Neosteneosaurus edwardsi, (Eudes-Deslongchamps, 1868), (Eudes-Deslongchamps), 1868

Scavezzoni, Isaure, Fischer, Valentin, Johnson, Michela M. & Jouve, Stéphane, 2024, Form and function of the pelvic girdle of Thalattosuchia and Dyrosauridae (Crocodyliformes), Geodiversitas 46 (6), pp. 135-326 : 234-244

NEOSTENEOSAURUS EDWARDSI ( EUDES-DESLONGCHAMPS, 1868)

For measurements, see Tables 7-9 .

The specimen NHMUK PV R 3701 is supposedly a juvenile or subadult individual.

Ilium

The ilium of Neosteneosaurus edwardsi ( Figs 52-55 ; 57 ; 58 ) is proportionally large like that of other teleosauroids, notably due to the presence of a well-developed postacetabular process and a greater bony acetabulum (e.g. Lemmysuchus obtusidens , Platysuchus multiscrobiculatus , Charitomenosuchus leedsi , Macrospondylus bollensis , etc.). Overall, the relative parallelepiped shape of the ilium of Neosteneosaurus edwardsi is similar in appearance to Lemmysuchus obtusidens and Charitomenosuchus leedsi than to Platysuchus multiscrobiculatus , Plagiophthalmosuchus gracilirostris , and Macrospondylus bollensis . Still, the ilium of Neosteneosaurus edwardsi (PETMG R178, NHMUK PV R 3701, NHMUK PV R 2076, and NHMUK PV R 3898) differs from that of Charitomenosuchus leedsi in displaying a flat anterior margin, and from that of Lemmysuchus obtusidens in possessing a proportionally larger preacetabular process. In parallel, the ilia of Neosteneosaurus edwardsi PETMG R 178, NHMUK PV R 3701 andNHMUK PV R 2076 are oriented differently than those of Lemmysuchus obtusidens ( Fig. 59 ) and Charitomenosuchus leedsi , which appear closer to Neosteneosaurus edwardsi NHMUK PV R 3898.

The preacetabular process of Neosteneosaurus edwardsi ( Figs 52-55 ) is proportionally long as its anteroposterior length approximately reaches that of the pubic peduncle, unlike that of Lemmysuchus obtusidens which is slightly shorter. In all specimens (PETMG R178,NHMUK PV R 3701, NHMUK PV R 2076, and NHMUK PV R 3898), the preacetabular process of Neosteneosaurus edwardsi is slender: the size of its mid-section dorsoventrally and mediolaterally is lesser or equal to half of its anteroposterior length. Moreover, the preacetabular processes of Neosteneosaurus edwardsi PETMG R 178, NHMUK PV R 3701, NHMUK PV R 2076, and NHMUK PV R 3898display an overall constant mediolateral and dorsoventral thickness (approximating that of the mid-section) throughout their anteroposterior length. For this reason, the ventral and dorsal margins of the preacetabular process almost appear mirrored with one another whereas the dorsal margin is overall straight and the ventral one subtlety concave. The dorsal margin of the ilium of Neosteneosaurus edwardsi (PETMG R178, NHMUK PV R 3701, NHMUK PV R 2076, and NHMUK PV R 3898) corresponding to the iliac crest is aligned with the dorsal border of the preacetabular process. The junction between the two is achieved through a subtle depression at the base of the preacetabular process in PETMG R178, NHMUK PV R 2076 and NHMUK PV R 3898. In NHMUK

PV R 3701, the junction is even less visible, presumably due to the deformation of the bone. The anterior margin of the ilium underneath the supraacetabular process is straight, unlike Charitomenosuchus leedsi .

The iliac crest of Neosteneosaurus edwardsi is relatively straight for about three-quarters of its length, then becomes gently convex posteriorly as it forms the apex of the postacetabular process. The latter takes the shape of an asymmetrical Lancet arch, as the convexity of its posteroventral margin displays a greater amplitude. The dorsal surface of the iliac crest of PETMG R178, NHMUK PV R 2076 and NHMUK PV R 3898 is not entirely flat but presents some low amplitude undulations throughout ( Figs 54 ; 55 ). The peak of the postacetabular process is almost in line with the iliac crest so that it points in the exact opposite direction of the preacetabular process. Comparatively, the ilia of Lemmysuchus obtusidens and Charitomenosuchus leedsi display relatively similar dorsal margins and apex for their postacetabular process, but differ in the shape of their posterior margin. Indeed, the posteroventral margin of the postacetabular process of Neosteneosaurus edwardsi PETMG R 178, NHMUK PV R 2076 and NHMUK PV R 3898 ( Figs 54 ; 55 ) forms a global sinusoid curve with the convex and concave portions showing equal shares. In addition, the concave part of the posterior margin of the ilium displays a small crest around its mid-length which is a feature not found in other teleosauroids (i.e. Lemmysuchus obtusidens , Platysuchus multiscrobiculatus , Charitomenosuchus leedsi , Macrospondylus bollensis ). On the lateral surface of the ilium, the area bordering the margins of the postacetabular process shows a series of ridges indicating the presence of a cartilage cap in vivo. The ridges are perpendicular to the margin of the ilium dorsally, but those become more tilted along the second half of the postacetabular process.

The ventral margin of the ilium of Neosteneosaurus edwardsi ( Figs 53-55 ) is strongly undulating with the pubic peduncle extending more ventrally than the ischial peduncle, as in other thalattosuchians (e.g. ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Thalattosuchus superciliosus , Lemmysuchus obtusidens , Charitomenosuchus leedsi , etc.). In Neosteneosaurus edwardsi , the large difference in the dorsoventral position of the peduncles and their global anteroposterior extension is typical of teleosauroids (i.e. Lemmysuchus obtusidens , Charitomenosuchus leedsi , Macrospondylus bollensis , Neosteneosaurus edwardsi ). Indeed, in teleosauroids, the pubic peduncle is positioned more ventrally unlike in metriorhynchoids (e.g. ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, Tyrannoneustes lythrodectikos , Suchodus durobrivensis , Thalattosuchus superciliosus , Geosaurus giganteus , etc.). Similar to other crocodyliforms, the posterior corner of the ischial peduncle of Neosteneosaurus edwardsi (PETMG R178, NHMUK PV R 3701, NHMUK PV R 2076, and NHMUK PV R 3898) greatly protrudes from the lateral surface of the ilium, whereas its anterior corner is set in the wall of the bony acetabulum. In NHMUK PV R 3898, the ischial peduncle also protrudes posteriorly and extends over the posterior margin of the ilium, masking its junction with the posterior margin. The ischial peduncle of the ilium forms the posterior border of the bony acetabulum, and was presumably the anchoring site for a structure similar to the antitrochanter of extant crocodylians ( Tsai & Holliday 2015). The facet of the ischial peduncle on the lateral surface of the ilium is wedge-shaped and not triangular similar to Lemmysuchus obtusidens , Macrospondylus bollensis and Charitomenosuchus leedsi , which contrasts with most metriorhynchoids (e.g. ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, Suchodus durobrivensis , Thalattosuchus superciliosus , etc.). The facet of the ischial peduncle is also dorsoventrally shorter than the pubic peduncle in PETMG R178,NHMUK PV R 2076, and NHMUK PV R 3898 (like in Pelagosaurus typus), whereas both are about the same height in NHMUK PV R 3701. The ventral surface of the ischial peduncle is mainly flat, but becomes concave anteriorly before its junction with the acetabular perforation as in Lemmysuchus obtusidens and Charitomenosuchus leedsi . In ventral view, the ischial peduncle takes the shape of an isosceles triangle, with its greatest axis oriented anteroposteriorly.

Similar to other teleosauroids (i.e. Lemmysuchus obtusidens , Charitomenosuchus leedsi , Macrospondylus bollensis ), the acetabular perforation of Neosteneosaurus edwardsi (PETMG R178, NHMUK PV R 3701, NHMUK PV R 2076, and NHMUK PV R 3898) forms an anteroposteriorly long but shallow indentation which completely separates both peduncle. The pubic peduncle of the ilium of Neosteneosaurus edwardsi NHMUK PV R 3701 and NHMUK PV R 2076 displays an anteroposterior length similar to that of the ischial peduncle, as in Pelagosaurus typus, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, and Charitomenosuchus leedsi . In PETMG R178 andNHMUK PV R 3898, the ischial peduncle largely exceeds the pubic peduncle in length anteroposteriorly (as in for example Thalattosuchus superciliosus , Cricosaurus suevicus , or Lemmysuchus obtusidens ). But on the other hand, the ischial peduncle of NHMUK PV R 3898 is drastically thinner mediolaterally whereas this is not seen in the other specimens. Indeed, in NHMUK PV R 3701 and NHMUK PV R 2076, the maximal mediolateral thickness reached by the pubic peduncle is either similar (NHMUK PV R 2076) or slightly greater (NHMUK PV R 3701) than that of the ischial peduncle. Compared to NHMUK PV R 2076 and NHMUK PV R 3701, PETMG R178 and NHMUK PV R 3898 are significantly larger and it is possible that it accounts for the difference in the size and shape of the ischial peduncle ( Figs 52-55 ). In all four specimens, the ventral surface of the pubic peduncle is slightly concave, similar other thalattosuchians (e.g. ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Thalattosuchus superciliosus NHMUK PV R 2054 , Lemmysuchus obtusidens , Charitomenosuchus leedsi , Macrospondylus bollensis ). In NHMUK PV R 2076 and NHMUK PV R 3701, the outline of the pubic peduncle ventrally is crescent-shaped (i.e. smoothly curved lateral and medial margins) with its tips begin rounded rather than sharp. In NHMUK PV R 3898 the ventral outline of the pubic peduncle is different as the anterior and medial side form a right-angled corner. The facet of the pubic peduncle on the lateral surface of the ilium displays a greater dorsal extension than the ischial peduncle in PETMG R178 (partially altered anteriorly), NHMUK PV R 2076 and NHMUK PV R 3898; the ilium of NHMUK PV R 3701 is too strongly altered to observe the exact shape of the pubic peduncle laterally. The silhouette the pubic peduncle draws on the lateral surface of the ilium of Neosteneosaurus edwardsi PETMG R 178, NHMUK PV R 2076 and NHMUK PV R 3898 forms two triangular shapes pointing dorsally. There are other thalattosuchians (mainly metriorhynchoids) whose pubic peduncle forms two triangular shapes (e.g. Proexochokefalos cf. bouchardi, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Tyrannoneustes lythrodectikos , Thalattosuchus superciliosus , ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763), but those of Neosteneosaurus edwardsi PETMG R 178, NHMUK PV R 2076 and NHMUK PV R 3898 drastically differs from the latter in displaying an exceedingly large posterior shape (more than three times the height of the anterior one). In comparison, the pubic peduncle of Sericodon jugleri and Charitomenosuchus leedsi also possesses two large triangular shapes, but the posterior one is rather elliptical.

Medially, the ilium of Neosteneosaurus edwardsi ( Figs 52-55 ) displays two distinct scars marking the position of the sacral rib attachment sites for each sacral, similar to Sericodon jugleri, Proexochokefalos cf. bouchardi, Charitomenosuchus leedsi , Indosinosuchus potamosiamensis ( Martin et al. 2019a) , but unlike Lemmysuchus obtusidens which possesses three scars. The sacral attachment sites occupy the whole anteroposterior length of the bone are positioned at the mid dorsoventral height of the bone. PETMG R178, NHMUK PV R 2076, NHMUK PV R 3898, and NHMUK PV R 3701 all share the same shape for each of their attachment sites, but their relative size varies across the specimens. Each attachment site is quadrangular in shape and appears like the mirrored version of the other. Indeed, both their dorsal and ventral borders converge towards the centre of the ilium, and their exterior side – either anterior or posterior – is parallel but drastically larger than the shared central margin. The linearity of the shared central delimitation contrasts with the curved one of Charitomenosuchus leedsi . The sacral rib attachment sites are delimited by a shallow rim ventrally which gradually increases in intensity to reach its maximal height dorsally. This effect is partly provoked by the relative inclination of the sacral rib attachment sites, which are dorsally sinking towards the ilium. Comparatively, in Charitomenosuchus leedsi and Lemmysuchus obtusidens the sacral rib attachment sites only form a shallow depression on the medial side of the ilium and thus present a steady border throughout. Similar to other teleosauroids, the sacral rib attachment sites of Neosteneosaurus edwardsi possess medially protruding bony insertions located near their dorsal border ( Figs 52-55 ). These processes presumably convey the existence of a matching concave shape on each sacral rib.

Ischium

The ischium of Neosteneosaurus edwardsi ( Figs 52 ; 53 ; 55-58 ) displays the typical hook-shaped anterior process of thalattosuchians (e.g. ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Thalattosuchus superciliosus , Torvoneustes carpenteri , Aeolodon priscus , Lemmysuchus obtusidens , Charitomenosuchus leedsi, Proexochokefalos cf. bouchardi, etc.). Indeed, the anterior margin of the ischium underneath the peduncles is markedly concave and culminates ventrally in a sharp process. The later extends slightly further anteriorly than the anterior peduncle does as in Aeolodon priscus, Proexochokefalos cf. bouchardi and Lemmysuchus obtusidens . The anterior peduncle of Neosteneosaurus edwardsi , which is borne by the peduncle bridge, is larger mediolaterally than it is anteroposteriorly long similar to other teleosauroids (e.g. Proexochokefalos cf. bouchardi, Lemmysuchus obtusidens , Macrospondylus bollensis , Charitomenosuchus leedsi , etc.) but unlike metriorhynchoids (e.g. ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, Thalattosuchus superciliosus , Cricosaurus suevicus , Torvoneustes carpenteri , etc.). Furthermore, the articular facet of the anterior peduncle of Neosteneosaurus edwardsi ( Figs 52 ; 53 ; 55 ; 56 ) has a slightly convex surface mainly anteriorly oriented as in Lemmysuchus obtusidens , Charitomenosuchus leedsi , Indosinosuchus potamosiamensis ( Martin et al. 2019a) , Sericodon jugleri and Macrospondylus bollensis . Hence, in anterior view, the anterior peduncle of Neosteneosaurus edwardsi displays a triangular outline pointing ventrally, like Charitomenosuchus leedsi and possibly Macrospondylus bollensis . In comparison, Lemmysuchus obtusidens has its ventral apex slightly truncated so that the articular facet appears more like a parallelepiped. In Proexochokefalos cf. bouchardi, the anterior peduncle is strongly pointed anteriorly so that the articular facet is oriented strictly dorsally, with however a small articular surface on the underside (but only laterally) for the pubis. In Sericodon jugleri the articular facet is incomplete, and it is too obstructed in Teleosaurus sp. NHMUK PV R 238.

The peduncle bridge of Neosteneosaurus edwardsi is proportionally short as its anteroposterior length reaches that of the posterior peduncle, as in Lemmysuchus obtusidens , but unlike Indosinosuchus potamosiamensis ( Martin et al. 2019a) , Macrospondylus bollensis and Charitomenosuchus leedsi . Sericodon jugleri, Proexochokefalos cf. bouchardi and Aeolodon priscus also show a short peduncle bridge, but it is proportionally shorter than in Neosteneosaurus edwardsi . The relative length of the peduncle bridge of Neosteneosaurus edwardsi , like for Lemmysuchus obtusidens , is induced by the relative position of the base of the peduncle bridge. Indeed, in both Neosteneosaurus edwardsi and Lemmysuchus obtusidens the peduncle bridge appears to stem from the base of the posterior peduncle, whereas it is located more ventrally in Indosinosuchus potamosiamensis ( Martin et al. 2019a) , Macrospondylus bollensis , Charitomenosuchus leedsi , Sericodon jugleri and Proexochokefalos cf. bouchardi. For this reason, the acetabular perforation of Neosteneosaurus edwardsi appears almost non-existent on the lateral side of the bone. Indeed, the ventral surface of the acetabular perforation corresponds to the dorsal surface of the peduncle bridge, which is actually concave surface and tilted medially so that its medial rim is more ventral than the lateral one. Hence, the acetabular perforation appears like a burrow medially leaning as in most teleosauroids and metriorhynchoids where it is laterally obstructed. In addition, the peduncle bridge is curved medially like Lemmysuchus obtusidens ( Figs 52 ; 57 ; 58 ), whereas it is more straight in for example Charitomenosuchus leedsi, Proexochokefalos cf. bouchardi, and Sericodon jugleri .

The posterior peduncle of the ischium of Neosteneosaurus edwardsi is proportionally large and displays a half-oval outline overall, with the greatest axis of this shape being aligned anteroposteriorly ( Figs 52 ; 53 ; 55 ; 56 ). The posterior peduncle displays two distinct surfaces dorsally: the lateral and medial facets. The lateral facet of the posterior peduncle accounts for a little more than half of the total surface of the peduncle and is slightly concave. The medial facet is strongly pitted and oriented medially as it was fused to the ilium in vivo. Starting from the base of both peduncles, the anterior and posterior margins of the ischium are strongly concave, with the anterior margin displaying the greatest degree of curvature. The area extending from the base of the peduncles up until the anteroposterior constriction is known as the shaft. The shaft of the ischium of Neosteneosaurus edwardsi PETMG R 178, NHMUK PV R 3701 and NHMUK PV R 3898 is relatively short and stout as its dorsoventral height is almost equal to its anteroposterior length, similar to Lemmysuchus obtusidens . The ischium of NHMUK PV R 2865 presents a bump posteriorly which undermines the identification of the exact position of the shaft constriction. For this reason, it appears slightly longer dorsoventrally than those of PETMG R178, NHMUK PV R 3701 and NHMUK PV R 3898. The shafts of Neosteneosaurus edwardsi PETMG R 178, NHMUK PV R 3701 and NHMUK PV R 3898 further differ from the dorsoventrally short shafts of Aeolodon priscus and Proexochokefalos cf. bouchardi, from the proportionally longer and thicker shaft of Macrospondylus bollensis , and also from the relatively more slender shafts of Teleosaurus sp. NHMUK PV R 238, Platysuchus multiscrobiculatus , Mycterosuchus nasutus , Indosinosuchus potamosiamensis ( Martin et al. 2019a) and Charitomenosuchus leedsi .

The anterior process of the ischium of Neosteneosaurus edwardsi is sharp and points strictly anteriorly, as in Aeolodon priscus , Macrospondylus bollensis, Proexochokefalos cf. bouchardi, Lemmysuchus obtusidens , and Platysuchus multiscrobiculatus . Similar to Charitomenosuchus leedsi , the ventral margin of the ischium of Neosteneosaurus edwardsi – the ischial blade – is not flat but overall convex in PETMG R178, NHMUK PV R 3701, NHMUK PV R 3898, and NHMUK PV R 2865. In Neosteneosaurus edwardsi , the ischial blade almost form a right-angled with the median of the shaft, whereas the distal blade is more tilted in Lemmysuchus obtusidens and Proexochokefalos cf. bouchardi (angle of approximately 45° and 54° with the median of the shaft, respectively). On the medial side of the ischium, the distal blade displays a heavily scarred area over most of its length (= the ischial suture). The latter corresponds to the area where both ischia were connected in vivo and was presumably covered in soft tissues. At the base of the anterior process, the ischial suture becomes smooth as in Proexochokefalos cf. bouchardi, Lemmysuchus obtusidens , Teleosaurus sp. OUMNH.J1638, and the metriorhynchoids ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804 and ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763 as opposed to the metriorhynchoids Thalattosuchus superciliosus NHMUK PV R 2054 and Torvoneustes carpenteri . The shape of the ischial suture is rather lenticular, with its thickest portion located around the peak of the curvature of the distal blade. Like in Torvoneustes carpenteri , ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763 and Thalattosuchus superciliosus , the ischial suture forms an angle of approximately 45° with the lateral surface of the distal blade so that both ischia were presumably connected through a right-angled junction ( Figs 57 ; 58 ).

The posterior process of the ischium of Neosteneosaurus edwardsi NHMUK PV R 3701, NHMUK PV R 3898, and NHMUK PV R 2865 appears relatively elongated and slender as in the subadult Aeolodon priscus MNHN.F.CNJ 78, but not as tubular as Platysuchus multiscrobiculatus , Teleosaurus sp. , Macrospondylus bollensis , and also Proexochokefalos cf. bouchardi (although the posterior process is quite thick throughout). The cylindrical aspect of the posterior process of Neosteneosaurus edwardsi

NHMUK PV R 3701, NHMUK PV R 3898, andNHMUK PV R 2865 is due to the shape of the concavity of the posterior margin of the ischium. In PETMG R178, the posterior process is bulkier due to a marked sinusoidal posterior margin of the ischium. Indeed, the posterior margin of PETMG R178 is markedly concave dorsally, and switches to strongly convex at around its mid-length, resulting in a dorsoventrally thick posterior process as in Sericodon jugleri . In comparison, Lemmysuchus obtusidens also has a thick posterior process, but the posterior margin of the latter has a different amplitude and hence presents an extended straight surface unlike in Neosteneosaurus edwardsi PETMG R 178.

Pubis

The pubis of Neosteneosaurus edwardsi ( Figs 52-54 ; 56-58 ) stands out from that of other teleosauroids in displaying the combination of a long and thin shaft, a large peduncle and a moderately long pubic symphysis (e.g. Lemmysuchus obtusidens , Machimosaurus , Platysuchus multiscrobiculatus , Macrospondylus bollensis , Charitomenosuchus leedsi ).

The peduncle of Neosteneosaurus edwardsi is mediolaterally large as it accounts for about one-fifth of the total proximodistal height of the pubis. Proximally, the outline of the peduncle of NHMUK PV R 2076 andNHMUK PV R 2865 approximates that of a droplet, with the sharp corner pointing laterally. In comparison, NHMUK PV R 3701 shows a more elliptical outline for its peduncle. The medial and lateral margins of the pubis underneath the peduncle are both concave with a similar degree of intensity. Also, the apex of each concavity is set at the same distance from the peduncle, all of which result in a relatively thin shaft mediolaterally. Indeed, the mediolateral constriction of the shaft reaches about 42% of the mediolateral width of the pubic peduncle. In addition, the shaft of Neosteneosaurus edwardsi is relatively elongated with the constriction being located at around 33% of the proximodistal height of the pubis, proximally ( Figs 52-54 ; 56 ).

Underneath the constriction, the pubis flares out distally and forms the pubic apron or plate. The medial margin of the pubis stops its course earlier than the lateral margin as it meets with the pubic symphysis. The latter is proportionally long similar to several most thalattosuchians (e.g. ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Suchodus durobrivensis , Lemmysuchus obtusidens , Machimosaurus , Charitomenosuchus leedsi ) as opposed to Macrospondylus bollensis , Pelagosaurus typus, Rhacheosaurus gracilis , Magyarosuchus fitosi Ősi, Young, Galàcz & Rabi, 2018 , Cricosaurus species and Geosaurus giganteus . In Neosteneosaurus edwardsi PETMG R 178, NHMUK PV R 3701, NHMUK PV R 2076 and NHMUK PV R 2865, the pubic symphysis accounts for about 29% of the total proximodistal height of the pubis of Neosteneosaurus edwardsi like for Lemmysuchus obtusidens and Charitomenosuchus leedsi . However, the pubic symphysis of NHMUK PV R 2076 is proportionally slightly longer than in the other specimens ( Figs 52 ; 57 ; 58 ). The junction between the pubic symphysis and the medial margin of the pubis is achieved through a right-angled corner as it is the case for the other thalattosuchians displaying a well-developed pubic symphysis. In Neosteneosaurus edwardsi PETMG R 178, NHMUK PV R 3701, NHMUK PV R 2076 and NHMUK PV R 2865, the pubic symphysis forms an angle of approximately 30°with the median of the shaft and the value reaches around 38° in PETMG R178, which are overall similar to the values of Lemmysuchus obtusidens and Charitomenosuchus leedsi . The pubic symphysis of Neosteneosaurus edwardsi is laterally connected to the distal blade of the pubis through an angle approximating 120-130°, which is lesser than in Lemmysuchus obtusidens , Charitomenosuchus leedsi , and Mycterosuchus nasutus . As a result, the pubic apron of Neosteneosaurus edwardsi is not as extensive as in Lemmysuchus obtusidens and Charitomenosuchus leedsi . The distal blade of Neosteneosaurus edwardsi displays a convex and symmetrical outline, similar to most thalattosuchians (e.g. Pelagosaurus typus, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Suchodus durobrivensis , Thalattosuchus superciliosus NHMUK PV R 2054 , Cricosaurus suevicus , Geosaurus giganteus , Lemmysuchus obtusidens , Machimosaurus , Macrospondylus bollensis , Charitomenosuchus leedsi , etc.). The distal blade of Neosteneosaurus edwardsi increases in thickness (anteroposteriorly) towards the lateral side of the bone. Compared to the pubic symphysis, the distal blade shows an important increase in thickness, as in ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Lemmysuchus obtusidens , Mycterosuchus nasutus , but unlike Suchodus durobrivensis , Thalattosuchus superciliosus NHMUK PV R 2054 which possess a more delicate pubis. Laterally, the distal blade of Neosteneosaurus edwardsi transitions to the lateral margin through a rounded right-angled corner.

Figures

FIG. 52. — Pelvic girdle elements of Neosteneosaurus edwardsi (Eudes-Deslongchamps, 1868), PETMG R178: A, left ilium in lateral view; B, left ilium in medial view; C, right ischium in lateral view; D, right pubis in anterior view;E, left pubis in anterior view. Arrow points anteriorly. Target indicates anterior. Pictures courtesy of Dr Michela Johnson. Scale bar: 1 cm.

FIG. 53. — Pelvic girdle elements of Neosteneosaurus edwardsi (Eudes-Deslongchamps, 1868), NHMUK PV R 3701: A, right ilium in medial view; B, right ilium in lateral view; C, right ischium in lateral view; D, right pubis in anterior view; E, left ischium in medial view. Arrow points anteriorly. Target indicates anterior. Scale bar: 1 cm.

FIG. 54. — Pelvic girdle elements of Neosteneosaurus edwardsi (Eudes-Deslongchamps,1868), NHMUK PV R 2076: A, left ilium in lateral view;B, right ilium in medial view;C, right ischium in lateral view;D, right pubis in anterior view;E, left ischium in medial view.Arrow points anteriorly.Target indicates anterior.Scale bar:1 cm.

FIG. 55. — Pelvic girdle elements of Neosteneosaurus edwardsi (Eudes-Deslongchamps, 1868), NHMUK PV R 3898: A, left ilium in lateral view; B, right ilium in medial view; C, left ischium in lateral view. Arrow points anteriorly. Target indicates anterior. Scale bar: 1 cm.

FIG. 57. — Reconstruction of the pelvic girdle of Neosteneosaurus edwardsi (Eudes-Deslongchamps, 1868), NHMUK PV R 3701 (A, C, E) and NHMUK PV R 2076 (B, D, F): A, B, right lateral views; C, D, anterior views; E, F, ventral views. Target indicates anterior. Arrow points anteriorly. The right pubis and left ilium of NHMUK PV R 3701 are mirrored. The right pubis of NHMUK PV R 2076 is mirrored. Scale bars: 5 cm.

FIG. 58. — Reconstruction of the pelvic girdle of Neosteneosaurus edwardsi (Eudes-Deslongchamps, 1868), NHMUK PV R 3898 (A, C, E) and NHMUK PV R 2865 (B, D, F): A, B, right lateral views; C, D, anterior views; E, F, ventral views. Target indicates anterior. Arrow points anteriorly. The right ilium and ischium of NHMUK PV R 3898 are mirrored. The right pubis and left ischium of NHMUK PV R 2865 is mirrored. Scale bars: 5 cm.

FIG. 59. — Pelvic girdle elements of Lemmysuchus obtusidens (Andrews, 1909), NHMUK PV R 3168 (holotype): A, left ilium in lateral view; B, left ilium in medial view; C, left pubis in lateral view; D, left ischium in lateral view; E, left pubis in anterodorsal view; F, right ischium in lateral view; G, surimposition of both ischia (right and left) of Lemmysuchus obtusidens, NHMUK PV R 3168. Target indicates anterior. Arrow points anteriorly. Scale bar: 1 cm.

FIG. 56. — Pelvic girdle elements of Neosteneosaurus edwardsi (Eudes-Deslongchamps,1868), NHMUK PV R 2865: A, left ischium in lateral view;B, right ischium in medial view; C, left pubis in anterior view. Arrow points anteriorly. Target indicates anterior. Scale bar: 1 cm.