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ABSTRACT Among the least studied portion of the pterosaur skeleton is the palate, which tends to be poorly preserved and commonly only visible from one side (the ventral portion). Even in

well-preserved specimens, the bones tend to be fused, with the limits of individual palatal elements obscured. To shed new light on this region, we employed advanced X-ray imaging techniques

on the non-pterodactyloid _Kunpengopterus_ (Wukongopteridae), and the pterodactyloids _Dsungaripterus_ (Dsungaripteridae), _Hongshanopterus_ (Istiodactylidae), and _Hamipterus_

(Hamipteridae). Our analyses revealed the presence of sutures between palatal bones in _Dsungaripterus and Kunpengopterus_, which resulted in different interpretations of the relation

between palatine, ectopterygoid, and pterygoid, leading to a new identification of the palatal openings. Furthermore, our study shows six main observations such as the variation of the angle

between the palatine rami and the variation in the relative sizes of the palatal openings. We also point out that the presence of a maxillopalatine fenestra (previously identified as

postpalatine fenestra), is unique within Diapsida. Although much more work needs to be done, we showed that advanced X-ray imaging techniques open a window for understanding pterosaur

cranial anatomy and provide a new perspective for investigating the evolutionary history of these flying reptiles. SIMILAR CONTENT BEING VIEWED BY OTHERS AVIALAN-LIKE BRAIN MORPHOLOGY IN

_SINOVENATOR_ (TROODONTIDAE, THEROPODA) Article Open access 10 February 2024 ONTOGENETIC VARIATION IN THE SKULL OF _STENOPTERYGIUS QUADRISCISSUS_ WITH AN EMPHASIS ON PRENATAL DEVELOPMENT

Article Open access 01 February 2022 MORPHOLOGY OF _PALAEOSPONDYLUS_ SHOWS AFFINITY TO TETRAPOD ANCESTORS Article 25 May 2022 INTRODUCTION Pterosaurs, the first vertebrates to achieve

powered flight, have been a subject of fascination for scientists for decades. Identifying individual bones in the skull of extinct clades can be challenging given the lack of living

descendants for comparison. This challenge is particularly challenging for pterosaurs, a group of extinct flying reptiles that lived during the Mesozoic Era. However, an accurate

interpretation of their anatomy is the fundamental prerequisite for a wide range of studies, including phylogeny, ecology, biology, and functional morphology1,2,3,4,5,6,7,8,9. As generally

known the normal condition of preservation regarding pterosaurs is that of crushed or flattened specimens and three-dimensionally preserved material is exceedingly rare (e.g.,10,11).

Additionally, cranial bones, including the palate, often exhibit fusion. Consequently, gaining an understanding of detailed skull architecture, especially the conformation of the palate in

pterosaurs, has always been difficult. Furthermore, the identification of the limits of several elements generally still lacks consensus12,13,14. Questions regarding the construction of the

pterosaur palate have been the subject of debate since the 19th century15,16,17,18,19,20,21,22. While several new specimens have come to light over the

years10,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37, the lack of clarity regarding the boundaries between different palatal bones has resulted in an ongoing debate38,39,40,41,42,43,44,45.

Recently, a specimen of the Jurassic pterosaur _Dorygnathus banthensis_, featuring several unfused cranial bones, presented a very different configuration of the palatal portion of the

maxilla13. This discovery led to a reinterpretation of the palate13 with broad implications (e.g., refs. 14,38,41). However, controversy persists, particularly concerning the extent and

shape of the palatines and whether a single, generalized palatal pattern configuration can be applied to Pterodactyloidea23,38,40,41,42,43. Here we review the palate structure in various

pterosaur taxa (Table 1), including both pterodactyloids and non-pterodactyloids. We introduce new insights based on CT-scans and CL-scans of _Kunpengopterus_ (Wukongopteridae),

_Hongshanopterus_ (Istiodactylidae), _Hamipterus_ (Hamipteridae), and _Dsungaripterus_ (Dsungaripteridae). Our findings shed light on the boundaries of several palatal bones and propose a

new configuration for the palate of numerous pterodactyloid clades. Additionally, we reinterpret distinct configurations for the palate of several non-pterodactyloid clades, offering

insights into potential evolutionary trends of this region in pterosaurs. MATERIALS AND METHODS The objective of this study was to examine the morphology and internal structure of palatal

bones using X-ray micro-computed tomography and laminography. The specimens were scanned using the following different types of X-ray instruments, depending on their different preservation

and size. X-ray micro-computed tomography (CT): The specimen of _Dsungaripterus_ (IVPP V 4063) was scanned using a GE v|tome|x m dual tube 300/180 kV system in the Key Laboratory of

Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), Chinese Academy of Sciences (CAS). The specimen was scanned with a beam energy of

240 kV and a flux of 200 μA at a resolution of 35.88 μm per pixel using a 360° rotation with a step size of 0.18°. Two specimens of _Dsungaripterus_ (IVPP V 26257, IVPP V 26258) and one

specimen of _Hamipterus_ (IVPP V 18943.3) were scanned using the 225 kV micro-computerized tomography in IVPP (developed by the Institute of High Energy Physics, CAS). The specimens of

_Dsungaripterus_ and _Hamipterus_ were scanned with a beam energy of 130 kV and a flux of 150 μA at a resolution of 34.50 μm per pixel, and 120 kV and a flux of 120 μA at a resolution of

25.09 μm per pixel respectively, using a 360° rotation with a step size of 0.5°. A total of 720 projections were reconstructed in a 2048 × 2048 matrix of 1536 slices using a two-dimensional

reconstruction software (IVPP-IHEP) developed by the Institute of High Energy Physics, CAS. Figure 1 shows examples of the scan results of the IVPP V 26257, which are primary data on which

the palatal bones were reconstructed. X-ray micro-computed laminography (CL): The flattened specimens of _Kunpengopterus_ and _Hongshanopterus_ were scanned using the CL scanner in the lab

at the IVPP (developed by the Institute of High Energy Physics, CAS for flat specimens). The specimens were scanned with a beam energy of 80 kV and a flux of 60 μA at a resolution of 9.02 μm

per pixel, and 70 kV and a flux of 70 μA at a resolution of 33.7 μm per pixel, respectively, using a 360° rotation with a step size of 0.5°. A total of 360 image slices with a size of 2048

by 2048 were reconstructed using a modified Feldkamp algorithm developed by the Institute of High Energy Physics, CAS. The imagery data obtained from CT and CL were using VG Studio Max 3.0

(Volume Graphics, Heidelberg, Germany) to segment, render, and reconstruct the 3D bones (Supplementary Data 1), and make the video 1. Regarding pterosaur phylogenies, there are several

proposals/hypothesis published, with two main phylogenetic schemes (Kellner2 and Unwin3), that have been modified with the addition of new taxa and the employment of different methodologies

(e.g., refs. 4,9,46). Here we have followed mainly Kellner et al.47. REPORTING SUMMARY Further information on research design is available in the Nature Portfolio Reporting Summary linked to

this article. RESULTS AND DISCUSSION The utilization of X-ray techniques (including CT-scan and CL-scan) has enabled us to investigate the internal structure of the palate of several

pterosaurs, thus revealing the boundaries of several bones despite their strongly fused external surface. The CT-scans of the thick palatal elements in all three _Dsungaripterus_ specimens

analyzed (e.g., Fig. 1) show irregular edges of the sutures between the bones, resembling the crenelate boundary of postage stamps (e.g., Fig. 1), which differentiate them from cracks or

fractures. In the case of the most complete specimen of _Dsungaripterus_ (IVPP V 4063), most sutures are clearly identifiable, allowing for the separation of the bones (Fig. 2). However, the

CT-scans of the specimen of _Hamipterus_ (IVPP V 18943.3) (Fig. 3a, b) studied here did not reveal any sutures, suggesting that all palatal elements are fused. In the case of the compressed

specimens of _Hongshanopterus_ and _Kunpengopterus_, we use CL-scan to identify any potential preserved suture. Regarding _Hongshanopterus_ (Fig. 3d, e), due to the preservation that shows

several fractures, no sutures could be confidently identified. In the case of _Kunpengopterus_ (Fig. 3f, g), there are fewer fractures, and the boundary between the ectopterygoid and

pterygoid could be seen (Fig. 3f). The remaining palatal elements in this specimen appeared to be fused. Despite the fact that no clear sutures were found in the specimens from _Hamipterus_

and _Hongshanopterus_ studied here (Figs. 3a, b, 4a, b), and only one suture was observed in _Kunpengopterus_ (Fig. 3f, g), CT-scan and CL-scan proved to be very informative since they made

it possible to observe the dorsal side of the palate. PALATAL RECONSTRUCTION OF _DSUNGARIPTERUS WEII_ (DSUNGARIPTERIDAE) The CT-scans of IVPP V 4063 provide a relatively clear picture of the

anatomy structure of the maxilla, palatine, pterygoid, and ectopterygoid, which differs from previous work on _Dsungaripterus_43. Except for the contact with the vomer, the boundary of the

posteroventral side of the maxilla is well established (Fig. 2a, b, e). The jugal process of the maxilla contacts the jugal (Fig. 2f) ventrally, forming the lateral edge of the palate, and

extends posteriorly to the ectopterygoid (Video 1 and Fig. 2b). Compared to the maxilla of _Dorygnathus banthensis_13 (Fig. 5d), the maxilla of _Dsungaripterus_ presents a process on the

ventromedial side directed posteriorly that is here referred to as the palatine process of the maxilla (Video 1 and Fig. 2e). This new process contacts the anterior ramus of the palatine

dorsomedially (Video 1 and Fig. 2b, e). With this new interpretation, the most anterior fenestra positioned lateral to the choanae is bordered by the maxilla anteriorly and the palatine

posteriorly, and therefore renamed here as the maxillopalatine fenestra. This opening has been called by most authors as the postpalatine fenestra (e.g., refs. 12,31,38) or suborbital

fenestra13. CT-scans did not reveal any suture at the grooves preserved on the ventral side of the maxilla that has been previously interpreted as the boundaries of the maxilla and the

palatine in several pterodactyloid taxa (e.g., refs. 28,38,43,48). The 3D reconstruction of the palatine in _Dsungaripterus_ shows two dorsoventrally flat palatine rami that form a

distinctive y-shape (Video 1 and Fig. 2b–d, g). According to our new interpretation, the palatine contacts all other palatal bones except for the ventral portion of the premaxilla (no

information is presently available for the vomer) and is involved in almost all palatal openings, except for the interpterygoid fenestra. The anterior ramus of the palatine ventromedially

contacts the palatine process of the maxilla, and both separate the maxillopalatine fenestra medially from the choana. The lateral ramus of the palatine contacts the lateral edge of the

palate, separating the maxillopalatine fenestra from the postpalatine fenestra referred to by others as the infraobital vacuity (e.g., refs. 18,36), the pterygoid-ectopterygoid

fenestra13,14, or the secondary subtemporal fenestra37,40,42. The lateral ramus of the palatine is elongated and overlays the anterior ramus on the dorsal side at the posterior region (Video

 1 and Fig. 2b–d, g). Medially, this lateral ramus becomes thinner, and contacts the dorsal surface of the pterygoid. At the posterior end, it contacts the opposing palatine, and both form

the posterior margin of the choanae. There is a small posterior process that contacts the pterygoid dorsally and the ectopterygoid laterally and contacts the subtemporal fenestra (Video 1

and Fig. 2b–d, g). A small foramen perforates the lateral rami of the palatine at the contact surface with the pterygoid and is here called the palatine foramen (Video 1 and Fig. 2b–d).

Since this foramen is ventrally covered by the pterygoid, it can only be observed from the posterodorsal view. The pterygoid is a plate-like bone with two processes (Video 1 and Fig. 2b, h).

The anterior process gradually tapers anteriorly, and it ventrally contacts the palatine anterior ramus. The medial process of the pterygoid covers ventrally the posterior part of the

palatine (Video 1 and Fig. 2b, h), and medially contacts its counterpart, separating the choanae and the interpterygoid fenestra. Posterior to the choanae, the pterygoid foramen is observed

between the palatine and the pterygoid (Fig. 2b). The articulation surface of the pterygoid with the ectopterygoid shows a rough texture (Video 1 and Fig. 2b, h). In the present specimen

(IVPP 4063), the pterygoid fuses with the quadrate and probably also with the basisphenoid. The medial process of the pterygoid could have been anteriorly in contact with the vomer, as the

slender vomer expands posteriorly to the posterior margin of the choanae43. Previously, the ectopterygoid was described as the “lateral process of the pterygoid”43. This bone can be divided

into two parts (Video 1 and Fig. 2b, i). The medial part is curved dorsoventrally, flattened, and has the dorsal surface perforated by several foramina (Video 1 and Fig. 2b, i). Medially, it

contacts the palatine and the pterygoid. The lateral portion of the ectopterygoid is positioned anterolaterally relative to the medial part, and it is a slender, tubular, and parabolic

arc-shaped element, that laterally contacts the jugal (Fig. 2f). The ectopterygoid separates the postpalatine fenestra from the subtemporal fenestra (Video 1 and Fig. 2b). THE PALATE OF

_KUNPENGOPTERUS SINENSIS_ (WUKONGOPTERIDAE) The specimen of _Kunpengopterus sinensis_ (IVPP 23674) also preserves a similar “y” shape palatine and also shows a palatine foramen which, as in

_Dsungaripterus_, can only be seen from the dorsal side (Fig. 3g). Based on the CL-scans, the bone previously described as the “lateral process of the pterygoid”41 is the ectopterygoid that

shows a clear boundary with the pterygoid (Fig. 3f). There are three palatal openings lateral to the choana, similar to that observed in _Dsungaripterus_. Furthermore, the palatine and

ectopterygoid are also similar in both taxa, suggesting that both have developed a similar palatal bone pattern. (Fig. 6b). The main difference is the presence of a small pterygoid foramen

in _Dsungaripterus_, while _Kunpengopterus_ exhibits a pterygoid fenestra that is more similar to the one observed in _Anhanguera_27 (Fig. 3), _Hamipterus_48 (Fig. 4), and _Caupedactylus_38

(Fig. 3h). THE PALATE IN NON-PTERODACTYLOIDS There are not many specimens of non-pterodactyloid pterosaurs that allow the observation of the palate13,16,24,25,40,44,49,50 (Table 1). Among

the best-preserved materials are BML R 278618 and CM 1143433 (Fig. 5a) representing _Rhamphorhynchus_, and _Cacibupteryx_ (IGO-V 20836 Fig. 5b), two Jurassic rhamphorhynchids. Our basic

reconstruction follows the one published by Ösi et al.13, but with different interpretations of bones and palatal openings (Fig. 6a). According to our interpretation, the palatine has two

rami, which form the medial and posterior margin of the maxillopalatine fenestra. Therefore, the opening identified by Ösi et al.13 as the suborbital fenestra and pterygoectopterygoid

fenestra should be redesignated as the maxillopalatine and postpalatine fenestrae. Furthermore, Ösi et al.13 have identified the palatine as being a long, flattened element positioned

lateral to the choanae. If, indeed, Ösi et al.13 are correct, then the palatal configuration of _Dorygnathus_, which also shows an apertura maxillo-premaxillaris not recognized in other

non-pterodactyloids, might differ from what we present here. Another member of the Rhamphorhynchidae with a well-preserved palate that, albeit still preserved in the matrix, was observed

through CT-scan51 is _Dearc sgiathanach_. Based on our analysis of the CL-scan of _Kunpengopterus_, the “y” shaped element observed on the dorsal part that was interpreted as being the

ectopterygoid51 is here regarded to be the palatine. This bone is positioned posterior to the margin of the most anterior opening -the maxillopalatine fenestra-. Both palatines meet at the

midline and contact the vomer. The original openings designated as the suborbital fenestra and pneumatic foramen (perhaps they meant the pterygoid-ectopterygoid fenestra) are, according to

our interpretations, the maxillopalatine fenestra and the postpalatine fenestra. There are at least two other quite distinctive palate configurations present in non-pterodactyloids. The most

extreme, as has been already pointed out before, is found in anurognathids where most elements are reduced to rodlike structures32,50,52,53,54. The other distinctive palate has been

reported in the wukongopterid _Kunpengopterus_ with different relation of the palatal openings, particularly the huge size of the postpalatine fenestra41. Based on our study, what originally

has been identified as the postpalatine and the secondary subtemporal fenestrae are actually the maxillopalatine and the postpalatine fenestrae, respectively (Fig. 6b). Furthermore, we here

reinterpret the ectopterygoid and the lateral process of the pterygoid of the original description41 as the palatine and the ectopterygoid, respectively (Fig. 6b). Previous reconstructions

of the palate of other non-pterodactyloid taxa are also reinterpreted here. The sole known specimen of _Parapsicephalus_ (GSM 3166)16,44 is not very well preserved and shows only the partial

right side of the palate that might follow the same pattern (Fig. 5c) as we report for the rhamporhynchids discussed previously. In _Campylognathoides_ (CM 11424)24,49 the bone observable

through the orbit and identified as the ectopterygoid24 is here the same as our interpretation (Fig. 5e). Lastly, in the palate of _Scaphognathus_ (GPIB 1304)25,40 the bones identified as

the ectopterygoid might be the palatine (Fig. 5f). THE PALATE IN PTERODACTYLOIDS The new interpretation of the palatal structure in _Dsungaripterus_ (Dsungaripteridae) can also be applied to

other pterodactyloid clades. CT-scans and CL-scans of _Hongshanopterus_35 (Istiodactylidae) (Fig. 3d, e) and _Hamipterus_48 (Hamipteridae) allowed the examination of the dorsal side of the

palate, indicating the presence of a “y” shape palatine structure as in _Dsungaripterus_. In several other pterodactyloids such as _Anhanguera_10,27,33,34 (Anhangueridae, Fig. 3d, j, q),

_Ludodactylus_55 (Ornithocheiridae, Fig. 3c) and probably also in _Caupedactylus_38 (Tapejaridae, Fig. 3h), also present a similar presence of a “y” shape palatine. Regarding palatal

openings, several pterodactyloid taxa show three main palatal openings positioned lateral to the choanae. Based on our study, the most anterior of these openings should be the

maxillopalatine fenestra. This appears to be the case of the tapejarid _Tupuxuara_14, and archaeopterodactyloid ctenochasmatids _Gnathosaurus_12 and _Liaodactylus_42 (Figs. 3j, i, 4c). Some

other pterodactyloids present only two openings lateral to the choana, such as _Pteranodon_31 (Pteranodontidae), _Tropeognathus_26 and _Anhanguera_27,56 (Anhangueridae), _Nyctosaurus_19

(Nyctosauridae), and _Aurorazhdarcho_57 (Ctenochasmatidae or _Pterodactylus_23, Pterodactylidae). The most anterior one, as in other pterodactyloids, is the maxillopalatine fenestra,

followed by the subtemporal fenestra (Figs. 3k–s, 4d, e). This suggests that they lack a postpalatine fenestra. The main reason for this is the possible lack of the development of a lateral

process of the ectopterygoid, that in the other studied pterodactyloid separates postpalatine fenestra from the subtemporal fenestra (Fig. 6c). In some specimens of _Anhanguera_ (SNSB-BSPG

1982 I 89), _Hongshanopterus_, _Gnathosaurus_, _Aurorazhdarcho_, the ectopterygoid shows a blunt incipient process directed into the subtemporal opening. As observed in non-pterodactyloids,

some palatal elements might also be reinterpreted in pterodactyloids. The palatine as presented in previous studies12,23,26,27,28,31,38,43,48 is here reinterpreted as the median maxilla

process (Fig. 6c). Also the bone interpreted as the ectopterygoid in some taxa28,31,35,38,42,43,48,58,59 are here considered as being the palatines, which shows two rami as observed in the

CT-scans of _Dsungaripterus_. The diverse shape of the maxillopalatine fenestra observed in non-pteradactyoids and pterodactyloids (Figs. 2, 3,4) is influenced by several factors, including

the shape and extension of the palatine process of the maxilla, the angle between the two rami of palatine, and the contact of the palatine lateral ramus with bony bar formed by maxilla and

jugal. The angle between the two rami of the palatine varies from ~30° in _Dsungaripterus_, _Caupedactylus_, _Tupuxuara_, _Nyctosaurus gracilis_, and _Pteranodon_, ~45° in _Hongshanopterus_,

_Aurorazhdarcho_, _Liaodactylus primus_, and _Gnathosaurus_, and 45°–60° in _Hamipterus_ and _Anhanguera_. In the region between the choanae and the interpterygoid fenestra, a pair of small

openings are present and vary within pterodactyloids in size. For example, in _Dsungaripterus_ these openings are small, forming a pterygoid foramen, while in _Anhanguera_, _Hamipterus_,

and _Caupedactylus_ they are large, forming a pterygoid fenestra (Figs. 3,4). There seems to be some variation in the sizes of these openings, that could be observed in some specimens of

_Anhanguera_, being more developed in some (SNSB-BSPG 1982 I 89, MN 4805-V, BSP 1987 I 46, and SAO 16494) and smaller in others (Fig. 3, RGM 401 880, AMNH 25555, SNSB-BSPG 1982 I 90, and

AMNH 22555). Although an extensive comparison of the pterosaur palate with other diapsids is beyond the scope of this paper, there are a few comments and differences that can be highlighted.

The most significant is the presence of a maxillopalatine fenestra, which is absent in other diapsids58,60,61 and might turn out to be a synapomorphy of Pterosauria. In crocodyliforms, the

suborbital fenestra is anteriorly formed by the maxilla and the palatine, and posteriorly by the pterygoid and ectopterygoid, lacking any maxillopalatine fenestra62. In prolacertiformes

(e.g., ref. 63) and lepidosauromopha58,60, the internal naris is positioned at the lateral side of the palate, followed by a postpalatine fenestra, and lacks any extra opening between them.

But the postpalatine fenestra is similar to the one observed in pterosaurs, since it is formed anteriorly by the palatine and posteriorly by ectopterygoid. To conclude, the new relation

established here between the palatine, ectopterygoid, maxilla, and pterygoid suggest some reinterpretation of the main palatal openings (Fig. 6d). Although it has to be acknowledged that

there is still much work on the pterosaur palate necessary to be able to establish stronger evolutionary trends on this portion of the pterosaur skull, six main general remarks can be

presented. * 1. In some non-pterodactyloids (e.g., _Rhamphorhynchus_ and _Cacibupteryx_), the anterior process of the pterygoids is not as developed as it is in pterodactyloids (Fig. 6d). *

2. The angle between the two rami of the palatine in some non-pterodactyloids are nearly 90°, in _Kunpengopterus_ is 45°, and in pterodactyloids are <60° (e.g., ~30° in _Dsungaripterus_,

~60° in _Hamipterus_). * 3. In pterodactyloids the jugal process of the maxilla extends posteriorly until the ectopterygoid, but not in the non-pterodactyloids (_Rhamphorhynchus_ and

_Cacibupteryx_). * 4. The last tooth is posterior to the anterior margin of maxillopalatine fenestrae in non-pterodactyloids (e.g., _Dorygnathus_, _Cacibupteryx_, _Rhamphorhynchus_, and

_Kunpengopterus_), but is anterior to the maxillopalatine fenestrae in toothed pterodactyloids (e.g., _Hongshanopterus_, _Anhanguera_, _Tropeognathus_, _Liaodactylus_, _Gnathosaurus_,

_Aurorazhdarcho_, _Hamipterus_, and _Dsungaripterus_). * 5. Pterodactyloids have a pair of pterygoid openings (foramen or fenestra) bordered by the lateral ramus of the palatine and the

median process of pterygoid. This opening is present in the non-pterodactyloid _Kunpengopterus_ and _Cacibupteryx_, but not in _Rhamphorhynchus_. * 6. Along with the great variation in the

sizes of the palatal openings such as the pterygoid foramen or fenestra, the posterior margin of the choanae moved posteriorly to the maxillopalatine fenestra in _Kunpengopterus_ and

pterodactyloids (Fig. 6d) and even posterior to the postpalatine fenestra in some pterodactyloids (e.g., _Caupedactylus_, _Tupuxuara_, and _Dsungaripterus_). DATA AVAILABILITY The authors

declare that the main data supporting the findings of this study are available within the article and its Supplementary Information file. Extra data were available from the corresponding

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Scholar  * Eaton, G. F. Osteology of Pteranodon. _Mem. Con. Acad. Arts Sci._ 2, 1–38 (1910). Google Scholar  Download references ACKNOWLEDGEMENTS We acknowledge our IVPP research team

members Long Xiang, Yan Li, Hongjiao Zhou, Ruijie Wang, Jinkun Mao, Rui Qiu, Yang Li, Xinjun Zhang and Junxia Wang for fieldwork and specimen preparation. The authors would like to thank Dr.

Yemao Hou, Pengfei Yin, Xiaoyi Dong, and Dr. Yanxin Gong for their help with the CT and CL scanning and 3D reconstructions in IVPP. We have benefited from discussions with Drs. Xing Xu,

Liping Dong, Jun Liu, Rui Qiu, Xin Cheng, Xinjun Zhang, and Yang Li. For granting access and assistance to the study of AMNH 25555, we thank Drs. Mark A Norell (American Museum of Natural

History) and Congyu Yu, Qigao Jiangzuo. Also, we would like to thank Prof. Lawrence M. Witmer (Ohio University) for kindly helping with the data file of CM 11434, Prof. Taissa Rodrigues

(Universidade Federal do Espírito Santo), Prof. Renan A.M. Bantim (Universidade Regional do Cariri) and Rodrigo V. Pêgas (Universidade Federal do ABC) for providing high-resolution photos

Anhangueridae, _Maaradactylus kellneri_, and _Tupuxuara leonardii_ respectively. We also thank Dr. Thomas Stidham and Dr. Paul Rummy for their constructive comments that highly improve the

standards of this manuscript. This work was supported by the following funding: National Natural Science Foundation of China (42288201, 42072028, 41572020, and 42302003), the Strategic

Priority Research Program (B) of CAS (XDB26000000), and the Youth Innovation Promotion Association of Chinese Academy of Sciences (2019075). AWAK acknowledges funding from the Conselho

Nacional de Desenvolvimento Científico e Tecnológico (CNPq # 308707/2023-0, #406779/2021-0, #406902/2022-4) and the Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de

Janeiro (FAPERJ #E-26/201.095/2022). AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * School of Ecology, Sun Yat-sen University, Shenzhen, 510006, China He Chen * Key Laboratory of Vertebrate

Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, 100044, China He Chen, Shunxing Jiang & Xiaolin Wang *

University of Chinese Academy of Sciences, Beijing, 100049, China He Chen & Xiaolin Wang * Laboratory of Systematics and Taphonomy of Fossil Vertebrates, Department of Geology and

Paleontology, Museu Nacional/UFRJ, Rio de Janeiro, 20940-040, Brazil Alexander W. A. Kellner Authors * He Chen View author publications You can also search for this author inPubMed Google

Scholar * Shunxing Jiang View author publications You can also search for this author inPubMed Google Scholar * Alexander W. A. Kellner View author publications You can also search for this

author inPubMed Google Scholar * Xiaolin Wang View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS All authors contributed to the interpretation

and discussion of results. H.C. designed the study, collected the data, and wrote the paper. S.J., A.W.A.K., and X.W. performed the research and contributed to the initial discussions.

CORRESPONDING AUTHOR Correspondence to Xiaolin Wang. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests. PEER REVIEW PEER REVIEW INFORMATION _Communications

Biology_ thanks David Unwin and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editors: Borja Figueirido and Luke R. Grinham.

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