Form and function of the pelvic girdle of Thalattosuchia and Dyrosauridae (Crocodyliformes) Author Scavezzoni, Isaure Universite de Liège, Evolution and Diversity Dynamics Lab, All. du Six Août 14, 4000 Liège (Belgique) isaure. scavezzoni @ gmail. com v. fischer @ uliege. be isaure.scavezzoni@gmail.com Author Fischer, Valentin Universite de Liège, Evolution and Diversity Dynamics Lab, All. du Six Août 14, 4000 Liège (Belgique) isaure. scavezzoni @ gmail. com v. fischer @ uliege. be v.fischer@uliege.be Author Johnson, Michela M. Department of Palaeontology, Staatliches Museum für Naturkunde Stuttgart, Museum am LÖwentor, Rosenstein 1, 70191 Stuttgart (Germany) michela. johnson @ smns-bw. de michela.johnson@smns-bw.de Author Jouve, Stéphane Sorbonne Universite, BUPMC - Pôle Collections, Tour Zamansky, 15 étage, bureau 1513, 4 place Jussieu, 75252 Paris Cedex 05 (France) stephane. jouve @ sorbonne-universite. fr stephane.jouve@sorbonne-universite.fr text Geodiversitas 2024 2024-05-02 46 6 135 326 https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/g2024v46a6.pdf journal article 10.5252/geodiversitas2024v46a6 1638-9395 11106598 urn:lsid:zoobank.org:pub:6ACF6A79-9149-4781-808D-478668673EB6 TELEOSAURUS GEOFFROY SAINT-HILAIRE , 1825 For measurements, see Tables 7-9 . Ischium The ischium of Teleosaurus sp. (NHMUK PV R 238 [ Fig. 43 ]) stands out with its combination of both a slender shaft and posterior process. Indeed, the ischium of Teleosaurus sp. displays a strongly concave anterior margin which partly accounts for the strong shaft constriction. In comparison, the shaft of Teleosaurus sp. OUMNH.J1638 is slightly more chunky due to a proportionally shorter shaft (dorsoventrally). Among teleosauroids, Mycterosuchus nasutus , Charitomenosuchus leedsi , Indosinosuchus potamosiamensis ( Martin et al. 2019a ) and Proexochokefalos cf. bouchardi also display an anteroposteriorly thin shaft, but the shaft of Proexochokefalos cf. bouchardi is proximodistally shorter.Among metriorhynchoids, Pelagosaurus typus BRLSI M.1410 and ‘ Metriorhynchus ’ brachyrhynchus NHMUK PV R 4763 show a slender shaft as well. In comparison, the posterior margin of the ischium of Teleosaurus sp. is subtly concave: its apex is located relatively proximally (around onefourth of total posterior length) and its concavity shows a greater amplitude so that the posterior margin of the ischium underneath the shaft appears straight. Compared to the other teleosauroids with a thin shaft, Indosinosuchus potamosiamensis ( Martin et al. 2019a ) , Charitomenosuchus leedsi and Proexochokefalos cf. bouchardi also display a more subtly concave posterior margin in relation to the anterior one, whereas Mycterosuchus nasutus possesses a markedly concave posterior margin. Proximally, the shaft of the ischium of Teleosaurus sp. flares out asymmetrically to form the anterior and posterior peduncles. Laterally, the base of the peduncle bridge is borne close to the rim of the posterior peduncle which partly obstructs the acetabular perforation as in most teleosauroids, as opposed to Indosinosuchus potamosiamensis ( Martin et al. 2019a ) , Charitomenosuchus leedsi and Macrospondylus bollensis . In Teleosaurus sp. , the peduncle bridge retains most of its base height throughout its lengths which give it a thick aspect as in Aeolodon priscus , Indosinosuchus potamosiamensis ( Martin et al. 2019a ) , Neosteneosaurus edwardsi and Lemmysuchus obtusidens . Overall, the peduncle bridge of Teleosaurus sp. is moderately long as its total length (including the anterior peduncle) is comparable to that of the posterior peduncle. The anterior peduncle of Teleosaurus sp. is not preserved in its entirety, but it does not ventrally protrude from the ventral margin of the peduncle bridge. FIG . 41. — Pelvic girdle elements of Mycterosuchus nasutus ( Andrews, 1909 ) : A , B , NHMUK PV R 2617, holotype; C , D , CAMSM J.1420 (referred); A , left pubis in anterior view; B , left pubis in posterior view; C , left ischium in medial view; D , left ischium in lateral view; E , left pubis in posterior view; F , left pubis in anterior view. Target indicates anterior. Cross indicates posterior. Pictures of CAMSM J.1420 courtesy of Dr. Michela Johnson. Scale bars: 1 cm. The posterior peduncle of Teleosaurus sp. is typically divided between the slightly concave articular facet participating in the hip acetabulum, and the rough articular facet connecting with the ischial peduncle of the ilium. The edge of the posterior peduncle forms a thick rounded rim which contrasts with the thinner rim of the other teleosaurids Indosinosuchus potamosiamensis ( Martin et al. 2019a ) and Platysuchus multiscrobiculatus . Distally, the shaft of the ischium of Teleosaurus sp. also flares out asymmetrically to form the anterior and posterior processes. The latter is strongly expanded posteriorly with an overall tubular shape, as in Pelagosaurus typus , Macrospondylus bollensis , and Platysuchus multiscrobiculatus . It is possible that Indosinosuchus potamosiamensis ( Martin et al. 2019a ) displayed a tubular posterior process similar to Teleosaurus sp. and Platysuchus multiscrobiculatus , however it is not preserved. The dorsal margin of the posterior process of Teleosaurus sp. possesses a low slope angle in relation to the ischial blade and, as a result, the dorsoventral thickness of the posterior process subtly decreases in size posteriorly. In addition, the posterior process of Teleosaurus sp. displays a thick and rounded apex, which contributes to the tubular aspect of the process, as in Platysuchus multiscrobiculatus but unlike Macrospondylus bollensis . In contrast, the anterior process of the ischium of Teleosaurus sp. forms a short and sharp hook pointing anterodorsally. Hence, the anterior process is not in line with the ischial blade, as in Aeolodon priscus . The dorsal margin of the anterior process is slightly concave (as it follows the curve of the anterior margin of the ischium) whereas the ventral margin is more straight. Overall, the dorsal and ventral margins of the anterior process appear to display the same length and inclination. As a consequence, the anterior process has a strong symmetrical aspect dorsoventrally, similar to an isosceles triangle. This strongly contrasts with the other teleosaurids Indosinosuchus potamosiamensis ( Martin et al. 2019a ) and Platysuchus multiscrobiculatus in which the anterior process is directly in line with the ischial blade. The ischial blade of Teleosaurus sp. connects the anterior and posterior processes along the ventral margin of the ischium. It displays an overall straight surface with a wide ischial suture on its medial side, as in Platysuchus multiscrobiculatus (and Charitomenosuchus leedsi but to a lesser extent). The ischial suture is identifiable as its surface is bevelled in relation to the medial surface of the ischium, and is also scarred throughout. In addition, the edge of the ischial suture forms a rim where it connects with the medial surface of the bone. Pubis The pubis of Teleosaurus sp. (OUMNH.J1638; Fig. 43 ) shows a relatively large peduncle proximally, which contrasts with Platysuchus multiscrobiculatus and Charitomenosuchus leedsi , but is similar to Macrospondylus bollensis and Neosteneosaurus edwardsi . The marked constriction of the shaft of Teleosaurus sp. also emphasizes the proximal flaring of the pubis to form the peduncle (which is more than twice as wide). However, the minimum constriction of the shaft of Teleosaurus sp. is slightly proportionally larger than what is observed in Macrospondylus bollensis and Neosteneosaurus edwardsi . In Teleosaurus sp. the shaft is moderately long as the maximum mediolateral constriction is set at around 1/3 of the total proximodistal length of the bone, which is similar to Macrospondylus bollensis and Neosteneosaurus edwardsi . In comparison, the shaft of Charitomenosuchus leedsi and Lemmysuchus obtusidens are proportionally shorter and reach 27.5% and 22.13% of the total length of the pubis, respectively. In Teleosaurus sp. , the concavity of the medial and lateral margins is relatively similar, which contrasts with most teleosauroids (e.g. Mycterosuchus nasutus , Platysuchus multiscrobiculatus , Macrospondylus bollensis , Charitomenosuchus leedsi , Neosteneosaurus edwardsi , and Lemmysuchus obtusidens ). This is due to the slow and gradual widening of the pubic apron underneath the shaft, which only shows a marked increase in width around the beginning of the pubic symphysis as in Machimosaurus . Indeed, around the level of the pubic symphysis, the medial margin of the pubis of Teleosaurus sp. forms a marked bent towards the medial side, so that the angle produced externally between the two surfaces of the medial margin reaches around 138°. As a result, the portion of the pubic apron bearing the pubic symphysis medially appears to strongly protrude from the rest of the pubic apron, hence forming a medial protuberance or flange (like in Machimosaurus ). The pubic symphysis of Teleosaurus sp. is well-developed as in most thalattosuchians, and reaches around 33% of the total proximodistal length of the bone. Dorsally, the pubic symphysis forms an almost right-angled corner with the medial margin (corresponding to the medial corner of the protuberance), whereas its transition with the distal margin of the pubic apron is achieved through an obtuse angle. In Teleosaurus sp. , the distal margin of the pubic apron is relatively straight which contrasts with other teleosauroids (e.g. Macrospondylus bollensis , Charitomenosuchus leedsi , Neosteneosaurus edwardsi , Lemmysuchus obtusidens , and Machimosaurus ). Laterally, the distal margin of the pubic apron forms a semi-circular corner at its junction with the lateral margin of the bone, which stands out from other teleosauroids. There is an indentation between the semi-circular corner and the lateral margin of the pubis which emphasizes its bulbous shape. This rounded-corner also slightly protrudes laterally from the rest of the lateral margin of the bone, forming a small lateral protuberance. In comparison, the lateral protuberance of Mycterosuchus nasutus is more laterally prominent, but less dorsoventrally thick than in Teleosaurus sp.