Opisuchus meieri, 2020

OPISUCHUS MEIERI AIGLSTORFER ET AL. , SP. NOV.

FIGS 2–5A, B, 6A, 7

Lsid:zoobank.org:act: 345AE1D6-15CB-4BC5-8DE6- E409A30A2A15.

Holotype: SMNS 91268 About SMNS , cranium with the mandible semi-articulated, both missing the anterior part, including some elements of the cervical column.

Etymology: The species is named after Dieter Meier, who found the specimen.

Type locality: Clay pit (Mohring Brick Quarry) Heiningen, approx. 40 km ESE of Stuttgart.

Type horizon: ‘Nodule’ horizon, basal Middle Jurassic ( Opalinum Subzone, Opalinum Zone, Aalenian ).

Diagnosis: A metriorhynchoid crocodyliform with the following unique combination of characters (proposed autapomorphies are indicated by an asterisk): rostrum wider than high (in the anterior-middle portion of the rostrum)*; weak bone ornamentation; maxilla ornamented with faint ridges*; elongated preorbital fossa shallowing to anterior; jugal not participating in the formation of the external preorbital fenestra; incipient lateral enlargement of the prefrontal; dorsolaterally oriented orbits; moderately elongated supratemporal fossae with subparallel margins; supratemporal fenestrae subequal in length as the orbits; 60–70° between posteromedial and posterolateral processes of frontal; frontal-postorbital suture ‘V’-shaped and posteriorly directed; parietal considerably involved in the intratemporal flange; elongated retroarticular process; carinated slender teeth with inconspicuous enamel ridges well-defined at the basal half of the crown; elongated axis with diapophysis.

Differential diagnosis: Opisuchus meieri clearly differs from Metriorhynchidae in lacking laterally expanded prefrontals overhanging the orbits, non-fully laterally oriented orbits, a lachrymal that is still visible in dorsal view and the presence of a mandibular fenestra. Among non-metriorhynchid metriorhynchoids the taxon is most similar to Pelagosaurus typus . From this taxon O. meieri unambiguously differs in:

- a weaker bone ornamentation, e.g. on frontal and postorbital ( Pelagosaurus typus shows a strongly pitted surface in these bones);

- a deep and elongated preorbital fossa, shallowing to anterior and forming a clear sulcus excavated on the lateral surface of the maxilla (in Pelagosaurus typus the fossa is shallower and terminates in a subtle sulcus);

- the participation of the nasal in the dorsal rim of the external preorbital fenestra (in Pelagosaurus typus the fenestra is enclosed by the maxilla and lachrymal);

- the angle formed by the posteromedial and posterolateral processes of the frontal, which is 60–70º, whereas in Pelagosaurus typus it is approximately 90º;

- the anterior margin of the supratemporal fossa, which is as anterior as the postorbital anterior margin, whereas in Pelagosaurus typus the margin of the fossa terminates posterior to the latter;

- the general shape of the supratemporal fossa, which is framed by subparallel margins (anterior and posterior, as well as medial and lateral, respectively), and possesses an anteromedial angle of about 60–70°, whereas the margins are not subparallel in Pelagosaurus typus and the angle is nearly 90°;

- a ‘V’-shaped (tip directed posteriorly) frontalpostorbital suture, whereas in Pelagosaurus typus this suture is irregular and straight or gently curved;

- in the wide notch on the parietal posterior to the intertemporal bar, which is not present in this strength in Pelagosaurus typus .

From other non-metriorhynchid Metriorhynchoidea, O.meieri clearly differs in the shape of the supratemporal fossa (all non-metriorhynchid metriorhynchoids where this feature has been described), the presence of a well pronounced external preorbital fenestra ( Teleidosaurus calvadosii ), weak bone ornamentation on the frontal ( Teleidosaurus calvadosii , Eoneustes spp. ), the lateral extent of the supratemporal arch ( Teleidosaurus calvadosii , Eoneustes spp. ) and a nonenlarged prefrontal ( Z. nargorum ). The dentition in O. meieri is slenderer with finer ornamentation than the dentition in Magyarosuchus fitosi , and the ornamentation does not reach the apical region in contrast to the condition in the latter.

DESCRIPTION AND COMPARISON

PRESERVATION AND GENERAL SHAPE

The specimen is preserved in a limestone concretion. It comprises a cranium with the partially articulated mandible and a few elements of the cervical region (i.e. atlas–axis complex and the first post-axial cervical vertebra, as well as some fragmented ribs). The anterior region of rostrum and mandible is missing. The specimen is only slightly dorsoventrally compressed but otherwise preserved three-dimensionally. Calcite veins cross both specimen and host sediment (micritic grey limestone).

The general skull shape in O. meieri is most similar to Pelagosaurus typus . With Teleidosaurus calvadosii ( Eudes-Deslongchamps, 1870) and Eoneustes spp. ( Mercier, 1933; NHMUK PV R 3353), both share a gradual increase of the skull width from rostrum to posterior part of the skull, lacking a distinct concavity anterior to the orbit. This distinguishes these taxa from, for example, the ‘Chinese teleosauroid’ and Teleosaurus cadomensis . The supratemporal arch is positioned more lateral relative to the outline of the skull in Teleidosaurus calvadosii , E. gaudryi , E. bathonicus and Metriorhynchidae than in O. meieri ( Wagner, 1858; Fraas, 1902; Andrews, 1913; Mercier, 1933; Gasparini & Dellapé, 1976; Gasparini et al., 2006; Young et al., 2010, 2012; Cau & Fanti, 2011; Herrera et al., 2013b, 2015; NHMUK PV R 3353). In O. meieri , Pelagosaurus typus (e.g. SNSB-BSPG 1890 I 5, NHMUK PV OR 32599) and Z. nargorum ( Wilberg, 2015a: fig. 1) the supratemporal arch is in line with the outline of the skull. The occipital surface in O. meieri is not fully vertical, but oriented posterodorsally. The slight dorsoventral compression of the specimen may slightly exaggerate this.

Although the bone surface is not well-preserved, we can still state that there is no indication for a strong bone ornamentation, a feature that O. meieri shares with Z. nargorum and most Metriorhynchidae ( Wagner, 1858; Fraas, 1902; Andrews, 1913; Gasparini & Dellapé, 1976; Pol & Gasparini, 2009; Young et al., 2010, 2012; Herrera et al., 2013b; Parrilla-Bel et al., 2013; Wilberg, 2015a). This distinguishes the specimen clearly from the metriorhynchoids Pelagosaurus typus , Teleidosaurus calvadosii , E. bathonicus and E. gaudryi , and from teleosauroids (e.g. S. bollensis , S. gracilirostris , Teleosaurus cadomensis , Platysuchus multiscrobiculatus and the ‘Chinese teleosauroid’), which all show distinctly pitted bone surfaces, at least on the frontal. In O. meieri , nasals and maxillae have faint longitudinal striae (parallel to the longitudinal axis of the rostrum). These are furthermore indicated on the frontal (radially oriented, accompanied by some shallow grooves), and faint on the postorbital and the squamosal (parallel to the postorbital bar) ( Fig. 2). A few pits preserved on the lachrymal indicate that this bone could have shown some ornamentation, like in E. gaudryi (NHMUK PV R 3353). It cannot be ruled out that the ornamentation was as strong as in Pelagosaurus typus (e.g. SNSB-BSPG 1890 I 5), but it appears less likely from what is preserved. The palatines are smooth ( Fig. 3), a common feature among Thalattosuchia.

CRANIAL OPENINGS

Preorbital fossa, external preorbital fenestra and preorbital opening: The area of the cranial openings in front of the orbits is poorly preserved in O. meieri . It allows only a rough estimate of the sutures. Fossa and fenestra located anterior to the orbit in metriorhynchids are not homologous with the antorbital fossa/fenestra of other archosaurs, but are neomorphic structures related to the drainage of salt glands and were named preorbital fossa and preorbital opening ( Fernández & Herrera, 2009). A trace of an exocrine gland itself is not preserved in O. meieri . However, there is an evident fossa in the specimen located anterior to the orbit. Based on the position and morphology, we consider this fossa as the preorbital fossa.

The preorbital fossa in O. meieri is elongated and dorsoventrally low ( Figs 2, 4, 5A, B), as in all known metriorhynchids [e.g. C. araucanensis (MLP 72-IV- 1–7), D. andiniensis (MOZ-PV 6146), Maledictosuchus riclaensis , Metriorhynchus superciliosus , Pu. potens (MCNAM-PV 2060) ]. Its orientation is parallel to the rostrum and it seems to be mainly housed by the maxilla; the lachrymal encloses the fossa posteriorly. The preorbital fossa vanishes anteriorly and forms a sulcus excavated on the lateral surface of the maxilla, similar to some metriorhynchids, e.g. C. araucanensis, MLP 72-IV-1–7 and Me. superciliosus, NHMUK PV R 6859. This opening is clearly larger than in Teleosauroidea and Pelagosaurus typus ( Fig. 5C; NHMUK PV OR 32599), but not as deep as in metriorhynchids. It is similar to E. gaudryi ( Fig. 5F; NHMUK PV R 3353), but slightly longer and more evident than in E. bathonicus ( Fig. 5E; Mercier, 1933). The external preorbital fenestra in O. meieri ( Figs 2, 4, 5A, B) is formed by the nasal (dorsally), lachrymal (dorsoposteriorly, posteriorly and ventroposteriorly) and maxilla (ventrally). At its posteromedial region the fossa houses the preorbital opening. The preorbital opening is partially covered by sediment, but it seems that the maxilla forms the anterior rim, while two processes of the lachrymal close the dorsal, ventral and posterior margins of the opening. The suture of lachrymal and nasal is not clearly preserved in this area. Thus, we cannot completely rule out a participation of the nasal. In Teleidosaurus calvadosii ( Fig. 5D; Eudes-Deslongchamps, 1870) there appears to be no distinct preorbital fossa/opening.

Orbit: It is subcircular to suboval ( Figs 2, 4). The size in relation to the general skull size is larger than in S. bollensis (e.g. SMNS 91414; Westphal, 1962) and more comparable to the size in Pelagosaurus typus (NHMUK PV OR 32599, SNSB-BSPG 1890 I 5) and S. gracilirostris (NHMUK PV OR 14792 and 15500). The orbit in O. meieri faces dorsolaterally, distinguishing the specimen from all Teleosauroidea, except for S. gracilirostris ( Westphal, 1961, 1962; Jouve, 2009; Martin & Vincent, 2013; Young et al., 2014; Johnson et al., 2018a, b). In O. meieri the orbit is oriented slightly more vertical than in S. gracilirostris . Its orientation is comparable to the condition in Pelagosaurus typus and Teleidosaurus calvadosii and not fully lateral as it is in Z. nargorum , ‘ Chile metriorhynchoid’ and Metriorhynchidae ( Fraas, 1902; Andrews, 1913; Gasparini et al., 2000; Young et al., 2010; Wilberg, 2015a). In O. meieri the anteroventral rim of the orbit is formed by the lachrymal and the anterodorsal rim by the prefrontal, which also contributes to the dorsal rim. The frontal terminates the dorsal margin with a small contribution of the postorbital, which in turn forms the posterior and the posteroventral margins. Most of the ventral margin of the orbit is formed by the jugal. There are no indications for the presence of sclerotic plates/rings. Sclerotic plates have been recorded for Pelagosaurus typus and metriorhynchids among thalattosuchians (e.g. Fraas, 1902; Pierce & Benton, 2006; Pol & Gasparini, 2009; Young & Andrade, 2009).

Supratemporal fossa: The frontal, postorbital, parietal andsquamosalformthemarginsofthefossa( Figs2, 4, 6A). It is large and nearly twice as long as the orbit. It reaches roughly as far anteriorly as the postorbital comparable to the condition in C. elegans (SNSB-BSPG AS I 504), C. araucanensis (MLP 72-IV-7-1), ‘ Metriorhynchus ’ casamiquelai (MGHF 1-08573) and G. grandis (SNSB-BSPG AS VI 1). Anterior and posterior, as well as lateral and medial, margins are subparallel. Medial and anterior margins form an angle of 60–70°, which is shared with a few metriorhynchids (e.g. Maledictosuchus riclaensis , Tyrannoneustes lythrodectikos , Pu. potens , G. grandis ). Among Thalattosuchia, the general shape is similar to D. andiniensis ( Gasparini et al., 2006) , D. maximus ( Plieninger, 1846) ( Young et al., 2012) and Ty. lythrodectikos ( Foffa & Young, 2014) ( Fig. 6H, I, K). In other non-metriorhynchid Metriorhynchoidea ( Fig. 6B–E), the anterolateral rim is less oblique and oriented more perpendicular to the longitudinal axis of the skull. This applies also to most teleosauroids (e.g. Fig. 6M–Q). In machimosaurins ( Fig. 6R–T), the supratemporal fossa is clearly more stretched in the anteroposterior direction. In Pelagosaurus typus the fossa is more rounded ( Fig. 6B). In O. meieri the fossa tapers in between the orbits anteriorly. The anterior shelf is more extended in O. meieri than in teleosauroids (e.g. ‘Chinese teleosauroid’, IVPP V 10098 View Materials ; S. bollensis, SMNS 91414; Teleosaurus cadomensis, Jouve, 2009 : fig. 1). The extension is more comparable to the condition present in basal Metriorhynchoidea ( Fig. 6B–D) and different to Metriorhynchidae ( Fig. 6F–L). The intratemporal flange is formed by the frontal, but with the participation of the laterosphenoid and the parietal. The suture of parietal and frontal cannot be discerned unambiguously, but the parietal takes at least part in the formation of the anterior flange comparable to the condition in Pelagosaurus typus (NHMUK PV OR 32599, SNSB-BSPG 1890 I 5).

Supratemporal fenestra: It is ovoid to teardropshaped ( Figs 2, 4, 6A), similar to the condition in Pelagosaurus typus ( Fig. 6B) and E. bathonicus ( Fig. 6D). It is bounded by frontal, laterosphenoid, prootic, postorbital, squamosal and quadrate. In contrast to the ‘ Chile metriorhynchoid’, Z. nargorum and Metriorhynchidae , its posterior margin terminates well before the posteriormost point of the parietal. Like in Teleidosaurus calvadosii ( Eudes-Deslongchamps, 1870) , E. bathonicus ( Mercier, 1933) and Z. nargorum ( Wilberg, 2015a) , the supratemporal fenestra is subequal in length to the orbit in O. meieri .

Infratemporal fenestra: The actual shape of the infratemporal fenestra cannot be reconstructed due to compression and fragmentary preservation of the lateral skull region ( Fig. 4). At least dorsally it is less anteroposteriorly elongated than it is the case in Teleidosaurus calvadosii ( Eudes-Deslongchamps, 1870: plate 5).

Suborbital fenestra: Parts of the suborbital fenestra are preserved in ventral view ( Fig. 3). It is elongated and anteriorly forms an acute angle, comparable to Pelagosaurus typus ( NHMUK PV OR 32599, SNSB-BSPG 1890 I 5). Anteriorly, and laterally, the suborbital fenestra is limited by the maxilla, medially by the palatine, and posteriorly by the ectopterygoid .

Secondary choana: Most of the secondary choana is missing due to preservation ( Fig. 3). Anteriorly it is closed by fusion of the palatines. Posteriorly and dorsally it is bounded by the pterygoid. A midline process, most likely the interchoanal septum, is indicated. It divides the choana as in Pelagosaurus typus ( NHMUK PV OR 32599; SNSB-BSPG 1890 I 5) .

CRANIUM

Maxilla: As in other thalattosuchians, the maxilla is anteroposteriorly elongated with a rather smooth surface, only with slight striation in dorsal and lateral views ( Figs 2, 4). Its dorsolateral surface is convex. The anterior part of the maxilla is not preserved. Medially it contacts with the nasal in an anteromedialposterolateral suture. Posteriorly, the sutures with the lachrymal and the jugal can be reconstructed only roughly. The general course of the suture with nasal and lachrymal is similar to Pelagosaurus typus (NHMUK PV OR 32599) and other basal Metriorhynchoidea, such as Teleidosaurus calvadosii and Eoneustes spp. As in both species of Eoneustes , the maxilla in O. meieri houses at least the anterior part of the preorbital fossa and most of the sulcus ( Figs 4, 5). The ventrolateral edge of the maxilla is straight in O. meieri . In ventral view, the maxilla is medially sutured to the palatine. The palatal part of the maxilla is flat with a smooth surface; it forms the anterolateral rim of the suborbital fenestra ( Fig. 3). At least in some teleosauroids (e.g. Teleosaurus cadomensis, Jouve, 2009 : fig 2B; L. obtusidens, Johnson et al., 2018a : figs 5–6), the maxilla terminates posterior to the anterior margin of the orbit in lateral view, whereas in O. meieri it terminates slightly anterior to this margin, comparable to the condition in Pelagosaurus typus (SNSB-BSPG 1890 I 5).

Nasal: The nasals are unfused and paired ( Figs 2, 4, 5A, B). There is no strong ornamentation. In dorsal view, the nasals are subtriangular, as in all thalattosuchians. However, the anteriormost region is not preserved. They are convex and have a distinct longitudinal depression along the midline, as in Metriorhynchoidea (e.g. Young et al., 2013a; Fernández et al., 2019) and some teleosauroids [e.g. S. bollensis (SMNS 15391, 15951b); S. gracilirostris (NHMUK PV OR 14792, NHMUK PV OR 757); Steneosaurus brevior (NHMUK PV OR 14781)]. The posteromedial processes contact the frontal medially and the prefrontals laterally, although the suture with the prefrontal is not clearly preserved. The nasal contacts the lachrymal through a short posterolateral process, comparable to the condition present in E. gaudryi (NHMUK PV R 3353) and (weaker) in some Pelagosaurus typus (see: NHMUK PV OR 32599; Pierce & Benton, 2006). Teleidosaurus calvadosii ( Eudes-Deslongchamps, 1870: plate 5) lacks this posterolateral process. The posterolateral processes are not elongated as in Metriorhynchidae , e.g. C. araucanensis , D. andiniensis and Me. superciliosus . The nasal–prefrontal suture appears to be longer than the nasal–lachrymal suture. The lateral margins of the nasals (nasal–maxilla sutures) meet more anteriorly in O. meieri and Pelagosaurus typus (NHMUK PV OR 32599) than in Teleidosaurus calvadosii ( Eudes-Deslongchamps, 1870: plate 5), Eoneustes spp. ( Mercier, 1933: fig. 1; NHMUK PV R 3353) and in Metriorhynchidae , indicating a more elongated shape for the nasals in the first taxa ( Fig. 2).

Lachrymal: Due to preservation, the actual shape of the lachrymal is difficult to discern, but as far as it can be reconstructed, it was trapezoidal in shape ( Figs 2, 4, 5A, B). Some pits that are preserved on the surface of the lachrymal indicate that there was at least some bone ornamentation. The dorsoventral height of the lachrymal is at least 40 % of the height of the orbit ( Figs 2, 4, 5A, B). Its relative size in comparison to the prefrontal is larger than in Z. nargorum and Metriorhynchidae ( Fraas, 1902; Andrews, 1913; Pol & Gasparini, 2009; Young & Andrade, 2009; Cau & Fanti, 2011; Young et al., 2012; Herrera et al., 2013b, 2015; Wilberg, 2015a), but smaller than in S. bollensis ( Westphal, 1962) , Teleosaurus cadomensis ( Jouve, 2009: fig. 2), Pelagosaurus typus ( Fig. 5C; Pierce & Benton, 2006; NHMUK PV OR 32599) and Teleidosaurus calvadosii ( Fig. 5D; Eudes-Deslongchamps, 1870). Anteriorly, the lachrymal borders the nasal and forms the posterior rim of the preorbital fossa and posteriorly it forms the ventral part of the anterior margin of the orbit. The lachrymal has a short anteromedial contact with the nasal and a long posteromedial one with the prefrontal ( Fig. 5A, B), different to the condition in Pelagosaurus typus ( Fig. 5C; NHMUK PV OR 32599; Pierce & Benton, 2006). Ventrolaterally, it meets the maxilla and the jugal. The suture with the maxilla is longer than the one with the jugal. The lachrymal is exposed in dorsal and lateral views, as in Teleosauroidea, Pelagosaurus typus , Teleidosaurus calvadosii and Eoneustes spp. (e.g. Eudes-Deslongchamps, 1870; Collot, 1905; Mercier, 1933; Westphal, 1962; Mueller-Töwe, 2006; Pierce & Benton, 2006; Jouve, 2009; Martin & Vincent, 2013; Johnson et al., 2018a). This is different to the state in Z. nargorum and Metriorhynchidae , where the lachrymal is only visible in lateral view ( Fraas, 1902; Andrews, 1913; Pol & Gasparini, 2009; Young & Andrade, 2009; Cau & Fanti, 2011; Young et al., 2012; Herrera et al., 2013b, 2015; Wilberg, 2015a).

Jugal: The jugal is a slender anteroposteriorly elongated bone. Both jugals are preserved only fragmentarily ( Figs 2, 4). The posterior half, forming the ventral rim of the infratemporal fenestra, is not preserved. Anteriorly the jugal contacts the maxilla and dorsally the lachrymal. It does not take part in the formation of the external preorbital fenestra, as in Pelagosaurus typus and Eoneustes spp. ( Fig. 5). This distinguishes O. meieri from most Metriorhynchidae , e.g. C. araucanensis , D. andiniensis , G. giganteus , and Me. superciliosus ( Andrews, 1913: fig. 56) where the jugal reaches further anteriorly and takes part in the margin of external preorbital fenestra. Posteriorly the jugal meets the postorbital in a suture along the posterior rim of the orbit. The jugal forms most of the ventral margin of the orbit and separates the lachrymal from the postorbital as in most thalattosuchians, e.g. L. obtusidens ( Johnson et al., 2018a) ; Pelagosaurus typus ( Pierce & Benton, 2006) ; Pu. potens ( Herrera et al., 2015) .

Prefrontal: Neither of the prefrontals is preserved well enough to unambiguously describe shape and ornamentation. However, at least an anteroposteriorly elongated semitrapezoidal shape can be reconstructed ( Figs 2, 4, 5A, B). The prefrontal contacts the nasal (anteriorly, medially and laterally), the frontal (medially) and the lachrymal (laterally). It forms the anterodorsal margin of the orbit and builds up much of its dorsal margin, reducing the contribution of the frontal to the posterior half of the dorsal rim. The prefrontal is not laterally extended overhanging the orbit, which distinguishes O. meieri from Z. nargorum and Metriorhynchidae ( Fraas, 1902; Andrews, 1913; Pol & Gasparini, 2009; Young &Andrade, 2009; Cau& Fanti, 2011; Young et al., 2012; Herrera et al., 2013b, 2015; Wilberg, 2015a). The general shape of the prefrontal in O. meieri is similar to Pelagosaurus typus , although slightly larger. Like in some specimens of the latter (e.g. SNSB-BSPG 1890 I 5) and in Eoneustes spp. there is an incipient lateral enlargement in the prefrontal in O. meieri . The prefrontal is clearly larger and more elongated than in Teleidosaurus calvadosii ( Fig. 5D) and E. bathonicus ( Fig. 5E), and slightly more than in E. gaudryi ( Fig. 5F; Eudes-Deslongchamps, 1870; Mercier, 1933; NHMUK PV R 3353). The prefrontal in O. meieri is different in shape and relatively longer than in Teleosauroidea, e.g. S. bollensis (SMNS 91414; Westphal, 1962), L. obtusidens ( Johnson et al., 2018a) and Teleosaurus cadomensis ( Jouve, 2009) .

Frontal: The frontal is fused, roughly rhombic in shape and forms a planar skull surface between the orbits ( Figs 2, 4). The cortical surface of the bone is not well preserved. However, there is no indication for a distinct pitted ornamentation as in teleosauroids like S.bollensis (e.g. SMNS 91414), S. gracilirostris (e.g. NHMUK PV OR 14792) and Teleosaurus cadomensis ( Jouve, 2009) or even like in Pelagosaurus typus , e.g. NHMUK PV OR 32599, SNSB-BSPG 1890 I 5. The anterior process of the frontal tapers between the posteromedial processes of the nasals. The nasal–frontal–nasal sutures form an angle of 35–40°, more acute than in Eoneustes spp. ( Collot, 1905; Mercier, 1933). The postorbital processes form an angle of about 60–70° with the midline of the skull, whereas in Pelagosaurus typus (e.g. NHMUK PV OR 32599, SNSB-BSPG 1890 I 5) and E. bathonicus ( Mercier, 1933) this angle is usually less acute (approximately 90°). In E. gaudryi , Teleidosaurus calvadosii , ‘ Chile metriorhynchoid’ and Z. nargorum this angle is almost 90° ( Eudes-Deslongchamps, 1870; Collot, 1905; Gasparini et al., 2000; Wilberg, 2015a). The frontal is sutured to the prefrontal along a straight line and forms the posterodorsal margin of the orbit. The frontal contribution to the dorsal rim of the orbit is more reduced than in some teleosauroids, e.g. S. bollensis (SMNS 91414) and L. obtusidens ( Johnson et al., 2018a) , but not as reduced as in Z. nargorum ( Wilberg, 2015a) . The minimal distance between orbits is subequal to the width of one supratemporal fossa as, for example, in C. lithographicus , D. andiniensis , G. grandis , Maledictosuchus riclaensis , Pu. potens and Ty. lythrodectikos . The postorbital processes contact the postorbital through a ‘V’-shaped suture with the apex pointing posteriorly, as in Z. nargorum and metriorhynchids, e.g. C. araucanensis (MLP 72-IV-7- 1), C. lithographicus ( Herrera et al., 2013b) , G. grandis (SNSB-BSPG AS VI 1), Neptunidraco ammoniticus ( Cau & Fanti, 2011) and Ty. lythrodectikos ( Foffa & Young, 2014) , whereas the suture is straight or irregular in Pelagosaurus typus (e.g. SNSB-BSPG 1890 I 5; Pierce & Benton, 2006), Teleidosaurus calvadosii ( Eudes-Deslongchamps, 1870) , E. bathonicus ( Mercier, 1933) , and most teleosauroids, e.g. L. obtusidens ( Johnson et al., 2018a) and Teleosaurus cadomensis ( Jouve, 2009) . The frontal extends posteroventrally and forms most of the intratemporal flange of the supratemporal fossa and the anterolateral rim of the supratemporal fenestra. The posterior process contacts the parietal forming the intertemporal bar; however, the suture cannot be discerned unambiguously.

Parietal: The actual size and shape of the fused parietal is difficult to discern due to preservation. It is a tri-radiate bone with an anterior process (from which two lateroventral processes appear to diverge and contribute to the intratemporal flange), and two posterolateral processes ( Fig. 2). The anterior process participates, at least, in the posterior part of the intertemporal bar, as in all thalattosuchians [e.g. ‘Chinese teleosauroid’ (IVPP V 10098 View Materials ); Pelagosaurus typus (SNSB-BSPG 1890 I 5); C. araucanensis (MLP 72-IV-7-1); D. andiniensis ( Pol & Gasparini, 2009) ]. Within the supratemporal fossa, the parietal contacts anterolaterally the laterosphenoid, and posterolaterally the prootic. It forms, together with the laterosphenoid, most of the medial shelf of the fossa. In C. araucanensis (MLP 72-IV-7-1) the parietal does not reach as anterior as it does in O. meieri and Pelagosaurus typus (e.g. NHMUK PV OR 32599). The parietal forms the dorsal margin of the fossa housing the temporo-orbital foramen. The posterolateral processes of the parietal contribute to most of the posterior margin of the supratemporal fossae. These processess are laterally sutured to the squamosals. Posterior to the intertemporal bar the parietal shows a wide ‘V’-notch between the posterolateral processes that is stronger than in Pelagosaurus typus (SNSB-BSPG 1890 I 5; NHMUK PV OR 32599). The dorsal part is not fully preserved, but the general shape is more similar to Teleidosaurus calvadosii ( Eudes-Deslongchamps, 1870) than to some Cricosaurus spp. , e.g. C. araucanensis (MLP 72-IV-7-1) and C. lithographicus (MOZ-PV 5787). In O. meieri the posterolateral processes of the parietal have a more posterolateral direction than in Pelagosaurus typus . They are more similar to Teleidosaurus calvadosii . In occipital view, the parietal has a ventral contact with the supraoccipital, however the suture is not preserved.

Squamosal: In dorsal view, the squamosal possesses a concave triangular shape, with an acute apex directed posterolaterally ( Fig. 2). The angle formed by the posterior and lateral processes of the squamosal (forming the posterolateral edge of the supratemporal fossa) is acute ( Fig. 6A), similar to the condition in E. bathonicus ( Fig. 6D), and D. andiniensis ( Fig. 6I). It forms the posterolateral edge of the supratemporal shelf and has a reduced contribution to the lateral margin of the supratemporal fenestra. The squamosal appears to form the lateral margin of the fossa housing the temporo-orbital foramen, while in Z. nargorum it also contributes to the dorsal margin of this fossa (this can be given with reservations only as the suture with the parietal is not fully clear). Anterolaterally the squamosal contacts the posterior process of the postorbital, anteroventrally the quadrate, medially the prootic, and posteriorly the parietal and the otoccipital. It does not reach as anterior as it is the case in Pl. multiscrobiculatus ( Westphal, 1962: fig. 24). Due to compression, the extension of the squamosal onto the occipital surface cannot be estimated. In lateral view ( Fig. 4) the squamosal appears to be intruding in between the postorbital and the quadratojugal. Unfortunately, the sutures are not clearly preserved in this area.

Postorbital: The postorbital is tri-radiate in lateral view comprising a short anterodorsal (frontal) process, a short and wide anteroventral process, and a long posterior one ( Figs 2, 4). The postorbital forms the posterior margin of the orbit. Laterally it overlies the jugal and forms most of the lateral wall of the postorbital bar. Posteriorly the postorbital contacts the squamosal, and forms most of the supratemporal arch. The frontal process of the postorbital does not reach as medial as it is the case in Teleosaurus cadomensis ( Jouve, 2009: fig. 1). The general shape and extension of the postorbital is most similar to the condition in Pelagosaurus typus (e.g. SNSB-BSPG 1890 I 5; NHMUK PV OR 32599). However, it clearly differs from the latter in the lack of a strong surface ornamentation and the course of the suture with the frontal. The lateral surface of the postorbital is generally convex. There is a shallow depression just posterior to the orbit. In lateral view the arch forms a dorsally concave curve and declines posteriorly ( Fig. 4).

Quadratojugal: The quadratojugal is preserved only fragmentarily in O. meieri . The ascending process forms the posterior margin of the infratemporal fenestra. Due to preservation most of the sutures cannot be identified ( Fig. 4) and a comparison to other taxa cannot be given.

Quadrate: The quadrates are completely preserved and partially exposed in dorsal and ventral views ( Figs 2, 3). A small portion can also be observed in lateral view, where the quadrate contacts the quadratojugal ( Fig. 4). Unfortunately, the occipital view is obscured by sediment and other bones. The quadrate takes part in the posterior supratemporal shelf, where it sutures the squamosal laterally and the prootic medially, and forms most of the posterior and the posterolateral margins of the supratemporal fenestra. It does not contact the laterosphenoid, as in most thalattosuchians ( Clark, 1986). In O. meieri the quadrate does not participate in the formation of the temporo-orbital foramen, as in C. araucanensis and Pelagosaurus typus , and unlike Teleosaurus cadomensis and Machimosaurus buffetauti , where the quadrate participates slightly to the ventrolateral margin (for further details see: Herrera et al., 2018). In ventral view, the quadrate is elongated, oriented anteromedial-posterolaterally, and widens from anterior to posterior. The crest on the ventral side [crest B of Iordansky (1964)] is present but not particularly developed. Ventromedially, the quadrate contacts the pterygoid, the basisphenoid and reaches the basal tuberosities of the basioccipital along their lateral margin, as in most thalattosuchians, e.g. C. araucanensis ( Herrera et al., 2018) , Pu. potens ( Herrera et al., 2015) , Pelagosaurus typus (SNSB-BSPG 1890 I 5; NHMUK PV OR 32599), S. cf. gracilirostris ( Brusatte et al., 2016) and To. coryphaeus . The orbital process of the quadrate is partially covered by sediment. However, it seems not firmly sutured to the braincase, as in other thalattosuchians ( Holliday & Witmer, 2009; Jouve, 2009; Fernández et al., 2011; Herrera et al., 2015, 2018; Wilberg, 2015a). The distal articular surface bears two condyles separated by a sulcus, as in most thalattosuchians (e.g. S. bollensis , S. brevior , Pelagosaurus typus , Metriorhynchus spp. , Ty. lythrodectikos and Pu. potens ), and is slightly below the level of the occipital condyle.

Supraoccipital: The supraoccipital is concave and subrhomboidal, with a rounded, ventral margin. It is wider than high in posterior view, as in most thalattosuchians, e.g. C. araucanensis ( Herrera et al., 2018: fig. 5), Pelagosaurus typus (SNSB-BSPG 1890 I 5; NHMUK PV OR 32599), Teleosaurus cadomensis ( Jouve, 2009) and Z. nargorum ( Wilberg, 2015a) . It can be seen in dorsal and posterior views ( Fig. 2). Dorsally, it is sutured to the parietal and ventrally and laterally it is bordered by the otoccipital. The supraoccipital is separated from the dorsal margin of the foramen magnum by the otoccipitals.

Otoccipital: Most of the otoccipitals are obscured by other bones or sediment ( Fig. 2). They form most of the occipital surface and participate in the dorsal and lateral margins of the foramen magnum, as in most thalattosuchians, e.g. C. araucanensis (MLP 72-IV-7-1), Pelagosaurus typus (SNSB-BSPG 1890 I 5; NHMUK PV OR 32599). The otoccipitals are flat, slightly concave posteriorly and contact the supraoccipital dorsally and the parietal and the squamosals dorsolaterally. The paroccipital processes are elongated and oriented posterolaterally. Due to sediment cover, a contribution to the occipital condyle cannot be verified.

Basioccipital: The basioccipital forms the occipital condyle and most of the basal tuberosities. The occipital condyle is set off well from the occipital plane and separated from it by a clearly developed column. The basal tuberosities are separated by a strong sulcus, just ventral of the median pharyngeal foramen. They are well pronounced and oblonged and clearly stronger than e.g. in D. andiniensis ( Pol & Gasparini, 2009) . Each tuber does not form a uniform convex surface but bears a lateroventral to mediodorsal depression, giving it a stepped shape: for each tuber the posterolateral convexity is located more dorsal than the anteromedial one, as in S. bollensis ( Herrera et al., 2018: fig. 1). There seems to be no pronounced lateral pharyngeal foramen, or it may be even absent, as in metriorhynchids ( Herrera et al., 2018). Distinct and relatively large lateral pharyngeal foramina are present in teleosauroids and in Pelagosaurus typus ( Herrera et al., 2018) . However, due to preservation we cannot completely rule out the presence of a small foramen in O. meieri .

Laterosphenoid: The laterosphenoid is a rectangularelongated bone and forms most of the lateral wall of the braincase ( Fig. 2). In dorsal view the laterosphenoid forms the medial and the anteromedial margin of the supratemporal fenestra ( Fig. 2). It participates more in the formation of the intratemporal flange than in Teleosaurus cadomensis ( Jouve, 2009) , and appears slightly wider in dorsal view than it is the case in Pelagosaurus typus (NHMUK PV OR 32599). Within the supratemporal fossa, the laterosphenoid contacts the parietal. The suture is long and curved, and ascends from anterolateral to posterodorsal. The laterosphenoid seems to be separated from the frontal by an anterolateral process of the parietal, but the suture is not clear in this area. Posteriorly, the laterosphenoid in O. meieri contacts the prootic through a vertical suture, forming a blunt crest separating anterior and posterior fossae for the attachment of the adductor musculature ( Fig. 2), as it was also described for both teleosauroids and metriorhynchoids [e.g. C. araucanensis (MLP 72-IV-7-1), Me. superciliosus (SMNS 10116), Pu. potens (MCNAM-PV 2060) , Pelagosaurus typus (SNSB-BSPG 1890 I 5), S. bollensis (SMNS 15951b), S. cf. gracilirostris (NHMUK PV OR 33095); furthermore described for D. andiniensis and ‘ Me. ’ casamiquelai ; see also: Holliday & Witmer (2009), Fernández et al. (2011), Herrera et al. (2015, 2018), Brusatte et al. (2016)].

Prootic: In dorsal view the prootic is part of the posterior shelf of the supratemporal fossa and forms the posteromedial rim of the supratemporal fenestra ( Fig. 2). It is triangular-shaped with an elongated posterolateral process. In O. meieri this process is laterally concave and terminates in the temporo-orbital foramen, as in other thalattosuchians [e.g. C. araucanensis (MLP 72-IV-7-1), Pu. potens (MCNAM-PV 2060) , Pelagosaurus typus (NHMUK PV OR 32599), Teleosaurus cadomensis ( Jouve, 2009) ; for further information see also Jouve (2009) and Herrera et al. (2018)]. The foramen is relatively smaller than in Pelagosaurus typus (NHMUK PV OR 32599, SNSB-BSPG 1890 I 5), but more comparable to the condition in C. araucanensis (MLP 72-IV-7-1) and Z. nargorum ( Wilberg, 2015a) . Anteriorly, the prootic is sutured to the laterosphenoid, and dorsally to the parietal. Laterally it contacts the squamosal and the quadrate.

Basisphenoid: The basisphenoid is roughly triangular-shaped and widely exposed in ventral view ( Fig. 3). It contacts the basioccipital posteriorly and the quadrate laterally. Anteriorly it appears to intrude in between the pterygoids in a ‘V-shaped’ suture, pointing to anterior. Anteriorly the basisphenoid terminates approximately at the level of the anteriormost point of the quadrates. In contrast to the condition in S. bollensis (SNSB-BSPG 1984 I 258; Herrera et al., 2018), where the basisphenoid bears two crests and a median sulcus, there is only one median crest in O. meieri , as it is also the case in Pelagosaurus typus (SNSB-BSPG 1890 I 5; NHMUK PV OR 32599). In Teleosaurus cadomensis there is also a median crest ( Jouve, 2009). The basisphenoid forms the anterior margin of the median pharyngeal foramen.

Pterygoid and ectopterygoid: The pterygoid is fragmented and most of the surface is not preserved.The general shape is roughly rhombic. The flanges appear to be oriented mainly horizontal.Anteriorly the pterygoid is sutured to the palatines, laterally to the ectopterygoids, posterolaterally to the quadrate and posteriorly to the basisphenoid. Most of the anterior surface forms a strong depression deepening to the anterior and comprising the posterior part of the secondary choana, as in Pelagosaurus typus (e.g. NHMUK PV OR 32599, SNSB-BSPG 1890 I 5) and Teleosaurus cadomensis ( Jouve, 2009) . In O. meieri and Pelagosaurus typus there is a distinct midline ridge dividing the depression. It is stronger than in Maledictosuchus riclaensis ( Parrilla-Bel et al., 2013) . With reservations, Parrilla-Bel et al. (2013) assign this crest to the parasphenoid. The ectopterygoids are preserved incompletely. They contact the pterygoids medially and form the posterior margin of the suborbital fenestra.

Palatine: The palatines are preserved incompletely and partially covered by sediment and the mandible. They contact each other along the midline. A pair of anteroposteriorly oriented maxillo-palatine grooves is visible, as in other thalattosuchians, e.g. C.araucanensis (MLP 72-IV-7-1), Maledictosuchus riclaensis ( Parrilla-Bel et al., 2013) , Pelagosaurus typus (NHMUK PV OR 32599) and To. coryphaeus ( Young et al., 2013a) . Laterally, the palatines contact the palatal region of the maxilla in a straight anteromedial-posterolateral suture. Posteriorly, two lateral processes meet the pterygoid in an anteromedial–posterolateral suture and form the anterior and anterolateral rim of the secondary choana. Posterolaterally, the palatines form the medial margin of the suborbital fenestrae. The angle formed by the maxilla–palatine suture and the midline is more acute in O. meieri than in S. bollensis (e.g. Westphal, 1962) and thus gives the palatines a more elongated shape than in the latter.

MANDIBLE

The mandible is still attached to the cranium and mainly exposed in ventral view ( Fig. 3). Mainly the post-symphyseal part is preserved. Due to compression, neither dorsoventral height nor the actual shape of the mandible can be reconstructed. In any case, it can be still seen that the mandible in O. meieri was elongated and slender like in C. araucanenis (MLP 72-IV-7-1), Pelagosaurus typus (NHMUK PV OR 32599) or Metriorhynchus (for examples, see Andrews, 1913). It was not dorsoventrally high and robust as in brevirostrine geosaurins like D. maximus (SMNS 8203) and D. andiniensis (MOZ-PV 6146).

Mandibular fenestra: The presence of a mandibular fenestra is indicated in ventral and lateral views ( Figs 3, 4). Its actual shape cannot be estimated due to strong compression, but it was at least as long as the orbit. The presence of a mandibular fenestra distinguishes O. meieri from Metriorhynchidae ( Young et al., 2012) . It shares this feature with Pelagosaurus typus , Teleidosaurus calvadosii and teleosauroids.

Dentary: Due to preservation, the dentary can be seen in dorsal, lateral and ventral views ( Figs 2–4). It is elongated and slightly curved. Most of the ventral surface is not preserved. At the anterior part, a weak dentary groove is present in O. meieri ( Fig. 3), as in other metriorhynchoids, e.g. C. elegans (SNSB-BSPG AS I 504), C. lithographicus (MOZ-PV 5787), C. suevicus (SMNS 9808), Pelagosaurus typus (NHMUK PV OR 32599). The dentary is sutured to the angular medially along all of its post-symphyseal length. Posteriorly, the dentary terminates in a suture with the surangular at about the height of the anterior rim of the orbit.

Splenial: Two fragments of the splenials are preserved medially to the angular and the dentary. The splenial is involved in the formation of the symphysis and reaches posteriorly at least till the anterior margin of the suborbital fenestra ( Fig. 3).

Coronoid: An elongated bone fragment between splenial and angular could represent the coronoid ( Fig. 3). Due to the fragmentary preservation, a description of the element cannot be given.

Angular: The angular is incompletely preserved. It is exposed mainly in ventral view ( Fig. 3). It contacts the dentary and the surangular laterally. Anteriorly, it reaches at least up to the posterior part of the symphysis, and medially contacts the splenial. Posteriorly it contributes to the ventral rim of the mandibular ramus. The angular forms the ventral margin of the mandibular fenestra and the ventral part of the retroarticular process ( Fig. 2; see description of articular for more details).

Surangular: The surangular can be seen in ventral view ( Fig. 3). Anteriorly it is sutured to the dentary through a mediolateral suture at about the height of the anterior rim of the orbit. The surangular forms most of the posterior part of the dorsal mandibular ramus and the dorsal margin of the mandibular fenestra. Its actual shape cannot be reconstructed due to strong fragmentation and fracturation. The posterior part of the surangular is preserved on the retroarticular process where it sutures articular and angular ( Fig. 2; see description of articular for more details).

Articular: Both articulars are more or less still in loose articulation with the quadrate. The left articular is only preserved as a fragment ( Fig. 3). The right articular is detached from the lower jaw and flipped. Thus, the anterior surface is now exposed in ventral view ( Fig. 3) and the retroarticular process extends on the dorsal side ( Fig. 2). The shape of the articular is elongated triangular. Together with the surangular and angular, the articular forms a long retroarticular process, which is dorsally concave with a hook-like posterior tip ( Fig. 2). The process in O. meieri is relatively longer than in Pelagosaurus typus (NHMUK PV OR 32599) and Teleidosaurus calvadosii ( Eudes-Deslongchamps, 1870) , but more comparable to the condition in C. araucanensis (MLP 72-IV-7-1) or L. obtusidens ( Johnson et al., 2018a) . In ventral view the glenoid fossa can be seen. It is divided by a ridge in two concave facets for the articulation with the quadrate, comparable to the condition in, for example, To. carpenteri and Ty. lythrodectikos ( Young et al., 2013a; Foffa & Young, 2014). The fossa is separated from the retroarticular process by a transverse crest. The glenoid fossa is wider than the retroarticular process. There is a relatively large depression that might house a foramen anterior to the glenoid fossa. The precise nature of this feature could not be verified. The medial fossa is deep and anteriorly the articular possesses a distinct medial process ( Fig. 3).

DENTITION

Preservation of dental material is limited. Except for some tooth fragments in the orbit ( Fig. 2) and in the maxilla (visible in ventral view; Fig. 3), there is only one fragmented and incompletely preserved tooth that allows study of shape and morphology. It is deposited inside the orbit ( Figs 2, 7). The tooth possesses a strongly bent root that is about 1.5 times longer than the crown. The crown is slender, slightly curved lingually and at least 12 mm long. Originally it was not more than 5 mm wide at the base of the enamel. The tooth bears a macroscopically unserrated, mesial carina that extends from the base to the apex of the crown. If the distal carina was equally strong, is not clear. The presence of a carina is a feature widely distributed among Thalattosuchia, e.g. in Machimosaurini ( Young et al., 2014; Johnson et al., 2018a), Cricosaurus (for detailed discussion of this genus see: Sachs et al., 2019), Dakosaurus (e.g. Young et al. 2012), Magyarosuchus fitosi ( Ősi et al., 2018) , Me. superciliosus , Pelagosaurus typus (SMNS 8666), Ty. lythrodectikos ( Young et al., 2013b) , Teleidosaurus calvadosii ( Eudes-Deslongchamps, 1870: table 5) and Z.nargorum ( Wilberg, 2015a) , among others. There are longitudinal ridges on the lower half of the crownin O.meieri ,whiletheapicalregionissmooth( Fig.7), as in C. lithographicus ( Herrera et al., 2013b) and Pelagosaurus typus (e.g. SMNS 8666). In Pl. multiscrobiculatus (SMNS 9930) the ridges reach at least further apically, and in S. bollensis the enamel ridges cover the complete crown (e.g. SMNS 18878, 51555, 91414). Teeth are macroscopically smooth in C. araucanensis (MLP 72-IV-7-1), C. elegans (SNSB-BSPG AS I 504), D. andiniensis (MOZ-PV 6146) and G.grandis (SNSB-BSPG AS VI 1). If the teeth that Young (1948) assigned to Peipehsuchus teleorhinus indeed belong to this taxon, cannot be verified here. In any case, they differ from O. meieri in the presence of strong enamel ridges along the complete tooth crown. The here described tooth is slenderer, with finer ornamentation than the dentition in Magyarosuchus fitosi . In the last, the ornamentation reaches the apical region and the carina disappears to the tooth base ( Ősi et al., 2018). For the metriorhynchoid Z. nargorum, Wilberg (2015a) described strong mesial and distal carinae, whereas they are not prominent in the here described specimen.

POSTCRANIAL

Atlas–axis complex and cervical column: Atlas and axis are not fully fused in O. meieri , in contrast to most teleosauroids and metriorhynchids figured by Andrews (1913). It is fully fused in L. obtusidens ( Johnson et al., 2018a) , Machimosaurus spp. (e.g. Young et al., 2014), S. bollensis ( Westphal, 1962: fig. 7) and S. larteti , but also in C. macrospondylus (MB.R. 1943.2), Cricosaurus sp. (MCNAM-PV 5099) and Metriorhynchus ( Andrews, 1913: fig. 61). Mueller-Töwe (2006) considered the unfused state in Pelagosaurus typus a primitive feature, while Hulke (1888) and Arthaber (1906) observed that the fusion of the odontoid process and axis is more likely an ontogenetic phenomenon and that the fusion enhances with age. Brochu (1996) showed that the fusion of odontoid and axis does indeed take place late in ontogeny in modern crocodiles. In O. meieri , we were able to identify the odontoid and the neural arch of the atlas, disarticulated from the first and deposited on the axis ( Figs 2, 3). The odontoid is nearly as wide as long. Its anterior and dorsal surfaces are mainly eroded. The lateral walls are strongly concave. The anterior articulation surface forms an obtuse angle with the two lateral contact surfaces to the anterior wedge. The axis is slenderer and more elongated than in (at least some) metriorhynchids, e.g. C. macrospondylus (MB.R. 1943.2), C. suevicus ( Fraas, 1902: table 7, fig. 5), Metriorhynchus ( Andrews, 1913: fig. 61), and in Machimosaurus buffetauti (SMNS 91415; Young et al., 2014), but more comparable to the condition in, for example, S. bollensis ( Westphal, 1962: fig. 7). In O. meieri it is about 35% longer than the odontoid, and amphyplatian to weakly amphicoelous. The left side of the axis is visible on the ventral side of the slab ( Fig. 3) showing the diapophysis, which distinguishes O. meieri from some teleosauroids like L. obtusidens ( Johnson et al., 2018a) or S. larteti ( Auer, 1909) , which lack a diapophysis [even though Auer considered the second rib as two headed, and the diapophysis missing due to preservation, figure 13 on plate 25 in Auer (1909) implies the lack of a pronounced diapophysis]. Westphal (1962) and Mueller-Töwe (2006) observed the presence of both parapophyses and diapophyses in Pelagosaurus typus and considered this a character distinguishing the species from ‘other’ teleosauroids ( Pelagosaurus was considered as Teleosauroidea at the time), for which they observed only a single-headed second rib and the lack of a diapophysis. Mueller-Töwe (2006) considered Pelagosaurus typus similar to metriorhynchids in this feature. However, the presence of diapo- and parapophyses in the axis seems to be a feature distributed in Thalattosuchia, e.g. G. lapparenti , Machimosaurus buffetauti , Metriorhynchus spp. ( Auer, 1909; Andrews, 1913; SMNS 91415), S. durobrivensis , S. leedsi (see also character coding in Ősi et al. (2018). The neural arch of the axis in O. meieri is not completely preserved, but it appears to be relatively high. The prezygapophysis is less distinct than the postzygapophysis, which reaches further posteriorly than the centrum like in Pelagosaurus typus and S. bollensis , but not as strong as in Machimosaurus buffetauti ( Martin & Vincent, 2013: fig. 9C; Young et al., 2014: fig. 36H). The axis is distinctly concave ventrally. The third cervical vertebra (CV3) is weakly opisthocoel to amphyplatian and is approximately as long as the axis. It is compressed, and the right diapophysis and parapophysis are still visible on the dorsal side of the slab ( Fig. 2), the left ones can be seen on the ventral side ( Fig. 3). CV3 is still associated with the third cervical rib. Several cervical ribs are preserved on the side of the slab that offers the dorsal view of the skull ( Fig. 2).