Character

Johnson, Michela M., Young, Mark T., Steel, Lorna, Foffa, Davide, Smith, Adam S., Hua, Stéphane, Havlik, Philipe, Howlett, Eliza A. & Dyke, Gareth, 2018, Re-description of ‘ Steneosaurus’ obtusidens Andrews, 1909, an unusual macrophagous teleosaurid crocodylomorph from the Middle Jurassic of England, Zoological Journal of the Linnean Society 182, pp. 385-418 : 390-408

Character note

Lemmysuchus obtusidens has two characteristics that are well developed in the holotype but not clear in other OCF teleosaurid specimens (because of the typically poor preservation of skulls, through dorsoventral crushing and/or shearing). These are: (1) a large nuchal crest on the supraoccipital and (2) large and pronounced paired occipital tuberosities (somewhat similar to those seen in dyrosaurid crocodyliforms, which are developed to a much greater extent; e.g. MNHN.F ALG 1). These characteristics, albeit in a reduced form, are also seen in Teleosaurus cadomensis Lamouroux, 1820 (MNHN cast of an adult skull, MNHN.F AC 8746; Jouve, 2009), S. heberti (MNHN.F 1890-13) and Machimosaurus buffetauti Young et al., 2015 (SMNS 91415; Martin & Vincent, 2013; Young et al., 2014a).

Description

The holotype of L. obtusidens, NHMUK PV R 3168, comprises a nearly complete skeleton ( Figs 1–3, 12A– D, 13–21) ( Andrews, 1909, 1913). The cranium and mandible adhere together so tightly that the cranium palatal view and mandible dorsal view is inaccessible; LPP.M.21, however, preserves the palatal view, which is easily accessible ( Fig. 8C, D), and NOTNH FS3361 preserves part of the rostrum, including the premaxillae ( Figs 10, 11). The cranium has experienced dorsoventral compression and has numerous fractures making it difficult to discern sutures from breaks. However, PETMG R39 is well preserved ( Figs 4–6), and the preorbital area, cranium palatal surface and part of the mandibular dorsal surface can be described from this specimen.

Cranium: The cranium of L. obtusidens (NHMUK PV R 3168) ( Figs 1–3) is ~1.4 m long ( Andrews, 1909, 1913). It is similar to Machimosaurus in terms of overall anatomy and robusticity. The rostrum is more robust but comparatively shorter than those of other Middle Jurassic teleosaurids (e.g. S. leedsi , S. heberti , Mycterosuchus nasutus ) ( Andrews, 1913) and comprises 61.2% of the total skull length [the 51% ratio given in Andrews (1913) was a typographical error]. The anterior premaxilla and dentaries are laterally expanded as in other teleosaurids (e.g. Andrews, 1909, 1913; Hua, 1999; Martin & Vincent, 2013; Young et al., 2014a). In NHMUK PV R 3168 ( Fig. 1), the preorbital region is deformed, possibly due to an infection of the bone caused by a bite (there is a large tooth deeply embedded in this region of the cranium). Conversely, PETMG R39 ( Figs 4, 5) and LPP.M.21 ( Fig. 8A, B) are well preserved in this area. Based on NHMUK PV R 3168 ( Figs 1–3), LPP.M.21 ( Fig. 8) and PETMG R39 ( Figs 4, 5), the orbits would have been large, oval in shape and oriented more anteroposteriorly than in most other teleosaurids (such as S. leedsi NHMUK PV R 3806). In dorsal view, the supratemporal fenestrae ( Fig. 1) are considerably longer than wide and are considerably longer than the orbits. The cranial description refers to the holotype (NMHUK PV R 3168) unless otherwise specified. Due to the fragility and heaviness of the NHMUK PV R 3168 cranium, the authors were unable to flip it over to observe the palates. Therefore, all information pertaining to the palatal surface comes from LPP.M.21.

Premaxillae: The premaxillae ( Figs 1, 2, 3A, C) are large and robust, surround the external narial opening and face anterodorsally. The external nares are laterally expanded and their posterior margins do not reach beyond the third premaxillary alveolar pair. The anterior two-thirds of the premaxilla is laterally expanded and the anterior margin is ventrally deflected, giving the snout a scooplike appearance. In LPP.M.21 ( Fig. 8A, B) and NOTNH FS3361 ( Figs 10, 11), the incisive foramen (=naso-oral fenestra) is very small and is situated in the middle of the suture of the premaxillae. In dorsal view, the premaxilla–maxilla suture is well developed and W-shaped. The left premaxilla– maxilla suture is directed proximodistally parallel towards the middle of the rostrum with two small, pointed, posterior-oriented processes edges in dorsal view. The premaxilla contains four teeth, with the fourth (posterior-most) being the largest. The first two premaxillary alveoli are nearly confluent, with a thin interalveolar lamina separating them. The interalveolar lamina is missing in NOTNH FS3361 and LPP.M.21, making it appear as though there were only three premaxillary teeth present (this feature is noted in Vignaud, 1997). There is a diastema between the last premaxillary tooth and the first maxillary tooth. In life, large dentary caniniform teeth would have been present (as in Machimosaurus and other large teleosaurids; Andrews, 1909, 1913; Martin & Vincent, 2013).

Maxillae: The maxillae ( Figs 1, 2, 3A, C) form a substantial part of the rostrum. Their lateral margins are sub-parallel in dorsal view. The maxilla separates the nasals from the premaxillae. The precise maxillary tooth count is difficult to determine but there are ~29 alveolar pairs ( Andrews, 1913). The specimen LPP.M.21 has 29 alveolar pairs ( Fig. 8C, D) and NOTNH FS3361 preserves ~26 alveolar pairs (the posterior portion of the maxilla is missing) ( Fig. 10E, F). The lateral surface of the maxilla is ornamented by well-spaced, deep foramina that are visible in both dorsal, lateral and anterior views ( Figs 1, 2, 3A, B). The maxillary tooth row ends anterior to the anterior-most border of the sub-orbital fenestra. Numerous, deep reception pits for dentary teeth are along the middle and anterior regions of the ventral-lateral margin of the maxillae ( Fig. 2). The posterolateral regions of both maxillae in PETMG R39 have a groove which follows approximately parallel with the long anterior process of the jugal ( Figs 4–6). This feature is shared with Machimosaurus , S. heberti (MNHN.F 1890-13) and S. edwardsi ( Martin & Vincent, 2013; Young et al., 2014a). There is a small pathology on the ventral right maxilla in NOTNH FS3361 ( Fig. 10).

Jugals: The jugals are triradiate and form the lateral border of the orbit ( Figs 1, 2, 4–6, 8A, B) as in other teleosaurids ( Andrews, 1909, 1913). The jugal is dorsally compressed by the postorbital-squamosal and is ventrally compressed by the dentary due to poor preservation. The anterior margin of the jugal runs between the lacrimal and posterior regions of the maxilla ( Figs 2, 3A, C). This feature is shared among S. edwardsi (PETMG R175), S. heberti (MNHN.F 1890-13), L. obtusidens (PETMG R39) ( Figs 4–6), M. hugii (NMS 7012) and possibly also M. buffetauti (the holotype SMNS 91415 is poorly preserved in this region). However, it is only in Lemmysuchus and Machimosaurus that the jugal is extremely elongate, it anteriorly extends and reaches the anterior end of the lacrimal. The postorbital-jugal or quadratojugal-jugal contacts cannot be seen clearly in NHMUK PV R 3168, as the specimen is crushed in those areas. In LPP.M.21, the postorbital-jugal contact is anteroposteriorly straight ( Fig. 8A, B). The quadratojugal-jugal contact is not clear in either NHMUK PV R 3168 or LPP.M.21.

Nasals: The nasals ( Figs 1, 2, 3A, C) are large triangular bones exposed on the dorsal surface of the posterior rostrum and orbital area. Both nasals (in NHMUK PV R 3168) are missing their anterior and posterior regions. The nasal anterior processes extend past the third maxillary tooth. Deformation, due to an embedded tooth previously mentioned from another animal (which is circular and has left a striated impression behind), obscures the view of the anterior region of the nasal anterior processes. The nasals have a little ornamentation, consisting of faint ridges. There is a faint internasal midline suture on the anterior rostrum; further posteriorly there is no internasal suture, suggesting the nasals are partially or completely fused. This is seen in NHMUK PV R 3168 as well as LPP.M.21 ( Fig. 8A, B), NOTNH FS3361 ( Fig. 10A, B) and PETMG 39 ( Fig. 4A, B). Both nasals form the beginning of a dorsally directed ‘dome’ towards the medial contact with the frontal. PETMG 39 ( Figs 4, 5) and NOTNH FS3361 ( Fig. 10) show the beginning of the ‘dome’ in the anterior nasals (as the posterior nasals are not preserved in NOTNH FS3361). In LPP.M.21 ( Fig. 8A, B), it is not clear if the nasals are convex (due to dorsoventral crushing, although this could be an ontogenetic feature), and the nasal anterior processes are approximately one-third of the posterior rostrum and have well-developed nearparallel suture contacts with the maxillae.

Prefrontals: The prefrontals ( Figs 1, 2) are slightly sub-circular in dorsal view and form the anteromedial border of the orbits. The prefrontal contacts the nasal medially and the lacrimal laterally. The frontalprefrontal contact cannot be clearly seen even in the better preserved PETMG R39 due to breaks in this area ( Figs 4–6). In LPP.M.21 (and to some extent on the right side in NOTNH FS3361), the prefrontal contacts the frontal posteromedially at a straight angle ( Figs. 8A, B). The prefrontals are well developed and tear-shaped ( Figs. 8A, B, 10).

Lacrimals: The lacrimals are better preserved in PETMG R39 ( Figs 4–6) and LPP.M.21 ( Fig. 8A, B) than in NHMUK PV R 3168 ( Figs 1, 2) even though the medial and posterior margins are not preserved well. The lacrimals are large and triangular as in other teleosaurid taxa ( Andrews, 1909, 1913) and constitute most of the anterior-lateral border of the orbits. Andrews (1913) reported paired openings ~ 5–7 cm anterior to the lacrimal in NHMUK PV R 3168 that he considered to be antorbital fenestrae, describing them as no more than 5 cm in length and longer than wide ( Andrews, 1913). PETMG R39 ( Figs 4–6), NOTNH FS3361 ( Fig. 10) and LPP.M.21 ( Fig. 8A, B) show that L. obtusidens did not have antorbital fenestrae. As such, we interpret these ‘openings’ in NHMUK PV R 3168 to be cracks caused by compression.

Frontal: The frontal ( Figs 1, 2, 3A, C) is a large and deep (dorsoventrally thickened) bone with no evidence of a midline suture. The anterior region slightly slopes anteriorly in conjunction with the posterior nasal and descends posteriorly, giving it a ‘domed’ appearance ( Figs 2, 3A, C). The anterior process is not preserved; however, it is well preserved in LPP.M.21 ( Fig. 8A, B), showing that it is as short as in most other teleosaurids (e.g. S. leedsi ; see Andrews, 1913). The frontal contributes to the posteromedial border of the orbits ( Figs 1, 2) and is well seen in LPP.M.21 ( Fig. 8A, B). The frontal forms a straight vertical contact with the postorbital in dorsal view and forms the anterior medial borders of the supratemporal fenestrae. The ornamentation on the frontal does not differ from other OCF teleosaurids and consists of pronounced irregular ridges radiating from the centre of the bone.

Postorbitals: The large, robust postorbitals ( Figs 1, 3A, C) form the lateral and part of the posteroventral border of the orbits. In lateral view, the dorsoventral suture of the postorbital contacts the squamosal and the left postorbital strongly contacts the frontal and forms the posterior margin of the orbit. Because both postorbitals are broken, the postorbital bars are not preserved in NHMUK PV R 3168. In LPP.M.21, the postorbital bar is similar to other OCF teleosaurids ( Fig. 8A, B). It forms the posterior margin of the orbit, is slightly anteroposteriorly thickened and of standard mediolateral length.

Parietal: The unornamented parietal ( Figs 1, 2, 3A, C) is a single bone with no trace of a midline suture that contributes to the medial and posterior borders of the supratemporal fenestrae. Dorsally the parietal does not overhang the occipital condyle. The parietal bar is relatively thin and anteroposteriorly elongated. The posterior region of the parietal is anteriorly concave. In LPP.M.21, there is little to no ornamentation on the parietal ( Fig. 8A, B).

Squamosals: The squamosals ( Figs 2, 3B, D) are large, anteroposteriorly elongate, L-shaped bones and are well preserved in LPP.M.21 ( Fig. 8A, B). The squamosal forms the posterolateral border of the supratemporal fenestrae and its posterolateral surface is concave. It contacts the quadrate posteroventrally in lateral view. The squamosal bar is robust and anteriorly contacts the postorbital bar (together forming the supratemporal arch). In NHMUK PV R 3168, the left squamosal is distorted and flattened due to poor preservation.

Quadrates: The quadrates ( Figs 1, 3B, D) are large, robust and are strongly sutured to the squamosals and quadratojugals. The anterodorsal region of the quadrate contacts the squamosal and quadratojugal while the posteroventral margin articulates with the angular (=jaw joint) and medially contacts the exoccipital. The posteroventral lateral and medial hemicondyles are approximately the same size and length. They are both elongated mediolaterally, are oval in shape and have rounded posterior edges. In occipital view, the hemicondyles posteriorly extend further than the exoccipitals. The right quadrate is well preserved while the left quadrate is not. In LPP.M.21, the quadrates are large and mediolaterally expanded in ventral view ( Fig. 8C, D).

Quadratojugals: The quadratojugals are dorsally and ventrally compressed and are not visible in dorsal view. The posterior region of the quadratojugal is expanded mediolaterally to accommodate the quadrate and extends slightly further than the outermost tip of the quadrate.

list. Scale bar: 10 cm. Ectopterygoids: Only the right ectopterygoid is preserved in NHMUK PV R 3168. Anteriorly it contacts with the maxilla. The contact with the pterygoids and palatines cannot clearly be seen. The dorsal surface of the ectopterygoid is slightly concave. The right ectopterygoid is preserved in LPP.M.21 and curves ventromedially ( Fig. 8A, B).

Supraoccipital: The supraoccipital is positioned ventral to the parietal and is only visible in occipital view ( Fig. 3B, D). The ventral edge is not triangular but curved so it appears as two ‘lobes’ ( Fig. 3). A large nuchal crest ( Fig. 3B, D) is situated directly in the middle of the supraoccipital.

Exoccipital: The exoccipitals make up the majority of the occipital surface of the cranium. The right side has been medially compressed and the dorsal rim curves medially, while the left side tilts dorsally and flares mediolaterally. The exoccipitals are dorsally expanded above the foramen magnum, as in M. buffetauti and M. mosae (Hua, 1999; Martin & Vincent, 2013). Laterally, the exoccipitals descend rapidly, so in occipital view, they appear almost box-like. The exoccipitals contribute to the occipital condyle. The paraoccipital processes are small and the lateral wings are elongate and robust. The foramen for cranial nerve XII is small and parallel to the foramen magnum ( Fig. 3B, D).

Basioccipital: The basioccipital contributes to the ventral region of the foramen magnum and is slightly wider than tall. The occipital condyle is larger and more circular than the foramen magnum. In ventral view (LPP.M.21), two well-developed and slightly anteroposteriorly elongated basioccipital tuberosities are visible, with the left one being larger due to variable preservation ( Fig. 8C, D).

Pterygoid: The right pterygoid wing is present in the holotype ( NHMUK PV R 3168 ), but it is poorly preserved; it is unclear how complete the pterygoid wing is in this specimen without access to the palatal view. The left pterygoid is similarly broken but the lateral pterygoid wing is accessible laterodorsally. It is large and elongated craniocaudally and lateromedially. The dorsal surface of the wing is concave and the posterior region curves anteromedially, possibly due to breakage. In ventral view ( LPP.M.21), the pterygoid is thin and elongated and contributes to the medial and posterior borders of the sub-orbital fenestrae, which are tear-shaped (thin anteriorly, wide and slightly rounded posteriorly) ( Fig. 8). In LPP.M.21, the anterior process of the pterygoid articulates with the palatines ( Fig. 8C, D) .

Palatines: All information from the palatines comes from LPP.M.21 and PETMG R39. The palatines ( Fig. 8C, D) are dorsoventrally thin, elongate bones and are similar in form to other teleosaurids, such as S. leedsi (NHMUK PV R 3806) ( Andrews, 1913). In LPP.M.21, the anterior regions of both palatines are not preserved and both posterior regions are slightly deformed; however, PETMG R39 preserves the anterior palatines that are slightly rounded, have small anterior processes and articulate with the posterior processes of the maxillae ( Fig. 4C, D). The palatines contact one another along the skull midline until posteriorly they are separated by the anterior process of the pterygoid. The anterior extensions of the palatine are nearly parallel to the maxillary tooth row, similar to M. buffetauti ( Martin & Vincent, 2013) .

Basisphenoid: The anterior surface of the basisphenoid (LPP.M.21) is deformed ( Fig. 8C, D). This structure has two elongated posterolaterally directed processes and comes into posterior contact with the quadrate.

Other elements: The proötic and laterosphenoid are not visible in dorsal or ventral views, and as a result we could not properly describe these bones.

Mandible: The mandible of NHMUK PV R 3168 is diagenetically deformed and attached to the cranium so that the dorsal surface is not visible. The mandibular symphysis measures ~ 58 cm, contributing ~42.3% of the entire length ( Young et al., 2015a). Among other specimens, only a short segment of the right mandibular ramus in PETMG R39 is preserved and it clearly shows the contact among the dentary, angular and splenials to be posterior to the mandibular symphysis on the ventral side. The majority of the mandible is also preserved in LPP.M.21, as the posterior-most areas are missing. Our mandibular description refers to the holotype ( NHMUK PV R 3168 ) unless otherwise specified .

Dentary: The dentary ( Figs 1, 2, 3A, C) is a long major element of the lateral surface of the lower jaw, as in the majority of crocodylomorphs. The anterior end of the dentary is spatulate and laterally enlarged as in Machimosaurus ( Young et al., 2014a) . There are ~29 (possibly one or two more alveoli) alveoli per dentary (at least 25 alveoli per dentary in LPP.M.21) of which ~22–24 are adjacent to the mandibular symphysis ( Andrews, 1913; Young et al., 2015a). Many of the teeth are missing but those still in situ are well preserved and complete. The four anterior-most teeth are elevated dorsally when compared to the rest of the tooth row, as normally seen in teleosaurids such as S. leedsi ( Andrews, 1913) . The dentition is strongly heterodont compared to other teleosaurids; the teeth in the anterior region are large and have a higher crown base to length ratio, whereas the posterior crowns are characterised by a lower ratio. The interalveolar distance is generally smaller than half the alveolar length but always longer than a quarter of the alveolar length.

Surangular and angular: The surangular ( Fig. 2) is thin and posteriorly elongated in lateral view. The surangular, in conjunction with the angular and articular bones, is anteroposteriorly elongated and forms a distinctive ‘V’ shape. The anterior region of each surangular gradually terminates near the last alveolus of the dentary. The posterior margin of the surangular is rounded and it bounds a small mandibular fenestra. The angular ( Fig. 2) is elongate and occupies a more extensive area than the surangular in lateral view. The angular is more robust than the surangular with a strong dorsal curvature ( Fig. 2) which articulates with the retroarticular process of the articular. The dorsal and the ventral surfaces of the angular are not viewable in NHMUK PV R 3168. The prearticulars, which are supposed to be present ( Andrews, 1913), are not seen.

Articular: The anterior region of the articular of NHMUK PV R 3168 is hidden by the quadrate and surrounding bones. The retroarticular process is, however, extremely elongate and triangular-shaped in dorsal view and it bears a strongly pronounced anteroposterior keel, which separates the medial and lateral grooves. Both grooves are concave, in particular the lateral ones. The posterior end of the retroarticular process is slightly rounded, concave and curves dorsolaterally. The glenoid fossa is large and faces mediodorsally.

Splenial: All of the information on the splenial comes from LPP.M.21. Only the anterior regions of these bones are preserved. The splenial ( Fig. 9) is situated medially and is mediolaterally thinner in width than the dentaries. Both splenials begin at approximately the 15 th mandibular alveoli in the dentaries. While the coronoids are not preserved, the sulci where they are hosted are. They participate with the mandibular symphysis, and the anterior extension begins at approximately the 21 st alveoli of the dentaries and continue parallel, and eventually past, the tooth row.

Dentition: As discussed above, the dentition of NHMUK PV R 3168 is both heterodont and serrated (with both true and false denticles; Young et al., 2015a). The holotype has 33 isolated teeth, as well as in situ teeth: ~ 29 in each dentary, 4 per premaxilla and ~29 (possibly more) per maxilla (verified by LPP.M.21). The teeth ( Fig. 12A–D) are conical, robust, single-cusped and bicarinate, as in Machimosaurus ( Martin & Vincent, 2013; Young et al., 2015a, b; Foffa et al., 2015; Fanti et al., 2016). They have a blunt apex in comparison to other Steneosaurus species ( Andrews, 1913). The enamel is thinner towards the base of the crown and becomes progressively thicker towards the apex ( Fig. 12A–D), much like in Machimosaurus ( Young & Steel, 2014) .

There are many protruding apicobasal enamel ridges on these teeth, giving them a ‘wrinkled’ texture. These apicobasal ridges are close to one another and run parallel from the base of the crown to approximately three quarters of the entire tooth. At the apex, the ridges are considerably shorter and are organized in the typical anastomosed pattern that has been described for other members of Machimosaurini ( Young et al., 2014a, 2015a; Jouve et al., 2016). Teeth with blunter apices are situated in the middle and posterior regions of the tooth row and those with sharper apices are near the anterior. The teeth have true denticles and false denticles ( Young et al., 2015a), although the latter cannot be seen clearly with the naked eye. True denticles are situated on the carina and false denticles are formed via interactions between the carina and enamel ridges ( Young et al., 2015a).

Postcranial skeleton: vertebral column and ribs: Most of the vertebral column of NHMUK PV R 3168 is preserved, so our description of vertebrae is based on this specimen unless otherwise specified.

The first (atlas) and second (axis) vertebrae are fused together, forming the well-developed ‘complex’ ( Fig. 13A) that is common in teleosaurids ( Andrews, 1913; Martin & Vincent, 2013). The axis neural arch is not present and the odontoid and intercentrum are not distinct from one another due to the degree of atlas– axis fusion. The lateral surfaces of the axis are concave and have large protruding regions for the parapophyses. There are no diapophyses present behind the odontoid process on the axis, which is slightly larger than the atlas.

The centra of the remaining six cervical vertebrae are amphicoelous, slightly longer in width than height, and have sub-circular anterior and posterior articular surfaces. There is a small notch in the middle of the dorsal margin of the centrum that is visible in anterior view. In lateral view, the centra are slightly spool-shaped with concave ventral margins similar to Machimosaurus ( Martin & Vincent, 2013) . The prezygapophyses are slightly anterior to the centrum edge, with the anterior articular facets facing ventrally and curving inwards. The postzygapophyses extend laterally just above the base of the neural spine. The posterior articular facets face dorsally and the transverse processes are laterally wide. The neural spine is rectangular and nearly as tall as the centrum.

Only one complete cervical rib is preserved. It is T-shaped in dorsal view and has a distinct dorsomedial curvature ( Fig. 13B). Both the tubercular and capitular processes of this rib are rounded, and its tubercular is larger than the capitular. The distal area behind the processes is short and does not extend posteriorly while the area in front is considerably more elongated.

Fourteen robust thoracic vertebrae are preserved in NHMUK PV R 3168 although only one is complete. The centra ( Fig. 14) are massive and appear spool-shaped in ventral view. The articular surfaces are amphicoelous and oval (slightly taller in length than wide). The neural spine is short and broad, and not as tall as the centrum. The transverse processes are long and wide and are positioned approximately at the centre of the neural arch. They are broadened anteroposteriorly, with rounded proximal ends ( Fig. 14). There is a second projection on the transverse process, separated from the vertebral body by a small concavity. This projection is small, circular and laterally faced.

The dorsal ribs ( Fig. 13C) are dichocephalous and have robust heads and bodies. The capitulum of these ribs is proximodistally lengthened and dorsally rounded ( Fig. 13C) and each neck is elongated, separating the capitulum from the tuberculum. The articular facets are flat and separated from the top of the tuberculum. The tuberculum is a small nodule located in the middle of the rib body. The articular facet and tuberculum are both laterally shifted so that they are nearly situated on the lateral edge of the body. The costal groove is deep and runs from the ventral tuberculum to near the end of the rib body, disrupting an otherwise sub-circular cross-section. The sternal end of the rib is anteroposteriorly flat, straight and thin in width.

There are three sacral vertebrae ( Fig. 15) ( Andrews, 1913). The first two are true sacral vertebrae and the first caudal vertebra acts as a pseudo-sacral, as it looks and functions as a third sacral. This ‘third’ sacral has large, mediolaterally expanding transverse processes and an expanded lateral iliac attachment area, much like the two true sacrals. The neural spines are short and robust and the sacral ribs curve and contact one another ( Andrews, 1913). The anterior margin of the posterior area of the second sacral vertebra ( Fig. 15B, D) has a large, expanded projecting flange. The presence of a ‘third’ sacral vertebra is an autapomorphy shared by L. obtusidens and Machimosaurus spp. within Thalattosuchia ( Young et al., 2014a).

Only 21 caudal vertebrae are preserved. However, it is likely that the total caudal vertebral count is similar to that of S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701), of around 36–38 ( Andrews, 1913) or even higher (as in S. edwardsi PETMG R 275). The caudal vertebrae become increasingly thinner and smaller from anterior to posterior. The typical posterior caudal vertebral centrum is thin, taller than wide and strongly hourglass-shaped. The neural spines are thin, tall and higher than the centrum.

Shoulder girdle and fore-limb: No coracoids are preserved. The scapula ( Fig. 16A, B) is of the typical thalattosuchian type similar to S. leedsi (NHMUK PV R 3806) ( Andrews, 1909, 1913), being an elongate bone with a slender body. The proximal and distal regions extend mediolaterally, with the distal end being slightly larger. The scapular glenoid fossa ( Fig. 16B) is half-moon shaped. The proximal region of the humerus ( Fig. 16C, D) is poorly preserved, so the deltopectoral crest and proximal head cannot be properly described. However, the proximal edge of the humeral head appears to be slightly curved, as seen in other OCF teleosaurids such as S. leedsi (NHMUK PV R 3806). The shaft of the humerus is straight and the distal end is rounded. There is a concave, oval ( Andrews, 1913) depression in the middle of the distal end of the humerus in lateral view ( Fig. 16D). The ulna is similar in shape to other Callovian teleosaurids such as S. leedsi ( Andrews, 1913) . The proximal region is slightly deformed and fractured. The radius is a squat, straight bone and is unornamented.

Pelvic girdle and hind-limb: The ischium ( Fig. 17A, B) is squat and robust and only preserved in NHMUK PV R 3168. The two proximal articulation processes are divided by a small yet deep oval notch. The smaller process has a circular proximal head while the larger process is posterolaterally curved. A large protruding ridge runs proximodistally in line with the second proximal process. Two small, sub-circular ‘bumps’, presumably for muscle attachment, are present ~ 10 cm from the posterior edge. These are not as prominent in other teleosaurids, such as S. leedsi . The ischial blade ( Fig. 17A, B) is large, expanded and thick, with the posteroventral, sub-square border. The anterior flange is thin and broken.

Both NHMUK PV R 3168 and PETMG R39 preserve an ilium. However, in the latter specimen, it is still articulated with the sacrum and femoral head, is missing the anterior side and is still partially covered in matrix. Conversely, the NHMUK PV R 3168 ilia ( Fig. 17C, D) are well preserved, square-shaped and compact. The anterior-facing vertical outer rim has a slight sub-horizontal curvature ( Fig. 17C, D). The medial attachment points of the sacral ribs are faint ( Fig. 17C) so that it is difficult to tell the anterior iliac facet and posterior iliac facet apart from one another ( Fig. 17C). The acetabular depression (or acetabular notch) is a smooth U-shaped arch in lateral view ( Fig. 17C) and is halfway through the ventral articulating points with the pubis and ischium. The anterior articulation facet in front of the incision is larger than that of the posterior articulation facet and extends ventrally. The supraacetabular crest ( Fig. 17D) is poorly developed, as is the shallow acetabulum ( Fig. 17D). The preacetabular (=anterior process) ( Fig. 17D) is shortened (with respect to other thalattosuchians) and well rounded and curves laterally.

The majority of one pubis is preserved in NHMUK PV R 3168 ( Fig. 17E, F) but the pubic boot is missing. Conversely, the ventral part of the pubis is possibly preserved in matrix in PETMG 39 (PETMG R31) ( Fig. 24D). The body and distal region of the neck of the NHMUK PV R 3168 pubis are deformed into curving medially. The anterodistal pubic plate is expanded and rounded along the ventral rim ( Fig. 17E, F).

All the information on the hind-limb comes from NHMK PV R 3168. The femur ( Fig. 18) is slender and long, with a weak sigmoidal curvature throughout the shaft, which is typical of many teleosaurids ( Andrews, 1909, 1913). The proximal head ( Fig. 18) extends medially into the acetabulum while the anterior region of the femoral head is ventrally curved. There is a large concavity on the posterolateral surface of the head. The posterior margin of the head is rugose, and this rugosity continues down through the neck of the femur. In dorsal view, the head is circular to sub-circular, with an expanded posteromedial tuber. The ‘fourth trochanter’ (i.e. no true process, just the rugose area mentioned before) is small compared to other Callovian teleosaurids and is situated on the medial neck of the femur ( Fig. 18). The two posterodistal condyles – medial (greater) and lateral (lesser) – are clearly visible with the medial condyle being slightly larger ( Fig. 18).

The tibia ( Fig. 19) is a robust bone with the proximal end being larger than the distal end. In dorsal view, the proximal end is heart-shaped. The tibial tuberosity ( Fig. 19A, C) is large and projects posterodistally. In lateral view, it is directed ventrally at a sharply obtuse angle ( Fig. 19C). The medial side of the tibial neck is slightly concave, while the lateral side is flat ( Andrews, 1913). The distal end is rounded, although it is obstructed by the distal area of the fibula. The fibula ( Fig. 19) is an elongate, slender and straight bone, with only the distal half preserved. It is slightly smaller in width ( Fig. 19A) than the tibia.

There are three ankles bones ( Fig. 20): the calcaneum ( Fig. 20A–D), astragalus ( Fig. 20E–G) and cuboid ( Fig. 20H, I). They are all robust and large, with well-developed articulation surfaces. Excluding the clear difference in the large size, the three ankle bones resemble those of other teleosaurids ( Andrews, 1913). All metacarpal and metatarsal fragments are slender, as are four complete phalanges (all relatively the same length).

Osteoderms: Fifty-six dorsal, mostly unarticulated osteoderms are present in NHMUK PV R 3168. Smaller osteoderms are box-shaped ( Fig. 21C), whereas larger ones are elongate and oval ( Fig. 21A, B). A prominent anteroposteriorly directed keel is present ( Fig. 21A), being more pronounced in larger osteoderms. The pits on the dorsal surface of larger osteoderms ( Fig. 21A) are oval, elongate, deep and spaced apart. They radiate outwards from the centre of the keel in a ‘starburst’ pattern. The pits generally become larger further from the centre of the osteoderms. Some pits merge with one another along the outermost lateral margins of the osteoderms. The ventral surfaces of all osteoderms are smooth and unaltered.