Introduction

The Araripe Basin in Northeast Brazil has long been recognized as a valuable site for paleontological research1,2,3,4, yielding numerous significant fossil discoveries from the Cretaceous Period across a wide diversity of taxonomic groups. Among these, the Santana Group stands out for its exceptional fossil preservation, providing valuable information about the morphology, ecology, and evolution of several clades, especially pterosaurs5,6,7,8,9. It has provided dozens of both toothed (ornithocheiriforms) and toothless (azhdarchoids) ornithocheiroid taxa, and hundreds of specimens overall10,11.

Despite over five decades of pterosaur studies in this unit, no archaeopterodactyloid taxa had been formally documented from this unit until now12. Here, we present the first archaeopterodactyloid from the Santana Group, based on a very distinctive specimen from the Romualdo Formation.

Ctenochasmatidae is a clade of pterodactyloid pterosaurs, which thrived during the Late Jurassic and Early Cretaceous. Recent discoveries have shed light on the diversity and ecological adaptations of this group, particularly through the examination of new fossil specimens from various geographic regions and geological periods13,14. These pterosaurs exhibit a remarkable evolutionary trajectory, characterized by diverse morphological adaptations and a broad geographical distribution. Recent discoveries from China, South America, and Europe have significantly enhanced our understanding of their ecology and highlighted the dynamic evolutionary history of this lineage15,16,17.

Ctenochasmatids thrived mostly from the Late Jurassic to the Barremian but declined progressively towards the late Early Cretaceous. Little is known about the later taxa and how the lineages moved and diversified between Laurasia and Gondwana. Indeed, the only Gondwanan ctenochasmatid taxa known from before this study are: the ctenochasmatine Pterodaustro guinazui, from the Albian of the San Luis province, Argentina, and the gnathosaurine Tacuadactylus luciae, from the Upper Jurassic of Uruguay; with other ambiguous material from Argentina and Chile as well18,19,20,21,22.

Within Ctenochasmatidae, the subclade Ctenochasmatinae is distinguished by elongated snouts and numerous fine teeth, adaptations associated with their unique feeding strategies. The evolutionary trajectory of this group has been illuminated by discoveries such as Liaodactylus primus, from the Upper Jurassic of western Liaoning, China14, which demonstrates a notable ecological transition from fish-catching to filter-feeding within the clade. An extreme morphology can be found in the ctenochasmatine Pterodaustro guinazui, which exhibits a thousand hyper-elongated baleen-like teeth on the lower jaw13,23,24. The extreme morphology of Pterodaustro indicates a hyper-specialization towards filter-feeding23. To account for the distinctiveness of this form, the clade Pterodaustrini was defined by Andres et al. 25 as the “most inclusive clade containing Pterodaustro but not Ctenochasma”, and includes Beipiaopterus, Gegepterus, and Pterodaustro according to recent works26,27,28.

Here we describe Bakiribu waridza gen. et sp. nov., a new pterodaustrinin pterosaur from the late Aptian-early Albian Romualdo Formation of the Araripe Basin, Northeast Brazil. This taxon exhibits a mosaic of traits shared with both South American and European relatives, contributing to our understanding of their evolutionary history and paleobiogeography from a low-latitude Gondwanan context.

Materials and methods

Specimen and locality

The material described here comprises one part and its counterpart of a typical calcareous concretion from the Romualdo Formation, Araripe Basin, Northeast Brazil (Fig. 1). The concretion contains two individuals of the new pterosaur species, along with four fossil fish (likely Tharrhias). The material was originally housed in the paleontology collection of the Museu Câmara Cascudo (MCC) at the Universidade Federal do Rio Grande do Norte (UFRN), Natal, Rio Grande do Norte state, Brazil, under catalog numbers MCC1271.1-V and MCC1271.2-V. The specimen had been stored in the museum’s collection for many years without formal identification, kept among other fossils originating from the Araripe region, unfortunately, without precise provenance and date of collection.

Upon identifying this material as a new species, we contacted the director of the Museu de Paleontologia Plácido Cidade Nuvens (MPSC) in Santana do Cariri, Ceará state, Brazil, and facilitated an agreement to transfer one-half of the concretion (MCC 1271.2-V) to their collection. This initiative aimed to support the preservation of significant specimens (such as holotypes) within their region of origin, contributing to local development. Consequently, part of the material is still housed at the Museu Câmara Cascudo (MCC 1271.1-V), while the other part is currently deposited at the Museu de Paleontologia Plácido Cidade Nuvens under a new register number, MPSC R 7312 (originally MCC 1271.2-V).

Fig. 1
figure 1

Modified from Aureliano & Ghilardi1, Fambrini et al2., and Heads et al4. Created with Adobe Illustrator, version 25.2 (Adobe Inc., https://www.adobe.com/illustrator).

Geographical and geological context. A, Araripe Basin in the South American context. B, Araripe Basin geological map. C, Simplified stratigraphic column of the basin, colors differentiate the pre-rift, rift, and post-rift sequences2, from base to top.

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Phylogenetic analysis

A phylogenetic analysis was conducted to investigate the relationships of the new species herein analyzed within Ctenochasmatidae. For this purpose, we have utilized as a basis a previous phylogenetic matrix26, with the inclusion of the species herein described, and revised codifications for the ctenochasmatids Ctenochasma elegans, Gegepterus changi, and Beipiaopterus chenianus (see Supplementary Material). The analysis was conducted under maximum parsimony, using the software TNT 1.529. The analysis was divided into two steps, following the same protocol as previous works26. New Technology Search (default parameters) was used for the first step, with random seed = 0. Subsequently, a Traditional Search swap was performed using trees from RAM (using TBR, 10000 replications, collapsing trees after search). All characters were treated with equal weight. A TNT file (in txt format) containing the data matrix, ready for analysis execution in TNT, is available as supplementary information.

Paleohistology and petrography

We sampled a portion of a tooth row from one of the halves of the calcareous concretion using an electronic Dremel® saw. The cut was perpendicular to the tooth axis and did not reach any cranial bone. We applied PaleoBOND® penetrant stabilizer to improve sample resistance. It was embedded into Araldite 2020® epoxy resin. The sample was later ground to a thickness of approximately 60 μm. It was photographed on an Olympus BX53M petrographic microscope with both parallel and crossed nicols, with the lambda compensator. We followed Cerda & Codorniú13 for tooth description. We followed Terra et al30. for carbonate rock classification.

Institutional abbreviations: IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China; MCC, Museu Câmara Cascudo, Natal, Rio Grande do Norte, Brazil; MIC, Contacto, Museo Interactivo de Ciencias, Universidad Nacional de San Luis, San Luis; MPSC, Museu de Paleontologia Plácido Cidade Nuvens, Santana do Cariri, Ceará, Brazil; SMNS, Staatliches Museum für Naturkunde Stuttgart, Germany.

Results

Systematic paleontology

Pterosauria Owen 1842.

Pterodactyloidea Plieninger 1901.

Ctenochasmatidae Kuhn 1967.

Ctenochasmatinae Nopcsa 1928.

Pterodaustrini Andres, Clark and Xu 2014.

Bakiribu waridza gen. et sp. nov.

Fig. 2
figure 2

Overview of the concretion containing the remains of Bakiribu waridza gen. et sp. nov. (holotype and paratype) and four associated fishes. A, Part (MCC 1271.1-V). B, Counterpart (MPSC 7312). C and D, Schematic drawings of MCC 1271.1-V and MPSC 7312, respectively. Scale bar equals 50 mm.

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Etymology. The generic epithet comes from bakiribú (Kariri word for ‘comb’), in allusion to the typical comb-like dentition of ctenochasmatids. The specific epithet comes from waridzá (Kariri word for ‘mouth’). Together, the binomial name not only highlights the distinctive dental morphology of the taxon but also honors the cultural heritage of the Kariri people, Indigenous inhabitants of the region where the fossil was discovered.

Holotype. MCC 1271-Va/MPSC 7312a (Figs. 2 and 3A and B), a partial rostrum. Based on position and orientation, fragments b, c, and d most likely belong to the same individual (Fig. 3B).

Paratype. MCC 1271-Ve/MPSC 7312e (Figs. 2 and 3A and C), a distinct partial rostrum. Fragments f and g are tentatively regarded as part of the same individual (Fig. 3C).

Horizon and Locality. This fossil was preserved in a calcareous concretion of the Romualdo Formation, Araripe Basin, Northeast Brazil. This unit is late Aptian-early Albian in relative age31. The precise locality of this concretion is unknown, but the Romualdo Formation outcrops east-west along the Araripe Plateau between the states of Pernambuco, Ceará, and Piauí1,2.

Diagnosis. Ctenochasmatine pterosaur with the following combination of features, including autapomorphies (marked with an asterisk): jaws extremely elongate (estimated rostral index of ~ 12–16); teeth closely packed together (interdental gaps under tooth diameter); high tooth density (17.6 teeth/cm); high tooth count (between 110 and 142 per jaw, per side, as preserved; total estimate = between 440 and 568); teeth long and slender (elongation index surpassing 1:60); acrodont-like tooth implantation on both jaws*; and tooth crowns subquadrangular in cross-section*.

Fig. 3
figure 3

Reconstruction of the type specimens of Bakiribu waridza gen. et sp. nov. A, close view of MCC 1271.1-V (main part). B, simplified schematic reconstruction of the holotype based on fragments a, b, c, and d. C, simplified schematic reconstruction of holotype based on fragments e, f, and g. Scale bar equals 10 mm.

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Description. The material comprises a large number of dentate jaw sections jumbled together, lying close to four fish specimens. An indeterminate metatarsal and an indeterminate pedal phalanx are also present, as are some indeterminate bone fragments.

It is difficult to determine the anatomical position of most jaw sections. However, four jaw fragments preserve the tip (Fig. 3). The preservation of four jaw tips suggests the presence of at least two specimens, which together would account for two upper and two lower jaws. The three best-preserved jaw fragments (MPSC 7312a, c, and e) all preserve a slightly expanded tip, with fragments a and c being of similar size, and both slightly more expanded than fragment b (Fig. 3A). The fourth jaw tip (fragment f) comprises a smaller fragment, not so well-preserved. We accordingly interpret the larger tips (a and e; Fig. 4A-D) as upper jaws and the less-expanded tips (c and f) as lower jaws, based on the proportions seen in Ctenochasma elegans SMNS 81,803, wherein the upper jaw tip is slightly more expanded than the lower one32. Based on their close position and similar orientation, we tentatively interpret fragments a and b as belonging to a single individual (herein elected as the holotype; Fig. 3B). Fragment e, which represents a second upper jaw tip (and therefore a second individual), is chosen as a paratype. Fragment f is tentatively identified as belonging to the same individual as fragment e (Fig. 3C).

Fig. 4
figure 4

Details of MCC 1271.1-V (main part) and respective schematic drawings. A and B, fragment e (paratype), a rostrum. C and D, fragment a (holotype), a rostrum. E and F, fragment d (holotype?), a partial dentary symphysis. Scale bars equal 10 mm.

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The jaw sections are all elongated and dorsoventrally compressed, as is typical of ctenochasmatines. Most jaw sections are almost straight in orientation. Still, one fragmentary mid-section is slightly upcurved (Fig. 4E, F), indicating the presence of a slight upturn along the rostrum, similar to the condition seen in Gegepterus changi33.

The jaw sections exhibit an extensive comb-like dentition, comprising a high number of slender, curved teeth. The teeth are oriented anterolaterally in the coronal plane and lateroventrally in the transverse plane. The teeth are quite closely packed together (interdental gaps are inferior to tooth diameter; see Fig. 4E, F), behind only those of Pterodaustro guinazui in which the teeth actually contact each other13. Preserved tooth density equals 17.6 teeth/cm. Estimated total skull length ranges from 9 to 12 cm (simple scaling based on Ctenochasma and Pterodaustro, respectively; see Tables S1-S3). The estimated total tooth count per jaw, per side ranges from 110 to 140 (see Tables S1-S3).

The jaw sections lack alveoli, and the teeth seem to be attached to the bone in an acrodont-like style (Fig. 4E, F). This is similar to the condition seen in the upper teeth of Pterodaustro guinazui, and unlike other pterosaurs23,33. Still, Bakiribu differs from Pterodaustro in that such acrodont-like implantation is present on both jaws, rather than only on the upper jaw as in Pterodaustro (23,33). The base of the teeth is slightly expanded, in a petiolate-like style (Fig. 4E, F). Presumably, the teeth were attached to the jaws through connective tissue, as has been proposed for the upper teeth of Pterodaustro guinazui (23,33).

In cross-section, tooth crowns are subquadrangular in shape, uniquely among ctenochasmatids (see Fig. 5). In other ctenochasmatids, tooth crowns are nearly circular, as in the ctenochasmatines Gegepterus changi, Ctenochasma elegans, and Pterodaustro guinazui13,32,33, as well as other ctenochasmatids such as Balaenognathus maeuseri, Pterofiltrus qiui, and Feilongus youngi; or elliptical, such as in the gnathosaurines Tacuadactylus luciae and Lusognathus almadrava15,16.

Paleohistology and petrography

The thin section showed a tooth row preserved in a calcareous concretion with moderate taphonomic artifacts (Fig. 5). There is no evidence of lithostatic compression. The concretion comprises a wackestone supported by ostracodes and foraminifera (Fig. 6). Foraminifera are less abundant and zoned at the same layer as the pterosaurs and fish. Diagenetic micrite and calcite slightly damaged the specimen. Nonetheless, dentine was preserved, and general tooth morphology could be assessed. The tooth outline is subrounded to subquadrangular in transversal view. The interdental space is short. The pulp cavity has been preserved.

Fig. 5
figure 5

Tooth histology of Bakiribu waridza gen. et sp. nov. MCC 1271.1-V b/MCC 1271.2-V b (A, B, D, E, G) and Pterodaustro guinauzi (MIC-V55 in F; MIC-V23 in H). A, tooth row in transversal view with a black box indicating the detailed area in B. Asterisk indicates interdental space. C, calcareous concretion showing the sampling site (arrow). Detail of tooth row in Bakiribu (G) and Pterodaustro (H). H, courtesy of Laura Codorniú. Polarized microscopy in A, B. Abbreviations: de, dentine; pc, pulp cavity; to, tooth. Scale bar in A, D, F = 200 μm; in C = 3 cm; in E = 100 μm; in G, H = 1 cm.

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Fig. 6
figure 6

Petrography of the calcareous concretion in which the holotype of Bakiribu waridza gen. et sp. nov. was found. A, wackestone containing several ostracod valves. Detail of ostracodes in dorsal (B) and transverse (C) sections (arrows). D, a layer of foraminifera accumulation. E, detail of foraminifera (arrows). Scale bar in A, D = 200 μm; B, C = 120 μm; E = µm.

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Phylogenetic analysis

Our search produced 27 most parsimonious trees, with 2191 steps each. The strict consensus tree (Fig. 7) has a consistency index of 0.355 and a retention index of 0.802. Bakiribu was recovered as the sister species of Pterodaustro guinazui in the strict consensus (Fig. 7), this relationship being supported by 5 synapomorphies: character 197(2), mandible main axis upturned; character 253(1), dentition extension surpassing 70% of jaw length; character 258(1) mesial teeth nearly touching (spacing under half of alveolar diameter); character 280(3), mesial tooth elongation surpassing 60 times width; and character 305(1), absence of upper alveoli.

Fig. 7
figure 7

Time-scaled strict consensus tree showing archaeopterodactyloid intrarrelationships. The remaining portion of the tree is identical to that of Pêgas (2025). Nodes: 1, Archaeopterodactyloidea; 2, Ctenochasmatoidea. Silhouettes retrieved from PhyloPic: Germanodactylus, Pterodactylus, and Cycnorhamphus by Matt Martyniuk and Huanhepterus by Scott Hartman, available under a CC BY 3.0 license (https://creativecommons.org/licenses/by-nc-sa/3.0/); Moganopterus, Forexopterus, and Pterodaustro by Cy Marchant (CC BY 4.0; https://creativecommons.org/licenses/by/4.0/), and Gnathosaurus by Dean Schnabel (CC0 1.0).

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Discussion

Phylogenetic relationships of Bakiribu and comments on the evolution of pterodaustrinins.

Before this study, the Pterodaustrini (sensu Andres et al25.) were thought to comprise three taxa: Pterodaustro guinazui, known from hundreds of specimens from the Albian Lagarcito Formation of Argentina23,34; Gegepterus changi, known from two specimens (including skulls) from the Barremian-Aptian Yixian Formation of China33; and Beipiaopterus chenianus, known from a single specimen (lacking a skull) from the same formation (see26,28). Morphological features supporting the close affinities of Pterodaustro guinazui and Gegepterus changi included an upturned rostrum and mandibular tips, a craniomandibular articulation posterior to the center of the orbit, an ascending process of the jugal anterodorsally inclined, and cheek alveoli set in grooves26,28.

However, the current study does not find support for these features as synapomorphies of a clade joining Pterodaustro and Gegepterus to the exclusion of Ctenochasma. An upturned rostrum and mandibular tips, a craniomandibular articulation posterior to the center of the orbit, and an ascending process of the jugal anterodorsally inclined are all features that can be seen in Ctenochasma elegans32; moreover, the craniomandibular articulation actually lies beneath the anterior, not posterior, half of the orbit in Gegepterus. The last two features can be seen in Ctenochasma taqueti as well35,36. Furthermore, the groove that houses the teeth of Pterodaustro guinazui and Gegepterus changi are not quite equivalent. The alveolar groove that is present in the lower jaw of Pterodaustro guinazui represents, in fact, a series of confluent alveoli, wherein each tooth contacts each other and no interdental gaps separate each tooth/alveoli (= aulacodonty; 13). This is distinct from the condition seen in Gegepterus changi, which is not aulacodont. In this form, the alveoli are individualized and separated by interdental gaps, though placed in a shallow lateral groove that runs along the dentigerous margin33. In other words, the lower alveoli of Pterodaustro guinazui are the groove itself, rather than being set in a groove as is the case with Gegepterus changi. It is thus clear that the grooves seen in the jaws of Pterodaustro guinazui and Gegepterus changi do not correspond, and should not be coded as such.

Following coding corrections about the aforementioned features, we presently recover Pterodaustro (and Bakiribu) as closer to Ctenochasma than to Gegepterus, which is recovered as a non-ctenochasmatine (Fig. 8). The relationship between Ctenochasma and Pterodaustrini (= Pterodaustro + Bakiribu), to the exclusion of Gegepterus, is supported by: characters 34(1), jaw anterior region with subparallel lateral margins; and 151(1), craniomandibular joint located below the posterior half of the orbit. Moreover, Pterodaustro and Ctenochasma share several features that are absent in Gegepterus, such as: character 257(1), tooth spacing approximately even along jaws; 264(2), mesial teeth long axis sigmoidal; character 265(1), all tooth crowns procumbent; and character 281(2), mesial teeth elongation surpassing 20 times width.

Gegepterus and Beipiaopterus are herein reinterpreted as closer relatives of Forfexopterus and related taxa (Elanodactylus and moganopterines) than to ctenochasmatines such as Pterodaustro (Fig. 8). Gegepterus and Beipiaopterus share with Forfexopterus characters 382(1), coracoid distal end with distinct cotyles; and 489(1), fourth wing phalanx with an expanded distal tip. Beipiaopterus further shares with Elanodactylus and Forfexopterus characters 483(1), third wing phalanx subequal or longer than the first; and 484(1), third wing phalanx subequal or longer than the second (unknown in Gegepterus).

Of note regarding Beipiaopterus is its fourth wing phalanx, previously misinterpreted as a third one - notice the curvature and expanded tip37 that render it indistinguishable from the fourth phalanges of Gegepterus and Forfexopterus (see33,38). It is presumable that the oddly hyperelongated element previously interpreted as a first phalanx actually represents phalanges 1 plus 2, with their articulation obliterated by breakage on the slab (see37).

Comments on the evolution of filter feeding in ctenochasmatids

Bakiribu waridza gen. et sp. nov. shares with Pterodaustro guinauzi the very dense brush-like tooth row. Notwithstanding, the interdental space in Bakiribu (Fig. 5.E) is twice as wide as in Pterodaustro (Fig. 5.F), without teeth contacting each other in a row. Teeth in Bakiribu are also slightly quadrangular in cross-section compared to the “pencil-like” circular shape seen in Pterodaustro guinazui and Gegepterus changi, as well as non-pterodaustrinin ctenochasmatids such as Ctenochasma SMNS 81,80332, Balaenognathus maeuseri NKMB P2011-63339, Feilongus youngi IVPP V1253940, Huanhepterus quingyangensis IVPP V 907041, Moganopterus zhuiana HGM 41HIII-041942, and Pterofiltrus qiui IVPP V1233943. Tooth cross-section, quantity, and size remained plesiomorphic in ctenochasmatids relative to Pterodaustro and Bakiribu, which present numerous, dense brush-like tooth rows of extreme elongation.

In certain ways, the dentition of Bakiribu is anatomically intermediate between the older Ctenochasma and the younger Pterodaustro, thereby showcasing an evolutionary transition within ctenochasmatines throughout space and time. More specifically, Bakiribu is intermediate between these forms in elongation, density, and count of the filamentous teeth; in these regards, values for Bakiribu are all higher than in Ctenochasma but lower than in Pterodaustro (Table S1).

Despite the less dense tooth row in Bakiribu compared to Pterodaustro, it featured filamentous teeth on both the upper and lower jaws. This unprecedented high density of filamentous teeth on both jaws might have rendered Bakiribu enhanced, unique filtering capabilities.

Taphonomical remarks and the regurgitalite interpretation of the fossil assemblage

The pterosaurs and fish were preserved within a wackestone concretion rich in non-oriented ostracodes and foraminifera, similar to other Romualdo Formation concretions3,44. The co-occurrence of densely packed, semi-articulated, and fragmented pterosaur bones (predominantly aligned in subparallel orientation) together with a cluster of similarly aligned fish supports the interpretation of the assemblage as a regurgitalite, a mass of indigestible material expelled orally by a predator45.

An alternative explanation is the floating carcass model, which posits that buoyant carcasses disarticulate through soft tissue decay before sinking (e.g.,46,47). However, this scenario fails to account for the observed bone breakage and the consistent alignment of elements. Regarding the alignment, the low-energy depositional setting of the Romualdo Formation would not facilitate hydraulic reorientation, and the absence of bone abrasion further indicates minimal post-mortem transport following decomposition.

The configuration of the fish within the concretion adds critical taphonomic context. Their uniform orientation mirrors a feeding behavior commonly observed in extant piscivorous vertebrates, particularly birds. Most piscivorous birds typically ingest their prey whole, head-first. Swallowing fish head-first minimizes the risk of injury from backward-facing spines and fins while facilitating smoother passage down the predator’s throat, reducing resistance and the likelihood of choking48,49,50. The tightly clustered arrangement of the fish, in close association with the pterosaur bones, further supports the regurgitalite scenario. Orally expelled material is often embedded in mucus envelopes that maintain cohesion during egestion, which also prevents the dispersion of skeletal elements and preserves their relative positioning within the mass51,52.

The type of association observed in the concretion, combined with its mode of preservation, is unusual for the Romualdo Formation (see Saraiva et al.44). When considered alongside the taphonomic evidence above, these features strongly support the interpretation of the fossil as a regurgitated mass.

There is no clear macroscopic evidence of digestive corrosion on the bones or scales. This suggests that the material was expelled shortly after ingestion, before significant chemical alteration in hard tissues could take place. Digestive etching is more characteristic of cololites and coprolites53, though it has been occasionally reported in regurgitalites (e.g.,54). Degrees of digestive modification within a single regurgitate can vary substantially: modern and fossil analogues document pellets containing minimally digested, sometimes nearly complete elements and/or articulated skeleton subsets, depending on prey type/size and short gastric residence prior to egestion53,55,56,57.

Fracturing of the pterosaur bones most likely occurred during ingestion, as a result of mechanical processing by the predator. The absence of associated soft tissues is consistent with the hard-part bias of regurgitalites, produced by preferential digestion of soft tissues, and may have been compounded by post-burial alteration. Syntheses on bromatolites and regurgitates emphasise these preservational filters, which parsimoniously explain the association of nearly complete fish (likely more recently ingested) with mostly defleshed, fractured pterosaur rostra and teeth (ingested earlier) in our material58,59.

Based on the spatial arrangement of the remains, it is plausible that the predator consumed the pterosaurs first, followed by the fish, and subsequently regurgitated a portion of the ingested mass, likely in response to mechanical discomfort or obstruction caused by pterosaur skeletal elements. Regurgitalites commonly record only a subset of the stomach contents, rather than the complete dietary inventory58,59. Consistent with this, studies of modern predators show that regurgitation often occurs without full gastric evacuation60. This framework explains the association of nearly complete fish with disarticulated and fractured pterosaur cranial elements in our specimen.

Among potential predators in the Romualdo Formation paleoecosystem, spinosaurid dinosaurs and ornithocheiriform pterosaurs stand out as likely candidates, given their piscivorous adaptations and documented presence in the region61,62,63. Notably, direct evidence of pterosaur consumption by spinosaurids, a spinosaurid tooth embedded in an ornithocheiriform cervical vertebra, has been reported from the same formation64.

Although large ornithocheiriforms are also present in the Romualdo Formation, their likely limited stomach volume may have precluded ingestion of such a substantial mass of bone and fish, with the possible exception of Tropeognathus mesembrinus, which reached wingspans exceeding 8 m65. Considering body size, feeding ecology, and existing evidence of pterosaur consumption, spinosaurids emerge as the most plausible producers of the regurgitalite described here, providing additional information on the group’s dietary behavior and trophic interactions.

On the presence of Ctenochasmatidae in the Romualdo Formation

Ctenochasmatids are well-represented in other Lower Cretaceous deposits, most particularly in the Jehol Group of China, as well as the Lagarcito Formation in Argentina66. The previous absence of ctenochasmatid remains in the Romualdo Formation, allied to the regurgitalite nature of the present discovery, suggests that the overall absence of ctenochasmatids in the Romualdo Formation may be attributed to environmental factors. It is plausible that the specimens described here are allochthonous, having been consumed by a large predator in a different environment and subsequently regurgitated within the Romualdo Formation depositional area, which comprises coastal to pelagic paleoenvironments (e.g.,3; Fig. 8).

Ctenochasmatids are overall associated with calm waters, such as lacustrine and lagoonal environments, being rare in fluvial deposits (e.g.,67) and seemingly absent from non-lagoonal marine environments until now. The Barremian-Aptian Yixian Formation, from China, where several ctenochasmatid species have been discovered (e.g., Gegepterus, Gladocephaloideus, Pterofiltrus), is characterized by lacustrine deposits, as well as the Aptian-Albian Lagarcito and Jiufotang formations, in Argentina and China, where respectively Pterodaustro and Forfexopterus were found. In turn, the Solnhofen Limestone beds (Upper Jurassic of Germany), from where Ctenochasma and Gnathosaurus stem, is mostly represented by calm lagoonal paleoenvironments68,69,70. Thus, ctenochasmatids are typically associated with calm water environments, which supports the allochthonous hypothesis.

Fig. 8
figure 8

Artistic reconstruction of the filter-feeding pterosaur Barikibu waridza gen et sp. nov. in the Early Cretaceous Romualdo Formation environment. The spinosaurid in the background represents the putative predator that produced the regurgitalite described herein. Author: Julio Lacerda.

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Conclusion

Bakiribu waridza gen. et sp. nov. represents the first unequivocal record of a ctenochasmatid pterosaur from the tropical latitudes of Gondwana and the first archaeopterodactyloid documented in the Romualdo Formation. Its unique combination of anatomical traits—particularly its very elongated jaws, dense dentition with long and slender teeth, subquadrangular crowns in cross-section, and acrodont-like tooth implantation in both jaws—sheds new light on the evolutionary trajectory of filter-feeding pterosaurs.

The exceptional preservation of the specimen within a regurgitalite, alongside head-aligned fish remains, provides rare direct evidence of trophic interactions in the Early Cretaceous Araripe paleoecosystem.

This discovery not only fills a paleobiogeographic gap in the distribution of Ctenochasmatinae but also underscores the significance of understudied, long-held museum specimens for revealing key evolutionary and paleoecological insights. Bakiribu adds to the growing evidence that the Araripe Basin serves as a critical window into Early Cretaceous biodiversity, ecological complexity, and continental-scale faunal exchanges.