Allaeochelys meylani, Rollot & AbdelGawad & Hamdan & El-Barkooky & Hassan & Joyce, 2025

Allaeochelys meylani sp. nov.

Figures 2 View Fig , 3 View Fig , 4 View Fig , 5 View Fig , 6 View Fig , 7 View ( , 8 View Fig , 9 View Fig , 10 View Fig , 11 View Fig , 12 View Fig , 13 View Fig , 14 View Fig , 15 View Fig , 16 View Fig , 17 View Fig .

Holotype. DPC 7742 , a partial cranium ( Fig. 2 View Fig ).

Type locality. MGL–23, Moghra , Egypt.

Type stratum. Lower units and F1 horizon.

Nomenclatural acts. This publication and its nomenclatural acts were registered at ZooBank on December 13, 2024, prior to publication. The LSID of the publication is urn:lsid:zoobank.org:pub: and that of the new species urn:lsid:zoobank.org:act:.

Diagnosis. Allaeochelys meylani sp. nov. can be diagnosed as a representative of Carettochelyidae by a bone surface ornamentation made up of thick ridges separated by equally sized grooves, presence of a quadrate fossa, presence of a midline carapacial keel, paired nuchal processes, and presence of a lip formed on the visceral side of the posterior peripherals and pygal. Allaeochelys meylani sp. nov. can furthermore be diagnosed as a member of Carettochelyinae by the complete loss of carapacial scutes, a contact between the maxilla and quadratojugal, a foramen posterius canalis carotici interni distant from the posterior border of the parabasisphenoid, and a deep quadrate fossa. Allaeochelys meylani sp. nov. can be differentiated from other carettochelyines by having exceptionally thick cranial bones, a broad bony wall posterior to the orbit, a large fossa formed by the maxilla and premaxilla at the anterior third of the triturating surface, an enlarged foramen arteriomandibulare, a shallow recess in the quadrate formed anterodorsal to the incisura columella auris, a fenestra ovalis completely surrounded by the prootic and opisthotic, a reduced hiatus acusticus, a greatly thickened parabasisphenoid with a tall posterior contact with the basioccipital, a single external foramen for the hypoglossal nerve, a subtle dorsal embayment of the common crus, notably large body size, and presence of a medial process on peripheral II.

Referred material. Early Miocene ( Burdigalian ), Moghra Formation : CGM 67151 , a carapace fragment that includes a partial nuchal, partial left costal I, and left peripherals I and II; DPC 3622 , a partial nuchal; DPC 6436 , a left peripheral IX; DPC 7741 , a pygal; DPC 12585 , a partial right peripheral VI; DPC 12637 , a left peripheral IV; DPC 14555 , costals VIII and suprapygal; CGM 67140 , a plastron fragment that includes a partial left hypoplastron and a partial left xiphiplastron. Early Miocene ( Burdigalian ), Wadi Faregh : BSPG unnumbered, a left peripheral I and partial nuchal ( Dacqué, 1912), now lost.

Etymology. The eponym ‘meylani’ is created in honor of Peter A. Meylan, an eminent turtle paleontologist who provided foundational studies on trionychian anatomy, systematics, and phylogeny ( Meylan, 1987, 1988).

Description

Cranium

General comments. The cranium of DPC 7742 ( Fig. 2 View Fig ) lacks its left half with the exception of the dorsomedial aspect of the left parietal, a small portion of the left frontal, and a tiny fragment that belongs to the left prefrontal. While the right dorsal skull roof is relatively complete, many structures are missing from the right ventral side and the midline, including the palatines, the complete vomer and parabasisphenoid, much of the pterygoid, basioccipital, and supraoccipital, and the complete squamosal.

The skull roof of DPC 7742 exhibits the typical ornamentation of carettochelyids consisting of thick ridges separated by equally sized grooves ( Fig. 2A View Fig ; Joyce, 2014; Skutschas et al., 2017). The specimen presents several additional features observed in other carettochelyids, such as a deep upper temporal emargination, a posteriorly enclosed incisura columella auris, a contact between the maxilla and quadratojugal, a low mandibular condyle, and the presence of a fossa that posteriorly excavates the quadrate ( Fig. 2 View Fig ; Danilov et al., 2017; Harrassowitz, 1922; Havlik et al., 2014; Joyce et al., 2018; Waite, 1905; Walther, 1922; White et al., 2023). DPC 7742 is larger than any other previously described carettochelyid cranium ( Danilov et al., 2017; Harrassowitz, 1922; Havlik et al., 2014; Joyce et al., 2018; Waite, 1905; Walther, 1922; White et al., 2023), with an approximate length of 15 cm (cm) from the anterior margin of the prefrontals to the most posterior preserved aspect of the parietals. By comparison to Carettochelys insculpta (NHMUK 1903.7.10.1), a total length of about 19.5 cm is estimated from the anterior margin of the prefrontals to posterior tip of the crista supraoccipitalis, suggesting a shell length of about 68 cm by reference to the same C. insculpta specimen. The cranium of DPC 7742 is less gracile than that of Anosteira pulchra ( Joyce et al., 2018) and overall similar in shape to that of Anosteira maomingensis ( Danilov et al., 2017) , Allaeochelys libyca ( Havlik et al., 2014) , Carettochelys niahensis ( White et al., 2023) , and Carettochelys insculpta ( Joyce, 2014; Rollot et al., 2024a; Waite, 1905). The specimen is notable in comparison to all previously described specimens by exhibiting exceptionally thick bones ( Fig. 2C, E View Fig ). Despite damage to the cranium, the posterolateral and posteromedial portions of the basioccipital-exoccipitals complex and pterygoid, respectively, form a broad base that suggests the former presence of elongate tubercula basioccipitale, much as in other carettochelyids. The small size of the orbits relative to that of the cranium, the fusion between the basioccipital and exoccipitals, the general size of the cranium (approximately 20 cm when complete), and the thickness of bones suggest that DPC 7742 belongs to a skeletally mature individual ( Figs. 2 View Fig & 3 View Fig ).

Nasal. The nasals are absent in DPC 7742, as in other carettochelyids ( Fig. 2A View Fig ; Danilov et al., 2017; Harrassowitz, 1922; Havlik et al., 2014; Joyce et al., 2018; Waite, 1905; Walther, 1922; White et al., 2023).

Prefrontal. The prefrontal forms the anterodorsal aspect of the cranium ( Fig. 3A–D View Fig ). The notably thick dorsal plate of the prefrontal defines the dorsal margin of the external nares, roofs the fossa nasalis, and forms a minor contribution to the dorsal margin of the orbit ( Fig. 3A, D, E View Fig ). The dorsal plate broadly contacts the maxilla ventrolaterally along a straight horizontal suture, the frontal posteriorly along a slightly convex suture, and its counterpart medially ( Fig. 3A & E View Fig ). The prefrontal, maxilla, and premaxilla jointly form the unusually thickened margins of the external nares ( Fig. 3E View Fig ). Thickened anterior margins contrast with the morphology observed in other carettochelyids, where the margins of the external nares are thin or barely thickened ( Danilov et al., 2017; Joyce et al., 2018; Rollot et al., 2024a, 2024b; Waite, 1905; Walther, 1922; White et al., 2023). Although the contribution of the prefrontal to the orbit appears to be relatively large in dorsal view, its contribution to the margin of the orbit per se is extremely small. This is mostly caused by a constriction of the prefrontal exposure along the orbit margin formed by the frontal posteriorly and the maxilla anteriorly, the two latter bones approaching one another very closely in this region ( Fig. 3D View Fig ). The descending process of the prefrontal of DPC 7742 laterally contacts the ascending process of the maxilla within the orbit along a broad and long suture that extends from the anterior limit of the foramen orbito-nasale to the anterior margin of the orbit ( Fig. 3D, E View Fig ). The process contributes to the anterodorsal and dorsal margin of the large foramen orbito-nasale. Posteriorly, the descending process of the prefrontal forms a protruding sheet of bone that is posteriorly damaged ( Fig. 3D View Fig ). This sheet likely had a posterior contact with the palatine and vomer, as in Carettochelys insculpta ( Rollot et al., 2024a) . The dorsal surface of this posterior bony process contacts the crista cranii, thereby delimiting an oval secondary foramen between the fossa orbitalis and fossa nasalis. In Carettochelys insculpta , such a foramen is not present, but the crista cranii of the frontal closely approaches the descending process of the prefrontal, forming a slit-like passage between the orbital and nasal fossae ( Fig. 4 View Fig ). This slit was recently named the ophthalmic slit because it serves as the passage for the ophthalmic branch of the trigeminal nerve (CNV 1; Rollot et al., 2024a). As the foramen observed in the anterodorsomedial corner of the orbit of DPC 7742 very likely had the same purpose as the ophthalmic slit in Carettochelys insculpta , we propose to name the foramen in DPC 7742 “ophthalmic nerve foramen.” An ophthalmic nerve foramen is also present in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys niahensis ( White et al., 2023) , but likely not in Anosteira pulchra ( Joyce et al., 2018) , in which a slit-like passage seems to be preserved. Along the posterodorsal aspect of the posterior extension of the descending process, the prefrontal contacts a small piece of bone which inserts between it and the crista cranii of the frontal ( Fig. 4B View Fig ). A supplementary bone can occasionally be identified between the prefrontal and vomer in Carettochelys insculpta . In NHMUK 1903.7.10.1 it is present only on the left side and occupies a space that on the other side is taken by the most posterior aspect of the descending process of the prefrontal. In DPC 7742, the additional bone is located slightly more dorsal and appears to be blockier in shape, but is found in a similar position to that of NHMUK 1903.7.0.1. We thus speculate that this small bony unit represents an ossification anomaly that might be related to the prefrontal. It is unlikely that this additional bone belongs to the palatine or the vomer, as the former bone lacks such an anterior extension in other carettochelyids, and the latter bears low dorsolateral processes that do not extend dorsally to such a degree ( Fig. 4B View Fig ).

Frontal. The frontal is a nearly square bone that forms the dorsomedial portion of the skull roof ( Fig. 3A View Fig ). The thickened dorsal plate of the frontal contacts the prefrontal anteriorly along a concave suture, the postorbital laterally along a concave suture, the dorsal plate of the parietal posteriorly along a straight transversal suture, and its counterpart medially ( Fig. 3A &D–E View Fig ). The frontal forms a short process anterolaterally that contributes slightly to the orbit margin and prevents the prefrontal and postorbital from contacting one another ( Fig. 3A & D–E View Fig ). Ventrally, the frontal forms a robust, dorsoventrally expanded crista cranii ( Figs. 3D View Fig & 4B View Fig ). The crista cranii forms the lateral wall of the rounded sulcus olfactorius, which is tall and relatively short, and appears to be slightly narrower than that of Allaeochelys libyca ( Rollot et al., 2024b) , Carettochelys niahensis ( White et al., 2023) , and Carettochelys insculpta ( Rollot et al., 2024a) . Within the roof of the orbit, the crista cranii laterally forms a series of small foramina with unknown affinities. A low ridge extends anterodorsally from the lateral surface of the crista cranii and parasagittally along the most anterior aspect of the frontal ventral surface, which delineates a depression in the roof of the orbit, as in Carettochelys insculpta , albeit deeper ( Rollot et al., 2024a). Anteroventrally, the crista cranii contacts the posterior aspect of the descending process of the prefrontal, and collectively with the latter forms the ophthalmic nerve foramen ( Figs. 3D View Fig & 4B View Fig ), as in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys niahensis ( White et al., 2023) . This contact between the crista cranii and descending process of the prefrontal is anteroposteriorly elongate in DPC 7742 and appears to be greater than that observed in Allaeochelys libyca ( Rollot et al., 2024b) but is overall similar to that of Carettochelys niahensis ( White et al., 2023) . The posteroventral part of the crista cranii is continuous with the descending process of the parietal and both bones extend relatively far ventrally, so that the foramen interorbitale was likely greatly reduced in size ( Fig. 3C View Fig ). A similar arrangement was likely present in Carettochelys niahensis ( White et al., 2023) , but not in Anosteira pulchra ( Joyce et al., 2018) and Carettochelys insculpta ( Rollot et al., 2024a; Waite, 1905; Walther, 1922).

Parietal. The left parietal is heavily damaged, but its right counterpart preserves most of its anatomy, with the exception of the most posterior and anteroventrolateral portions ( Fig. 3A–C View Fig ). On the skull roof, the thickened parietal contacts the frontal anteriorly along a transverse suture, the postorbital anterolaterally, and its counterpart medially ( Fig. 3A View Fig ). Within the upper temporal fossa, the parietal contacts the prootic ventrolaterally and the supraoccipital posteroventrolaterally ( Fig. 3A, D & F View Fig ). The parietal forms the medial and anteromedial margins of the upper temporal emargination, which is deep as in other carettochelyids ( Danilov et al., 2017; Havlik et al., 2014; Joyce et al., 2018; Waite, 1905; Walther, 1922; White et al., 2023). The ventral aspects of the descending process of the parietal, or processus inferior parietalis, are damaged on both sides of the specimen. The remaining, dorsal aspects of the descending process, however, are developed as a ventrally expanded sheet of bone that forms the anterolateral part of the secondary braincase wall and is anteriorly continuous with the crista cranii of the frontal. The parietal forms the medial portion of the well-developed processus trochlearis oticum, which constitutes a distinct overhanging lip best seen in ventral view ( Fig. 3A–B View Fig ). This lip extends anteriorly along the ventrolateral and lateral surface of the postorbital and jugal, respectively, as in Carettochelys insculpta , but less distinctly so ( Rollot et al., 2024a). Ventromedial to this lip and continuous with the processus trochlearis oticum, two shallow fossae can be identified along the lateral surface of the braincase wall ( Fig. 3B View Fig ). The anterior fossa is formed by the parietal, located just posterior to the suture with the frontal, and is anterolaterally bordered by a shallow ridge formed by the parietal and frontal. The posterior fossa is encompassed by the prootic and parietal and is larger than the anterior one. Such fossae were not reported for other carettochelyids, but their shallow nature might complicate their recognition in many fossils. Nevertheless, a similar anterior fossa is present in Allaeochelys libyca ( Rollot et al., 2024b) , but both fossae are clearly absent in Carettochelys insculpta ( Rollot et al., 2024a) . The braincase is greatly enlarged anterolaterally suggesting the development of broad cerebral hemispheres ( Fig. 3B View Fig ), as in Carettochelys insculpta ( Rollot et al., 2024a) . The most anterior section of the braincase, i.e. the area that housed the olfactory bulbs, is notably constricted in DPC 7742, and narrower than in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) . At the level of its contact with the supraoccipital within the braincase, a dorsoventral constriction of the braincase is apparent, corresponding to the cartilaginous rider ( Werneburg et al., 2021). Additional contacts of the parietal with the pterygoid and epipterygoid are generally present in carettochelyids, but the damage that affects the anteroventral portions of the descending process of the parietal prevents us from making any further statements.

Postorbital. The postorbital forms the posterior margin of the orbit and the anterior margin of the deep upper temporal emargination ( Fig. 3A & D–E View Fig ). The postorbital contacts the frontal laterally along a rounded, convex suture, the jugal ventrolaterally, the quadratojugal posteroventrolaterally, and the parietal posteromedially ( Fig. 3A & D–E View Fig ). The ventrolateral half of the postorbital is notably enlarged ( Fig. 3E View Fig ), forming the dorsal part of a thin but mediolaterally expanded bony wall posterior to the orbit that is reminiscent of the septum orbitotemporale seen in pleurodires (sensu Gaffney et al., 2006) and trionychids. This septum is buttressed by a ventral ridge that is continuous with the ventral ridges of the parietal medially and the jugal ventrally, as in Carettochelys insculpta ( Rollot et al., 2024a) . At about one third of its length, the ridge that crosses the ventral surface of the postorbital gives off a short accessory ridge that extends anterodorsally ( Fig. 3B View Fig ). Those two ridges collectively divide the ventral surface of the postorbital into three distinct, concave areas: one facing anteroventrally, one facing anteromedially, and one facing posteriorly.

Jugal. The jugal is a relatively small bone that forms the posteroventral wall of the orbit and the anterior margin of the lower temporal fossa collectively with the maxilla ( Fig. 3D–E View Fig ). On the external surface, the jugal contacts the postorbital dorsally, the maxilla anteroventrally, and the quadratojugal posteriorly and posteroventrally ( Fig. 3D–E View Fig ). Medially, an additional contact between the jugal and palatine, as seen in Carettochelys insculpta , might have occurred, but this cannot be ascertained with certainty as the palatine is missing. The contribution of the jugal to the orbit margin is greatly restricted by a descending process of the postorbital and an ascending process of the maxilla ( Fig. 3D–E View Fig ). This contrasts with available specimens of Anosteira maomingensis ( Danilov et al., 2017) , Anosteira pulchra ( Joyce et al., 2018) , and Carettochelys niahensis ( White et al., 2023) , where the jugal forms most of the posterior or posteroventral margin of the orbit. In Carettochelys insculpta , the degree of contribution of the jugal to the orbit margin appears to be quite variable as affected by both ontogenetic and individual variation, with larger individuals having a reduced contribution ( Rollot et al., 2024a; Walther, 1922). The jugal of DPC 7742 forms a well-developed medial process that broadly overlays the maxilla and forms the ventral half of the septum orbitotemporale, which is otherwise formed by the postorbital ( Fig. 3E View Fig ).

Quadratojugal. The quadratojugal is a large, platelike bone that forms the lateral margin of the deep upper temporal emargination ( Fig. 3A & D View Fig ). The quadratojugal contacts the quadrate posteriorly along a deeply concave suture, the postorbital anterodorsally, the jugal anteriorly, and the maxilla anteroventrally below the jugal ( Fig. 3A & D–E View Fig ), as in Carettochelys niahensis ( White et al., 2023) and Carettochelys insculpta ( Waite, 1905; Walther, 1922). A cheek emargination is completely absent in DPC 7742 ( Fig. 3D View Fig ). Although the cheek emargination is generally reduced in carettochelyids, inter- and intraspecific variation occurs and emargination varies from a moderate state in Anosteira maomingensis ( Danilov et al., 2017) to very shallow in Anosteira pulchra ( Joyce et al., 2018) and Carettochelys niahensis ( White et al., 2023) . In Carettochelys insculpta , individual variation must also be considered as cheek emargination ranges from a shallow notch (see Rollot et al., 2024a) to complete absence ( Waite, 1905). The quadratojugal in DPC 7742 does not contribute to the cavum tympani ( Fig. 3D View Fig ). The posterodorsal process of the quadratojugal is short and barely extends above the cavum tympani ( Fig. 3D View Fig ). A posterior contact with the squamosal was likely absent, as in other carettochelyids, as the dorsal surface of the quadrate just posterior to the posterodorsal process of the quadratojugal is smooth and lacks an articular facet. The posteroventral process of the quadratojugal is short and posteriorly ends slightly anterior to the level of the incisura columella auris ( Fig. 3D View Fig ). The process is dorsoventrally tall, much as in Allaeochelys libyca ( Havlik et al., 2014; Rollot et al., 2024b), but unlike Carettochelys insculpta , where it ends in a low, pointed process ( Rollot et al., 2024a).

Squamosal. The squamosals are not preserved in DPC 7742.

Premaxilla. Although the premaxilla is damaged in DPC 7742, it is complete enough to allow confirmation that it is a single, fused, midline element that is missing most of its left half ( Fig. 3E View Fig ). The premaxilla is a small but thick bone that forms the ventral margin of the external nares and floors the fossa nasalis anteriorly ( Fig. 3E View Fig ). The only preserved contact of the premaxilla is lateral with the maxilla ( Fig. 3E View Fig ). We are not able to assess other possible contacts of the premaxilla as its medial and posterior aspects are missing, but comparison with Carettochelys insculpta suggests that none were present. Together with the maxilla and the prefrontal, the premaxilla forms the greatly thickened margins of the external nares ( Fig. 3E View Fig ). This thickening is unique among carettochelyids, as the margin of the external nares is otherwise either thin or only slightly thickened ( Danilov et al., 2017; Joyce et al., 2018; Rollot et al., 2024a, 2024b; Waite, 1905; Walther, 1922; White et al., 2023). The foramen praepalatinum is not developed, as in other carettochelyids ( Danilov et al., 2017; Rollot et al., 2024a; Waite, 1905; Walther, 1922). Instead, the premaxilla anteriorly frames the enlarged foramen intermaxillaris ( Fig. 3B View Fig ).

Maxilla. The right maxilla is preserved almost fully intact. On the external surface, the maxilla contacts the premaxilla anteromedially, the prefrontal dorsally, the jugal posteriorly, and the quadratojugal posteroventrally ( Fig. 3D–E View Fig ). Articular scars and a comparison with Carettochelys insculpta suggest the maxilla may have had additional contacts with the palatine and pterygoid. Anteriorly, the maxilla forms the lateral margin of the external nares, which are extremely thickened ( Fig. 3E View Fig ). This morphology is unique among carettochelyids, as this area is either thin or barely thickened in other taxa ( Danilov et al., 2017; Joyce et al., 2018; Rollot et al., 2024a, 2024b; Waite, 1905; Walther, 1922; White et al., 2023). The maxilla forms the anterior and ventral margin of the orbit and the anteroventral and ventral margin of the large foramen orbito-nasale ( Fig. 3D View Fig ). The maxilla floors much of the fossa orbitalis and forms the foramen supramaxillare in the anterior third of the fossa ( Fig. 5A, B View Fig ; sensu Albrecht, 1967). The foramen supramaxillare leads into the canalis infraorbitalis, which extends anteroventrolaterally through the maxilla ( Fig. 5C View Fig ). At about the same level as the foramen supramaxillare, the maxilla forms the foramen alveolare superius, which is located within the nasal cavity just anteroventromedial to the foramen orbito-nasale ( Fig. 5A, B View Fig ), as in Carettochelys insculpta . The foramen alveolare superius leads into the canalis alveolaris superior, which extends anterolaterally and merges with the canalis infraorbitalis ( Fig. 5C View Fig ). The resulting canal retains the name canalis alveolaris superior (sensu Albrecht, 1967) and extends anteriorly through the maxilla. Several canals branch from the canalis alveolaris superior to its course towards the most anterior portion of the cranium, and we here report the major accessory canals that were identified in the CT scans. Just anterior to the point where the canalis alveolaris superior merges with the canalis infraorbitalis, two canals successively branch off the canalis alveolaris superior at the level of the anterior margin of the orbit. These canals extend dorsally within the maxilla and exit the cranium along the anterior wall of the fossa orbitalis ( Fig. 5B, C View Fig ). At about mid-length between the external nares and anterior margin of the orbit, another canal branches off the canalis alveolaris superior and extends anteromedially through the maxilla and premaxilla, but its anterior exit remains unclear in the CT scans. In Carettochelys insculpta , however, this canal exits along the ventral margin of the external nares at the suture between the maxilla and premaxilla ( Rollot et al., 2024a). Anteriorly, the canalis alveolaris superior of DPC 7742 exits the skull by means of a maxillary foramen located along the ventrolateral margin of the external nares ( Figs. 3E View Fig & 5C View Fig ). This foramen is relatively small and is also present in Carettochelys insculpta ( Rollot et al., 2024a) and likely Carettochelys niahensis ( White et al., 2023) . The abovementioned two canals and their respective foramina very likely contained branches of the superior alveolar artery, as in Carettochelys insculpta . The superior alveolar artery enters the foramen alveolare superius and extends anteriorly through the canalis alveolaris superior ( Rollot et al., 2024a). The position of an anterior foramen for the canalis alveolaris superior along the lateral margin of the external nares seen in carettochelyids is quite unusual for turtles, as the canalis alveolaris superior generally gives off numerous, small accessory canals that connect to the ventrolateral surface of the maxilla and the triturating surface, and anteriorly ends within the maxilla and premaxilla in a series of very small canals that either become mixed up with the porosity of the bones or join the anterior and ventral surfaces of these bones. Carettochelys insculpta possesses a protruding, fleshy snout ( Walther, 1922), and the location of a foramen for the passage of a branch of the superior alveolar artery along the ventrolateral margin of the bony external nares may be linked to the need to supply the proboscis with blood, relative to other turtles that lack a proboscis. Posterior to the foramen supramaxillare, the maxilla forms a groove in the floor of the fossa orbitalis that extends posteromedially from the foramen, closely approaching the maxilla-jugal suture in the posteroventromedial corner of the orbit, and extending towards ventral along the posteromedial surface of the maxilla ( Fig. 5A View Fig ). This vertical portion of the groove corresponds to the location of the foramen palatinum posterius in other carettochelyids ( Danilov et al., 2017; Joyce et al., 2018; Waite, 1905; Walther, 1922), and we therefore interpret this passage as such in DPC 7742. Given the inferred position of the foramen palatinum posterius, the foramen was likely formed by the maxilla and palatine as in Anosteira maomingensis ( Danilov et al., 2017) and Anosteira pulchra ( Joyce et al., 2018) . In Carettochelys insculpta , however, bony contributions to the foramen palatinum posterius are variable and subject to ontogenetic variation as the foramen is formed by the palatine and maxilla in juveniles but only by the palatine in adults ( Rollot et al., 2024a). Individual variation might also affect which bones are contributing to the foramen palatinum posterius, as the pterygoid closely approaches the foramen in other specimens, but this remains unclear as detailed descriptions are lacking for the specimens of interest (see Waite, 1905; Walther, 1922).

The triturating surfaces of DPC 7742 are highly unusual, not only for carettochelyids specifically, but also among turtles in general. In lateral view, the ventral margin of the maxilla forms a wavy labial margin, which is partially created by the development of a low, tooth-like cusp below the eye ( Fig. 3D View Fig ). In ventral view, the low but broad labial ridge jointly formed by the premaxilla and maxilla is not straight for its entire length, as in carettochelyids. Instead, the labial ridge forms a short process at about one-third of its anteroposterior length that protrudes medially into the triturating surface and separates it into a half-cup-like fossa anteriorly and a triangular groove posteriorly ( Fig. 5D, E View Fig ). The fossa is formed by the most anterior part of the maxilla and the whole premaxilla. A nuanced fossa is present in Carettochelys insculpta ( Rollot et al., 2024a) , but not in Anosteira maomingensis ( Danilov et al., 2017) and Anosteira pulchra ( Joyce et al., 2018) . A closer look at the CT scans of the recently published stained juvenile specimen of Carettochelys insculpta USNM 327960 (see MorphoSource; Rollot et al., 2024a) reveals that the shape of this fossa is reflected in the shape of the rhamphotheca. In USNM 327960, the ventral, cutting edge of the rhamphotheca is not straight but rather forms a slight lateral excavation for a short distance at the level of the posterior part of the fossa formed by the maxilla. We therefore suggest that a similar structure was present on the rhamphotheca in DPC 7742. As the fossa is larger than that identified in Carettochelys insculpta (adult or juvenile; Rollot et al., 2024a), it is very likely that the rhamphotheca of DPC 7742 was excavated to a greater degree than in Carettochelys insculpta . Although little is known about the anatomy of the rhamphotheca in turtles, we hypothesize that the function of this excavation in the rhamphotheca was to allow the processing of specific types of food. Carettochelys insculpta is a generalist omnivore with a predilection towards herbivory ( Georges & Kennett, 1989; Heaphy, 1990), and the similarity between the labial ridges and triturating surfaces of Carettochelys insculpta and DPC 7742 highlight that the two taxa likely had similar diets. The presence of a hollow on the rhamphotheca might represent a functional advantage in shearing fibrous food, but further studies on the anatomy of turtle rhamphothecae are needed to test this hypothesis.

Palatine. The palatines are not preserved in DPC 7742.

Vomer. The vomer is not preserved in DPC 7742.

Pterygoid. Only the posterior half of the right pterygoid is preserved in DPC 7742 ( Figs. 3B View Fig & 6 View Fig ). The preserved portion of the pterygoid contacts the basioccipital-exoccipital complex posteromedially, the quadrate posterolaterally and laterally, the opisthotic posterodorsally and dorsally, and the prootic anterodorsally ( Fig. 3B–C & F View Fig ). The medial surface of the pterygoid and anteroventral surface of the basioccipital-exoccipital complex are intact and show the medial articulation facets with the parabasisphenoid ( Fig. 6D View Fig ). The ventral surface of the posterior half of the pterygoid is excavated to form a deep pterygoid fossa ( Fig. 6C, D View Fig ), as in Anosteira maomingensis ( Danilov et al., 2017) , Allaeochelys crassesculpta ( Harrassowitz, 1922) , Allaeochelys libyca ( Havlik et al., 2014; Rollot et al., 2024b), and Carettochelys insculpta ( Waite, 1905; Walther, 1922), but not Anosteira pulchra ( Joyce et al., 2018) . The pterygoid fossa of DPC 7742 is also notably broad, as in Anosteira maomingensis ( Danilov et al., 2017) and Allaeochelys libyca ( Havlik et al., 2014; Rollot et al., 2024b), but not in Carettochelys insculpta ( Rollot et al., 2024a; Waite, 1905; Walter, 1922) where the fossa is narrow. The ventromedial margin of the pterygoid fossa is marked by a low ridge that extends anteroposteriorly for about half of the preserved length of the pterygoid ( Fig. 6D View Fig ). The ridge is broken, but likely formed a well-developed, enfolded ridge that partially covered the pterygoid fossa ventrally, as in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Joyce, 2014; Walter, 1922), but not Anosteira maomingensis ( Danilov et al., 2017) and Anosteira pulchra ( Joyce et al., 2018) , where the ridge appears to be absent. Posteriorly, the pterygoid forms the entire foramen posterius canalis carotici interni, which is located just ventrolateral to the small fenestra postotica, to which the pterygoid only contributes ventrally ( Fig. 6C View Fig ). The foramen posterius canalis carotici interni is hidden from ventral view ( Fig. 6D View Fig ), as in Allaeochelys libyca ( Rollot et al., 2024b) . The foramen posterius canalis carotici interni leads into the canalis caroticus internus, which is a long canal oriented anteromedially that crosses the full preserved portion of the pterygoid ( Fig. 6B View Fig ). The anterior third of the canalis caroticus internus is more medially inclined than the rest of the canal, and the anterior end of the preserved portion of the canal is located at the level of the inferred sutural contact between the pterygoid and parabasisphenoid. The missing portion of the canal anteriorly corresponds to the canalis caroticus basisphenoidalis, and the canalis caroticus internus is completely preserved and apparently longer than that of Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) , mostly because it enters the skull posteriorly. The area formed by the pterygoid and that separates the foramen posterius canalis carotici interni from the fenestra postotica forms a smooth, curved bony margin ( Fig. 6C View Fig ), which we interpret as corresponding to the location of the split between the internal carotid artery and stapedial artery by reference to the circulatory system of Carettochelys insculpta ( Rollot et al., 2024a) . Dorsomedial to the foramen posterius canalis carotici interni, the pterygoid forms the lateral margin of a small foramen, which is medially bordered by the opisthotic ( Fig. 6C View Fig ). The foramen is located in the same position as the foramen oropharyngeale (sensu Evers & Al Iawati, 2024), which in Carettochelys insculpta ( Rollot et al., 2024a) and Allaeochelys libyca ( Rollot et al., 2024b) serves as the passage of the glossopharyngeal nerve (CN IX) from the recessus scalae tympani to the back of the skull. Here, the foramen leads into a small canal that can only be traced in the CT scans for a short distance along the pterygoid-opisthotic suture. It is likely that the canal extends further anteriorly to join the recessus scalae tympani, as in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) , but we are not able to observe it.

The pterygoid floors the cavum acustico-jugulare and recessus scalae tympani ( Fig. 6A View Fig ). The posterior third of the cavum acustico-jugulare is greatly constricted, forming a funnel-like passage towards the central part of the cavum ( Fig. 6A View Fig ). The posterodorsal surface of the pterygoid forms a low, but moderately broad and elongate bony platform that contacts the paroccipital process of the opisthotic dorsally ( Fig. 6A View Fig ), as in other carettochelyids ( Danilov et al., 2017; Havlik et al., 2014; Joyce, 2014; Rollot et al., 2024a, 2024b). The area anterior to the recessus scalae tympani is slightly raised and forms a cup-like articulation facet for the contact of the pterygoid with the broad and expanded processus interfenestralis of the opisthotic ( Fig. 6A View Fig ). The anterior and lateral edge of this cup-like platform also form low ridges that embrace the anterior and lateral aspects of the processus interfenestralis ( Fig. 6A View Fig ). Anterior to this raised, cup-like platform, the pterygoid is inclined anteroventrally and forms an articulation facet for the dorsal contact with the prootic ( Fig. 6A View Fig ). The central part of the cavum acustico-jugulare is slightly expanded mediolaterally, but the anterior third of the cavum is constricted like its posterior third by raised ridges of the pterygoid medially and laterally ( Fig. 6A View Fig ). Anteriorly, the cavum acustico-jugulare is closed by a narrow wall of bone formed by the prootic dorsally and the pterygoid ventrally and is therefore not anteriorly continuous with the canalis cavernosus ( Fig. 6A View Fig ). Laterally, the pterygoid forms the anteroventral margin of the enlarged foramen arteriomandibulare, which served as a passage for the mandibular artery and lateral head vein from the cavum acustico-jugulare towards the lateral side of the cranium. Just lateral to the lateral raised ridge that delineates the anterior portion of the cavum acustico-jugulare, the pterygoid forms a narrow bony platform collectively with the prootic, which we interpret as an extremely constricted canalis cavernosus that extends between the foramen arteriomandibulare and foramen nervi trigemini, as in Carettochelys insculpta ( Rollot et al., 2024a; see Prootic for further details).

Epipterygoid. Although the right trigeminal area is present, the right epipterygoid is not preserved in DPC 7742, but indirect evidence is available suggesting that it was likely present. Some portions of the anterolateral braincase wall formed by the prootic are preserved, including the posterior half of the foramen nervi trigemini sensu stricto (sensu Rollot et al., 2024b). The anterodorsal margin of the foramen nervi trigemini is formed by an anteroventral process of the prootic, as observed in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) . In the latter two taxa, this bony bump of the prootic also serves as an articulation facet with the dorsal edge of the epipterygoid. This suggests by analogy that the epipterygoid was present in DPC 7742 as well. Additional, albeit more equivocal evidence can be found in the area between the foramen arteriomandibulare and foramen nervi trigemini. The pterygoid and prootic form a narrow, bony platform that extends between these two foramina. According to our digital reconstructions, the anterior half of this platform is exclusively formed by the prootic, although the sutural contact between the pterygoid and prootic in that area remains unclear in the CT scans. The lateral surface of this narrow platform appears to be broken, but that could also correspond to an articulation facet as observed in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) , where the epipterygoid medially rests on the pterygoid in the same area. In DPC 7742, however, we note that the lateral surface of the prootic below the bony platform is smooth and does not exhibit a rough surface similar to the articulation facet of Allaeochelys libyca ( Rollot et al., 2024b) . As the bony arrangement between the prootic, pterygoid, and quadrate is overall similar in DPC 7742, Allaeochelys libyca , and Carettochelys insculpta , we hypothesize that the epipterygoid in DPC 7742 was likely similar in shape and had similar contacts than that of its two abovementioned relatives.

Quadrate. The quadrate forms the posterolateral aspect of the cranium, and the right element is fully preserved in DPC 7742. The quadrate forms the lateral third of the processus trochlearis oticum and the anterodorsal, anterior, and ventral margins of the cavum tympani ( Fig. 7 View ( ). The quadrate also fully encloses the incisura columella auris ( Fig. 7A View ( ), as in other carettochelyids ( Danilov et al., 2017; Havlik et al., 2014; Joyce, 2014; Joyce et al., 2018; Waite, 1905; Walther, 1922). The cavum tympani is funnel-shaped and lacks any evidence of an antrum postoticum ( Fig. 7A View ( ). Though variable, at least a minor antrum postoticum is present in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) . As a result, the broad, triangular scar that articulates with the squamosal is not interrupted by the antrum postoticum in DPC 7742.

Within the upper temporal fossa, the quadrate contacts the prootic anteromedially and the opisthotic posteromedially and forms the posterolateral margin of the large foramen stapedio-temporale ( Figs. 2A View Fig & 7E View ( ). Within the lower temporal fossa, the quadrate contacts the prootic anterodorsomedially, the pterygoid anteroventromedially, and the quadratojugal anterolaterally ( Fig. 3B View Fig ). The quadrate forms the posterior margin of the enlarged foramen arteriomandibulare, which deeply expands posteriorly within the latter bone. Although some parts of the margins formed by the quadrate are damaged (i.e. the dorsal and ventral margins), the posterior portion of the margin is smooth and appears to be intact in the CT scans, highlighting that the foramen arteriomandibulare is greatly expanded and therefore larger than that of Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) . The quadrate is recessed just dorsal to the foramen arteriomandibulare, creating a fossa posteromedial to the processus trochlearis oticum, of which the anterior half is formed by the prootic ( Fig. 7D View ( ). The quadrate is also slightly recessed just anterodorsal to the mandibular condyle and forms two fenestra-like passages between the lower temporal fossa and the quadrate fossa, of which the lateral passage is the largest ( Fig. 7D View ( ). The medial passage occupies a similar position to the anterior quadrate foramen of Allaeochelys libyca (sensu Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) , but instead of leading into a canal that extends dorsally through the quadrate and joins the quadrate fossa, it constitutes a fenestra that directly opens into the quadrate fossa. The mandibular condyle is low and ventrally oriented as in other carettochelyids ( Figs. 3D View Fig & 7A View ( ; Danilov et al., 2017; Havlik et al., 2014; Joyce et al., 2018; Waite, 1905; Walther, 1922). The lateral articular facet is larger than the medial one ( Fig. 7D View ( ), also similar to other carettochelyids, although the size difference between the facets seems more significant in Allaeochelys libyca ( Rollot et al., 2024b). A narrow and deep, centrally placed sulcus separates the two articular facets from one another, shaping the transition from one facet to the other as a steep boundary ( Fig. 7B & D View ( ), which slightly differs from the more curved and smoother transition seen in Anosteira maomingensis ( Danilov et al., 2017) , Anosteira pulchra ( Joyce et al., 2018) , Allaeochelys libyca ( Rollot et al., 2024b) , and Carettochelys insculpta ( Rollot et al., 2024a) . The posterior surface of the quadrate is greatly excavated ( Fig. 7B View ( ) and forms a deep quadrate fossa as in Allaeochelys crassesculpta ( Harrassowitz, 1922) and Allaeochelys libyca ( Havlik et al., 2014) , which is slightly deeper than that in Carettochelys insculpta ( Rollot et al., 2024a; Waite, 1905; Walther, 1922). Within the quadrate fossa, the quadrate has several ridges that delineate shallow recesses and give the quadrate fossa a complex surface ( Fig. 7B View ( ). Such a complex surface is also visible within the quadrate fossa of Allaeochelys libyca ( Rollot et al., 2024b) and maybe to a lesser extent in large individuals of Carettochelys insculpta ( Rollot et al., 2024a) . Posterolateral to the quadrate fossa, the quadrate forms a slightly medially-enfolded ridge that starts from slightly above the lateral aspect of the mandibular condyle and extends dorsomedially. A similar ridge is present in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) , where it forms the posterolateral margin of the quadrate fossa. However, in DPC 7742, this ridge delineates an additional shallow, narrow fossa, where the anterior margin is marked by another low ridge that extends dorsoventrally and forms the actual entrance for the quadrate fossa ( Fig. 7B View ( ). Dorsomedial to the quadrate fossa, the quadrate forms the lateral margin of the fenestra postotica and the lateral wall of the cavum acustico-jugulare. Along the posterior third of the cavum acustico-jugulare, the quadrate forms a low ridge near mid-height that delineates dorsal and ventral grooves, which we interpret as the path of the stapedial artery and lateral head vein, respectively ( Fig. 7C View ( ). The dorsal groove extends anteriorly and can be followed within the cavum acustico-jugulare along the dorsal aspect of the quadrate. Anterolaterally, the groove is continuous with a shallow recess that is located just anterodorsal to the incisura columella auris ( Fig. 7C View ( ). The ventromedial floor of the recess forms the posterodorsal margin of the foramen arteriomandibulare and the anterior wall of the recess forms the posterior wall of the canalis stapedio-temporalis. The medial margin of the recess anterior wall and the prootic collectively form a ridge that delineates a fenestra between the cavum acustico-jugulare ventrally and canalis stapedio-temporalis dorsally, and serves as a passage for the stapedial artery ( Fig. 7C View ( ). Anteroventral to this fenestra, the recess is continuous with a groove that extends anteroventrally along the ventral surface of the prootic and passes through the anterior margin of the foramen arteriomandibulare to connect to the lateral side of the cranium. The groove is reminiscent with that identified in the same area in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) , which was shown to reflect the path of the mandibular artery, and we herein follow this interpretation for the groove in DPC 7742. The path described above for the stapedial (and mandibular) artery is very similar to that of Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) , although these two differ from DPC 7742 in that they lack the medial recess of the quadrate and instead have a clearly defined groove.

Prootic. The right prootic is almost completely preserved in DPC 7742. Within the upper temporal fossa, the prootic contacts the parietal anteromedially, the supraoccipital posteromedially, the opisthotic posteriorly, and the quadrate laterally ( Fig. 3A View Fig ). The prootic also forms the anteromedial margin of the foramen stapedio-temporale and the medial half of the robust processus trochlearis oticum ( Figs. 3A View Fig & 8A View Fig ). Within the lower temporal fossa, the prootic contacts the descending process of the parietal anterodorsomedially, the pterygoid anteroventromedially, and the quadrate posterolaterally ( Fig. 3B View Fig ). A contact with the epipterygoid is also inferred to have occurred anteriorly (see Epipterygoid; Fig. 8B, C View Fig ). The prootic forms the posterior and dorsal margin of the foramen nervi trigemini sensu stricto (sensu Rollot et al., 2024b) and the anterior and anterodorsal margin of the foramen arteriomandibulare ( Fig. 8C View Fig ). Between the foramen nervi trigemini sensu stricto and foramen arteriomandibulare, the prootic laterally forms a broad bulge ( Fig. 8C View Fig ), which visually separates the foramen nervi trigemini sensu stricto from the foramen arteriomandibulare as in Allaeochelys libyca ( Rollot et al., 2024b) . Ventrally, the prootic and pterygoid collectively form a narrow platform that extends from the foramen arteriomandibulare to the foramen nervi trigemini sensu stricto ( Fig. 8C View Fig ). As described above, we infer that the posteroventral half of the epipterygoid was likely located in that area and medially contacted the prootic and pterygoid (see Epipterygoid). The morphology of the area between the foramen arteriomandibulare and foramen nervi trigemini sensu stricto would therefore be greatly reminiscent of that observed in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) , in which the epipterygoid forms the anterolateral wall of an extremely constricted canalis cavernosus. This hypothesis is further supported by the absence of a canal that extends anteromedially from the anterior wall of the cavum acustico-jugulare into the braincase, by the great degree of similarity in the morphology of the cava acustico-jugulare of DPC 7742, Allaeochelys libyca ( Rollot et al., 2024b) , and Carettochelys insculpta ( Rollot et al., 2024a) , and by the location of the lateral foramen of the canalis nervus hyomandibularis proximalis (CN VIIhyo; sensu Rollot et al., 2021), which transmits the proximal part of the hyomandibular branch towards the canalis cavernosus, just medial to the anterior margin of the foramen arteriomandibulare. The prootic forms a groove along its ventral surface, dorsomedial to the anterior margin of the foramen arteriomandibulare, which extends anteroventrally from the canalis stapedio-temporalis to the anterior margin of the foramen arteriomandibulare. This groove likely transmitted the mandibular artery (see Quadrate). The prootic also forms three shallow recesses along the anterior wall of the cavum acustico-jugulare, between the anterior margin of the fenestra ovalis and anterior margin of the foramen arteriomandibulare. The recesses are located dorsomedially, dorsally, and ventrally, and separated from one another by low ridges. The prootic forms the anterior half of the cavum labyrinthicum, the anterior half of the anterior semicircular canal, and the anterior margin of the fenestra ovalis ( Fig. 8A, B View Fig ). The fenestra ovalis is completely enclosed by the prootic and opisthotic ( Fig. 8A View Fig ), which differs from Carettochelys insculpta , where it is not fully surrounded by bone ( Rollot et al., 2024a). The anterior half of the lateral semicircular canal is not enclosed by bone, and the prootic forms the lateral margin of a groove that contained the anterior aspect of the lateral semicircular duct. The prootic also forms the anterior margin of the hiatus acusticus ( Fig. 8B View Fig ), which is reduced relative to that of Carettochelys insculpta ( Rollot et al., 2024a) . In DPC 7742, the prootic and opisthotic contact one another vertically along the medial aspect of the cavum labyrinthicum and the supraoccipital dorsally, which restricts the hiatus acusticus to a small, ventral opening bordered by the prootic, opisthotic, and parabasisphenoid ( Fig. 8B View Fig ). In Carettochelys insculpta , although the size of the hiatus acusticus varies during ontogeny, a contact between the prootic and opisthotic along the medial aspect of the cavum labyrinthicum is not apparent, giving the hiatus acusticus an hourglass shape, which is bordered by the supraoccipital, prootic, opisthotic, pterygoid, and parabasisphenoid ( Rollot et al., 2024a). Within the braincase of DPC 7742, the prootic forms a relatively small but deep fossa acustico-facialis, in which three foramina, two large and one small, can be identified. The large, anterodorsal foramen leads directly into the cavum labyrinthicum and transmitted the vestibulocochlear nerve (CN VIII; Fig. 8B View Fig ). Posterior to that foramen, a small foramen that is barely visible in the CT scans leads into a short canal that extends from the fossa acustico-facialis to the cavum labyrinthicum. This foramen and associated canal are also inferred to have transmitted a ramus of the vestibulocochlear nerve. The more ventral large foramen leads into the canalis nervus facialis, which transmitted the facial nerve laterally through the prootic ( Figs. 6B View Fig & 8B View Fig ). At about mid-distance between the fossa acustico-facialis and canalis cavernosus, the canalis nervus facialis gives off a branch that extends ventrally through the prootic and pterygoid. This split is inferred to correspond to the location of the geniculate ganglion, from which the vidian and hyomandibular nerves originate. The ventral canal is the canalis pro ramo nervi vidiani, which extends ventrally through the prootic and pterygoid to join the most anterior portion of the canalis caroticus internus, transmitting the vidian nerve ( Fig. 6B View Fig ). The lateral canal, or canalis nervus hyomandibularis proximalis, conveyed the hyomandibular nerve laterally through the prootic from the geniculate ganglion to the canalis cavernosus ( Fig. 6B View Fig ). Although the facial nerve system is very similar to that of Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2021, 2024a), two minor differences can be identified. First, the location of the geniculate ganglion in DPC7742 is slightly more medial relative to the canalis cavernosus than in Allaeochelys libyca and Carettochelys insculpta , which seems to result from a longer canalis nervus hyomandibularis proximalis. The second, minor difference is linked to the position of the junction between the canalis pro rami nervi vidiani and canalis caroticus internus. In Allaeochelys libyca and Carettochelys insculpta , the canalis pro rami nervi vidiani joins the canalis caroticus internus at about mid-length of the latter, whereas it combines with the canalis caroticus internus much more anteriorly in DPC 7742.

Fig. 7 (See legend on previous page.)

Opisthotic. The right opisthotic is almost completely preserved in DPC 7742, lacking only the posterior end of the paroccipital process. The opisthotic contacts the supraoccipital dorsomedially, the prootic anteriorly, the quadrate anterolaterally, the basioccipital-exoccipital complex ventromedially, and the pterygoid posteroventrolaterally ( Fig. 3A & F View Fig ). An additional contact of the paroccipital process with the squamosal was likely present posterolaterally, as in Carettochelys insculpta , as the articular scar is preserved. The opisthotic forms the dorsomedial margin of the fenestra postotica and the posterodorsomedial wall of the cavum acustico-jugulare ( Fig. 8A View Fig ). Dorsomedial to the foramen posterius canalis carotici interni, the opisthotic forms the medial margin of the foramen oropharyngeale. The paroccipital process of the opisthotic has a broad and elongate contact with the basioccipital-exoccipital complex and pterygoid ventrally, which greatly constricts the fenestra postotica medially. This ventral expansion of the paroccipital process forms the posterior wall of the wide recessus scalae tympani. The opisthotic forms the posterior half of the cavum labyrinthicum, the posterior half of the posterior semicircular canal, the posterior half of the lateral semicircular canal, the posterodorsal and posterior margins of the hiatus acusticus, and the dorsal, posterior, and ventral margins of the fenestra ovalis, which is completely surrounded by the prootic and opisthotic ( Fig. 8A, B View Fig ). The opisthotic ventrally forms a broad processus interfenestralis, which forms the posterior wall of the cavum labyrinthicum and the anterior wall of the recessus scalae tympani ( Fig. 8A View Fig ). The ventral aspect of the processus interfenestralis is developed as a massive footplate that rests on the pterygoid and also contacts the prootic anteriorly, the parabasisphenoid anteromedially, and the basioccipital-exoccipital complex posteromedially ( Fig. 8A View Fig ). Medial to the processus interfenestralis, the opisthotic forms a nearly vertical and slightly curved sheet of bone that forms a small portion of the braincase wall posterolaterally and, collectively with the medial edge of the processus interfenestralis, completely encloses the fenestra perilymphatica, as in adult Carettochelys insculpta ( Rollot et al., 2024a) . Along the posteroventral part of this bony sheet, the opisthotic forms a foramen that leads into a short canal that connects to the posterior part of the cavum labyrinthicum ( Fig. 8B View Fig ). In Carettochelys insculpta , this foramen corresponds to the foramen medialis nervi glossopharyngei, which transmits the glossopharyngeal nerve from the braincase to the cavum labyrinthicum ( Rollot et al., 2024a). We identify the foramen in DPC 7742 as the foramen medialis nervi glossopharyngei by reference to Carettochelys insculpta , but note that in the latter taxon, this foramen is only present in juveniles and is absent in adults ( Rollot et al., 2024a). Slightly posterolateral to the foramen medialis nervi glossopharyngei and within the cavum labyrinthicum, the opisthotic forms a small foramen internum nervi glossopharyngei. The latter foramen leads into a canal that extends posterolaterally and joins the recessus scalae tympani by means of the foramen externum nervi glossopharyngei. The foramen externum nervi glossopharyngei is located along the most dorsal aspect of the base of the processus interfenestralis, at about one third of the mediolateral width of the process. Just posteromedial to the fenestra perilymphatica, the opisthotic forms the anterior and dorsal margin of the foramen jugulare anterius ( Fig. 3B View Fig ).

Supraoccipital. The supraoccipital is heavily damaged and only its most anterior and right ventrolateral aspects are preserved in DPC 7742. The supraoccipital contacts the parietal anterodorsally, the prootic anterolaterally, the opisthotic posteroventrolaterally, and slightly contacts the basioccipital-exoccipital complex posteroventrally along the margin of the foramen magnum ( Fig. 3A, C–D & F View Fig ). The supraoccipital forms the dorsal margin of the cavum labyrinthicum, the posterior part of the anterior semicircular canal, and the anterior part of the posterior semicircular canal. Thus, it completely encloses the foramen aquaducti vestibuli and roofs the posterior half of the braincase. Within the braincase at the level of contact with the parietals, the supraoccipital anteriorly ends as a step-like protrusion, which corresponds to the cartilaginous rider ( Werneburg et al., 2021). Although the exposure of the supraoccipital on the skull roof is moderate to minor in all carettochelyids, the preserved portions of the supraoccipital in DPC 7742 are too damaged to assess a possible exposure on the skull roof. The suture between the supraoccipital crest and parietals varies substantially between taxa and individual variation in the degree of exposure of the supraoccipital on the skull roof was described for the extant Carettochelys insculpta (see Joyce, 2014; Danilov et al., 2017; Joyce et al., 2018; Rollot et al., 2024a). Most of the supraoccipital crest is missing. The most posterior portion of the preserved supraoccipital nonetheless bears a short, dorsolaterally oriented process, which corresponds to the base of the expanded plate of the supraoccipital crest ( Fig. 3F View Fig ). The process extends posteriorly and slightly laterally, indicating that the plate was expanding mediolaterally towards the posterior to become broader posteriorly, similar to that of Anosteira pulchra ( Joyce et al., 2018) , Allaeochelys libyca ( Rollot et al., 2024b) and adult Carettochelys insculpta ( Rollot et al., 2024a) .

Basioccipital-exoccipital complex. The basioccipital and exoccipitals are completely fused in DPC 7742 and we, therefore, segmented them as a single osteological unit ( Fig. 3B–C & F View Fig ). The right exoccipital part of the greatly thickened basioccipital-exoccipital complex is almost completely preserved and lacks only the occipital condyle, whereas the basioccipital part lacks most of its left lateral aspect. The basioccipital-exoccipital complex contacts the parabasisphenoid anteriorly along a tall contact, the supraoccipital anterodorsomedially, the opisthotic dorsally and dorsolaterally, and the pterygoid ventrolaterally ( Fig. 3B–C & F View Fig ). The anterior contact with the parabasisphenoid is notably higher than in Allaeochelys libyca ( Rollot et al., 2024b) and adult Carettochelys insculpta ( Rollot et al., 2024a) . The basioccipital-exoccipital complex forms the posterolateral wall of the braincase, the lateral and ventral margins of the foramen magnum, the posteromedial wall of the recessus scalae tympani, and the posterior and ventral margins of the foramen jugulare anterius ( Fig. 3C & F View Fig ). Posterolateral to the foramen jugulare anterius and along the posteromedial corner of the recessus scalae tympani, the basioccipital-exoccipital complex forms a relatively large canal that extends posteroventrolaterally and exits the cranium by means of the foramen jugulare posterius. The foramen jugulare posterius is located along the posterodorsal surface of the basioccipital-exoccipital complex, directly dorsal to the posterior end of the neurapophyseal ridge (sensu Rollot et al., 2024a) and just medial to the suture with the opisthotic. The neurapophyseal ridge extends along most of the posterior surface of the basioccipital-exoccipital complex, starting dorsomedially from the suture with the supraoccipital (from which it also likely extended), and trends posteroventrolaterally on the posterior surface of the basioccipital-exoccipital complex ( Fig. 3F View Fig ). A similar neurapophyseal ridge is present in Carettochelys insculpta ( Rollot et al., 2024a) and Allaeochelys libyca ( Rollot et al., 2024b) , although less pronounced in the latter taxon. The neurapophyseal ridge separates the occipital fossa ventromedially from a broad fossa dorsolaterally, whose dorsolateral half is formed by the opisthotic. These fossae are also found in Carettochelys insculpta but are shallower ( Rollot et al., 2024a). The posterior end of the neurapophyseal ridge forms a moderately thick bony platform between the foramen jugulare posterius dorsally and the single foramen externum nervi hypoglossi. Within the braincase, posteroventromedial to the foramen jugulare anterius, the basioccipital-exoccipital complex forms two internal foramina, the foramina internum nervi hypoglossi, of which the anterior foramen is the smallest. The anterior foramen leads into a hypoglossal nerve canal that extends posteroventrally but for which the posterior part is not clearly discernible in the CT scans. The posterior foramen also leads into a hypoglossal nerve canal, which extends posteroventrolaterally and exits the skulls by means of the foramen externum nervi hypoglossi, which is located ventromedial to the posterior end of the neurapophyseal ridge. As the path of the anterior hypoglossal nerve canal was directed towards the posterior canal and only one external foramen for the hypoglossal nerve is present, we assume that the two hypoglossal nerve canals merged within the basioccipital-exoccipital complex, posteriorly forming a single hypoglossal nerve canal that joined the foramen externum nervi hypoglossi. A single external foramen for the hypoglossal nerve was also described in Anosteira maomingensis ( Danilov et al., 2017) , which contrasts with Anosteira pulchra ( Joyce et al., 2018) , Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) , all of which have two external foramina for the hypoglossal nerve. The posterolateral end of the basioccipital-exoccipital complex is missing, so that the right tuberculum basioccipitale is not fully preserved. The broken area, however, forms a relatively broad rugose surface ( Fig. 3F View Fig ), suggesting that the basioccipital-exoccipital was somewhat more expanded posteriorly and likely formed an elongate tuberculum as in other carettochelyids ( Havlik et al., 2014; Waite, 1905; Walther, 1922). The central part of the basioccipital-exoccipital complex, i.e. the area that corresponds to the basioccipital, ventrally forms a semicircular depression, which is marked by irregular ridges ( Fig. 3B View Fig ). A similar depression is also present in Anosteira pulchra ( Joyce et al., 2018) , Allaeochelys libyca ( Havlik et al., 2014; Rollot et al., 2024b), and Carettochelys insculpta ( Rollot et al., 2024a) .

Parabasisphenoid. Most of the parabasisphenoid is not preserved in DPC 7742. We tentatively identify a small piece of bone located just ventral to the hiatus acusticus as belonging to the parabasisphenoid ( Fig. 3C View Fig ), as its position is similar to that of the dorsolateral aspect of the parabasisphenoid in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) . Given its extremely small size, we are only able to describe a few contacts of the putative parabasisphenoid, which are with the prootic anterolaterally, the opisthotic posterolaterally, the basioccipital-exoccipital complex posteriorly, and the pterygoid ventrolaterally. The surrounding bones indicate that the parabasisphenoid was much thicker than that of Allaeochelys libyca ( Havlik et al., 2014; Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) .

Endosseous labyrinth. The right endosseous labyrinth is completely preserved in DPC 7742 ( Fig. 9 View Fig ). The semicircular canals are thick. The anterior semicircular canal is the longest of the three, and the posterior and lateral semicircular canals have approximately the same length ( Fig. 9 View Fig ). The anterior semicircular canal anteriorly joins the vestibule at the level of the anterior ampulla. The posterior end of the posterior semicircular canal is confluent with the posterior portion of the lateral semicircular canal forming a secondary common crus ( Fig. 9B View Fig ; sensu Evers et al., 2019). The common crus is low as in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Evers et al., 2019; Rollot et al., 2024a). The dorsal embayment of the common crus is extremely subtle in DPC 7742 ( Fig. 9A View Fig ), which differs from Allaeochelys libyca ( Evers et al., 2022; Rollot et al., 2024b) and Carettochelys insculpta ( Evers et al., 2019; Rollot et al., 2024a) where the embayment is clearly defined, although slightly less pronounced in the latter. The lateral semicircular canal only forms a proper canal along its posterior portion, which is barely detached from the vestibule and creates a dorsoventral slit-like passage ( Fig. 9C View Fig ), as in Allaeochelys libyca ( Rollot et al., 2024b) and Carettochelys insculpta ( Rollot et al., 2024a) . Anteriorly, the lateral semicircular canal is merged with the lateral ampulla ( Fig. 9A View Fig ).

Shell

The available shell material of Allaeochelys meylani sp. nov. mostly consists of isolated plates of the carapace, with the exception of one fragment. All the material was collected from the Moghra Formation but is not directly affiliated with the available cranium. We here describe and figure elements that are either complete or only suffer minor damage, allowing their identification with relative ease (pictures of additional, fragmentary material are available upon request). All plates exhibit the typical ornamentation of the Allaeochelys / Carettochelys lineage, consisting of thick ridges separated by equally sized grooves. Much like the cranium, their most striking feature is their remarkably large size.

Nuchal. We identify two elements as nuchals. CGM 67151 is a large carapace fragment that includes a partial nuchal, left peripherals I and II, and left costal I, and the preservation and sutural contacts between the bones makes their identification clear ( Fig. 10 View Fig ). Most of the nuchal is not preserved, but the lateral portion of the element shows that the nuchal forms the anterior margin of the carapace and contacts peripheral I laterally and costal I posterolaterally ( Fig. 10 View Fig ).

The second element that can confidently be identified as a nuchal is DPC 3622 ( Fig. 11 View Fig ). This fossil is not complete, lacking its anterior and lateral margins ( Fig. 11A, B View Fig ). The approximate length and width of the preserved part are 7 cm and 8 cm, respectively. The posterior margin of DPC 3622 is intact and preserves the posterolateral articulation facet with costal I and the concave articulation facet for neural I ( Fig. 11C View Fig ). The narrow nature of this facet suggests that the neurals were narrow and elongate, as in Carettochelys insculpta . The nuchal forms a pair of processes in the posterior quarter on its ventral surface ( Fig. 11B, C View Fig ), which are typical of pan-carettochelyids ( Joyce, 2014). The base of the nuchal processes is expanded posteriorly, forming a shallow, cup-like depression ( Fig. 11B, C View Fig ).

Peripherals. We identify five elements as peripherals. CGM 67151 preserves the left peripherals I and II ( Fig. 10 View Fig ). The left peripheral I is complete and approximately 7 cm long, and contacts the nuchal medially, left costal I posteromedially and left peripheral II posterolaterally ( Fig. 10 View Fig ). The left peripheral II lacks its posterolateral end, but the length of the full element can be estimated to be about 6–7 cm. The left peripheral II contacts left peripheral I anteromedially and left costal I medially ( Fig. 10 View Fig ). The element has a short but broad medial process that protrudes into left costal I ( Fig. 10 View Fig ). The process is distinctly visible on the dorsal side of the carapace but to a much lesser extent on the visceral side ( Fig. 10 View Fig ).

DPC 12637 can be identified as a left peripheral IV, which is approximately 6 cm long ( Fig. 12 View Fig ). The element has a C shape in cross section and forms four facets for articulation with the hyoplastron along its ventromedial side ( Fig. 12C–D & F–G View Fig ). The articulation facets for the hyoplastron are large, with a slight, gradual decrease in size posteriorly ( Fig. 12D & F View Fig ). Anterior to the most anterior facet, the ventromedial margin of the peripheral is delineated by a smooth margin that shows the anterior end of the bridge ( Fig. 12D View Fig ). This allows identification as the peripheral IV by comparison to Carettochelys insculpta . Dorsomedially, the peripheral forms an articulation facet for the left costal rib II ( Fig. 12D & F View Fig ). The external surface of the peripheral is crossed by a low ridge that extends anteroposteriorly at about mid-height of the element to form the lateral margin of the shell, and this morphology is absent in Carettochelys insculpta ( Fig. 12A View Fig ).

DPC 12585 is approximately 6 cm long, V-shaped in cross section, possesses 6 facets ventromedially for articulation with either the hyo- or hypoplastron, and has a straight medial margin ( Fig. 13 View Fig ). As the element lacks a smooth margin anterior to the hyo-hypoplastral facets (which is diagnostic for peripheral IV), a smooth margin posterior to the hyo-hypoplastral facets (which is diagnostic for peripheral VII), and lacks a medial process that protrudes medially into the hyo-hypoplastral suture (typical of peripheral V), the morphology of the element is consistent with that of a right peripheral VI in Carettochelys insculpta , and is identified as such herein. The dorsomedial part of the peripheral, i.e. the area that forms the articulation facet for the right costal IV, is missing ( Fig. 13 View Fig ). The peripheral is dorsoventrally flatter than peripheral IV.

The last element that we identify as a peripheral is DPC 6436 ( Fig. 14 View Fig ). The element is nearly intact and measures approximately 7 cm in length and 8 cm in width. The large size, flatness, and square shape of the element have affinities with a posterior peripheral. However, a dorsomedial portion of the element and most of the ventromedial lip are missing, which precludes assessment of its exact morphology and, consequently, prevents us from identifying it precisely as a peripheral VIII, IX, or X. Dorsomedially, at about mid-length, the peripheral has an articulation facet for a costal rib end ( Fig. 14B View Fig ).

Costals. CGM 67151 preserves most of a left costal I. It is a large element and almost as long as broad that only lacks a small portion of its medial and lateral sides ( Fig. 10 View Fig ). The left costal I contacts the nuchal anteriorly, left peripheral I anterolaterally, and left peripheral II laterally ( Fig. 10 View Fig ). A lateral contact with left peripheral III can also be reasonably inferred, as most of left peripheral II is preserved and it barely extends beyond about mid-length of left costal I. The lateral margin of left costal I is concave as a result of the medial process of left peripheral II that protrudes into the costal.

DPC 14555 is a carapacial fragment including the bilateral costals VIII and the suprapygal ( Fig. 15 View Fig ). The left costal VIII only lacks the most lateral aspect that formed the associated costal rib, whereas the right costal VIII only preserves its medial half ( Fig. 15 View Fig ). The preserved contacts of costal VIII are with its counterpart medially and the suprapygal posteromedially ( Fig. 15 View Fig ). By reference to other pan-carettochelyids, we also infer that costal VIII had a contact with costal VII anteriorly and peripheral X posterolaterally ( Adrian et al., 2020; Broin, 1977; Carbot-Chanona et al., 2020; Clark, 1932; Dollo, 1886; Harrassowitz, 1922; Hay, 1906; Nessov, 1977; Ramsay, 1887; Tong et al., 2010; Waite, 1905). A contact with the posteromedial edge of peripheral IX might have occurred as well, as such a contact was reported in Kizylkumemys schultzi ( Nessov, 1977) , Anosteira ornata ( Hay, 1906) , Allaeochelys delheidi ( Dollo, 1886) , Allaeochelys crassesculpta ( Harrassowitz, 1922) , Allaeochelys parayrei ( Broin, 1977) , Allaeochelys liliae ( Carbot-Chanona et al., 2020) , and some specimens of Carettochelys insculpta ( Joyce, 2014) . The anterior margin of costals VIII collectively forms a rounded and regular, uninterrupted margin, indicating that an anteromedial contact with a neural is absent and that DPC 14555 likely had no more than 7 neurals ( Fig. 15A View Fig ), as in other pan-carettochelyids ( Adrian et al., 2020; Broin, 1977; Carbot-Chanona et al., 2020; Clark, 1932; Harrassowitz, 1922; Hay, 1906; Nessov, 1977; Ramsay, 1887; Tong et al., 2010; Waite, 1905; Zangerl, 1947). Collectively with the suprapygal, costals VIII form a low keel along the dorsal midline of the carapace ( Fig. 14A View Fig ), consistent with most pan-carettochelyids ( Adrian et al., 2020; Broin, 1977; Carbot-Chanona et al., 2020; Cheng, 1961; Chow & Liu, 1955; Clark, 1932; Harrassowitz, 1922; Hutchison et al., 2004; Nessov, 1977; Tong et al., 2010; Waite, 1905; Zangerl, 1947), but not Kizylkumemys khoratensis ( Tong et al., 2005) .

Suprapygal. A suprapygal is part of DPC 14555, along with the two costals VIII described above. The suprapygal is relatively complete and lacks its posterolateral aspect on both sides ( Fig. 15 View Fig ). It is approximately 7 cm long along the midline and contacts costal VIII laterally ( Fig. 15 View Fig ). The posterior surface of the suprapygal forms an intact, sutural surface for the articulation with the pygal for most of its width ( Fig. 15A View Fig ). Although not preserved, the posterolateral aspect of the suprapygal likely had a contact with peripheral X, as in other pan-carettochelyids ( Broin, 1977; Carbot-Chanona et al., 2020; Clark, 1932; Dollo, 1886; Harrassowitz, 1922; Hay, 1906; Nessov, 1977; Waite, 1905). Along its dorsal surface, the suprapygal forms a low keel that extends anteroposteriorly along the midline of the carapace as in most pan-carettochelyids ( Fig. 15A View Fig ; Adrian et al., 2020; Broin, 1977; Carbot-Chanona et al., 2020; Cheng, 1961; Chow & Liu, 1955; Clark, 1932; Harrassowitz, 1922; Hutchison et al., 2004; Nessov, 1977; Tong et al., 2010; Waite, 1905; Zangerl, 1947), but not Kizylkumemys khoratensis ( Tong et al., 2005) .

Pygal. DPC 7741 is identified as a pygal, which is almost complete and only lacks its left posterolateral edge ( Fig. 16 View Fig ). This element is approximately 9 cm long and 8 cm wide. The lateral surface of the pygal forms an articulation facet that is deep and V-shaped and serves as a contact area with peripheral X ( Fig. 16D View Fig ). The dorsal part of the suture is continuous towards the anterior surface of the pygal, forming an articulation facet for contact with the suprapygal anteriorly ( Fig. 16C View Fig ). The ventral part of the pygal-peripheral X suture is limited to the lateral surface of the pygal, so that the anteroventral surface (i.e., visceral side) of the pygal is smooth and forms a thick lip ( Fig. 16B–D View Fig ), which in pan-carettochelyids extends laterally on the posterior peripherals ( Joyce, 2014). Along its dorsal surface, the pygal forms a low keel that extends along its approximately anterior half ( Fig. 16A View Fig ).

Hypoplastron. CGM 67140 is a left plastral fragment that consists of a partial hypoplastron and a partial xiphiplastron ( Fig. 17 View Fig ). The element mostly preserves the medial half of the left hypoplastron, showing the medial suture with its counterpart and the medial margin of the inguinal notch. The hypoplastron posteriorly contacts the xiphiplastron along a straight suture for most of its width, but it has a well-defined sinusoid shape at its lateral end on the visceral side of the element ( Fig. 17C View Fig ). The preserved, medial portion of the hypoplastron is notably broad, reminiscent of the hypoplastron of other Allaeochelys taxa and also that of Carettochelys insculpta ( Joyce, 2014) .

Xiphiplastron. CGM 67140 includes a partial left xiphiplastron that represents about the anterior third of the element ( Fig. 17 View Fig ). The medial side of the left xiphiplastron forms a sutural surface for contact with its counterpart. The xiphiplastron anteriorly contacts the hypoplastron. The hypo-xiphiplastron suture is straight for most of its width but forms a well-defined sinusoid line laterally ( Fig. 17 View Fig ).