Ventral Morphology and Ecological Implications of Cindarella eucalla (Artiopoda, Xandarellida) from Chengjiang Biota, China

Reviewer #1 (Public review):

Summary:

The manuscript by Zhang et al. analyzed 17 specimens of Cindarella eucalla with 3D technology and discussed the anatomical findings, the relationship to other artiopods, and the ecology of the animal. The results are excellent and the findings are very interesting. However, the discussion needs to be extended, as the point the authors are trying to make is not always clear. I also recommend some restructuring of the discussion. Overall this is an important manuscript, and I'm looking forward to reading the edited version.

Strengths:

The analyses, the 3D data is excellent and provides new information.

Weaknesses:

The discussion - the authors provide information for the findings, but do not discuss them in detail. More information is needed.

Reviewer #2 (Public review):

Summary:

Zhang et al. present very well-illustrated specimens of the artiopodan Cinderella eucalla from the Chengjiang Biota. Multiple specimens are shown with preserved appendages, which is rare for artiopodans and will greatly help our understanding of this taxon. The authors use CT scanning to reveal the ventral organization of this taxon. The description of the taxon needs some modification, specifically expansion of the gut and limb morphology. The conclusion that Cinderella was a fast-moving animal is very weak, comparisons with extant fast animals and possibly FEA analyses are necessary to support such a claim. Although the potential insights provided by such well-preserved fossils could be valuable, the claims made are tenuous and based on the available evidence presented herein.

Strengths:

The images produced through CT scanning specimens reveal the very fine detail of the appendages and are well illustrated. Specimens preserve guts and limbs, which are informative both for the phylogenetic position and ecology of this taxon. The limbs are very well preserved, with protopodite, exopodite, and endopodites visible. Addressing the weaknesses below will make the most of this compelling data that demonstrates the morphology of the limbs well.

Weaknesses:

Although this paper includes very well-illustrated fossils, including new information on the eyes, guts, and limbs of Cinderella, the data are not fully explained, and the conclusions are weakly supported.

The authors suggest the preservation of complex ramifying diverticular, but it should be better illustrated and the discussion of the gut diverticulae should be longer, especially as gut morphology can provide insights into the feeding strategy.

The conclusion that Cinderella eucalla was fast, sediment feeding in a muddy environment, is not well supported. These claims seem to be tenuously made without any evidence to support them. The authors should add a new section in the discussion focused on feeding ecology where they explicitly compare the morphology to suspension-feeding artiopodans to justify whether it fed that way or not. To further explore feeding, the protopodite morphology needs to be more carefully described and compared to other known taxa. The function of endites on the endopodite to stir up sediment for particle feeding in a muddy environment would also need to be more thoroughly discussed and compared with modern analogs. The impact of their findings is not highlighted in the discussion, which is currently more of a review of what has been previously said and should focus more on what insights are provided by the great fossils illustrated by the authors.

The authors argue that their data supports fast escaping capabilities, but it is not clear how they reached that conclusion based on the data available. Is there a way this can be further evaluated? The data is impressive, so including comparisons with extant taxa that display fast escaping strategies would help the authors make their case more compelling. The authors also claim that the limbs of Cinderella are strong, again this conclusion is unclear. Comparison with the limbs of other taxa to show their robustness would be useful. To actually test how these limbs deal with the force and strain applied to them by a sudden burst of movement, the authors could conduct Finite Element Analyses.

Reviewer #3 (Public review):

This paper provides an interesting description of the ventral parts of the Cambrian xandarellid Cindarella eucalla, derived from exceptionally preserved specimens of the Chengjiang Biota. These morphological data are useful for our broad understanding and future research on Xandarellida, and are generally well-represented in the description and accompanying figures. The strengths of this work rest in this morphological description of exceptional fossil material, and this is generally well supported. In addition, the authors put this description in the context of the morphology of other xandarellids and Cambrian arthropod groups, with most of these parallels being useful and reasonably supported, though in several places homology is assumed and this currently lacks evidence. The manuscript goes on to use these morphological data and comparisons to other groups (particularly trilobites) to make suggestions for the ecology of Cindarella eucalla and other xandarellids. The majority of my comments on this work relate to this latter aim - the ecological conclusions drawn are generally derived through morphological comparisons, where a specific morphology has been suggested as an adaption to a particular ecological function in another extinct arthropod group. However, the original suggestions for ecological function are untested, and so remain hypotheses. Despite this, they are frequently presented as truisms to enable ecological conclusions to be drawn for Cindarella eucalla. I have listed my comments and queries on the study below for the authors to address or respond to, and I hope they are useful to the authors.

Comments:

There are a number of ecological and functional morphology conclusions stated that seem put too strongly to be considered sufficiently supported by the evidence given. These relate to both the description of C. eucalla, and comparisons to other extinct arthropod taxa (notably trilobites). Many of these latter statements are assumptions of functional morphology, and should not be repeated as truisms, rather than they represent suggested functions and ecologies based on the known morphological descriptions. This aspect occurs throughout the article, and, for me, is the primary concern.

Author response:

Reviewer #1 (Public review):

Summary:

The manuscript by Zhang et al. analyzed 17 specimens of Cindarella eucalla with 3D technology and discussed the anatomical findings, the relationship to other artiopods, and the ecology of the animal. The results are excellent and the findings are very interesting. However, the discussion needs to be extended, as the point the authors are trying to make is not always clear. I also recommend some restructuring of the discussion. Overall this is an important manuscript, and I'm looking forward to reading the edited version.

Strengths:

The analyses, the 3D data is excellent and provides new information.

Weaknesses:

The discussion - the authors provide information for the findings, but do not discuss them in detail. More information is needed.

We are committed to enhancing the quality of our manuscript further and, in response to your comments, will implement the following improvements:

(1) Comparative Analysis of Eyes: We will expand our discussion to include a detailed comparative analysis of the eyes of Cindarella eucalla with those of other artiopods (e.g. Xandarellids, trilobites, living insects), focusing on morphology, size, and other relevant characteristics.

(2) Segmental Mismatch Discussion: We will provide an in-depth exploration of the specifics and significance of the segmental mismatch to offer a clearer understanding of its implications. We will also compare the characteristics of this mismatch in our focal species with those observed in extant arthropods, such as spiders and myriapods. This comparison will be further enriched by integrating our phylogenetic analysis, thereby providing a broader evolutionary context.

(3) Methodological Clarity: We will provide more detailed information on the parameters used for the analyses in the Methods section, especially the phylogenetic sections and the X-ray tomography section.

(4) Phylogenetic Analysis: We will engage in a more in-depth discussion of certain characters (e.g. anterior sclerite, hypostome, endopodite, segmental mismatch, etc.) within our phylogenetic analyses to clarify their relevance and contribution to our findings.

Reviewer #2 (Public review):

Summary:

Zhang et al. present very well-illustrated specimens of the artiopodan Cinderella eucalla from the Chengjiang Biota. Multiple specimens are shown with preserved appendages, which is rare for artiopodans and will greatly help our understanding of this taxon. The authors use CT scanning to reveal the ventral organization of this taxon. The description of the taxon needs some modification, specifically expansion of the gut and limb morphology. The conclusion that Cinderella was a fast-moving animal is very weak, comparisons with extant fast animals and possibly FEA analyses are necessary to support such a claim. Although the potential insights provided by such well-preserved fossils could be valuable, the claims made are tenuous and based on the available evidence presented herein.

Strengths:

The images produced through CT scanning specimens reveal the very fine detail of the appendages and are well illustrated. Specimens preserve guts and limbs, which are informative both for the phylogenetic position and ecology of this taxon. The limbs are very well preserved, with protopodite, exopodite, and endopodites visible. Addressing the weaknesses below will make the most of this compelling data that demonstrates the morphology of the limbs well.

Weaknesses:

Although this paper includes very well-illustrated fossils, including new information on the eyes, guts, and limbs of Cinderella, the data are not fully explained, and the conclusions are weakly supported.

The authors suggest the preservation of complex ramifying diverticular, but it should be better illustrated and the discussion of the gut diverticulae should be longer, especially as gut morphology can provide insights into the feeding strategy.

The conclusion that Cinderella eucalla was fast, sediment feeding in a muddy environment, is not well supported. These claims seem to be tenuously made without any evidence to support them. The authors should add a new section in the discussion focused on feeding ecology where they explicitly compare the morphology to suspension-feeding artiopodans to justify whether it fed that way or not. To further explore feeding, the protopodite morphology needs to be more carefully described and compared to other known taxa. The function of endites on the endopodite to stir up sediment for particle feeding in a muddy environment would also need to be more thoroughly discussed and compared with modern analogs. The impact of their findings is not highlighted in the discussion, which is currently more of a review of what has been previously said and should focus more on what insights are provided by the great fossils illustrated by the authors.

The authors argue that their data supports fast escaping capabilities, but it is not clear how they reached that conclusion based on the data available. Is there a way this can be further evaluated? The data is impressive, so including comparisons with extant taxa that display fast escaping strategies would help the authors make their case more compelling. The authors also claim that the limbs of Cinderella are strong, again this conclusion is unclear. Comparison with the limbs of other taxa to show their robustness would be useful. To actually test how these limbs deal with the force and strain applied to them by a sudden burst of movement, the authors could conduct Finite Element Analyses.

Here are the key points we plan to address:

(1) Gut and Limb Morphology: We will expand our description of the gut and limb morphology of C. eucalla, providing a more detailed comparison and analysis. This will include a revised discussion on the function and ecological implications of these features.

(2) Fast-Moving Animal Claim: We acknowledge your concern about the conclusion that C. eucalla was a fast-moving animal. We will conduct a more detailed comparison among C. eucalla and other Cambrian artiopods and living arthropods, focusing on morphological and functional aspects. We will also reconsider our claim and will be more cautious in our conclusions. If the comparison proves insufficient, we will remove this assertion from the manuscript. But we may no longer conduct Finite Element Analysis, as a comprehensive and cautious analysis would require a massive project to complete.

(3) Sediment Feeding in a Muddy Environment: We will revise the section discussing the feeding ecology of C. eucalla. We will enhance this section by comparing the morphology of C. eucalla to that of suspension-feeding artiopods, which will help to substantiate our claims. Additionally, we will expand the discussion to include a more detailed examination of endites, gnathobases, and other relevant anatomical structures.

(4) Impact of Findings: We will endeavor to highlight the impact of our findings in the discussion, focusing on the insights provided by the well-preserved fossils illustrated in our study.

Reviewer #3 (Public review):

This paper provides an interesting description of the ventral parts of the Cambrian xandarellid Cindarella eucalla, derived from exceptionally preserved specimens of the Chengjiang Biota. These morphological data are useful for our broad understanding and future research on Xandarellida, and are generally well-represented in the description and accompanying figures. The strengths of this work rest in this morphological description of exceptional fossil material, and this is generally well supported. In addition, the authors put this description in the context of the morphology of other xandarellids and Cambrian arthropod groups, with most of these parallels being useful and reasonably supported, though in several places homology is assumed and this currently lacks evidence. The manuscript goes on to use these morphological data and comparisons to other groups (particularly trilobites) to make suggestions for the ecology of Cindarella eucalla and other xandarellids. The majority of my comments on this work relate to this latter aim - the ecological conclusions drawn are generally derived through morphological comparisons, where a specific morphology has been suggested as an adaption to a particular ecological function in another extinct arthropod group. However, the original suggestions for ecological function are untested, and so remain hypotheses. Despite this, they are frequently presented as truisms to enable ecological conclusions to be drawn for Cindarella eucalla. I have listed my comments and queries on the study below for the authors to address or respond to, and I hope they are useful to the authors.

Comments:

There are a number of ecological and functional morphology conclusions stated that seem put too strongly to be considered sufficiently supported by the evidence given. These relate to both the description of C. eucalla, and comparisons to other extinct arthropod taxa (notably trilobites). Many of these latter statements are assumptions of functional morphology, and should not be repeated as truisms, rather than they represent suggested functions and ecologies based on the known morphological descriptions. This aspect occurs throughout the article, and, for me, is the primary concern.

We plan to address the following points in upon revision:

(1) Homology Assumptions: You pointed out that we have assumed homology in certain instances without sufficient evidence. We will revise the manuscript to include a more detailed analysis of the anterior sclerite and exite, considering phylogenetic relationships and morphological comparisons to provide a more robust discussion.

(2) Ecological and Functional Morphology: We acknowledge that our conclusions regarding the ecological function were presented with too much certainty. We will adopt a more cautious approach in our discussion, ensuring that our ideas are clearly labeled as such and are supported by a comparison of relevant studies on Cambrian artiopods and extant arthropods, including fluid dynamics, functional morphology, etc. We will re-evaluate the ecological function section, and if it does not adds value and clarity to the manuscript—our speculations do not contribute to the understanding of the specimen or may lead to misunderstandings—we will remove the relevant parts. We believe future changes reflect a more cautious and rigorous approach to the ecological and functional interpretations of C. eucalla.