Dental microwear of a basal ankylosaurine dinosaur, Jinyunpelta and its implication on evolution of chewing mechanism in ankylosaurs

Tai Kubo; Wenjie Zheng; Mugino O Kubo; Xingsheng Jin

doi:10.1371/journal.pone.0247969

. 2021 Mar 10;16(3):e0247969. doi: 10.1371/journal.pone.0247969

Dental microwear of a basal ankylosaurine dinosaur, Jinyunpelta and its implication on evolution of chewing mechanism in ankylosaurs

Tai Kubo ^1,^*, Wenjie Zheng ², Mugino O Kubo ³, Xingsheng Jin ²

Editor: Anthony R Fiorillo⁴

PMCID: PMC7946176 PMID: 33690686

Abstract

Jinyunpelta sinensis is a basal ankylosaurine dinosaur excavated from the mid Cretaceous Liangtoutang Formation of Jinyun County, Zhejiang Province, China. In the present study, its dental microwear was observed using a confocal laser microscope. Jinyunpelta had steep wear facets that covered most of buccal surfaces of posterior dentary teeth. Observation of dental microwear on the wear facet revealed that scratch orientation varied according to its location within the wear facet: vertically (i.e. apicobasally) oriented scratches were dominant in the upper half of the wear facet, and horizontally (i.e. mesiolaterally) oriented ones were in the bottom of the facet. These findings indicated that Jinyunpelta adopted precise tooth occlusion and biphasal jaw movement (orthal closure and palinal lower jaw movement). The biphasal jaw movement was widely observed among nodosaurids, among ankylosaurids, it was previously only known from the Late Cretaceous North American taxa, and not known among Asian ankylosaurids. The finding of biphasal jaw movement in Jinyunpelta showed sophisticate feeding adaptations emerged among ankylosaurids much earlier (during Albian or Cenomanian) than previously thought (during Campanian). The Evolution of the biphasal jaw mechanism that contemporaneously occurred among two lineages of ankylosaurs, ankylosaurids and nodosaurids, showed high evolutionary plasticity of ankylosaur jaw mechanics.

Introduction

Ankylosaurs were herbivorous dinosaurs that emerged in the Middle Jurassic and prospered until the end of Cretaceous [1, 2]. During the Late Cretaceous, compared to other contemporaneous megaherbivores, such as ceratopsians and hadrosaurs, ankylosaurs likely fed on less fibrous plants growing in lower layers of paleovegetation [3, 4]. Ankylosaurs were assumed to feed mainly on herbaceous ferns [4], which were dominant in stomach contents of an Early Cretaceous nodosaurid ankylosaur, Borealopelta, implying that this animal fed on ferns selectively [5]. Stomach contents of another Early Cretaceous basal ankylosaur, Kunbarrasaurus, also contained possible fern sporangia along with vascular tissue, angiosperm fruits, and small seeds [6, 7]. Between two main ankylosaurian families, i.e. Nodosauridae and Ankylosauridae, the former was assumed to have consumed more fibrous and tougher food than the latter, but dental microwear of Late Cretaceous North American taxa did not show distinction between these two families [3]. In addition to diet, jaw mechanics are revealed via ankylosaur dental microwear. Contrary to the expectation that ankylosaurs adopted simple orthal jaw movement due to their small and simple leaf-shaped teeth [8–10], dental microwear of derived Late Cretaceous taxa, such as an ankylosaurid Euoplocephalus [11] and nodosaurids, Panoplosaurus and Hungarosaurus, [3, 12] indicated biphasal jaw mechanism that adopted both orthal closure and palinal lower jaw movements.

It has been shown by analyses of skull morphometrics and dental wear that ankylosaurs evolved the biphasal jaw mechanism convergently in different ankylosaurian lineages [13]. According to Ősi et al. [12], basal ankylosaurs used orthal jaw movement, during which teeth rarely occluded. Precise tooth occlusion evolved convergently among basal nodosaurids and at the common ancestor of derived North American ankylosaurids. An Early Cretaceous nodosaurid Sauropelta might have adopted palinal jaw movements. This would also be the cases for Late Cretaceous nodosaurids, Struthiosaurus and Panoplosaurus as well as for a Late Cretaceous ankylosaurid Ankylosaurus. On the other hand, there were clear evidences of palinal jaw movements for Late Cretaceous nodosaurids Edmontonia, Panoplosaurus, Hungarosaurus, and a Late Cretaceous ankylosaurid Euoplocephalus [13]. Asian ankylosaurids, however, were thought to retain ancestral orthal jaw movement without tooth occlusion [13]. The evolutionary pattern of jaw mechanism in ankylosaurs is more complex than those of other herbivorous dinosaur taxa. For example, hadrosaurids exhibited a continuous evolutionary trend toward a more efficient masticatory system throughout the Cretaceous, such as an increase of functional teeth and the invention of new dental tissue types [14, 15]. The dental microwear of more ankylosaur specimens is needed to determine if the many convergences found by Ősi [13] are the true pattern of evolution or an artifact of sample size. Also, to deduce the factors that promoted the convergent evolution of sophisticated feeding adaptations in different ankylosaurian lineages, data from ankylosaur species that lived in various regions and periods were needed. In this study, we observed the dental microwear of Jinyunpelta to deduce its jaw movement and to reconstruct the evolution of the feeding mechanism in Asian and Cretaceous ankylosaurids.

Materials and methods

Jinyunpelta sinensis is the most basal ankylosaurine and the oldest ankylosaur with a tail club, which was excavated by a joint team of Zhejiang Museum of Natural History (ZMNH), Jinyun Museum, and Fukui Prefectural Dinosaur Museum during 2013 from Albian–Cenomanian Liangtoutang Formation of Jinyun County, Zhejiang Province, China [16]. As the excavation was conducted by the provincial museum, Zhejiang Museum of Natural History, and the fossil site was in the Zhejiang province of China, no permits were required for the excavation. The purpose of the excavation was to rescue fossil specimens from the reclamation work that completely flatten the hill, which contained these fossils. During the excavation, five associated specimens and isolated materials of Jinyunpelta were found from the construction site. The subsequent description was based on two specimens (Holotype ZMNH M8960 and Paratype ZMNH M8963) as other specimens were still under preparation [16]. The holotype skull ZMNH M8960 is dorsoventrally compressed and its upper and lower teeth rows are tightly occluded, therefore existence or absence of wear facet(s) on teeth could not be determined. Recently, it was clarified through preparation that another Jinyunpelta specimen ZMNH M8961 conserved the posterior part of dentaries and maxillae (Fig 1). The specimen is publicly deposited and accessible by others in a permanent repository as ZMNH is a provincial museum. Due to postmortem damages, most teeth were fallen out from teeth sockets and surfaces of many in situ teeth were abraded, but several posterior-most teeth of the right dentary were untouched exposing their buccal sides. Also, one left dentary tooth exposed an undamaged lingual surface (Fig 1f).

Fig 1 — (a) Right rostrolateral view of the skull of *Jinyunpelta* ZMNH M8961. (b) close up view of buccal sides of the right posterior dentary tooth row and (c) its line drawing, in which wear facets were drawn in gray and asterisks indicate molded teeth. (d) Dental microwear at the apical border of wear facet on the tooth A. The white rectangle in 10× photosimulation indicates the area where 100× photosimulation was taken. (e) Dental microwear of the wear facet on the tooth B. The white rectangle in 10× photosimulation indicates the area where 100× photosimulation was taken. (f) Dental microwear of the buccal surface of the tooth C. (g) Close up of the lingual side of the left dentary showing the tooth D (h) Dental microwear of the lingual surface of the tooth D. All photosimularions were taken from molds using a confocal laser microscope (VK-9700) with either a 100× or 10× objective lens. The field of view is 140×105 μm for 100× lens and 1403×1052 μm for 10× lens. Photosimularions were mirrored in the horizontal direction to match its direction with the real tooth surfaces. Scale bars are 10 cm for (a), 1cm for (b) and (g), 0.2 mm for 10× photosimulation images and 20 μm for 100× photosimulation images. Abbreviations: den, dentary; l, left; mx, maxilla; or, orbit; r, right; wf, wear facet.

We followed the molding procedures of Kubo and Kubo [17]. Teeth of ZMNH M8961 that preserved shiny surfaces with none or minor visible damages were selected and cleaned by cotton swabs soaked in acetone. After the cleaning, molds were taken using high-resolution A-silicone dental impression material (Dr. Silicon regular type, DentKist, Inc., Korea). Buccal surfaces of six right dentary teeth that include two wear facets and one possible wear facet (Fig 1c) and one lingual surface of the left dentary tooth (Fig 1f) were molded.

The presence of microwear was observed using a confocal laser microscope (VK-9700, Keyence, Osaka, Japan) and when the preservation of the entire visual field was satisfactory (e.g. the existence of scratches and absence of large crack), the dental impressions were scanned using a violet laser (wavelength 408nm) with 10× and long-distance 100× objective lenses (numerical apertures 0.30 and 0.95 respectively). For a long-distance 100× objective lens, the scan pitches were 0.138 μm for one pixel in x- and y- axes, and for a 10× objective lens that are 1.379 μm. A vertical resolution was 1 nm for both lenses. By scanning, the light intensity of reflected laser, color information, and height data (Z position) were obtained for each XY coordinate point at each focus point. Using these data, VK-9700 generates real color ultra-depth images (photosimulation), from which dental microwear were visually checked. Each photosimulation was 1024×768 pixels, therefore covering the area of 141×106 μm with long-distance 100× objective lens and 1412×1059 μm with 10× objective lens.

Previous work has shown that scratch orientation differs apicobasally within the same wear facet in some ankylosaurs, reflecting a multiphasic, complex jaw mechanism [12]. Therefore, we scanned wear facets in apicobasal direction using 10× objective lens, to make the image of the entire apicobasal section by combining photosimulation images. To show apicobasal changes of orientation of scratches, one wear facet was divided into five apicobasal sections and another wear facet was divided into apical and basal halves. Then orientation of scratches observed in photosimularion of each section were measured using software imageJ [18]. Rose diagrams were generated from these data (see S1 File) for each section using the ‘circular’ package of a statistical software R [19, 20].

Results

The teeth are preserved in both sides of the maxillae and dentaries of ZMNH M8961. However, the teeth in both maxillae are fragmentary, with buccal crown impressions of several left maxillary teeth being preserved in the matrix. The teeth are well-preserved in the posterior portion of the right dentary, with eight posterior adjoining teeth exposing their buccal view (Fig 1). A few teeth that are positioned more apical (dorsal) to adjacent teeth were probably functional when the animal lived and exhibited steeply inclined wear facets on their buccal sides (Fig 1b). Also, one tooth of the left dentary is well-preserved, exposing its lingual view. The dentary teeth are relatively small, with 6.4–6.7 mm mesiodistally, similar to those of other ankylosaurids, but smaller than those of nodosaurids [13]. Compared with other ankylosaurids, the teeth are slightly larger than those of Pinacosaurus granger (holotype AMNH 6523: 4 mm, ZPAL Mg D-II/1: 4–5 mm) [13, 21], and Euoplocephalus (AMNH 5405: 3–5 mm) [13], But smaller than those of Gobisaurus (9.5 mm) [22], and Saichania (PIN 3142/250: 7–8 mm) [13]. The crowns are buccolingually compressed, and leaf-shaped in buccal or lingual view, as in other ankylosaurs [23]. The dentary teeth of ZMNH M8961 bear 8–9 marginal denticles, similar to those of ‘Tianzhenosaurus’ (assigned to Saichania in Arbour and Currie [1]) [24], and Kunbarrasaurus (7–9 denticles) [25, 26], outnumber those of ‘Crichtonsaurus bohlini’ (IVPP V12745: 5–6 denticles) [27], juvenile Pinacosaurus granger (7 denticles) [28, 29], and Liaoningosaurus (7 denticles) [30, 31], but less than those of the holotype Pinacosaurus granger (AMNH 5405: 11 denticles). This denticles count of ZMNH M8961 is relatively low among ankylosaurs, which generally have 8–17 per tooth [23, 32, 33]. The buccal and lingual sides of crown is marked by longitudinal ridges extending ventrally from the denticles. The primary ridge positions almost in the center of the crown. The cingulum at the base of the crown is swollen, as in other ankylosaurs [23, 33]. Three highly worn teeth have very deep wear facet that occupies almost the entire buccal surface, similar to Hungarosaurus [13], and Zuul [33] and show clear contrast with the wear facets of Saichania (PIN 3142/250) that are more apically positioned [13], or the cases in juvenile Pinacosaurus granger [13, 28, 29], Liaoningosaurus [30, 31], and ‘Crichtonsaurus bohlini’ (IVPP V12745) [27], where little to no wear were observed on any of the teeth.

By examining photosimulated images of mold surfaces, it was confirmed that microwear was preserved in four teeth, which hereafter referred to as tooth A, B, C, and D (Fig 1b and 1h): buccal wear facets of two right dentary teeth (teeth A and B), the buccal surface of the right dentary tooth that does not have wear facet (tooth C), and the lingual surface of the left dentary tooth that do not have wear facet (tooth D). These tooth surfaces must have been affected by taphonomic processes to some extent as cracks were observed on the surface of the wear facet of the tooth B (Fig 1d). Taphonomic processes, however, tend to obliterate rather than create dental microwear [34], thus the observed orientation and density of scratches were unlikely to be affected by taphonomy.

The tooth that is positioned anterior to the tooth C (hereafter referred to as tooth E) also showed wear facet, however, its surface was likely chipped out postmortem as it did not show any dental microwear. Wear facets of tooth B and E extends almost the entire buccal side of a crown above the base of the cingulum. The basal portion of tooth A was embedded in the matrix and the entire exposed apical portion of its buccal surface formed a wear facet. Enamel-dentine interface on wear facets of Jinyunpelta was not clear as there is no visible step. Probably their enamel is very thin, in the photosimularion at the border of wear-facet (Fig 1c), the band of slightly shiny area was observed that is less than 0.1 mm thick, which probably is the layer of polished enamel.

The density of microwear features was low in surfaces without visible wear (tooth C and D: Fig 1f and 1h) compared with that in wear facets (Fig 1d and 1e), where the entire area was covered by numerous scratches. Microwear features on surfaces of tooth C and D were only scratches (Fig 1f and 1h). That of wear facets were mostly scratches but on the basal side of wear facets, there are some pit-like structures observed (Figs 2 and 3). The dental microwear of wear facet was probably produced by both attrition (tooth-tooth contact) and abrasion (tooth-food contact) whereas that of other surfaces was made solely by abrasion (tooth-food contact). Therefore, these difference between microwear features of wear facets and other surfaces meets the expectation that occlusal surface is much highly scratched than non-occlusal surface [35] and further confirming that observed scratches were not extensively affected by the postmortem taphonomic process.

(a) The buccal wear facet of the tooth B. (b) Dental microwear along the entire apicobasal axis of the wear facet that is enclosed by the black rectangle in Fig 2a. Scratch orientations were measured from five apicobasal sections (I-V) and rose diagrams were drawn to show orientations of scratches. Each section within a rose diagram represents 20 degrees and the length of each bar reflects the number of scratches oriented in that direction. Anatomical directions were shown in the rose diagram of section V. Numbers of measured scratches were 37, 42, 56, 49, and 40 for the section I to V respectively. (c) The close up of the middle region of the wear facet, where scratch orientations change apicobasally and is enclosed by the white rectangle in Fig 2b. Scale bars are 1 mm for (a) and (b) and 0.5mm for (c).

Fig 3 — Photosimulation of the buccal wear facet of tooth A taken by a 10× lens. Scratch orientations were measured from apical and basal sections and rose diagrams were drawn to show orientations of scratches. Numbers of measured scratches were 35 for the apical section and 52 for the basal section. For the explanation of a rose diagram see the caption of Fig 2. Scale bar represents 1mm.

Directions of scratches were more aligned on wear facets (Fig 1d and the lower half of Fig 1c) compared with that on surfaces without visible wear (tooth C and D: Fig 1e and 1f). The orientation of scratches changes between apicobasal positions within wear facets of teeth A and B. This orientation change can be observed clearer in the wear facet of tooth B compared with that of tooth A, because of its better preservation throughout the apicobasal axis (Fig 2). In the wear facet of tooth B, at the apical region, scratches were oriented apicomesial-distobasally about 40 degrees from the apicobasal axis (Fig 2). In the middle region, scratches of different orientations crossed each other; the ones that inclined mesially (anteriorly) about 40 degrees from the apicobasal axis and another one that inclined distally (posteriorly) about 60 degrees from the apicobasal axis. At the basal regions, Most scratches were almost horizontal, inclined distally (posteriorly) about 80 degrees from the apicobasal axis (Fig 2). In the wear facet of tooth A, scratches were inclined mesially (anteriorly) about 20 degrees from the apicobasal axis at the apical area of the wear facet (Figs 1c and 3). At the basal half of the wear facet, scratches of two orientations coexist, one that inclined mesially (anteriorly) about 30 degrees from the apicobasal axis that are located mostly in the mesial half and another one that inclined distally (posteriorly) about 60 degrees from the apicobasal axis that are located in the distal half (Fig 3).

Discussion and conclusions

Scratch orientation found in wear facets of Jinyunpelta teeth changed from mesially inclined ones at the apical position of wear facet to more distally inclined ones at the basal position, which is almost identical to that of a nodosaurid ankylosaur Hungarosaurus [12: Fig 6]. Therefore, the chewing jaw movement of these two taxa must be similar. The orientation of scratches, which inclines 20 to 40 degrees mesially from the apicobasal axis in the apical region of the wear facet indicates that occlusion starts with orthal and possibly slight proal movement in Jinyunpelta. The existence of two scratch orientations that cross each other at the middle region of the wear facet might reflect an abrupt shift of lower jaw movement from orthal to the backward and slightly upward direction. The scarcity of low-angled scratches in the apical region of dentary teeth indicates, during this backward traction, the pressure on the apical region of wear facet from the antagonist upper tooth was not as strong as that on the basal region of the wear facet. The dominance of the low-angled, mesiobasal-apicodistal oriented scratches at the basal region of the wear facet indicates that the chewing cycle ended with the orthopalinal (sensu Varriale [36]) movement of the lower jaw.

As stated by Mallon and Anderson [3] “The microwear signal in one area of a tooth often differed from that in another area of the same tooth”. In some dinosaurian taxa, the area within the wear facet that occluded with the antagonist tooth changes with the phase of chewing cycle. If the direction of jaw movements changes along with the phase of the chewing cycle (e.g. Leptoceratops and ankylosaurs with biphasal jaw movement), the orientation of dental microwear differs in different areas of wear facet [12, 36]. Therefore, preferably, observation of the entire apicobasal axis within a wear facet is needed to reconstruct the jaw movement of the entire chewing cycle. However, this is practically impossible in many cases as the preservation of the whole wear facet is rarely satisfactory to analyze dental microwear.

Scratches of Jinyunpelta are dense and fills the entire field of view (Fig 1d and 1e). Taphonomic processes tend to obliterate microwear features [34, 35], therefore these dense and aligned scratches are probably produced when the animal was alive. Although only qualitative comparison is possible, microwear were compared between Jinyunpelta and other ankylosaurs using figures published in previous studies of Ősi [12, 13] and Mallon and Anderson [3]. It should be noted that different imaging devices and magnifications were used for different studies, so the results of this comparison should be taken with caution. Scratches were scarcer in Hungarosaurus [12: Fig 5, 13: Fig 11A], Edmontonia [13: Fig 11F and 11H], Ankylosaurs [13: Fig 12D], and Gargoyleosaurus [13: Fig 12H] than Jinyunpelta. Pits were more dominant in Edmontonia [13: Fig 11E and 11G], anterior maxillary tooth of Euoplocephalus (AMNH5405) [13: Fig 12E], Saichania [13: Fig 12C], and Gargoyleosaurus [13: Fig 12H] compared with Jinyunpelta. Microwear of an isolated ankylosaurid tooth (TMP 1991.050.0014) [3: Fig 1] and maxillary tooth of Euoplocephalus (AMNH 5405) [13: Fig 12F] were dominated by dense and roughly aligned scratches that resemble the microwear of Jinyunpelta. These similarities and differences of dental microwear of Jinyunpelta and other ankylosaurs likely correspond to similarities and differences in their diets and jaw mechanism.

Among ankylosaurs, precise tooth-tooth occlusion was more widely seen among nodosaurids compared with ankylosaurids. Among ankylosaurids, the precise tooth occlusion was previously known only for the Late Cretaceous North American taxa (Fig 4) and the definite evidence of palinal jaw movement was known only for Euoplocephalus [11, 13]. The precise tooth-tooth occlusion with palinal jaw movement of Jinyunpelta confirmed in this study, however, indicates a sophisticated chewing jaw movement evolved much earlier among ankylosaurids, in the late Early (Albian) or early Late (Cenomanian) Cretaceous (Fig 4). It should be noted that, however, this conclusion is based on two teeth from one individual, therefore more studies on mid-Cretaceous ankylosaurids are awaited.

Fig 4 — The color of each genus name represents the continent they lived: red, Asia; orange, North America; green, Europe. Modified from Ősi et al. [13: Fig 15]. The phylogenetic relationship of ankylosaurs followed Zheng et al. [16].

This study is the first to show solid evidence of precise tooth-tooth occlusion in an Asian ankylosaur. Asian ankylosaurs had been known to exhibit none or small nearly horizontal apical wear facets [13]. Therefore, steep wear facets of dentary teeth of Jinyunpelta that cover the most area of buccal surface is unique among Asian ankylosaurs. The lack of sophisticated feeding adaptations in Asian ankylosaurs and its presence in Late Cretaceous ankylosaurs of Europe and North America, was suspected to have been reflecting habitat differences among different continents [13]. The finding that contemporaneous Asian ankylosaurs, Jinyunpelta and Gobisaurus, differ in their chewing systems, indicated that these differences reflect local habitat differences and/or dietary differences among closely related taxa. The finding of tooth occlusion and biphasal jaw mechanism in Jinyunpelta that is phylogenetically nested within Asian taxa without tooth occlusion indicates the evolution of a complex feeding mechanism likely occurred convergently twice among ankylosaurids and at least once among nodosaurids, which suggest feeding mechanism of ankylosaurs was highly plastic. Roughly contemporaneous emergence of palinal jaw movement within both ankylosaurids and nodosaurids during the late Early to the early Late Cretaceous (Fig 4) corroborates the idea that these functional novelties of ankylosaurs jaw movement were triggered by a global phenomenon. The emergence and radiation of angiosperms may be a candidate for such a global change [13], although future studies on the timing of changes in paleoflora in different localities and diet reconstructions of associated megaherbivores are needed to test this hypothesis.

Supporting information

S1 File. Orientations of scratches in apicobasal sections of wear facet of tooth A and B.

(XLSX)

Click here for additional data file.^{(12.9KB, xlsx)}

Acknowledgments

We thank the following people for participating fieldwork in 2013: S. Gu (ZMNH), C. Chen (Jinyun Museum), K. Miyata (Fukui Prefectural Dinosaur Museum), and several local farmers. We thank C. Yu, A. Liu, and Y. Sheng (ZMNH) for preparing the specimens and H. Sakaki (University of Tokyo) for help in molding dental impressions at ZMNH. We also thank the editorial work of A. R. Fiorillo (Perot Museum of Nature and Science) and thorough reviews of two reviewers, A. Ősi (Hungarian Academy of Sciences) and F. J. Varriale (King’s college) that significantly improved the manuscript.

Data Availability

All relevant data are within the paper and its Supporting information files.

Funding Statement

TK was funded by JSPS KAKENHI grant number 19J40003. WZ and XJ were funded by Chinese Natural Science Foundation (41602019). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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PLoS One. doi: 10.1371/journal.pone.0247969.r001

Decision Letter 0

Anthony R Fiorillo

14 Jan 2021

PONE-D-20-40068

Dental microwear of a basal ankylosaurine dinosaur, Jinyunpelta and its implication on evolution of chewing mechanism in ankylosaurs.

PLOS ONE

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Additional Editor Comments :

Both reviewers are of the opinion that this paper is a worthy contribution after revision. Each reviewer has provided very specific guidance on the manuscript itself, while also suggesting the use of English can use some polish. I encourage the authors to follow the reviewers' comments closely and that they resubmit to the journal at the appropriate time.

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Comments to the Author

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The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Partly

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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: No

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5. Review Comments to the Author

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Reviewer #1: This is an important work for a better understanding of ankylosaur feeding mechanism, and the results, presented here, widens our knowledge on the feeding characters of Mesozoic herbivores in general. I would be more than happy to see this manuscript published but before doing this, I strongly recommend to complete the work with the followings:

Main comments:

- The descriptive part of the Results section should be more detailed. The original Zheng et al. (2018) paper did not details the dentition since teeth in the holotype specimen cannot be observed. Based on this new specimen, I suggest to add a separated block with the description of the few individual teeth in the preserved section, and their comparision with some other Asian ankylosaurs (e.g. the contemporaneous Gobisaurus) would be very useful. What about with the dentary tooth anterior to tooth C? It seems that at least one toth is also preserved in the maxilla. Some words about it (preservation, relative size, worn, not worn, etc.) would be also useful.

- Nothing is written about the general macrowear patterns of the teeth. How is the enamel preserved on the teeth? Is there any information about the enamel-dentine interface (where is it flush or step)? How is the relative wear ratio between the individual dentary teeth (i.e. A, B, C)? All this information would help a lot to better understand the jaw mechanism of Jinyunpelta and that of ankylosaurids.

- Authors used 4 teeth in this work that have microwear features preserved, but microwear features have been described in the Results section only from tooth B and A. I understand that on the other teeth (C, D) scratches are much less, but still present, according to MS line 126. Perhaps some basic comparison of these features between the individual teeth and between the teeth of Jinyunpelta and those of other ankylosaurs (see some data in Mallon and Anderson 2014, Ősi et al. 2016) can be added, e.g. pit-scratch number and ratio, main scratch orientation. The free Microware softwer is very easy to use for this purpose. A rose diagram might be also added to simply numerically demonstrate the orientation of scratches from the different regions of the teeth. Authors state that on the teeth where only abrasive wear is present, microwear features are much less than on the teeth bearing wear due to occlusion. What kind of other differences can be observed between the microwear features of the two type of wear?

- The authors write that they used a confocal microscope for getting high resolution pictures on the details of the microwear features. Why do they not get and analyzed then 3D data of these images since in this technice, as written in the Material and Methods section, a vertical component („height data (Z position)”) is also measured? The main point of a confocal microscope is that a 3D model can be got from a surface texture and the software can generate various data (complexity, anisotropy, etc. see Ungar 2003, Winkler et al. 2017) for comparative purposes. In this form, the images taken by the confocal microscope do not yield more than well-prepared scanning images.

- A basic drawing on the preserved tooth rows and the position and extension of their wear facets would be very informative. Perhaps Fig. 2B could be a bit larger to see as much details from the tooth crowns as possible. Unfortunately, the pdf I’ve got for review contained very poor resolution figures…

Some small comments, typos and corrections have been added directly in the annotated pdf.

Reviewer #2: General Comments

The manuscript represents the results of important original research examining facet development and dental microwear in a specimen of the ankylosaurid Jinyunepelta. This study is a valuable contribution to the literature on jaw mechanics in Ankylosauria as it fills a gap in our understanding of the paleoecology, biogeography, and evolution of mastication in Asian members of this group. It is a natural successor to the work of Ősi and others 2017 and builds on the discoveries and conclusions of that publication. The work is worthy of publication. I find the methods sound but the manuscript requires revision in the text and supplied figures.

An important aspect of this manuscript is the presentation of evidence for biphasal motion from microwear in Jinyunepelta. However, microwear from only a single tooth of one individual convincingly displays striations that indicate both orthal and palinal jaw action. The authors mention evidence of additional palinal wear on their “Tooth A” from the same specimen but do not provide a figure that highlights this wear. Figure 1 does show wear from tooth A but most of the striations are tilted mesially and it is difficult to discern scratches that indicate the palinal motion mentioned in the text. The authors should address how they know the wear on tooth B is not an artifact of preservation by figuring the wear they describe is present on tooth A. The preservation of real wear on tooth B is partially corroborated by its similarity to previously published ankylosaurs; however, the authors should also give serious consideration to amending the text of their conclusions to recognize the tenuous nature of having microwear from just one specimen. Further details regarding suggestions for how they can strengthen their evidence are included in the more specific comments by line below (Lines 140-142 & 149-152 and Lines 192-197).

There are grammatical and typographical errors in the manuscript that would benefit from further editing during the revision process. I have made some editorial suggestions by line in my review, but they are not exhaustive because my primary goal was the scientific merit of the study.

Some of the text would be better served if it were moved to other sections of the manuscript (ex. methods, conclusions). I have made note of these suggestions for reorganization in the specific comments by line under “Text of Manuscript”. (Lines 71-83, Lines 83-85, Line 86, Lines 87-89)

Text of Manuscript

Lines 29-32 & Lines 213-216 “Parallel evolution of the biphasal jaw mechanism, which contemporaneously occurred among two lineages of ankylosaurs, ankylosaurids and nodosaurids, might reflect changes in paleoflora during the late Early to the early Late Cretaceous”. There is unfortunately little evidence to support this, and the authors should consider amending the language of the introduction and conclusion to suggest that this is only a possibility and not a certainty. There could be alternative factors that caused the change. Ősi et al. 2017 suggest this and make the more general uncertain statement in their conclusions that this could be a possibility. See their bullet point #6 on pages 565-566, “One possible reason for the appearance of these functional morphological novelties might be paleofloral change during the Cretaceous, but this cannot be supported at the moment.” The reason this cannot be supported is because it is beyond the scope of the research that is in these papers. Correlation and timing in the turnover of both the dinosaurian fauna and the paleoflora would be needed, and even then, that would only be circumstantial correlation and not direct evidence of relationship.

Line 42: Perhaps change “Among two main ankylosaurian” to “Between the two main ankylosaurian” Among is used for comparing objects greater than two.

Lines 45-46 “Not only diets but also jaw mechanism were implicated in ankylosaur dental microwear” I understand the intent of this sentence, but it could be stated more clearly, Try “In addition to diet, jaw mechanics are revealed via ankylosaur dental microwear”.

Lines 46-47 “Contrary to the expectation that ankylosaurs adopted simple orthal jaw movement due to their small and simple leaf-shaped teeth.” Who is expecting this and why? Please provide a reference for this expectation. Provide justification via referral to previously published literature for this statement other than the shape and size of their teeth. There is nothing inherent about small teeth that necessitates orthal mastication. However, simple leaf shaped teeth have previously been interpreted to indicate orthal mastication. Please provide a reference for this statement. There are previous authors who have suggested that Ankylosaurs chewed through orthal mastication (Orthal pulping). References in reference #10 should help. Also see Weishampel & Jianu, 2000 and Weishampel and Normal, 1989. Additional text may not be necessary, only referral to publications that claimed orthal mastication.

Lines 55-56 “Within these groups with tooth occlusion, palinal jaw movement evolved convergently several times.” This sentence seems redundant as it says basically the same thing as the previous sentence. Perhaps remove it to be more concise. Or if the authors intended further convergence within each of these groups perhaps connecting it with the previous sentence by saying “and within each of these groups tooth occlusion and palinal movement appears to have evolved several times.”

Lines 56-57: “An Early Cretaceous nodosaurid Sauropelta might have been adopted palinal jaw movements” Remove ‘been’ from this sentence.

Line 57: reverse the order of these words “be also”

Lines 66-68. This is a cumbersome sentence; try rewording to something like; “The dental microwear of more ankylosaur specimens is needed to determine if the many convergences found buy Ősi and others 2017 are the true pattern of evolution or an artifact of sample size.”

Line 70: Change “were demanded” to “are needed”

Lines 71-83: The text on these lines describes the specimen and the condition of the teeth. They therefore belong more appropriately at the beginning of the materials and methods section as a description of the material examined in this analysis.

Line 79: Change “Lately” to “Recently”

Line 86: Was it the intention of the authors to indicate that Asian forms rarely showed high angle and not low-angle? In their paper Ősi and others 2017 state: “In Asian ankylosaurids (e.g. Gobisaurus, Pinacosaurus spp., Saichania, Tarchia) tooth wear is either restricted to the apical cusps slightly exposing the underlying dentine, or it is more extensive basally as a smooth surface, yet does not penetrate the thin enamel. Steep wear facets, similar to those seen in nodosaurids, are present neither on lingual/labial sides of the crown, nor on the cingulum.”. They also note that Gobisaurus and Tarchia have low angle facets.

Lines 83-85: “Further, a few teeth of the right dentary that positioned more apical (dorsal) to adjacent teeth, which were probably functional when the animal lived, exhibited steeply inclined wear facets on their buccal sides (Fig 1b).” This statement is more appropriately placed in the results section.

Line 86: “This contradicts with the notion of Ősi et al. [10] that Asian ankylosaurids rarely showed low-angled apical wear, implying the absence of precise tooth occlusion.” This sentence might be better reserved for the discussion and conclusions section as it is follows from what microwear and facet shape look like on Jinyunpelta.

Lines 87-89: “In this study, therefore, we observed the dental microwear of Jinyunpelta to deduce its jaw movement and to reconstruct the evolution of the feeding mechanism in Asian and Cretaceous ankylosaurids.” Once lines 71-85 have been moved to the sections suggested above, lines 87-89 might be better placed after line 70. This line is a natural continuation of the ideas the authors have been setting up in the introduction and the purpose of their work. Try removing the word “therefore” from the sentence to make it concise.

Line 107: There appear to be 8 visible dentary teeth in Fig 1b, perhaps placing a marker or asterisk above or below the teeth in the figure to indicate which of the 6 were molded.

Line 109: Change “Preservation of dental impressions” to “The presence of microwear”

Line 110” How did the authors determine what satisfactory preservation is? Please provide a small description of what that means and what criteria was used to determine if preservation was satisfactory?

Line 121: Perhaps altering the beginning of this sentence will make it more concise. “Previous work has shown that scratch orientation differs apicobasally…”

Line 127: Perhaps change (Fig. 1) to (Fig. 1b,f) because those are the figures that show the identification of the teeth examined.

Line 134: Perhaps indicating this in the text by telling the reader with referral to figures. For instance, this can be easily accomplished with only a slight change to line 134 to “The density of scratches was low in non-wear facets (Fig. 1e,g) and high in wear facets (Fig 1c,d).

Line 136-137: “Therefore, this difference in microwear densities meets the expectation” What expectation are being referred to here? This can be as simple as quoting and adding a reference for this. If it is the same as (reference 15) then the authors could reiterate that reference for this sentence.

Line 139: Perhaps change (Fig. 1) to be more specific like the suggestion for line 134 above.

Lines 140-142 & 149-152: “This orientation change can be observed clearer in the wear facet of tooth B compared with that of tooth A, because of its better preservation throughout the apicobasal axis (Fig 2).” “At the basal half of the wear facet, preservation of microwear was not as good as the apical half, but it seemed scratches of two orientations coexist, one that inclined mesially (anteriorly) about 30 degrees from the apicobasal axis and another one that inclined distally (posteriorly) about 60 degrees from the apicobasal axis” The authors should include in Fig 2 whatever images they have of photosimulations that depict microwear on the basal wear facet of tooth A showing (posterior) palinal motion. Despite the poor preservation of tooth A, wear from this tooth is important evidence that is missing from this publication. Currently only one tooth is figured (Tooth B) with clear indications of biphasal motion. The reader is required to trust that Tooth A also contains scratches that indicate palinal motion. Therefor the notion that biphasal jaw action is present in Jinyunepelta is based on one tooth from one specimen. That is tenuous evidence and would be more convincing if the authors depicted any other teeth from this specimen that supports palinal motion. If the claim is made that there are two sets of scratches visible on tooth A then images can be provided of what is seen that support the statement, no matter how poor the preservation might be.

Line 162: Perhaps remove “less” to be more concise.

Line 163: “facet and more inclined” change to “facet to more distally inclined”

Line 167: “occlusion start with orthal movement” or it may mean slight proall + orthal motion

Line 169: “backward and slightly upward direction” This type of motion has been referred to as orthopalinal by several authors Varriale, (2016), Mallon and Anderson (2014) & Nabavizadeh (2020)

• Nabavizadeh A. New reconstruction of cranial musculature in ornithischian dinosaurs: implications for feeding mechanisms and buccal anatomy. The Anatomical Record. 2020;303: 347–362. doi:10.1002/ar.23988

Line 183-184 “These taxa, including Jinyunpelta, also resemble in their chewing manner that adopted biphasal jaw movement.” This sentence is difficult to understand, try rephrasing it to be clearer.

Line 184-185 “Scratches of Jinyunpelta are much denser than other ankylosaurs that fills the entire field of view and are almost countless” Can the authors provide any quantitative defense of this statement? For example, number per unit area. Alternatively, they could qualitatively discuss why they think this is real by direct comparison with figures from published results of other ankylosaurs and why it is not an artifact of preservation or taphonomy. The sentence is also difficult to understand try using another word than countless, perhaps “too numerous” would be a better choice.

Lines 192-197: As detailed above, only one tooth from one specimen shows evidence of biphasal motion. This is not enough evidence for solid confirmation of biphasal motion. Perhaps provide more evidence of figures from tooth A that help solidify the claims of the manuscript and/or amend the language of the text to be more uncertain by suggesting that microwear from more individuals of Jinyunpelta are necessary to confirm this result.

Figures and Figure Captions

Figure 1:

• Text and abbreviations in figure are small and difficult to read. Please consider making the text larger or bolded for visibility. Some text does not stand out well against the photographs. Perhaps increasing the font size and bolding the letters will help. The authors could also try adding a white shadow behind the black text to make it stand out.

• The text above many of the scale bars is illegible because it does not stand out against the background of the photograph. Please make the text larger and bolder or place the scale bar dimensions in the figure captions for each sub-letter.

• (a) does not seem like an exactly right lateral view of the specimen but one that is offset somewhat to be a rostrolateral.

• Perhaps increasing the size of the dots in the lines or changing them to dashes to make them more visible.

• Add rectangles to (c) and (d) to show the location of the 100x photosimulations in the 10x images.

Figure 2:

• Placing a scale bar in a) would be helpful. It would be instructive to have scale bars in (b) and (c) as well

• In figure 2 a) is bolded but b) and c) are not. Bold them so that these sub-figure labels have greater visibility and to be consistent among them.

Figure 3:

• The authors may have misinterpreted the double-colored bars in figure 3 compared to what is depicted in a similar figure in Ősi et al. 2017. In Ősi et al. 2017 orthal (dorsal) movement of the dentary is green and palinal (posterior) movement is blue. When they are present together this indicates biphasal because orthal is one phase and palinal is the other phase (See Ősi et al. 2017, page 563, under jaw mechanisms read their section 3). Figure 3 of this manuscript is showing grey as orthal and black as biphasal which is redundant because one of the phases of biphasal motion is orthal. Perhaps change grey and black to be orthal and palinal or color the entire bar of these ankylosaurs to be black for biphasal.

• Placing the labels Ankylosauridae and Nodosauridae to the side of their respective branches rather than over the branches would make these labels more readable.

References

Some of the references have all major words capitalized but others do not. Perhaps review the references list to standardize citations to a common formatting.

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Reviewer #1: Yes: Attila Ősi

Reviewer #2: Yes: Frank J. Varriale

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PLoS One. 2021 Mar 10;16(3):e0247969. doi: 10.1371/journal.pone.0247969.r002

Author response to Decision Letter 0

15 Feb 2021

Main comments:

- The descriptive part of the Results section should be more detailed. The original Zheng et al. (2018) paper did not details the dentition since teeth in the holotype specimen cannot be observed. Based on this new specimen, I suggest to add a separated block with the description of the few individual teeth in the preserved section, and their comparison with some other Asian ankylosaurs (e.g. the contemporaneous Gobisaurus) would be very useful. What about with the dentary tooth anterior to tooth C? It seems that at least one tooth is also preserved in the maxilla. Some words about it (preservation, relative size, worn, not worn, etc.) would be also useful.

We wrote a new section that describes Jinyunpelta‘s dentitions at the beginning of the Results section. We compared tooth size and denticle number with that of other ankylosaurids (lines 142-161). The tooth anterior to the tooth C show wear facet but it does not preserve microwear, probably it surface was chipped out postmortem, we added an explanation about this tooth (lines 170-171). The teeth in both maxillae are fragmentary, with only buccal crown impressions of several left maxillary teeth being preserved in the matrix (lines 136-138), thus we could not obtain enough information for maxillary tooth.

- Nothing is written about the general macrowear patterns of the teeth. How is the enamel

preserved on the teeth? Is there any information about the enamel-dentine interface (where is it ﬂush or step)? How is the relative wear ratio between the individual dentary teeth (i.e. A, B, C)? All this information would help a lot to better understand the jaw mechanism of Jinyunpelta and that of ankylosaurids.

We wrote sentences in the Results section to describe macrowear and enamel-dentine interface of Jinyunpelta as follows (lines 170-177). “The tooth that is positioned anterior to the tooth C (hereafter referred to as tooth E) also showed wear facet, however, its surface was likely chipped out postmortem as it did not show any dental microwear. Wear facets of tooth B and E extends almost the entire buccal side of a crown above the base of the cingulum. The basal portion of tooth A was embedded in the matrix and the entire exposed apical portion of its buccal surface formed a wear facet. Enamel-dentine interface on wear facets of Jinyunpelta was not clear as there is no visible step. Probably their enamel is very thin, in the photosimularion at the border of wear-facet (Fig. 1c), the band of slightly shiny area was observed that is less than 0.1 mm thick, which probably is the layer of polished enamel”

- Authors used 4 teeth in this work that have microwear features preserved, but microwear

features have been described in the Results section only from tooth B and A. I understand that on the other teeth (C, D) scratches are much less, but still present, according to MS line 126. Perhaps some basic comparison of these features between the individual teeth and between the teeth of Jinyunpelta and those of other ankylosaurs (see some data in Mallon and Anderson 2014, Ősi et al. 2016) can be added, e.g. pit-scratch number and ratio, main scratch orientation. The free Microware software are very easy to use for this purpose. A rose diagram might be also added to simply numerically demonstrate the orientation of scratches from the diﬀerent regions of the teeth. Authors state that on the teeth where only abrasive wear is present, microwear features are much less than on the teeth bearing wear due to occlusion. What kind of other diﬀerences can be observed between the microwear features of the two type of wear?

We described and compare microware feature Jinyunpelta and other ankylosaurs (lines 245-259). Microwears of wear facets and other surfaces were compared in more detail (lines 178-182). We also made rose diagrams for tooth A and B to visually show how scratch orientations change along the vertical axis (Fig. 2 and 3).

By using the word “non-wear facet”, we may have misunderstood as if these surfaces have visible macrowear due to abrasion. Although at the microscopic level these surfaces have scratches due probably to abrasion, we used “non-wear facet” just to indicate the surface outside of wear facet or the surface of a tooth without wear facet. To avoid this misunderstanding, we reworded all “non-wear facet” in the manuscript.

component („height data (Z position)”) is also measured? The main point of a confocal microscope is that a 3D model can be got from a surface texture and the software can generate various data (complexity, anisotropy, etc. see Ungar 2003, Winkler et al. 2017) for comparative purposes. In this form, the images taken by the confocal microscope do not yield more than well-prepared scanning images.

We aimed to apply DMTA analysis to Jinyunpelta when scanned by a confocal microwear. However, we found DMTA analysis needs extremely good preservation. When a 10x lens was used for scanning, there are lots of noises on 3D images, which made it impossible to analyze. Using a 100x lens, we can get a good 3D image, but it requires superb preservation of the fossil that is not the case for our specimen (image of x100 lens is equivalent in its pixel resolution to about x700 image of SEM). However, we found photosimulation images we got were good enough to conduct conventional 2D dental microwear analysis and write this manuscript. We would love to look for well-preserved specimens of ankylosaurs and conduct DMTA analysis in the future.

We enlarged Fig. 2b and also added a line drawing of Fig. 2b as Fig. 3c.

Some small comments, typos and corrections have been added directly in the annotated pdf.

We checked all corrections on the PDF files and addressed all of them. In the following, we describe our revisions, which are not simple typo corrections.

perhaps some basic data should be added, i.e. it is an ankylosaur, form which age and locality.

The sentence was added “Jinyunpelta sinensis is a basal ankylosaurine dinosaur excavated from the mid Cretaceous Liangtoutang Formation of Jinyun County, Zhejiang Province, China ” (lines 20-21).

and in the European Hungarosaurus as well, see Ősi et al. 2014, 2016.

The sentence was rewritten from “Among ankylosaurids, the biphasal jaw movement was previously only known from the Late Cretaceous North American taxa,” to “The biphasal jaw movement was widely observed among nodosaurids, among ankylosaurids, it was previously only known from the Late Cretaceous North American taxa, and not known among Asian ankylosaurids.” (lines 28-30).

Would be good to specify it better with definitive ages based on fossils

Rewritten from “adaptations emerged among ankylosaurids much earlier than previously thought.” to “much earlier (during Albian or Cenomanian) than previously thought (during Campanian)”. (lines 31-32)

Is the exact number, even the minimum number of individuals unknown? Or there is five associated/articulated specimens, plus isolated material?

Rewritten from “more than five individuals” to “five associated specimens　and isolated materials of Jinyunpelta” (lines 82-83).

I do not think that the results, presented here, contradict with the notion of Ősi et al., just simply shows that these type of wear facets are rare but present in some asian ankylosaurs.

This sentence was deleted.

these pixel size is not the same as written in lines

These are pixel numbers for images we obtained from our confocal microscope. It may be changed during figure making, uploading, and so on.

This "non-wear facet" phrase is controversial to me suggesting that there were no wear at all. However, this is not the case, since even if there was no occlusion of the upper and lower teeth, there should have been at least tooth-food contact.

So, I may suggest to use simply "wear facet" for this, or differentiate them as "attritive wear facet" and "abrasive wear facet".

We did not find visible wear facet or visible wear on these surfaces. Scratches were observed only by microscope. As suggested “non-wear facet” is misleading so we avoided using this term throughout the manuscript.

During attrition both tooth-tooth and tooth-food contacts play a role since both is related to food processing.

Rewritten from “by attrition (tooth-tooth contact)” to “by both attrition (tooth-tooth contact) and abrasion (tooth-food contact)”. (lines 182-183)

Please add here, e.g. compare Fig. 1d and Fig.1e

The sentence was rewritten from “. Directions of scratches were more aligned on wear facets compared with non-wear facets (Fig1).” to “Directions of scratches were more aligned on wear facets (Fig. 1d and the lower half of Fig. 1c) compared with that on surfaces without visible wear (tooth C and D: Fig. 1e, f).” (lines 188-189)

I think these scratchere are not really inclined, but simply oriented. So, I suggest to add a precize direction of the scratches, in this case: scratches are oriented apicomesial-distobasally about 30 degrees.

Rewritten as “scratches were oriented apicomesial-distobasally about 40 degrees from the apicobasal axis”. (line 193)

But why? This type of movement has allowed contact between the apical region of one tooth and the basal part of the occluding tooth, resulting in the low-angled scratches at the base (eroded cingular region) of the wear facet.

We assumed “During this backward traction, the apical region of wear facets did not have contact with the antagonist tooth.” Because we could not find many horizontal scratches on the apical region of dentary teeth. However, as the reviewer pointed out apical region must have contacted with the basal region of the antagonist tooth. So we rewrite it as “The scarcity of low-angled scratches in the apical region of dentary teeth indicates, during this backward traction, the pressure on the apical region of wear facet from the antagonist upper tooth was not as strong as that on the basal region of the wear facet. ” (lines 230-233).

Please, rephrase.

We rewrite “the evolution of a complex feeding mechanism could be evolved easily among ankylosaurs.” to “the evolution of a complex feeding mechanism likely occurred convergently twice among ankylosaurids and at least once among nodosaurids, which suggest feeding mechanism of ankylosaurs was highly plastic”. (lines 282-284)

Please, indicate (perhaps on Fig part C and D) from which part the wear facet are these 100x images.

The change was made in Fig. 1 as suggested.

Scale bar for these figure parts would be very useful.

Scale bars were added to Fig. 2.

Reviewer #2: General Comments

mention evidence of additional palinal wear on their “Tooth A” from the same specimen but do not provide a figure that highlights this wear. Figure 1 does show wear from tooth A but most of the striations are tilted mesially and it is difficult to discern scratches that indicate the palinal motion mentioned in the text. The authors should address how they know the wear on tooth B is not an artifact of preservation by figuring the wear they describe is present on tooth A. The preservation of real wear on tooth B is partially corroborated by its similarity to previously published ankylosaurs; however, the authors should also give serious consideration to amending the text of their conclusions to recognize the tenuous nature of having microwear from just one specimen. Further details regarding suggestions for how they can strengthen their evidence are included in the more specific comments by line below (Lines 140-142 & 149-152 and Lines 192-197).

We added the figure of tooth A as figure 3 and apicobasal change of scratch orientation was analyzed for both tooth A and B. We also added caution that the conclusion of this study was drawn only from two teeth of one specimen and future studies on this topic are awaited. (lines 266-267).

We corresponded to all suggestions given, please see below

We moved all sections as suggested, please see below.

Text of Manuscript

We have deleted this sentence from the abstract and rewrite the last part of the manuscript to express that more studies are needed to prove the coevolution of paleoflora and megaherbivore dinosaurs as “Roughly contemporaneous emergence of palinal jaw movement within both ankylosaurids and nodosaurids during the late Early to the early Late Cretaceous (Fig 4) corroborates the idea that these functional novelties of ankylosaurs jaw movement were triggered by a global phenomenon. The emergence and radiation of angiosperms may be a candidate for such a global change [13], although future studies on the timing of changes in paleoflora in different localities and diet reconstructions of associated megaherbivores are needed to test this hypothesis..” (lines 284-290)

Line 42: Perhaps change “Among two main ankylosaurian” to “Between the two main

ankylosaurian” Among is used for comparing objects greater than two.

Change was made following the suggestion (line 44).

Lines 45-46 “Not only diets but also jaw mechanism were implicated in ankylosaur dental　microwear” I understand the intent of this sentence, but it could be stated more clearly, Try “In addition to diet, jaw mechanics are revealed via ankylosaur dental microwear”.

This sentence was rewritten following the suggestion (line 47-48).

Following the suggestion, Weishampel & Jianu (2000), Weishampel and Norman (1989), and Hwang (2005) were cited (line 49).

Lines 55-56 “Within these groups with tooth occlusion, palinal jaw movement evolved

convergently several times.” This sentence seems redundant as it says basically the same thing as the previous sentence. Perhaps remove it to be more concise. Or if the authors intended further convergence within each of these groups perhaps connecting it with the previous sentence by saying “and within each of these groups tooth occlusion and palinal movement appears to have evolved several times.”

This sentence was removed as suggested.

Lines 56-57: “An Early Cretaceous nodosaurid Sauropelta might have been adopted palinal jaw movements” Remove ‘been’ from this sentence.

Line 57: reverse the order of these words “be also”

Changes were made following the suggestions (line 57 and 58).

Lines 66-68. This is a cumbersome sentence; try rewording to something like; “The dental

microwear of more ankylosaur specimens is needed to determine if the many convergences found buy Ősi and others 2017 are the true pattern of evolution or an artifact of sample size.”

This sentence was rewritten as suggested (lines 66-68).

Line 70: Change “were demanded” to “are needed”

This word was changed as suggested (line 70).

These lines were moved to the materials and methods section (line 75-92).

Line 79: Change “Lately” to “Recently”

Changed as suggested (line 87).

Yes, we miswrote “high” as “low”. This sentence was deleted to correspond to other comments.

Lines 83-85: “Further, a few teeth of the right dentary that positioned more apical (dorsal) to

adjacent teeth, which were probably functional when the animal lived, exhibited steeply inclined wear facets on their buccal sides (Fig 1b).” This statement is more appropriately placed in the results section.

This sentence was moved to the result section (lines 139-141).

Thank you for the suggestion. Adding this sentence to the conclusion section may be redundant because in the conclusion section there is a sentence “Therefore, steep wear facets of dentary teeth of Jinyunpelta that cover the most area of the buccal surface is unique among Asian ankylosaurs”. So, we simply removed this sentence.

Lines 87-89: “In this study, therefore, we observed the dental microwear of Jinyunpelta to deduce its jaw movement and to reconstruct the evolution of the feeding mechanism in Asian and Cretaceous ankylosaurids.” Once lines 71-85 have been moved to the sections suggested above, lines 87-89 might be better placed after line 70. This line is a natural continuation of the ideas the authors have been settng up in the introduction and the purpose of their work. Try removing the word “therefore” from the sentence to make it concise.

We followed this suggestion, moved sentences and deleted “therefore” (lines 70-72).

Line 107: There appear to be 8 visible dentary teeth in Fig 1b, perhaps placing a marker or asterisk above or below the teeth in the figure to indicate which of the 6 were molded.

Asterisks were added above the teeth that were molded in Fig. 1c that is newly added line drawing of Fig. 1b, and were mentioned in the caption of Fig. 1 (line 96).

Line 109: Change “Preservation of dental impressions” to “The presence of microwear”

Changed as suggested (line 115).

The explanation “(e.g. the existence of scratches and absence of large crack)” was added (lines 116-117).

Line 121: Perhaps altering the beginning of this sentence will make it more concise. “Previous work has shown that scratch orientation differs apicobasally…”

Line 127: Perhaps change (Fig. 1) to (Fig. 1b,f) because those are the figures that show the

identification of the teeth examined.

Changes were made as suggested (lined 126 and 163).

Line 134: Perhaps indicating this in the text by telling the reader with referral to figures. For

instance, this can be easily accomplished with only a slight change to line 134 to “The density of scratches was low in non-wear facets (Fig. 1e,g) and high in wear facets (Fig 1c,d).

Line 136-137: “Therefore, this difference in microwear densities meets the expectation” What

expectation are being referred to here? This can be as simple as quoting and adding a reference for this. If it is the same as (reference 15) then the authors could reiterate that reference for this sentence.

I added words “meets the expectation that occlusal surface is much highly scratched than non-occlusal surface” and added the citation Teaford (2007) that visualized the difference between dental microwear of non-occlusal and occlusal surfaces of mammals and how it is lost due to taphonomic processes (lines 185-187).

Line 139: Perhaps change (Fig. 1) to be more specific like the suggestion for line 134 above.

Changes were made accordingly (lines 188-189).

We added a new figure (Fig. 3) to show the scratch orientation of tooth A and analyzed the scratch orientation of the upper and lower half to show its change along apicobasal orientation.

Line 162: Perhaps remove “less” to be more concise.

Line 163: “facet and more inclined” change to “facet to more distally inclined”

Line 167: “occlusion start with orthal movement” or it may mean slight proall + orthal motion

Changes were made according to suggestions (lines 223, 224, and 228).

Line 169: “backward and slightly upward direction” This type of motion has been referred to as orthopalinal by several authors Varriale, (2016), Mallon and Anderson (2014) & Nabavizadeh (2020)

Rewritten as “… the chewing cycle ended with the orthopalinal (sensu Varriale [36]) movement of lower jaw” (lines 234-235).

Line 183-184 “These taxa, including Jinyunpelta, also resemble in their chewing manner that

adopted biphasal jaw movement.” This sentence is difficult to understand, try rephrasing it to be clearer.

I rewrote this section to make a more detailed comparison between the microwear of Jinyunpelta and other ankylosaurs. Consequently, this sentence was deleted.

It is hard to conduct quantitative comparisons between Jinyunpelta and other ankylosaurids, for this revision as we do not have molds of other ankylosaurids and comparisons between images taken by a different type of microscope (optical, scanning electron, and confocal laser) may not be appropriate. Therefore, we visually compared microwear images of Jinyunpelta and other ankylosaurs qualitatively and added a section in lines 245-259.

As written above, we added the figure and analysis of tooth A, also we stated the caution as follows “It should be noted, however, that this conclusion is based on two teeth from one individual, therefore more studies on mid-Cretaceous ankylosaurids are awaited.” (lines 266-267)

Figures and Figure Captions

Figure 1:

• The text above many of the scale bars is illegible because it does not stand out against the

background of the photograph. Please make the text larger and bolder or place the scale bar

dimensions in the figure captions for each sub-letter.

• (a) does not seem like an exactly right lateral view of the specimen but one that is offset

somewhat to be a rostrolateral.

• Perhaps increasing the size of the dots in the lines or changing them to dashes to make them more visible.

• Add rectangles to (c) and (d) to show the location of the 100x photosimulations in the 10x

images.

Texts were enlarged and changed to bold font. White rims were added to black texts and black rims were added to white texts. Scale bars were heightened and black rims were added. Scale bar dimensions were removed from the figure and mentioned in the caption. Dot lines were enlarged and rectangles were added to (c) and (d) to indicate areas of 100x photosimulations. The caption was changed from “right lateral” to “right rostrolateral” in line 90.

Figure 2:

• Placing a scale bar in a) would be helpful. It would be instructive to have scale bars in (b) and (c) as well

• In figure 2 a) is bolded but b) and c) are not. Bold them so that these sub-figure labels have

greater visibility and to be consistent among them.

Scale bars were added to Fig. 2b and c and within figure texts were bolded.

Figure 3:

• Placing the labels Ankylosauridae and Nodosauridae to the side of their respective branches rather than over the branches would make these labels more readable.

In the legend of figure 3, “biphasal” was rewritten as “palinal” and the placement and direction of “Ankylosauridae” and “Nodosauridae” were changed following the suggestions.

References

Some of the references have all major words capitalized but others do not. Perhaps review the references list to standardize citations to a common formating.

All citations were checked to standardize the format.

Attachment

Submitted filename: Response to the reviewers.docx

Click here for additional data file.^{(42.5KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0247969.r003

Decision Letter 1

Anthony R Fiorillo

17 Feb 2021

Dental microwear of a basal ankylosaurine dinosaur, Jinyunpelta and its implication on evolution of chewing mechanism in ankylosaurs.

PONE-D-20-40068R1

Dear Dr. Kubo,

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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Reviewers' comments:

PLoS One. doi: 10.1371/journal.pone.0247969.r004

Acceptance letter

Anthony R Fiorillo

19 Feb 2021

PONE-D-20-40068R1

Dental microwear of a basal ankylosaurine dinosaur, Jinyunpelta and its implication on evolution of chewing mechanism in ankylosaurs.

Dear Dr. Kubo:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 File. Orientations of scratches in apicobasal sections of wear facet of tooth A and B.

(XLSX)

Click here for additional data file.^{(12.9KB, xlsx)}

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Data Availability Statement

All relevant data are within the paper and its Supporting information files.

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Dental microwear of a basal ankylosaurine dinosaur, Jinyunpelta and its implication on evolution of chewing mechanism in ankylosaurs

Tai Kubo

Wenjie Zheng

Mugino O Kubo

Xingsheng Jin

Roles

Abstract

Introduction

Materials and methods

Fig 1. Dental microwear of Jinyunepelta.

Results

Fig 2. Changes in the orientation of scratches along the apicobasal axis of wear facet of posterior right dentary tooth B.

Fig 3. Changes in the orientation of scratches along the apicobasal axis of wear facet of posterior right dentary tooth A.

Discussion and conclusions

Fig 4. Evolution of chewing mechanism in ankylosaurs.

Supporting information

Acknowledgments

Data Availability

Funding Statement

References

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Anthony R Fiorillo

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Author response to Decision Letter 0

Decision Letter 1

Anthony R Fiorillo

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Acceptance letter

Anthony R Fiorillo

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Supplementary Materials

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PERMALINK

Dental microwear of a basal ankylosaurine dinosaur, Jinyunpelta and its implication on evolution of chewing mechanism in ankylosaurs

Tai Kubo

Wenjie Zheng

Mugino O Kubo

Xingsheng Jin

Roles

Abstract

Introduction

Materials and methods

Fig 1. Dental microwear of Jinyunepelta.

Results

Fig 2. Changes in the orientation of scratches along the apicobasal axis of wear facet of posterior right dentary tooth B.

Fig 3. Changes in the orientation of scratches along the apicobasal axis of wear facet of posterior right dentary tooth A.

Discussion and conclusions

Fig 4. Evolution of chewing mechanism in ankylosaurs.

Supporting information

Acknowledgments

Data Availability

Funding Statement

References

Decision Letter 0

Anthony R Fiorillo

Roles

Author response to Decision Letter 0

Decision Letter 1

Anthony R Fiorillo

Roles

Acceptance letter

Anthony R Fiorillo

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

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