Skull.

The snout is short, laterally broad and anteriorly rounded (Figs 2, 3 and 5). The maximum length of the skull of the holotype, from the snout tip to the posterior margin of the medial quadrate condyle, is about 385 mm. Its maximum width, at the level of the jugals, is approximately 285 mm. It is therefore a remarkably broad skull relative to its length (Fig 2). The orbits of this taxon are circular and slightly upturned. The supratemporal fenestrae are circular and smaller than the orbits. The infratemporal fenestrae are rectangular and longer than high. The suborbital fenestrae are relatively large and anteroposteriorly elongate. The external surface of the skull is heavily sculpted (Figs 2, 3 and 5).

The premaxillae are wider than long and rounded anteriorly. This pair of bones forms most of the narial margin (Fig 2A and 2B). The external nares are large, circular in profile, and slightly wider than long. They face anterodorsally (Fig 3C). Their margin is smooth, having no ridges, and being situated at the same level as the dorsal surface of the premaxillae. Two deep, anterolaterally directed grooves are situated posterolateral to the external naris. Dorsally, the premaxillo-maxillary suture is straight, slightly bowed, and extends medially from the shallow premaxillo-maxillary notch to the nasal (Fig 2A and 2B). Ventrally, the premaxillo-maxillary suture is posteromedially directed and placed far from the posterior margin of the incisive foramen (Figs 2C–2D and 5E–5F). The incisive foramen is relatively small and circular in outline.

In Lohuecosuchus, the number of premaxillary teeth is not the same in all the preserved specimens. Each premaxilla of the holotype bears four alveoli, with the third being the largest (Fig 2C and 2D). The paratypes, HUE-02920 and HUE-04263, bear five premaxillary teeth, with a small second tooth whose alveolus converges with the third (Fig 5B, 5E and 5F). In these specimens, the largest premaxillary alveolus is the fourth.

The maxillae are wide and relatively short. Dorsally, a shallow lateral notch for reception of the fourth dentary tooth separates the premaxilla and the maxilla (Fig 2A and 2B). The dorsal surface of the rostrum presents well-developed rostral canthi. Two shallow depressions extending mediolaterally can be observed on the anterior region of the dorsal surface of the maxilla in the holotype, the left one being more marked. A projected posteriorly sharp process is located between the lacrimals and nasals. In ventral view, there is a large, anterolateral foramen on the palatal shelf of each maxilla near the premaxillo-maxillary suture (Figs 2C–2D and 5E–5F). The maxillae each have ten alveoli closely spaced with narrow interalveolar spaces (Figs 2C–2D, 5B and 5E–5F). However, the left maxilla of the holotype presents eleven alveoli (Fig 2C and 2D). In all specimens the fourth alveolus is the largest. The maxillae constitute the anteromedial corner, and about half of the lateral rim, of the suborbital fenestrae. A parasagittal foramen is located at the mid-length of the medial margin of each maxilla (Figs 2C–2D, 5B and 5E–5F). Nevertheless, none of the foramina for the palatine branch of the cranial nerve V is enlarged.

In Lohuecosuchus, the maxillary teeth are extremely robust with respect to the skull proportions (Figs 2C–2D, 5B and 5E–5F). The great development of the teeth is related to the pronounced expansion of the lateral profile, which is especially prominent in the posteriormost portion of the maxillae, affecting the morphology of the ectopterygoid.

Both nasals reach the posterior margin of the naris, separating the premaxillae, but without forming a complete internarial bar (Fig 2A and 2B). The posteriormost portions of the nasals taper gradually and are separate medially for a short sagittal rostral process of the frontal. In turn, each nasal forms a short and acute posterior process between the frontal and prefrontals.

The lacrimals are rectangular and form the anterior margin of the orbits, contacting the jugals posterolaterally, the maxillae anterolaterally, and the nasals and the prefrontals medially. They are longer than the prefrontals (Figs 2A–2B and 5A). Due to preservation, the prefrontal-lacrimal suture is not recognizable in most of the specimens. The dorsal surface of each lacrimal close to the orbit forms a well-marked crest with the prefrontal.

Although the limits of the prefrontals with the lacrimals are not recognized, the sutures of the prefrontals with the rest of the adjacent elements are markedly visible in the holotype and HUE-02920 (Figs 2A–2B and 5A). The prefrontals are wide, with their dorsal surface extending from the midpoint of the medial rims of the orbits to the level of the posteromedial branch of the maxillae. Anteriorly, each prefrontal projects a short and blunt dorsal process. Prefrontal pillars are not well preserved in any of the specimens due to the collapse of the skull table. As preserved, they are columnar parasagittal structures that dorsally begin at the medial border of the prefrontal, close to the frontal suture. The pillars have well-developed medial processes which contact the sagittal plane. Laterally, the prefrontal pillars form a wide lamina that extends transversally the complete ventral side of the prefrontal body. In anterior view, this lamina forms a wide concave wall under the anteromedial corner of the orbits.

The frontal bears a long and slender anterior process separating the prefrontals and extending between the nasals for a short distance (Figs 2A–2B and 5A). This anterior process does not extend beyond the anterior margins of the prefrontals. The margins of the orbits are slightly upturned, and the dorsal surface of the frontal between the orbits is shallowly concave (Figs 3C and 5C). The frontal forms the posteromedial corners of the orbits, and posteriorly, the anteromedial margins of the supratemporal fenestra.

The parietal is flat, and its dorsal surface is flush with the medial margins of the supratemporal fenestrae (Figs 2A–2B and 5A). Posteriorly, it bears a dorsal midline depression. Its suture with the frontal is almost linear and intersects the supratemporal fenestrae.

Dorsally, the postorbitals are crescentic in shape (Figs 2A–2B and 5A). A descending process is inset on the ventral side and forms the dorsal portion of the postorbital bar. The postorbital portion of the postorbital bar is subtriangular in cross-section and represents half of its length. The postorbitals form the posterior rims of the orbits and the anterolateral corners of the supratemporal fenestrae. The postorbital-jugal sutures are not clearly visible.

The squamosals have a flat dorsal surface (Figs 2A–2B and 5A). The posterolateral process slopes ventrally, forming the anterolateral wall of the paraoccipital process. In dorsal view, the posterolateral tip of the squamosals is ornamented. This tip is weakly developed and is placed almost over the paroccipital processes that, in this view are slightly posterolaterally projected. A notch, visible in lateral and occipital view, separates the ornamented dorsal surface of the skull table from the unornamented paroccipital process (Figs 3A–3B and 5D). In lateral view, an anterior process of the squamosals underlies the postorbitals to reach the postorbital bars (Figs 3C–3D and 8A–8B). This anterior projection forms a prominent boss under the postorbitals, as can be observed in dorsal view (Figs 2A–2B and 5A). The lateral squamosal rims and groove for insertion of the ear flap musculature are longitudinally developed. The dorsal rim is shorter and restricted to the rear part. The ventral rim is more prominent and overhangs the otic recess. The squamosals form most of the dorsal outline of the otic aperture (Fig 8A and 8B). In occipital view, the squamosals constitute the lateral half of a prominent depression on the occipital surface, lateral to the postemporal fenestra (Figs 3A–3B and 5D).

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Fig 8. Left posterodorsolateral view of the otic region of HUE-04498, holotype of Lohuecosuchus megadontos gen. et sp. nov.

(A) Photograph of the specimen. (B) Interpretative drawing.

https://doi.org/10.1371/journal.pone.0140679.g008

The cranioquadrate passage is an open groove extending from the otic aperture to the rear of the otic recess (Figs 3A–3B, 5D and 8A–8B). It does not form a tube enclosed laterally by the squamosal and quadrate. Details within the groove are difficult to recognize but, probably, the ventral surface is formed by the exoccipital. Therefore, the absence of contact between the squamosal and quadrate posterior to the otic aperture is interpreted.

The jugals form the posteroventral margin of the orbit (Figs 2A–2B and 5A). The anterior ramus of the jugal extends to the eighth maxillary alveolus and tapers anteriorly. The ventral outline has a marked concavity behind the tooth row corresponding with the size of the posterior teeth and the morphology of the ectopterygoid. The posterior ramus of the jugals is robust and slightly compressed laterally, but not laminar. The postorbital bars are inset medially on the jugals, being slender. The basal section of the postorbital bars is anteroposteriorly compressed. The jugals bear a relatively large foramen on the internal surface, posterior to the base of the postorbital bar.

The quadratojugals form the posterior margin of the infratemporal fenestra, contacting the postorbitals, and preventing the contact of the quadrate with the margin of the fenestra (Figs 2A–2B, 5A and 8A–8B). A large spine is present on the right quadratojugal of HUE-02920 (Fig 5A). These spines are broken in the holotype. The quadratojugal-jugal suture lies at the posteroventral corner of the infratemporal fenestra. The quadratojugals extend posteriorly lateral to the quadrate, but does not participate in the condyle.

The dorsal surface of the quadrates is smooth (Figs 2A–2B, 5A and 8A–8B). The foramen aëreum is located on the dorsomedial surface and opens at the end of a low crest. The quadrates form the posteroventral margin of the external otic aperture. As described above, the quadrates do not contact the squamosal in the rear part of the otic notch, creating a laterally open cranioquadrate passage. In ventral view, two well-marked parallel and sinusoidal crests that extend along the main axes of the quadrates are identified. These crests define a groove that ends at the foramen for cranial nerve V (Figs 2C–2D, 5B and 5E–5F). One of these, roughly similar to the “crest A” sensu Iordansky (1973) [44], extends laterally parallel to the suture with the quadratojugal, and medially very close to the ventromedial edge of the supratemporal fenestra. The other one possibly corresponds to the “crest B” sensu Iordansky (1973) [44]. It extends near to the medial border of the quadrates. The quadrate condyles are both wider than high (Figs 3A–3B and 5D). The main axis of the articular surfaces of the condyles is almost horizontal, with a slight ventral deflection on the medial hemicondyle. The medial hemicondyle is smaller than its lateral counterpart. The quadrates form the posterior wall of the ventral part of the supratemporal fenestra, contacting the ventral outline of the temporal canal on the posterior fenestral wall.

The palatines are joined along the midline (Figs 2C–2D, 5B and 5E–5F). Their palatal surface is relatively wide and their lateral outlines are nearly straight, except on their anterior portion, where they are rostro-laterally widened. Anteriorly, they form a broad and blunt rectangular process between the maxillae that does not extend beyond the anterior margin of the suborbital fenestrae. The palatines are short and, although they form most of the medial outline of the suborbital fenestrae, they do not reach the anteromedial or posteromedial corners of these fenestrae. The palatine-pterygoid suture is slightly curved and projects anteriorly (Figs 2C–2D, 5B and 5E–5F).

The ectopterygoids are thick and robust. They contact the posteromedial area of the maxillae, forming the medial wall of the posteriormost two, and sometimes three, maxillary alveoli (Figs 2C–2D, 5B and 5E–5F). The anterior process of the ectopterygoids tapers against the maxilla and does not form a palatal shelf. In the rear part of the hypertrophied tooth row, the ectopterygoids are slightly projected laterally, partially embracing the posterior part of the last alveolus. A short ascending process forms part of the medial side of the postorbital bars and contacts with the descending process of the postorbitals. Each ectopterygoid forms the posterolateral margins of the suborbital fenestrae (Figs 2C–2D, 5B and 5E–5F).

The ventral surface of the pterygoids is almost flat, these bones being slightly depressed sagittally. The choana is completely surrounded by the pterygoids (Figs 2C–2D, 5B and 5E–5F). The choana is teardrop in shape, longer than wide and posteroventrally oriented. There is no septum dividing the choana. A thin sagittaly elongate groove between the pterygoids extends anteriorly from the choana. Laterally, each pterygoid contacts the ectopterygoid. The ectopterygoids, which lie on the ventrolateral pterygoid surface, do not extend beyond the posterior tip of the pterygoid wing. In ventral view, the ectopterygoid-pterygoid sutures show a zigzag pattern. They contact the posterolateral corner of the suborbital fenestrae anteriorly (Figs 2C–2D and 5E–5F). Posteriorly, the pterygoid wings do not reach the length of the quadrate hemicondyles. However, the pterygoid wings surpass the level of the posterior margin of the posteromedial pterygoid processes.

The two most complete preserved skulls, HUE-04498 and HUE-02920, are slightly compressed dorsoventrally in the rear part, and this is especially evident in the area of the lateroventral wall of the braincase (Figs 3A–3B and 5D). Therefore, a detailed description of this area is not possible. The laterosphenoids are almost complete and distorted, but their dorsal processes are triangular, ending as incompletely preserved capitate processes, probably being anteroposteriorly expanded. The laterosphenoid-quadrate sutures are vertical below the supratemporal fenestra. These sutures reach the dorsal borders of the trigeminal foramen, strongly deformed or unexposed in all the specimens.

The supraoccipital is wider than high in occipital view. It presents a subtriangular outline (Figs 3A–3B and 5D). There is a well-marked nuchal crest along its midline, which does not reach the exoccipital. The postemporal fenestrae are dorsoventrally flattened, but it is possible to recognize their ventral margin, constituted by well-developed external occipital protuberances. The lateral borders of the supraoccipital form the dorsomedial margin of well-marked depressions located lateral to postemporal fenestrae (Figs 3A–3B and 5D). It is not evident whether the supraoccipital takes part of the dorsal surface of the skull table because it is not possible to recognize the parieto-supraoccipital suture. There is a sagittal depression at the posterior outline of the cranial table, affecting the rear part of the parietal and the dorsal part of the supraoccipital (Figs 2A–2B and 5A).

The exoccipitals form the dorsolateral margin of the foramen magnum, which is crushed dorsoventrally in all available specimens (Figs 3A–3B and 5D). The exoccipitals meet above this opening. The dorsal half of the exoccipitals also forms the posterior surface of the paraoccipital processes, which exceeds the level of the medial margin of the quadrate condyles. The dorsal surface of the exoccipitals appears depressed in contact with the squamosals. The ventral region of the exoccipitals laterally contacts the quadrates. The ventrolateral margins of this region bear the foramen caroticum posterius and, lateral to the occipital condyle, the medial margin the foramen vagi (Figs 3A–3B and 5D). Due to the preservation, the foramina for hypoglossal nerve (XII) cannot be identified. In the otic region, the exoccipitals form the inner wall of the cranioquadrate grooves (Fig 8A and 8B), and connect dorsally with the quadrate and ventrally with the squamosal, separating them.

The basisphenoid is well exposed in occipital view, below the ventral margin of the basioccipital, and shows a vertical occipital surface (Figs 3A–3B and 5D). The contact area with the pterygoids is not clear. The basisphenoid forms the ventromedial margin of the crushed medial eustachian foramen. Therefore, the lateral eustachian openings cannot be recognized. In lateral view, collapse of the braincase obscures contact areas between the basisphenoid and adjacent elements (Figs 3A–3B and 5D).

The occipital region of the basioccipital forms most of the occipital condyle (Figs 3A–3B and 5D). The occipital condyle does not bear a well-developed neck. Its dorsal wall forms the ventral margin of the foramen magnum. Sagittally, on its ventral half, the basioccipital bears a well-marked crest, extending longitudinally from the posteroventral end of the occipital condyle to the ventral margin of the basioccipital. This ventral margin is wide and has a sagittal concavity at the end of the ridge, between both basioccipital tubera. The basioccipital also forms the dorsolateral margin of the medial eustachian foramen.

Lower jaw.

The maximum length of the lower jaw in the holotype, from the tip of the retroarticular process to the anterior margin of dentary, is about 470 mm. Its maximum height, from the ventral margin of the dentary to the posterior tip of the glenoid fossa, is approximately 110 mm (Fig 4A–4F).

The dentary is a long, tall and robust element that constitutes more than half of the length of the lower jaw. The dentary of the holotype has fourteen closely spaced and circular alveoli, nine of which bear complete teeth (Fig 4A–4F). HUE-04378 has fifteen alveoli (Fig 6D–6F) and HUE-05161 has fourteen, with eight complete teeth (Fig 6A–6C). However, in the latter specimen the third alveolus has been reabsorbed. The fourth, tenth and eleventh teeth are the largest in the holotype, whereas the fourth, ninth and tenth are the largest teeth in both HUE-04378 and HUE-05161 (Figs 4A–4F and 6A–6C). Considering the reabsortion indicated above, the largest dentary alveolus caudal to the fourth is the tenth. In all specimens there is a diastema between the seventh and eighth alveoli. The tooth row is laterally projected, especially in its anterior area. The dentary symphysis is robust and extends posteriorly to the level of the fourth alveolus. The lateral surface of the dentary is heavily ornamented, except in its posterior region. An external mandibular fenestra is absent in all specimens (Figs 4A–4B, 6A and 6D).

The splenial covers the medial surface of the mandibular ramus. It is smooth and almost flat (Figs 4C–4D, 6B and 6E). It is imperforate, with no foramina on its surface. Anteriorly, the splenial extends up to the level of the fourth dentary alveolus, near the symphysis, but do not form part of it. At its anterior border, delimiting the Meckelian groove, the ventral process is longer than the dorsal. Posterodorsally, the splenial contacts the last five alveoli, beginning with the tenth and forming the medial wall of the posteriormost three alveoli (Figs 4E–4F, 6C and 6F). The rear portion of the splenial forms the anterior border of the foramen intermandibularis caudalis (Figs 4C–4D, 6B and 6E).

The right coronoid is preserved in articulation on the holotype, but it is broken anteriorly and, therefore, the foramen intermandibularis medius cannot be observed (Fig 4C and 4D). The coronoid is crescent-shaped. In this specimen, its caudal margin is damaged and presents a small notch in its middle area. The posterior border of the coronoid forms the anterodorsal margin of the mandibular fossa.

The angular forms near the posteroventral portion of the jaw, extending from close to the posteriormost tip of the retroarticular process to an acute process on the ventral surface of the dentary, at approximately the level of the penultimate dentary alveolus (Figs 4A–4D, 6A–6B and 6D–6E). In labial view, its anterior half is strongly ornamented with large shallow depressions, but its rear half is smooth and lacks foramina, as well as their lingual, ventral and back surfaces (Figs 4A–4B, 6A and 6D). In lateral view, a low pronounced ridge extends parallel to the suture with the dentary. In its lingual surface, angular forms most of the foramen intermandibularis caudalis. The medial ascending lamina does not extend anterior to the coronoid (Figs 4C–4D, 6B and 6E).

The surangular is a long and robust bone (Figs 4A–4F and 6A–6F). It forms almost half of the dorsal length of the mandible. It presents a flat, broad and anteroposteriorly elongate shelf on its dorsal surface (Figs 4E–4F, 6C and 6F). The anterior end of the surangular bears two processes, with the dorsal process being longer than its ventral counterpart (Figs 4A–4B, 6A and 6D). An enlarged foramen, bound by the anterior processes, is present at the anterior end. Dorsally, a process contacts the posteromedial margin of the last alveolus and separates the splenial and dentary. Posteriorly, the surangular extends to the posterior end of the retroarticular process and contacts the lateral wall of the glenoid fossa (Figs 4E–4F, 6C and 6F). Except in the anterior and posterior processes, the labial face of the surangular is heavily ornamented (Figs 4A–4B, 6A and 6D).

The articular forms the glenoid fossa and retroarticular process (Figs 4C–4F, 6B–6C and 6E–6F). The retroarticular process is long and wide and posterodorsally oriented, with a strongly concave dorsal surface. The foramen aëreum is obscured and its position on the retroarticular process is unclear. The lingual surface of the articular is concave and tapers ventrally to an anterior process, forming the posterior wall of the mandibular fossa (Figs 4C–4D, 6B and 6E).

Dentition.

The dental formula of Lohuecosuchus megadontos includes four or five premaxillary alveoli, ten or eleven maxillary alveoli and fourteen or fifteen alveoli in the dentary (Figs 2C–2D, 3C–3D, 4A–4F, 5B–5C, 5E–5F and 6A–6F). The pattern of dentary-maxillary occlusion is lingual. Variations from anterior to posterior tooth morphology are similar in the lower and upper tooth rows. Preserved maxillary and dentary teeth in the holotype are conical. Most teeth are pointed, but robust. All maxillary and mandibular teeth have a flat lingual surface. Two longitudinal well-marked and smooth carinae are developed from the base to the apex, on the mesial and distal surfaces. Both carinae do not show neither denticles nor crenulations. The crowns have a D shaped cross-section with the mesial and distal carinae lingually displaced. The labial surface is thus concave, and the apex is lingually directed. The enamel has neither ridges nor ornamentation. Relative size of all teeth of the series is larger than those for the same tooth positions in other eusuchians. As discussed above, there are some differences in the size of the teeth, probably related to the rostral festooning. Besides that, the last preserved mandibular tooth, which is located on the penultimate alveoli, has a short, wide and blunt molariform crown (Fig 4A–4F). The exact number of this type of tooth in the dentary (up to three) or its presence or absent in the maxilla (in which the presence should be restricted to the last alveolus) cannot be confirmed, but this morphotype is not uncommon as isolated elements in the fossil site.

Lohuecosuchus mechinorum sp. nov.

(Figs 9 and 10)

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Fig 9. Skull MDE/CM-616, holotype of Lohuecosuchus mechinorum gen. et sp. nov.

(A, B) Dorsal views. (C, D) Ventral views. A and C, photographs of the specimen. B and D, interpretative drawings. Sutures are figured with plain lines. The dashed lines represent tentatively reconstructed sutures. The lined areas represent broken bones. Specimen from the late Campanian-early Maastrichtian site of Fox-Amphoux (Var, France).

https://doi.org/10.1371/journal.pone.0140679.g009

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Fig 10. Skull MDE/CM-616, holotype of Lohuecosuchus mechinorum gen. et sp. nov.

(A, B) Posterior views. (C, D) Lateral views. A and C, photographs of the specimen. B and D, interpretative drawings. Sutures are figured with plain lines. The dashed lines represent tentatively reconstructed sutures. The lined areas represent broken bones. Specimen from the late Campanian-early Maastrichtian site of Fox-Amphoux (Var, France).

https://doi.org/10.1371/journal.pone.0140679.g010

Skull.

The skull is brevirostral and unidirectionally deformed (Figs 9A–9D and 10A–10D). The maximum length of the skull, from the snout tip to the posterior margin of the lateral quadrate condyle, is about 290 mm. Its maximum width, at the level of the quadratojugals, is approximately 180 mm. Its outline is markedly festooned, especially in the left side of its anterior maxillary margin, probably due to deformation. The orbits are rounded and their edges are upturned relative to the dorsal surface (Fig 9A and 9B). Anteroposteriorly, the supratemporal fenestrae are slightly oval and smaller than the orbits. The infratemporal fenestrae are narrow, probably as a result of the deformation. The suborbital fenestrae are anteroposteriorly elongated and very narrow, especially in the rostral region (Fig 9C and 9D).

The premaxillae are wider than long and anteriorly rounded (Fig 9A–9D). Premaxillae form much of the margin of the naris, which is large, wider than long and anterodorsally projected (Figs 9A–9B and 10C–10D). In dorsal view, the premaxillo-maxillary suture is slightly curved. It extends from the notch for reception of the fourth mandibular tooth to the lateral suture of the nasal, forming a short posterior premaxillary process that reaches the level of the third maxillary alveolus (Fig 9A and 9B). In palatal view, the premaxillo-maxillary suture is straight, being posteromedially directed near the sagittal axis (Fig 9C and 9D). It is located far from the posterior margin of the incisive foramen, which is small and anteroposteriorly oval, probably due to deformation. Each premaxillary branch has five alveoli, the first two being the smallest of the series and the fourth the largest.

The maxillae are almost twice as long as wide (Fig 9A–9D). In dorsal view, they present an antero-lateral notch for the reception of the fourth mandibular tooth, which bears the suture that separates the premaxilla and maxilla (Fig 9A and 9B). Two shallow depressions, extending mediolaterally on the anteromedial area of the dorsal surface of the maxilla, are identified. They are extending up to the fourth maxillary alveolus. According to Martin (2010) [22], these depressions, which are symmetrical in both maxillary branches, do not have a post mortem origin. Posteriorly, there is a short pointed process in the left maxillary branch that gets inside the lacrimal. This structure is not observed in the right maxillary branch because the suture is unclear. In ventral view, no foramina for palatine ramus of cranial nerve V are observed (Fig 9C and 9D). The palatal surface is elevated relative to the tooth row on the right maxilla. However it is not possible to observe this elevation in the left maxilla due to deformation of this element. The right maxilla preserves twelve alveoli, but a crack may be obscuring a thirteenth (Fig 9C and 9D). On the left maxilla there are thirteen alveoli. The second and third teeth are preserved. The alveoli are round, the first three being the smallest, and the fourth being the largest in the series. The fifth maxillary alveolus is slightly smaller than the fourth and much larger than successive alveoli. The maxillae form the anterior and half of the lateral margins of the suborbital fenestrae, but are not involved in the medial margins of these fenestrae (Fig 9C and 9D).

Dorsally, the nasals are wide and laterally expanded in their posterior half, and narrow in their more anterior region, where they contact the posterior margin of the naris. They separate both premaxillae medially (Fig 9A and 9B). In their rear region, the nasals are thinner and are separated by a sharp anterior process of the frontal, forming two posterior nasal processes between the frontal and prefrontals.

The lacrimals are rectangular. The posterolateral sutures, in the area of contact with the jugals, are not well-preserved (Fig 9A and 9B). The lacrimals are longer than the prefrontals. The lacrimals form the rostral region of the orbits and constitute the distal portion of the dorsal preorbital ridges.

The prefrontals are elongated and form the anteromedial margins of the orbits (Fig 9A and 9B). Both are separated by a long and narrow anterior process of the frontal. This anterior process extends beyond the anterior margin of the prefrontals. At the middle region of the frontal, the prefrontals are mostly elevated on the dorsal surface of the rostrum, forming a marked ridge ahead of the anteromedial margin of the orbit. A small foramen is observed in the prefrontal wall of the orbits.

The frontal is highly ornamented, and this hinders detailed observation of sutures with adjacent elements (Fig 9A and 9B). This bone constitutes the anteromedial margins of the supratemporal fenestrae and the slightly elevated posteromedial margins of the orbits. A long and narrow anterior process extends beyond the anterior margin of the prefrontals in its more rostral region. In dorsal view, the posterior contact of the frontal with the parietal cannot be appreciated, although it is possible to observe the sutures between both elements in the medial wall of the supratemporal fenestrae (Fig 9A and 9B). The dorsal surface of the frontal is slightly depressed.

The parietal presents large and deep depressions constituting the ornamentation of dorsal surface (Fig 9A and 9B). Its dorsal surface is slightly depressed respect to the rest of the skull table. The limits of this bone with the squamosals and the frontal are not clear. Meanwhile, the contact region of the parietal with the supraoccipital bears a notch at its posterior margin with two small projections on both sides. The parietal forms most of the medial margins of the supratemporal fenestrae, being slightly projected above them.

In dorsal view, the postorbitals are longer than wide. Each is approximately half the length of the squamosal (Fig 9A and 9B). The postorbitals form the anterolateral margins of the supratemporal fenestrae. The sutures of these bones with the squamosals and the frontal can only be observed in the right side. The postorbital bars are massive and are inset into the anteroventral region of the postorbitals (Figs 9A–9B and 10C–10D).

The right squamosal is almost complete, whereas the left one is posterolaterally broken (Fig 9A and 9B). The dorsal surface of the squamosals is flat and ornamented. The suture of the squamosals with the parietal cannot be observed. Posteriorly, the squamosals present a narrow, elongated and ventrally oriented projection. The posterior margins of the squamosals slightly overhang the occipital areas. In their lateral surface, there is a shallow groove for insertion of the ear flap musculature, whose lower margin is projected anteriorly, contacting with the postorbital bar (Fig 10C and 10D). The squamosals constitute the largest part of the roof of the otic aperture. Their posterior region does not contact the quadrates.

The left jugal is incomplete on its rear region (Fig 9A and 9B). The jugals constitute the lateral margin of the infratemporal fenestrae and the lateral margins of the orbits, forming a thick border. Anteriorly, the jugals project an acute rostral process that reaches the eighth maxillary alveolus. In dorsal view, their posterior development is short and does not exceed the limit of the posterior margins of squamosals (Fig 9A and 9B). A small medial foramen is developed ahead of the basis of the postorbital bars.

Both quadratojugals are preserved. The right quadratojugal is almost complete, but the left one is broken in its lateral region (Fig 9A–9D). These elements are long and ornamented, and form the posterior margins of the infratemporal fenestrae. The quadratojugal projects a long anterior process excluding the quadrate from the fenestra. The suture between the quadratojugals and the jugals is slightly anterior relative to the rear angles of the infratemporal fenestrae. The quadratojugal spines are not preserved. Posteriorly, neither quadratojugal reaches the posterior end of the quadrate ramus. They do not participate in the mandibular condyles.

The quadrate branches have a short longitudinal development compared to those of the lobes of the squamosals (Fig 9A and 9B). The dorsal surface of the quadrates is smooth except in the contact area with the quadratojugal, where it is slightly ornamented. The rear portion of the quadrates is flat, but rises slightly in the region of the otic recesses. The quadrates form the ventral margins of cranioquadrate grooves, which are posterolaterally open because the posterior absence of quadrate-squamosal contact (Fig 10C and 10D). The foramen aëreum is placed dorsally, close to the medial edge of the quadrates (Fig 9A and 9B). Both condyles have slightly elevated dorsal margins (Fig 10A and 10B). The lateral condyles are larger than the medial. A dorsal notch between them is observed. Moreover, the medial condyles are ventrally directed. In ventral view, a well-marked longitudinal ridge, extending parallel to the suture of the quadrates with the quadratojugals, is observed. In addition, a shorter second ridge extends parallel to the medial edges of the quadrates (Fig 9C and 9D).

The palatines are thick and elongate. They constitute most of the medial walls of the suborbital fenestrae (Fig 9C and 9D). They have parallel lateral edges in the posterior half, but the edges are slightly widened at the anterior half. Rostrally, the palatines form a wide and rounded process, which extends beyond the anterior margins of the suborbital fenestrae. The sutures of the palatines with the pterygoid have a zigzag pattern, and they reach the posteromedial region of the suborbital fenestrae.

The ectopterygoids are thick and form the posterolateral margins of the suborbital fenestrae (Fig 9C and 9D). Anteriorly, each projects a short process along the medial maxillary margin, forming the medial wall of the last two alveoli. The posterior processes of the ectopterygoids are long and robust. These bones show a linear medial suture with the pterygoids that does not reach the posterior margins of the pterygoid wings. The dorsal processes contact the ventral bases of the postorbital bars. The exact relationship of the ectopterygoids with the postorbitals is not known (Fig 10C and 10D).

The pterygoids are markedly expanded caudoventrally, and the posterolateral margins of the pterygoid wings almost reach the posterior edge of the quadrate (Fig 9C and 9D). Nevertheless, the pterygoid wings extend beyond the posterior margin of the posteromedial pterygoid processes, which are well-developed and posteriorly expanded. Despite deformation of the basioccipital region, the relative short pterygoids can be seen ventral to the median Eustachian opening. The choana is rounded, being posteroventrally projected. It is completely surrounded by the pterygoids and placed in a slightly depressed area in the middle of the pterygoid surface.

Although lacking well-preserved margins, the laterosphenoids seem to be wide and laterally expanded.

The supraoccipital is subtrapezoidal and wider than high in occipital view (Fig 10A and 10B). The postemporal fenestrae cannot be recognized due to the occipital region of the skull is collapsed. The supraoccipital has a marked sagittal crest beginning at the dorsal margin and extending longitudinally along the supraoccipital. Despite its poor preservation, a dorsal exposure of the supraoccipital is preserved on the posteromedial portion of the skull table (Fig 9A and 9B).

The exoccipitals constitute much of the occipital area of the skull and form the dorsolateral edge of the foramen magnum, both exoccipitals contacting above it. In its dorsal margin, the exoccipitals are very depressed (Fig 10A and 10B). The paroccipital processes extend laterally beyond the margin of the medial condyle of the quadrate. A thick tubercle on the ventral edge of the paroccipital process can be observed in other allodaposuchids; although Martin (2010) [22] stated that the tubercles are not present in the specimen from Fox-Amphoux, it is recognized in the right paroccipital process. Two foramina are distinguished in the medioventral area of the right exoccipital, near the occipital condyle. They may correspond to the hypoglossal (XII) and vagus foramina. In lateral view, the exoccipitals form the ventral half of the internal wall of the otic aperture, posteriorly preventing the contact between squamosal and quadrate (Fig 10C and 10D).

Deformation of the braincase displaced the medial processes of the pterygoids, which are hidden the basisphenoid. Due to this, we can neither provide an accurate description of this element in occipital view nor observe the basisphenoid rostrum.

The basioccipital is trapezoidal in occipital view, being wider than high (Fig 10A and 10B). Its dorsal half constitutes the occipital condyle, which lacks a well-developed neck. The basioccipital plate is vertical and bears a longitudinal sagittal crest. Deformation does not allow precise assessment of the ventral margin of the basioccipital.

Dentition.

The dental formula of Lohuecosuchus mechinorum includes five premaxillary alveoli and twelve or thirteen maxillary alveoli. The two teeth preserved in the maxilla have conical morphology and are pointed and slightly curved ventrolingually. Their lingual surfaces are flat and their mesial and distal margins have lingually displaced longitudinal carinae. The labial surfaces are markedly convex, imparting a D-shape to the cross-section of the crown. The enamel is not ornamented.

Method.

A cladistic analysis has been performed in order to establish the phylogenetic relationships of Lohuecosuchus based on the data matrix of Brochu and Storrs (2012) [48]. Character 51 (largest dentary alveolus immediately caudal to fourth) has been modified because the lower jaw of Lohuecosuchus could not be codified with the existing states in the matrix. A new state, “the largest dentary alveolus immediately caudal to fourth be the tenth”, has been added. According to Delfino et al. (2008) [28], a new state has been added for the characters 148 (quadrate and squamosal not in contact on the external surface of the skull, posteriorly to the external auditory meatus) and 149 (caudal margin of otic aperture not defined and gradually merging into the exoccipital) due to the presence of a cranioquadrate passage laterally open in Hylaeochampsa and allodaposuchids.

Additionally, Shamosuchus djadochtaensis [49] (Campanian, Mongolia), Pietraroiasuchus ormezzanoi [11] (Albian, Italy), Pachycheilosuchus trinquei [50] (Albian, United States) and Late Cretaceous taxa Al. subjuniperus, Ar. gascabadiolorum, the type series of Lohuecosuchus megadontos and the holotype of L. mechinorum have been incorporated to the phylogenetic analysis, based on direct examination of fossil specimens. For Al. precedens, the re-scoring published by Blanco et al. (2014) [6] based on the specimen from Oarda de Jos (Romania) [28] has been used, with some modifications. Character 89 (position of incisive foramen) is recoded as 0, due to it does not reach the premaxillary teeth; character 105 (end of maxilla in palatal view with respect to infratemporal fenestra) is recoded as 0, because it terminates anterior to the lower temporal bar; character 117 (lateral edges of palatines) is recoded as 0, due to they are anteriorly smooth; character 119 (posterolateral margin of the suborbital fenestra) is recoded as 1, considering that it is concave; character 120 (lateral edges of palatines) is recoded as 0, due to they are parallel; character 142 (posterior angle of the infratemporal fenestra) is recoded as 0, because it is formed by the quadratojugal; character 152 (dermal bones of skull roof) is recoded as 1, due to the overhang the rim of the supratemporal fenestra; and character 181 (morphology and orientation of medial quadrate hemicondyle) is recoded as 0, because the hemicondyle is small and ventrally oriented. Character 131 (morphology of the anterior frontal process) has been considered as unknown, because the limits of the frontal are unclear in the only specimen of this taxon where this region is preserved. The final data matrix includes 103 taxa and 189 morphological characters. Bernissartia fagesii was set as outgroup. The matrix was analysed with TNT [51] using heuristic searches based on 1000 random addition sequence replicates. Bootstrap frequencies and Bremer support values have also been calculated using TNT.

Results.

The analysis recovered 8431 most parsimonious trees of 734 evolutionary steps, with a consistency index (CI) of 0,332 and a retention index (RI) of 0,798. The obtained topology (Fig 11) is consistent with those presented in some previous phylogenetic analyses [5, 9, 11, 12, 28], and monophyly of the higher groups of Eusuchia is recovered. The strict consensus reveals a monophyletic clade formed by Allodaposuchidae and Hylaeochampsidae, exclusively composed by European Cretaceous forms. This clade is recognized as the sister group of Crocodylia. Pietraroiasuchus, Pachycheilosuchus and the paralligatorid Shamosuchus are placed as non-eusuchian neosuchians, in contrast with the eusuchian affinities for these taxa suggested in several phylogenetic proposals [11, 27]. Therefore, Eusuchia is recognized here as composed by a monophyletic group formed by Hylaeochampsidae and Allodaposuchidae on the one hand, and Crocodylia on the other. In this analysis, Eusuchia is supported by the presence of dorsal osteoderms lacking keels (character 38, state 0), an ectopterygoid that abuts with the maxillary tooth row (character 104, state 0), a choana entirely surrounded by the pterygoids (character 121, state 1), and a posteriorly oriented external surface of the basioccipital ventral to the occipital condyle (character 170, state 1).

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Fig 11. Calibrated cladogram corresponding to the strict consensus tree obtained in the phylogenetic analysis.

The black rectangles represent the stratigraphic distribution of each taxon. Numbers at nodes indicate bootstrap frequencies over 50%, and Bremer support, over 2 (in parentheses).

https://doi.org/10.1371/journal.pone.0140679.g011

The European clade formed by hylaeochampsids and allodaposuchids is supported by the absence of anterior perforation for mandibular ramus of cranial nerve V (character 52, state 1); presence of a splenial excluded from mandibular symphysis, with its anterior tip ventral to Meckelian groove (character 54, state 1); external naris not bisected but contacted by nasals (character 82, state 1); pterygoid ramus of the ectopterygoid bowed, showing a concave posterolateral margin of suborbital fenestra (character 119, state 1); absence of contact of quadrate and squamosal on the external surface of the skull, posteriorly to the external meatus (character 148, state 0); and caudal margin of otic aperture not defined and gradually merging into the exoccipital (character 149, state 0).

Hylaeochampsidae is supported by the presence of procumbent anterior dentary teeth (character 48, state 0); a maxilla that comprises part of the lower temporal bar (character 105, state 1); the anterior tip of frontal forming broad and complex sutural contact with the nasals (character 131, state 1); a massive postorbital bar (character 133, state 0); reduced or absent quadratojugal spine (character 140, state 1); presence of a prominent knob on ventral surface of quadrate ramus (character 180, state 1); and an ectopterygoid maxillary ramus constituting more than two-thirds of the lateral margin of the suborbital fenestra (character 185, state 1).

Allodaposuchidae is supported by the presence of a maxillary posterior process within the lacrimal (character 128, state 1), ventral margin of the postorbital bar being part of the lateral jugal surface (character 135, state 1), upturned dorsal edges of the orbits (character 137, state 1), dermal bones of the skull roof overhanging the rim of the supratemporal fenestra (character 152, state 1), a shallow fossa at the anteromedial corner of the supratemporal fenestra (character 153, state 0), and a planar skull table surface (character 156, state 1).

Within Allodaposuchidae, Al. precedens is diagnosed here by the presence of an occlusion pit between the maxilla and the premaxilla (character 91, state 1); linear occlusion of the dentary teeth with the maxillary tooth row (character 92, state 2); very large medial jugal foramen (character 102, state 1); capitate process of laterosphenoid laterally oriented toward midline (character 166, state 0); anteroposteriorly wide basisphenoid ventral to the basioccipital (character 172, state 1); and basisphenoid exposed as a broad sheet ventral to the basioccipital (character 173, state 0). Allodaposuchus subjuniperus is supported by the dorsal projection of the naris (character 81, state 1), presence of four teeth in the premaxilla (character 87, state 1), and massive postorbital bar (character 133, state 0). Arenysuchus gascabadiolorum does not present any synapomorphy in this analysis.

The genus Lohuecosuchus is supported by a naris wider than long (character 83, state 1), presence of prominent preorbital ridges (character 97, state 1), and straight pterygoid ramus of the ectopterygoid, resulting in a linear posterolateral margin of the suborbital fenestra (character 119, state 0). Lohuecosuchus mechinorum is supported by the presence of a massive postorbital bar (character 133, state 0), and basisphenoid not broadly exposed ventral to the basioccipital, the pterygoid being short ventral to the median Eustachian opening (character 173, state 1). Lohuecosuchus megadontos is supported by the presence of deep notch lateral to the naris (character 86, state 1), prominent canthi rostralii (character 96, state 1), and quadratojugal-jugal suture forming the posterior angle of infratemporal fenestra (character 142, state 2).