Novel information on the cranial anatomy of the tapejarine pterosaur Caiuajara dobruskii

PLOS ONE RESEARCH ARTICLE Novel information on the cranial anatomy of the tapejarine pterosaur Caiuajara dobruskii Lucas Canejo ID1*, Borja Holgado ID1,2¤*, Luiz C. Weinschütz3, João H. Z. Ricetti3, Everton Wilner3, Alexander W. A. Kellner1 1 Laboratory of Systematics and Taphonomy of Fossil Vertebrates, Departamento de Geologia e Paleontologia, Museu Nacional/Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil, 2 Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Catalonia, Spain, 3 Centro de Pesquisa Paleontológica, Universidade do Contestado, Mafra, SC, Brazil ¤ Current address: Departamento de Ciências Biológicas, Universidade Regional do Cariri (URCA), Crato, CE, Brazil * (LC); (BH) a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Canejo L, Holgado B, Weinschütz LC, Ricetti JHZ, Wilner E, Kellner AWA (2022) Novel information on the cranial anatomy of the tapejarine pterosaur Caiuajara dobruskii. PLoS ONE 17(12): e0277780. https://doi.org/10.1371/journal. pone.0277780 Editor: Laura Beatriz Porro, University College London, UNITED KINGDOM Received: June 11, 2022 Accepted: November 3, 2022 Abstract Caiuajara dobruskii is a tapejarid pterosaur from the Cretaceous of the ‘Cemitério dos Pterossauros’ (pterosaur graveyard) site, a unique pterosaur bonebed which is located at the municipality of Cruzeiro do Oeste (Paraná, Brazil). Preliminary inferences on Caiuajara morphology were founded on a few partial skeletons, with no detail on the skull anatomy. Here we describe a new specimen from the pterosaur graveyard site, which corresponds to the most complete skull of Caiuajara dobruskii known so far. Furthermore, we describe and compare other specimens including the holotype, a paratype, and several other undescribed specimens. The new specimen preserves the posterior portion of the skull, allowing a better comprehension of its morphology and provides an appreciation of the anatomic structures of the basicranium, enabling better interpretation of this region. We also described the lower jaw of Caiuajara, reporting a unique feature of its symphyseal which adds to the diagnosis for the species. A variability in the premaxillary crest is also noted in different specimens of Caiuajara, which might be interpreted as sexual dimorphism or ontogenetic variability. Therefore, those new findings allow a better comprehension of its skull and enables a more precise comparison between the skulls of those extinct flying reptiles. Published: December 15, 2022 Copyright: © 2022 Canejo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: The authors received no specific funding for this work. Competing interests: The authors have declared that no competing interests exist. Introduction Pterosaurs were the first vertebrates to acquire active flight and lived during most of the Mesozoic Era, with their latest record dated to 66 million years ago [1–7]. Notwithstanding their remains are found in all continents [8–10], the pterosaur fossil record is frequently limited to fragmentary and isolated individuals with occasional biased stratigraphic control [5, 8, 11, 12]. This has caused several taxonomic controversies, with the establishment of several ambiguous taxa [12–16], and debatable proposals about their ontogeny and intraspecific variability [12, 17–20]. The only cases in the fossil record of unquestionable ontogenetic series of pterosaurs are scant [21–26], of which most of these are found in bonebeds. Only three occurrences of PLOS ONE | https://doi.org/10.1371/journal.pone.0277780 December 15, 2022 1 / 23 PLOS ONE Cranial anatomy Caiuajara dobruskii pterosaur bonebeds have been reported: in Argentina (San Luis Province), the ctenochasmatid Pterodaustro guinazui was found in the outcrops of the Albian Lagarcito Formation [22, 23, 27, 28]; in Northwestern China (Xingjiang Autonomous Region), the anhanguerian Hamipterus tianshanensis [25, 26] was recovered in outcrops of the Lower Cretaceous Tugulu Group; and in Southern Brazil (Paraná), the tapejarine Caiuajara dobruskii was found in the mid-tolate Cretaceous ‘Cemitério dos pterossauros’ (pterosaur graveyard) site of the municipality of Cruzeiro do Oeste, state of Paraná [24]. The sole Brazilian site of ‘Cemitério dos pterossauros’ is the only bone bed known so far where more than one pterosaur species was found: the already mentioned Caiuajara dobruskii Manzig et al. 2014, which is the predominant species in the vertebrate assemblage; and Keresdrakon vilsoni Kellner et al. 2019 [29]. Dinosaurs were also present in these outcrops, represented by two known species: Vespersaurus paranaensis Langer et al. 2019 [30] and Berthasaura leopoldinae Souza et al. 2021 [31] together with the squamate lepidosaur Gueragama sulamericana Simões et al. 2015 [32]. No remains of eggs or soft tissue, occasionally recorded in other deposits (e.g., [25, 33]) have been reported so far. The ‘Cemitério dos pterossauros’ site comprises a sequence of aeolian sandstones in to the Caiuá Group and, together with the sediments of the Bauru Group, represent an ancient desert that covered part of southern Brazil in the Cretaceous period. The huge amount of pterosaur specimens belonging to Caiuajara displays a high morphological variability, both in size and shape. Some of such traits were originally pointed out as ontogenetic features, like the size and inclination of the sagittal crest [24], referring to most of the individuals as juvenile and subadults. However, its original description does not mention the bones forming the posterior portion of the skull due the lack of preservation. In this sense, the need for anatomical information for this area of the skull remains unsolved to date. In this work, we describe a nearly complete skull, which represents the best-preserved skull of Caiuajara dobruskii known so far (Fig 1). In addition to this, we reassess some of the previously described specimens and compare them with the new ones undescribed so far, allowing both a revision of the original diagnosis of Caiuajara dobruskii as well elucidating the variability in the cranial morphology. Material and methods Material The specimen CP.V 8175 was collected in 2014, at the ‘Cemitério dos pterossauros’ site and it is housed at the collection of the Centro de Pesquisa Paleontológica, Universidade do Contestado (CENPALEO). Together with the new specimen which constitutes the focus of our results (CP.V 8175), we also analysed the specimens of the Caiuajara dobruskii type series (CP.V 1005; CP.V 1050–1 and CP.V 1449) as well as other not previously described specimens (C (...truncated)