment. It would be good if this paper could also be reviewed by someone with expertise in this kind of osteohistological analysis, which I have little experience with. We accept that the support values are low with the data available to us. In the original manuscript, we noted on this low support values. We re-ran the analysis by reviewing the characters as carefully as possible, and coded the characters that may be affected by ontogenetic changes as "missing (?)" (Lines 347-355). The resulting phylogenetic tree did not differ from the one from previous analysis. While we cannot be conclusive about the phylogenetic position of Fukuipteryx considering the low support values, in terms of the significance of the analysis, we have provided a workable hypothesis that there is an unknown clade of basalmost birds (as represented by Fukuipteryx) to be tested with additional fossil specimens in the future. Min Wang has performed studies involving osteohistological analyses on Mesozoic birds in the past. We would appreciate it if our paper is reviewed by a reviewer with expertise in osteohistological analyses if our editor feels it is appropriate.
I feel that everything I've written above makes for a straightforward, if not especially high-profile, study. Unfortunately, the manuscript does suffer from editorial problems throughout-there are numerous spelling errors, and several sentences don't make sense. I do not want to hold the quality of the language in the paper against the authors, but it is clear that the paper will need to heavily revised in order for it to be clearly understandable by most readers. I have noted a small number of such issues below, as well as other minor comments. The revised manuscript was reviewed by a native English speaker and grammatical errors are corrected. It is acknowledged in the acknowledgement section. Line 50: Ornithuromorpha is misspelled Corrected. Line 50: The statement about enantiornithines going extinct at the end of the Cretaceous should be supported by a reference We included a reference. Lines 53-55: This sentence doesn't make sense as written--I think 'suppressed' is not the right word here?
Corrected. Description of holotype: What is the difference between 'incomplete' and 'partial'?
To avoid confusion, "incomplete" is used throughout the current manuscript. Description: The authors frequently use the term 'skeleton' instead of 'bone' or 'element' Corrected.

Reviewer #2 (Remarks to the Author):
Review of "A new and bizarre basal bird (Theropoda, Avialae) from the Early Cretaceous of Japan", by Imai and co-authors.
I am happy to know about the discovery of this new and remarkable Cretaceous avian from Japan. Congratulations to the authors for such an interesting discovery, constituting one of the very few preserved three-dimensionally. The preservation is very good and affords valuable anatomical information not only allowing support the validity of the new taxon, but also to discuss evolutionary aspects of early birds as a whole. The high quality images they offer are quite useful to know the osteology of these basal birds. No doubt, the manuscript deserves publication in Communication Biology. Although I have enjoyed by reading the provocative conclusions expressed in the ms, I am not entirely convinced of them.
General considerations about the ms are as follows: 1. The anatomical descriptions are perfect, but I recommend expanding a little bit the universe of comparisons, including other basal birds (particularly pygostilians). Thus, the paper requires more explanations to justify why Fukuipteryx falls outside Ornithothoraces, instead of being a basal member of Pygostilia. We made comparisons of the specimen against Ornithothoraces to contrast the lack of the ornithothoracine characters in Fukuipteryx (Lines 303-321).
2. The ms begins with a conclusion: convergence was a common topic among basal birds, and Fukuipteryx represents one of these cases. I am not saying that convergence was not presence in this part of the tree of life, but I believe the allocation of Fukuiteryx outside Pygostilia seems counterintuitive. It it hard to believe that such a "modern" kind of pygostile present in Fukuiteryx results case of convergence with that of derived pygostilians (e.g., enantiornithes). Considering that the pygostyle independently evolved within Theropoda (in oviraptorosaurs, therizinosaurs, and birds), there is a possibility that the pygostyle evolved independently in a avialan clade basal to Jeholornis. Upon receiving the reviewer's comment, we re-run the phylogenetic analyses with as much conservative approach as possible in coding character states (Lines 347-355), and the position of Fukuipteryx in the most parsimonious tree remained the same. We do not consider that the "modern kind of pygostyle" as noted in the above comment is not present in 3. Although I guess that Fukuiteryx is a pygostilian, I agree with the authors that it does not associate immediately with any of the currently recognized basal pygostilian clades (i.e., Confuciusornithidae, Sapeornithididae, Enantiornithes). Thus, this is the reason I encourage the authors to review their original interpretations, but also considering the possibility that Fukuipteryx represents a pygostilian not particularly related with any of the currently recognized clades.
We agree with the reviewer that Fukuipteryx constitutes its own clade that was unknown previously. Our interpretation has to remain similar to the previous one, because the result of our revised phylogenetic analysis did not change from the previous one. We realize the incompleteness of the specimen may contribute to the enigmatic position of Fukuipteryx within the Avialae, and it is noted in the manuscript. We would like to emphasize that, while we do not intend to persist our phylogenetic interpretation of the specimen, it is currently the most possible hypothesis with the data we are given by the specimen and previous studies. We hope that additional data on these very basal clades of avialans be provided in the future and enigmatic position of Fukuipteryx outside of the Pygostilia be clarified.
Particular observations on the ms are as follows: ABSTRACT I recommend modifying the text, by almost repeating what it is said in the main text about that early Cretaceous birds "are currently known from the two-dimensionally-preserved specimens from north-eastern China, Las Hoyas (Spain), and Araripe (NE Brazil)". Current knowledge on basal birds does not restrict to China alone. Due to the restriction in number of words in the abstract, we were unable to expand the sentence as suggested. However, replaced the word "exclusively from" to "largely from" to avoid excluding other localities.

DIAGNOSIS
With the aim to quickly realize the size of the specimen, I suggest comparison with a living bird. For example: "A non-ornithothoracine bird the size of a sparrow/chicken/turkey..." (choose the correct one).

Based on our skeletal reconstruction, the specimen is similar to a pigeon in size, and we included it in the revised manuscript (Line 111).
Lines 122-123 -Authors cite Anchiornis as a "non-avian theropod". However, different recent papers ( To be fair, we replaced the term "non-avian theropod" with a more inclusive cladistic name "paravian" when referring to Anchiornis. All previous studies agree on the paravian affinity of Anchiornis.
Lines 137-138 -Authors say that dorsal centrum of Fukuipteryx bears large and deep, suboval lateral excavations, as in Confuciusornis, but not in more stemward avialans such as Jeholornis and Archaeopteryx. Important is to also include that enantiornithes also bear such large excavation on dorsal centra.

Zhou and Zhang (2003), ref. 30, makes a statement that all enantiornithes bear this feature, and it is therefore cited in the manuscript (Line 139).
Lines 152-155 -Please, insert information about the number of free caudals in enantiornithes and basal ornithurines.

The above information is included in the manuscript with references (Lines 158-160).
Lines 152-155 -Why do you assume Fukuipteryx had more than five free caudals? We do not assume the animal has more than five, but we suggest it is possible there were additional free caudals when it was alive, as most basal pygostylians have more than five of them. This was made clear in the revised manuscript (Lines 158-160).
Lines 176 -178 -Similarities that Fukuipteryx shares with some enantiornithes in the particular shape of pygostile, can be used in support that Fukuipteryx is a bird related with enantiornithes, rather than consider these features as convergent acquisitions. As discussed in the manuscript (Lines 303-321), the furcula, coracoid, and metacarpals do not exhibit enantiornithine features. Confuciusornithids also share a relatively-large, rod-like pygostyle with Fukuipteryx. These lines of evidence support that Fukuipteryx is closer to non-ornithothoracine birds than to any enantiornithines.
Lines 183-184 -Authors say "Thus, such feature may have been already present in basalmost birds with pygostyle as suggested in that of F. prima". I suggest to change this phrase for "Thus, such feature may have been already present in basalmost pygostilians as suggested in that of F.prima". The sentence was rephrased as suggested (Lines 188-189).

DISCUSSION
Ideas developed in present "Discussion" are based on the assumption that Fukuipteryx is an avialan less derived than Jeholornis. However, Fukuipteryx exhibits several enantiornithine/ornithotoracine features suggesting a higher position among birds.
With the above sentence, we simply argued that F. prima is an avialan but not basal paravians (i.e., dromaeosaurids, troodontids and other taxa that belong to Paraves but not to Avialae). We do not argue here whether Fukuipteryx is more derived than Archaeopteryx, Jeholornis, nor Rahonavis. Such argument is made later in the discussion.
Lines 296-297 -Authors say "Furthermore, F. prima exhibits numerous primitive features comparable to non-ornithothoracine birds". Please, list these features. These features are listed following the above sentence (Lines 305-308).
Lines 308-309 -Authors say that Fukuipteryx "exhibits several primitive features that cannot be explained solely by ontogeny. For example, the pygostyle is large, robust and well-fused". Nevertheless, this kind of pygostile gathers a set of clearly derived features, being morphologically far from a primitive condition, as represented by Sapeornithidae and Confuciusornithidae.
In the paragraph, we list the primitive skeletal characters of Fukuipteryx that cannot be exclusively ascribed to ontogenetic variation (those characters that can be safely used in the phylogenetic analysis without confusing developmental and evolutionary features). The sentence was rephrased in the revised manuscript. As suggested by the reviewer the pygostyle is comparable to those in Sapeornithidae and Confuciusornithidae. However, it is primitive in comparison to the pygostyle of Ornithothoraces.
Line 314 -Another feature considered by authors as "primitive" for Fukuipteryx is pelvic elements unfused each other. But this is an ontogeny-dependent feature, and cannot be taken as indicative for a basal position of Fukuipteryx among Avialae. As discussed in the manuscript, in most Early Cretaceous birds (especially non-ornithothoracines) the pelvic elements do not fuse throughout ontogeny (Lines 340-344). This feature alone does not indicate the basal position of Fukuipteryx, but is one of the multiple lines of evidence that the animal is a basal avialan. To be conservative, though, we coded the character states related to pelvic fusions missing (0→?) in the revised phylogenetic analysis.
Lines 325-327 -The strict consensus tree supports the basal position of Fukuipteryx prima within Avialae and outside of Ornithothoraces. I highly respect authors for cladistics analysis they did, but the placement of Fukuipteryx as a bird less-derived than Jeholornis seems counterintuitive. General aspect of each of the available bones of Fukuipteryx (particularly the complex shape of the pygostile) suggests it as a pygostilian bird. I recommend to discuss this point, as well as to make some comments if it is closer to Enantiornithes or Jinguofortisidae. The enigmatic position of Fukuipteryx within Avialae and its implications are discussed in Lines 362-378. In Lines 310-326, we discuss that Fukuipteryx lacks enantiornithine features and is clearly not close to enantiornithes. Fukupteryx shares some features with Jinguofotisidae as already noted in Lines 207-210, 271-273, and 305-306.
Lines 341-343 -Authors state that "skeletal features of F. prima demonstrate that the shortening and fusion of caudal vertebrae are not necessarily associated with the flight adaptations". Authors are right about that the origin of a pygostile does not necessarily had an univocal relation with flying capabilities. However, and regarding Fukuipteryx, I am unable to recognize which are those "skeletal features" which are not related with flight. On the contrary, all the wing bones of Fukuipteryx closely resemble those of a flying bird.
As the reviewer says, Fukuipteryx possesses limb skeletal features that are comparable to other flight-capable avialans (including Archaeopteryx), but not to the extent of enantiornithines or ornithuromorphs. We feel it was a little too much over-interpretation and decided to omit the part for more conservative approach.
Line 348 -Authors defend that the pygostile evolved independently from flight capabilities. However, the kind of pygostile present in Fukuipteryx seems more derived than that of Confuciusornis, resembling that of enantiornithes. A "pygostile" (that is: fusion of distal caudals) evolved in oviraptorosaurs and pygostilian birds, and may have evolved many times among basal birds. However, a pygostile with the system of crests and grooves present in Fukuipteryx gathers much more characteristics than "fused vertebrae" alone. I am unable to say that such a complex pygostile IS NOT related with flight control. We agree with the reviewer that the pygostyle in Fukuipteryx may be flight-related. However, we disagree with the reviewer in suggesting the pygostyle of Fukuipteryx is "more derived than that of Confuciusornis, resembling that of enantiornithes". According to Wang and O'Connor (2017) in reviewing the pygostyles of Early Cretaceous birds, it is stated that typical enantiornithine pygostyles are well-fused and individual processes cannot be recognized in adults. They also exhibit "paired dorsolateral ridges demarcating a deeply incised dorsal surface." "Ventrally, the body is very narrow, with a pair of ventrolateral processes". These features result in the appearance of "X-shaped in proximal view". In the pygostyle of Fukuipteryx, the individual transvers processes and neural spines are visible, no dorsolateral or ventrolateral processes are present, and it is triangle-shaped in proximal view.
Lines 352-353 -Authors refer about that "The discovery of Fukuipteryx prima further increases the geological distribution of non-ornithothoracine birds." But if Fukuiraptor, instead, is a basal pygostilian, then this paleobiogeographic conclusion could be incorrect. Accepting Fukuipteryx as a member either of Enanthiornithes or Ornithothoraces, then the paleobiogegraphic conclusion results more congruent with already known pygostilian/ornitothoracine temporal and paleobiogeographic distributions. As already discussed, Fukuipteryx lacks ornithothoracine features. It still extends the geographical distribution of the non-ornithothoracine pygostilians to further East of Asia.

ILLUSTRATIONS
The illustrations of the present ms are excellent and I hope they become fully published. I have inserted some observations close to some of the illustrated bones. By observing them, it seems clear that Fukuipteryx (even accepting it is a pygostilian), it does not comfortably fit among enantiornithes, for example. Thus, although I do not share author´s results depicting Fukuipteryx as a non-ornithothoracine bird, I agree with them in viewing Fukuipteryx as a bizarre pygostilian! Notes on the figures are as follows: Figure 3b. The well-developed latero-dorsal crests conform a derived character, absent in basal pygostilians, but present in enantiornithines. This view is almost identical to Mirarce (Atterholt et al., 2018).

Latero-dorsal crests in the pygostyle of enantiornithines including Mirarce is absent in Fukuipteryx.
We guess what the reviewer mentions here is the last free caudal vertebra of Fukuipteryx that appears X-shaped in the cranial view. However, these caudal vertebrae are not fused with the pygostyle, resulting in the triangular-shape of the element. Figure 4b. The furcula is robust, but different from enantiornithes in lacking a hypocleidium. We agree with the reviewer, and this supports our interpretation that Fukuipteryx is not enantiornithine. Figure 4c. The acromial process of coracoid does not surpass the cranial level of coracoid, similar to basal birds and different from derived ornithothoracines. We agree with the reviewer. Figure 4c. The coracoid exhibits a modern aspect in being strut-like, different from most basal birds. Thus, it fits well among derived pygostilians. However, it differs from enantiornithines in the following features: 1) proximal end is robust, apparently different from more slender one of enantiornithes; 2) the glenoid is CONCAVE, different from the flat or convex one of enantiornithes; 3) the dorsal surface of coracoid seems devoid of the typical excavation of enantiornithes. Strut-like coracoid is also found in Jeholornis, a basalmost Early Cretaceous avialan. Thus, the strut-like coracoid, while widespread among modern birds, can be present in much more basal birds. We agree with the reviewer that the coracoid lacks typical enantiornithine features, especially the convex glenoid, which is a diagnostic character of the group. Figure 5a. The hole present on the proximo-medial corner of humerus, is it an artifact of preservation? How it relates with the broken proximal half of deltopectoral crest? It does not appear to be an artifact of preservation. The inner surface of the "hole" is smooth and does not exhibit any inner-bone texture that would appear if the bone is "excavated" during the preservation. The deltopectoral crest presumably terminates at the "hole" because the proximal corner of the "hole" exhibits smooth surface indicating the crest did not extend beyond it. Figure 5b. This extensive and rectangular deltopectoral crest is also present among enantiornithes. It seems that the rectangular deltopectoral crest is common among non-ornithothoracines (Wang et al. 2016) and enantiornithes as suggested by the reviewer. . Figure 5c. Could you offer information if an interosseous groove -a characteristic of many enantiornithes-is present or not on the radius?
No, we did not observe interosseous groove on the radius.