Torvoneustes carpenteri, (WILKINSON, YOUNG & BENTON, 2008)

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 : 202-205

TORVONEUSTES CARPENTERI ( WILKINSON, YOUNG & BENTON, 2008)

For measurements, see Tables 7-9 .

Ischium

The ischium of Torvoneustes carpenteri ( Figs 34 ; 35 ) strongly resembles those of Cricosaurus araucanensis , Dakosaurus maximus and Lemmysuchus obtusidens in displaying a strongly reduced anterior process and a large posterior one. This effect is mainly imputable to the shape of the anterior and posterior margins of the ischium of Torvoneustes carpenteri : the anterior margin is concave throughout with a large focal width whereas the posterior margin displays a strong sinusoidal shape. Indeed, the posterior margin is proximally concave and switches to convex around its mid-length and hence forms the rounded extremity of the posterior process. The early change in convexity of the posterior margin results in a dorsoventrally high posterior process, unlike those of most metriorhynchoids (i.e. Pelagosaurus typus, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, Cricosaurus bambergensis , etc.).

The posterior process of the ischium of Torvoneustes carpenteri is overall oval, with its apex decentred and pointing posteroventrally rather than strictly posteriorly as in Lemmysuchus obtusidens . The entirety of the apex of the posterior process is scarred along its margin both laterally and medially, and this pitted area forms a continuum with that of the distal blade. These structures mark the presence of a cartilage cap in vivo. The extremity of the posterior process transitions to the ventral margin of the ischium – and thus the distal blade – through a rounded corner.

The distal blade of Torvoneustes carpenteri displays a relatively straight surface with limited undulations, similar to most thalattosuchians (e.g. Pelagosaurus typus, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Thalattosuchus superciliosus NHMUK PV R 2054 , Cricosaurus araucanensis , Cricosaurus bambergensis , Dakosaurus maximus , Aeolodon priscus , Lemmysuchus obtusidens , Platysuchus multiscrobiculatus, Proexochokefalos cf. bouchardi, Teleosaurus sp. , Macrospondylus bollensis , etc.). On the medial side of the distal blade the pitted area is globally larger than on the lateral side, and shows limited bursts of enlargement drawing a series of wavy outlines. The greatest burst of pitted area on the distal blade is located near the base of the anterior process.In Thalattosuchus superciliosus NHMUK PV R 2054 , ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, and Dakosaurus maximus , this area is mediolaterally thicker and forms a dorsal platform when both ischia are joined. It is possible that a similar structure was borne by the ischia of Torvoneustes carpenteri due to the outline of the pitted area anteriorly ( Fig. 34 ). The whole pitted area on the medial side of the distal blade corresponds to the ischial suture where both ischia were connected through soft tissues in vivo.

The anterior process of Torvoneustes carpenteri ( Fig. 34 ) is sharp and drastically smaller than the posterior process: the dorsoventral height of its base accounts for less than half of the dorsoventral height of the base of the posterior process. Also, the anteroposterior length of the anterior process exceeds the dorsoventral height of its base giving the process an elongated aspect. Overall, the anterior process points strictly anteriorly, so that it is directly in line with the ventral margin of the ischial blade as in Dakosaurus maximus , ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804 (or the teleosauroids Macrospondylus bollensis , Neosteneosaurus edwardsi, Proexochokefalos cf. bouchardi). This orientation of the anterior process contrasts with the more anterodorsally recurved one found in other thalattosuchians (e.g. Pelagosaurus typus, Thalattosuchus superciliosus NHMUK PV R 2054 , Cricosaurus bambergensis , Geosaurus giganteus , Aeolodon priscus , Teleosaurus sp. , Lemmysuchus obtusidens , etc.). The anterior process of Torvoneustes carpenteri is composed of a relatively straight dorsal margin (corresponding to the ventral flank of the anterior margin) and a convex ventral one which merge into a pointed extremity.

The anterior peduncle of Torvoneustes carpenteri appears reduced due to both its relative and absolute small size. In this way, it is comparable to Pelagosaurus typus, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, Thalattosuchus superciliosus NHMUK PV R 2054 , and Geosaurus giganteus (and for example the teleosauroids Aeolodon priscus, Proexochokefalos cf. bouchardi, Sericodon jugleri , Teleosaurus sp. ). Indeed, the maximum dorsoventral thickness of the anterior peduncle of Torvoneustes carpenteri is inferior to any section of the peduncle bridge, which is similar to the aforementioned taxa but greatly contrasts with Cricosaurus araucanensis , Cricosaurus suevicus , Cricosaurus bambergensis among metriorhynchoids, and other teleosauroids.

The anterior peduncle is borne on the extremity of the peduncle bridge, which is an elongated process in Torvoneustes carpenteri ( Fig. 34 ). Similar to Pelagosaurus typus, Thalattosuchus superciliosus NHMUK PV R 2054 , Cricosaurus araucanensis , Cricosaurus suevicus , Cricosaurus albersdoerferi , and Geosaurus giganteus , the peduncle bridge of Torvoneustes carpenteri extends further dorsally (or proximally) than the posterior peduncle which creates additional space for the acetabular perforation between the peduncles. The dorsal margin of the peduncle bridge of the ischium is concave and forms the ventral border of the acetabular perforation whereas the ventral margin of the peduncle bridge is slightly convex. Both margins are slightly divergent towards the base of the process, so that the peduncle bridge slightly thickens towards its junction with the shaft of the ischium. The base of the peduncle bridge is located slightly more ventrally than in ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Cricosaurus araucanensis , Cricosaurus albersdoerferi which renders the acetabular perforation more apparent laterally as in other metriorhynchoids (i.e. Pelagosaurus typus, Thalattosuchus superciliosus NHMUK PV R 2054 , Geosaurus giganteus , and Dakosaurus maximus ). Still, the acetabular perforation forms a hollow area on the medial side of the peduncle bridge which extends until the base of the posterior peduncle as in other thalattosuchians (e.g.‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763, ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 3804, Torvoneustes carpenteri , Cricosaurus araucanensis , Dakosaurus maximus , Lemmysuchus obtusidens , Macrospondylus bollensis , Charitomenosuchus leedsi , Neosteneosaurus edwardsi ).

The posterior peduncle of Torvoneustes carpenteri is large and accounts for about 3/4 of the anteroposterior width of the shaft ( Fig. 34 ). In Torvoneustes carpenteri , the posterior peduncle slightly protrudes dorsally, which renders the acetabular perforation clearly visible on the lateral side of the ischium, as in Thalattosuchus superciliosus NHMUK PV R 2054 , Geosaurus giganteus , and Dakosaurus maximus among metriorhynchoids.

Figures

FIG. 34. — Right ischium of Torvoneustes carpenteri (Wilkinson, Young & Benton, 2008), BRSMG Cd7203 (paratype): A, right ischium in medial view; B, right ischium in lateral view. Arrow points anteriorly. Pictures courtesy of Dr. Davide Foffa. Scale bar: 1 cm.

FIG. 35. — Reconstruction of the pelvic girdle of Torvoneustes carpenteri (Wilkinson, Young & Benton, 2008), BRSMG Cd7203: A, right lateral view; B, anterior view; C, ventral view; D, dorsal view. Scale bar: 5 cm.