Temnodontosaurus platyodon Conybeare 1822.

Temnodontosaurus trigonodon Theo­dori, 1843.

Temnodontosaurus nuertingensis Huene, 1931.

Temnodontosaurus eurycephalus McGowan, 1974.

Temnodontosaurus crassimanus Blake, 1876.

Temnodontosaurus azerguensis Martin et al., 2012.

Temnodontosaurus zetlandicus Seeley, 1876.

The referral of UMO BT 011237.00 to Temnodontosaurus at the generic level is justified in the section on taxonomic assignment. At the species level, we leave the specimen in open nomenclature but note several similarities to Temnodontosaurus trigonodon, as discussed in the same section.

Based on a lower jaw length of about 148 cm, the animal’s total length is estimated at approximately 6.6 m (using a jaw-to-skull ratio of 1:0.975 from the reconstructed skull of Temnodontosaurus trigonodon, Maisch and Hungerbühler 2001, fig. 3, and a skull-to-total length ratio of 1:4.6 for specimen SMNS 15950, Huene 1931a).

Skull. Premaxilla. There are three fragments of the premaxillae, which exhibit signs of potential bioerosion and subaqueous pre-burial dissolution (Fig. 3).

Right lateral side: The anterior situated fragment of the premaxilla (Fig. 4A) includes the labial wall and base of the dental groove, with the lingual wall missing. The inner side of this wall (medial side) displays distinct, slightly anterior directed pseudoalveoli (Bennion et al. 2023). The pseudoalveoli are formed by localized thickenings of the labial wall of the premaxilla, accompanied by shallow, bowl-shaped pits at the base of the dental groove. Anterior pseudoalveoli in the premaxilla are described for two specimens of Temnodontosaurus trigonodon: the holotype PKB 1 and GPIT PV 30038 (Bennion et al. 2023, fig. S4). This feature is also observed in the incomplete Middle Jurassic member of the clade Ophthalmosauria Argovisaurus martafernandezi (Miedema et al. 2024, figs 3, 4).

The mode of tooth implantation is aulacodont (sensu Mazin 1983), a synapomorphic characteristic observed in all Neoichthyosauria (Maisch and Matzke 2000; Sander 2000; Maisch 2010). The inner side of the labial wall is collapsed in the area of the horizontally running intraosseous canal (sensu Lomax et al. 2019: “internal canal”; Serafini et al. 2022: “intraosseous channel”), thus providing a view of its inner surface (Fig. 4A).

The posterior located fragment of the right premaxilla (Fig. 4A) also shows the pseudoalveoli described above in the anterior region. These are initially clearly pronounced but become weaker posteriorly, losing relief and disappearing completely in the last third, merging into a smooth wall, as in nearly all neoichthyosaurians (Moon and Kirton 2016; Miedema et al. 2024). This area is presumably the contact zone with the maxilla, which fits under the premaxilla like a tongue. In the pseudoalveoli, a fine fan of flat, narrow retroventrally directed grooves emerges halfway up from a small foramen.

Lateral view of both fragments (Fig. 4B, C): In low angle light, the premaxillary fossa is visible, from which a complex system of shallow neurovascular grooves branches off both ventrally and dorsally (Fig. 4B) extending from foramina (Fig. 4C). The grooves branch from the fossa, even in areas where there are no foramina. Anteriorly, the groove system becomes more pronounced and denser. The first posteriorly located grooves (Fig. 4B1) point anteriorly, while the more anteriorly located grooves (Fig. 4B2) increasingly diverge in various directions. The ventrally running grooves partly form an arc, initially running posteriorly and then bending anteriorly. The grooves branch out up to two times.

The posterior fragment initially shows a pronounced premaxillary fossa posterior, which disappears after 23 cm and anteriorly resolves into several sections, each of which has a neurovascular foramen at its anterior end (Fig. 4C). These sections of the fossa are initially shallow and become progressively deeper toward the next foramen located anteriorly. The distances between the foramina become shorter anteriorly. These are clearly radiating from a point that should be approximately at the level of the gap between the two fragments (Fig. 4C). On the posteriorly located fragment, these foramina point posteriorly; on the anteriorly located piece, they point anteriorly. These foramina are associated with the intraosseous canal.

A 6 cm long groove in the central canal leads anteriorly into a 13 mm long oval opening (Fig. 4A), located above the third pseudoalveolus, and is connected here with the interosseous canal. From the interosseous canal, the superficial foramina originate, from which a branching neurovascular groove system arises. This observation corresponds with the CT analyses by Lomax et al. (2019, fig. 2G). The position of that opening to the interosseous canal (Fig. 4A) in relation to the location of the superficial foramina and their partially posterior exit direction (Fig. 4B1, 2C) indicates that the interosseous canal branches partly posteriorly, as also described for a platypterygiid ichthyosaur by Serafini et al. (2022; fig. 8B–D).

A groove system in the premaxilla, a common feature of many Neoichthyosauria, was described for the holotype of Temnodontosaurus trigonodon by Theodori (1854) and is also visible in the Temnodontosaurus trigonodon specimen SMNS 13128 (Fraas 1913). The premaxillary groove is a single structure in Temnodontosaurus platyodon (McGowan 1995), T. zetlandicus, Ichthyosaurus acutirostris (Laboury et al. 2022), T. azerguensis (Martin et al. 2012) and Suevoleviathan disinteger (Maisch, 1998b). This differs from Temnodontosaurus nuertingensis, in which the premaxilla exhibits two parallel rows of grooves and foramina (Huene 1931b; Maisch and Hungerbühler 1997). In Ophthalmosaurus icenicus, Moon and Kirton (2016) describe a longitudinal groove with foramina but without diverging grooves.

In the fragment of the left premaxilla, both walls bounding the dental groove are present, with the lingual wall clearly projecting below the labial wall (see also cross-section Fig. 22). Viewed ventrally, there is a longitudinal, slightly concave flattening on the ventral side of the labial wall of the dental groove, which forms the contact with the maxilla (Fig. 5A).

On the lingual wall, several shallow, 2–5 mm wide, trough-shaped depressions run over the ventral margin and disappear after 3 cm (Fig. 5B). The genesis and function of these grooves is as yet unclear. On the dorsal margin of the bone is a groove representing the suture to the nasal, which was already partially overlapped by the premaxilla (Fig. 5C). On the right premaxilla, there are pathological changes on the lateral side (Pardo-Pérez et al. 2018, fig. 3G).

Owing to the incompleteness of the material, it is not possible to draw any definitive conclusions regarding the overall morphology of the snout. All premaxillary fragments show growth of bivalves and serpulids.

Jugal. Both jugals (Fig. 6) are present, having been found isolated in the sediment and partially dissolved due to pre-burial processes. Both anterior ends and the posterior end of the left jugal are broken off.

UMO BT 011237.00 reveals in lateral view (right jugal) the triangular facet for the anteroventral process of the quadratojugal (Maisch and Hungerbühler 2001) at the posterior end. On the left jugal, it is only faintly visible in lateral view (Fig. 6A). In Temnodontosaurus trigonodon, the posterior end of the jugal appears bifurcated due to an anteroventral process of the quadratojugal, which overlaps the jugal (Maisch 1998a; Maisch and Hungerbühler 2001; Maisch 2010). Huene (1931a) further describes the quadratojugal as "fitting into a recess of the jugal“ (own translation) in Temnodontosaurus trigonodon (specimen SMNS 15950), a feature visible in lateral view. This same connection, characterized by the bifurcated posterior part of the jugal and an overlapping quadratojugal, is also evident in Temnodontosaurus zetlandicus (see Laboury et al. 2022).

Both jugals of UMO BT 011237.00 show ventrally in the anterior region two longitudinal grooves separated by a narrow ridge, representing the ventral facet for the maxilla (Fig. 6B). The grooved area on the anterior third of the medial side could tentatively articulate with the maxilla as well.

In the left jugal there is a groove for articulation with the lacrimal dorsally in the anterior third (Fig. 6C). The left jugal shows posteriorly the rest of the postorbital facet (Fig. 6A). On the medial surface, a prominent medial ridge extends from the dorsomedial region of the posterior third of the jugal, runs ventromedially along its medial surface, and in the anterior third forms the medioventral margin of the jugal (Fig. 6C). The mid-ventral region of the jugal bears numerous shallow, medially oriented grooves (Fig. 6B, C) that curve posteriorly at the medial crest and fade out after only a few millimetres.

Quadratojugal. Both quadratojugals of UMO BT 011237.00 were found isolated in the sediment and are heavily corroded. The right quadratojugal is roughly triangular in lateral view, it has a distinct concave area posteriorly in ventral view, the facet for the quadrate (Fig. 7A, C). The bone is thickest there (approximately 3 cm). Anteriorly, the bone tapers into a thin lamina, forming the anterior process (Maisch and Hungerbühler 2001) (Fig. 7A). In Temnodontosaurus trigonodon (FWD 443), Maisch and Hungerbühler (2001, fig. 1, 2) describe this process as overlapping the jugal, giving the jugal a bifurcated appearance in lateral view (see also Maisch 1998a). The corresponding facet on the right jugal is described above in the section on the right jugal.

Due to severe corrosion of the bone fragment, the exact outline of the quadratojugal cannot be determined. In medial view, a distinct ?facet extends anteroventrally to posterodorsally along the anterodorsal margin of the quadratojugal (Fig. 7B). Since the facet runs posterodorsally, and a long, triangular process of the quadratojugal extends dorsally between the postorbital and the squamosal in Temnodontosaurus trigonodon, specimen FWD 443 (Maisch and Hungerbühler 2001), we infer that the facet overlaps the posterior margin of the postorbital.

The left quadratojugal (Fig. 7C) is severely corroded; only the ventral margin, which is also thickened anteriorly with a ventrally oriented concave shape, is preserved (facet for the quadrate). The dorsal part is largely dissolved. At the anterior margin of the quadrate facet, the bone has cavernous structures, suggesting degenerative changes. A small coral has settled on the outer surface postmortem (Fig. 7D).

Quadrate. Little can be said about the shape of the quadrates of UMO BT 011237.00 because both are heavily eroded. The original bone surface is preserved only in parts. The entire pterygoid lamella (Moon and Kirton 2016) of the left quadrate is missing, almost only the articular condyle is preserved.

The right quadrate is more complete, no statements can be made about the extent of the dorsal region, as it is presumably eroded (Fig. 8).

The articular condyle of the right quadrate runs convexly upward in direction to the ?facet of the quadratojugal (Fig. 8B). The articular condyle is massive and well-developed as in species currently referred to Temnodontosaurus for which the quadrate is preserved (e.g., Fraas 1913; Godefroit 1993; Swaby and Lomax 2020; Laboury et al. 2022), with the exception of T. azerguensis (Martin et al. 2012). A pit-shaped depression, the facet for the stapes (Romer 1956; McGowan 1973, fig. 9C) is visible in posterior view. Articulation surfaces to other skull elements cannot be recognized anymore.

Pterygoid. Both pterygoids are present in their full length (65 cm), the right one is nearly in its original position, while the left one is slightly shifted outwards (Fig. 9). The pterygoids consist of a posterior part, the quadrate ramus (Moon and Kirton 2016) and an anterior part, the palate ramus. In both pterygoids of UMO BT 011237.00, the 11.5 cm wide quadrate ramus reveals the lateral and medial lamellae, while the dorsal lamella is only visible in its base in the left pterygoid. The medial lamella is broken off in the left pterygoid, and in the right pterygoid, the posteromedial tip of the medial lamella is missing. The lateral lamella slopes dorsally at its posterior extremity, which is visible in the left pterygoid (Fig. 9). The posterolateral tip of the lateral lamella is broken off in the left pterygoid. In posteroventral view (Fig. 10), a dorsolateral concavity is visible between the medial lamella and the base of the dorsal lamella of the left pterygoid, forming the recess for the stapes.

The medial lamella of the right pterygoid lies in original articulation on the pterygoid facet of the basisphenoid. Two pit-like foramina are located 2.5 cm anterior to the posterior margin on the right pterygoid. On the left pterygoid, a slightly larger foramen is located approximately 1 cm from the posterior margin about midway between the medial and dorsal lamellae. The medial attachment of the medial lamella is characterized in both pterygoids by a narrow furrow that initially appears to separate it from the main trunk anteriorly at the narrowest point of the pterygoid but is lost after a few centimeters (Fig. 9). At the point where the pterygoids widen to the lateral lamella, the ventral surface near the outer edge shows an area of about 2 cm wide and 5 cm long with a distinct longitudinal striation.

The palatal ramus is a planar, elongated structure that reaches a width of 7.5 cm at the anterior end of the subtemporal fenestra. The lateral borders of the pterygoids are weakly concave in the area of the subtemporal fenestrae, similar as in the Temnodontosaurus trigonodon specimen SMNS 13128 (Fraas 1913) and unlike in Temnodontosaurus zetlandicus and the Temnodontosaurus trigonodon specimen SMNS 15090, where the lateral borders of the pterygoids ae more strongly concave (Huene 1931b; Laboury et al. 2022).

Anterior to the subtemporal fenestra the palatal ramus tapers continuously anteriorly to terminate in a narrow, dorsoventrally oriented, weakly laterally concave tip that receives the vomer. In the middle area of both pterygoids, there is a distinct longitudinal striation in the ventromedial area over a length of about 10 cm. The anterior end of the right palatal ramus extends to a point approximately 18 cm anterior to the midpoint of the internal nares (the thin anterior ends likely extended further originally and are broken off) The extension of the palatal rami differ to the Temnodontosaurus trigonodon specimen SMNS 15090 (Huene 1931b) and Temnodontosaurus zetlandicus (Laboury et al. 2022), where the palatal rami of the pterygoids terminate at the midpoint of the internal nares.

Palatine. Only a fragment of the left palatine is preserved, with both the anterior and posterior ends broken off. It is tilted laterally by approximately 90°, with its medial articulation with the pterygoid and the vomer facing the observer. The connection between palatine and vomer in the anterior region is a tongue-and-groove connection (Fig. 11A).

Posteriorly, on the originally ventral side of the tilted left palatine, there is a flat edge showing that the palatine overlaps the pterygoid dorsally (Fig. 11B). No conclusions can be drawn about the posterior extent of the palatines or their involvement in the anterior margin of the subtemporal fenestra, as this region is covered by the angular on the right side and broken off on the left.

Despite the dislocation of the right palatine, it is clear that its anterior medial margin forms the lateral wall of the internal naris. A posterior wall of the internal naris, as described by (Huene 1931b, SMNS 15090) for Temnodontosaurus trigonodon, is not visible, as the right palatine is obscured by the vomer in this region.

Vomer. The vomers are present but are posteriorly covered by the pterygoids and are partially hidden under the mandibular symphysis. Where the vomers form the medial margin of the internal nares, they exhibit a shallow but distinct curvature over a length of approximately 10 cm. The medial profile of the vomers is convex in cross-section, suggesting close contact with the pterygoids, which have a matching counterprofile (Fig. 11C). On the right vomer, lateral to the posterior process, is the attachment to a broken lamella that presumably represents the attachment surface for the ventral underlapping palatine (Fig. 11D). The vomers are overall elongated, similar to those in Temnodontosaurus zetlandicus (Laboury et al. 2022) and Temnodontosaurus trigonodon (Huene 1931b, SMNS 15090). The morphology differs from Temnodontosaurus nuertingensis (Huene 1931b), where the vomers are broader and distinctly constricted at the internal naris.

Epipterygoid. In specimen UMO BT 011237.00, the tentatively basal portion of the right epipterygoid is preserved in isolation. The foot, viewed anteriorly, tapers to a columnar shaft (Fig. 12A). The shaft forms a narrow ridge on the right posteriorly (Fig. 12C). Viewed laterally (Fig. 12B), the base of the epipterygoid appears as the lower half of a crescent. The convex basal surface (foot) exhibits a strongly fissured to bulging surface approximately 1.5 cm wide and 9 cm long (Fig. 12C, E), which indicates a cartilaginous connection to the pterygoid ventrally and to the quadrate posterolaterally, as described for Ichthyosaurus by Appleby (1961) and McGowan (1973).

In medial view, a rugose area extends from the tip of the foot of the epipterygoid, terminating in a process after 4.5 cm (Fig. 12D, E). The medial flank of the epipterygoid has a grit-like uneven surface. Laterally, the surface is smooth and trough-shaped concave (Fig. 12B, C). Dorsally, with the exception of the broken shaft, the bone ends in the concave shape described above, which bends medially to end abruptly on the medial side.

Ossified epipterygoids are known in the Early Jurassic ichthyosaurs Ichthyosaurus (Appleby 1961; McGowan 1973), Protoichthyosaurus (Sollas 1918; Lomax et al. 2020), Stenopterygius (Miedema et al. 2024) and Eurhinosaurus mistelgauensis (Spicher et al. 2025). Godefroit (1993) describes a facet for the epipterygoid on the quadrate and an epipterygoid process on the parietal of Temnodontosaurus platyodon (Godefroit 1993).

Basioccipital. The basioccipital lies isolated and is displaced from its original anatomical position. It is rotated 116° posteriorly in the horizontal plane and an additional 153° around its own longitudinal axis. The basioccipital is severely eroded; however, the slightly concave facet for the stapes, as well as a part of the extracondylar area are recognizable (Fig. 13A, B1). Due to poor preservation, the basioccipital of specimen UMO BT 011239.00 Temnodontosaurus sp. is displayed for comparison in Fig. 13B2. Thus, little can be said about the morphology of the basioccipital, but the preserved part of the extracondylar area suggests that it is extensive, as in all temnodontosaurids (McGowan and Motani 2003; Swaby and Lomax 2020).

Stapes. Both stapes are near their original positions on the skull slab (Fig. 13B). The left stapes of UMO BT 011237.00 has a pronounced convex medial head. Beyond the head, the bone narrows into a slender, laterally flattened curved shaft and ends in the band-shaped narrow distal facet, the facet for the quadrate (Fig. 13C) (Andrews 1910; McGowan 1973; Moon and Kirton 2016). In anteroventral view (Fig. 13C), a shallow anterior depression is visible. Maisch (2002) describes this depression in Temnodontosaurus cf. trigonodon also as a facet for the quadrate. For Temnodontosaurus trigonodon, the illustrations from Fraas (1913) and Swaby (2020) suggest that the stapes may also articulate with the pterygoid anteriorly.

The medial head of the left stapes is clearly delimited from the shaft and significantly larger than the lateral end, similar to the thunnosaurian Stenopterygius quadricissus (Miedema and Maxwell 2019), Hauffiopteryx typicus (Marek et al. 2015) and Protoichthyosaurus prostaxalis (Lomax et al. 2019). This differs from the morphology of the stapes in Temnodontosaurus azerguensis (Martin et al. 2012), a juvenile specimen of Temnodontosaurus cf. trigonodon (Maisch 2002) and Ichthyosaurus (McGowan 1973).

Only the convex medial head of the right stapes of UMO BT 011237.00 is visible. Unlike the pit-like relief of the right stapes head, it displays a surface characterized by narrow ridges.

Opisthotic. The right opisthotic is well preserved. Based on the position of the facets for the basioccipital and stapes, we follow the orientation described by McGowan (1973) for Ichthyosaurus. The facets for the basioccipital and stapes are located ventromedially. The boundary between the two facets is unclear because the entire surface is highly fissured, indicating a cartilaginous connection (Fig. 14D). From the posterior margin of the basioccipital facet, a shaft extends dorsolaterally and terminates in the paroccipital process, which itself bears a dorsally flattened supratemporal facet (Fig. 14A, B). The paroccipital process is extremely short and robust, as also described by Maisch (2002) for a juvenile specimen of Temnodontosaurus cf. trigonodon.

The surface of the approximately triangular supratemporal facet has a fine pitted-grooved texture. On the dorsolateral edge of the facet, there is a small centrally located protruding ledge. Laterally, the opisthotic appears distinctly flattened, with its ventral edge interrupted by a prominent notch, which extends ventrally almost to the impression of the membranous labyrinth. This is the groove for the glossopharyngeal nerve (Appleby 1961; Maisch 2002). In anterior view (Fig. 14C), a strong bone wall forms the lateral and ventral walls of the impression of the membranous labyrinth, tapering dorsally and ventrally to a tip. The impression of the membranous labyrinth is deeply concave (approximately 1.5 cm from the edge of the medial wall) with a smooth, fine-pored surface (Fig. 14C).

Prootic. The presumed right prootic is poorly preserved, with severe erosion at its margins (Fig. 15). Anteriorly it exhibits a convex shape, while posteriorly, the pear-shaped impression of the membranous labyrinth is visible. Overall, the fragment appears somewhat bowl-shaped.

Parabasisphenoid. The basisphenoid is excellently preserved and, in ventral view, partially articulated in the skull slab. Viewed ventrally, the basisphenoid (length: 9.5 cm, width: 12 cm) presents as a broadly rectangular, ventrally flattened bone with rounded posterolateral margins (Fig. 16A).

The anterior margin of the basisphenoid is distinguished by well-developed basipterygoid processes that extend anterolaterally. Medially, two significantly smaller processes are present on either side of the base of the cultriform process, the projecting impressions of the trabecular cartilages (see McGowan 1973; Moon and Kirton 2016). The surface between the tips of the basipterygoid process and the projecting impressions of the trabecular cartilages on either side is concave.

The right facet for the pterygoid and the pterygoid are present nearly articulated, while on the left side, the pterygoid facet is exposed and well-visible. The pterygoid facets each occupy about one third of the area of the basisphenoid. Their medial borders extend in a straight line from the basipterygoid process anteriorly to the middle of the slightly curved posterior margin of the basisphenoid, where the facets almost meet (distance < 2 cm).

Centrally located in the basisphenoid is the broad-oval internal carotid foramen, with an internal diameter of 12 mm (Fig. 16B). It is a single opening that is funnel-shaped and bordered by smooth bone (Fig. 16B). On the right side of the foramen, there is a pit about 2 cm long and 0.8 cm wide, and 0.2 cm deep, which is absent on the left side. It runs parallel to the long axis of the overlying parasphenoid and does not run toward the internal carotid foramen.

In the centre of the parabasisphenoid, in front of the internal carotid foramen, is the basal plate of the parasphenoid, which has a trident shape with a shortened middle tip. The lateral sutures with the basisphenoid run parallel to the edges of the pterygoid facets.

On the ridge of the sagittal part of the basal plate, there is a groove approximately 40 mm long and up to 3 mm wide, which terminates at the transition to the cultriform process. A posterior part of the parasphenoid, which would divide the internal carotid foramen into two foraminae, as described for Temnodontosaurus in Maisch and Matzke (2000) and for Temnodontosaurus cf. trigonodon by Maisch (2002, MB.R.2878.3, fig. 1A), is not present (Fig. 16B).

The cultriform process is abruptly sheared off at the anterior margin of the basisphenoid during embedding and compaction. After 23 cm the cultriform process is fractured. It measures 45 cm in length, reaching approximately 8 cm anterior to the midpoint of the internal nares; the tip at the anterior end is broken off. The cross-section of the cultriform process is triangular, possibly V-shaped, in the posterior region. Anteriorly it appears increasingly laterally flattened, appearing L-shaped (with the open side pointing to the left) toward the tip. Overall, the impression is that the cultriform process is asymmetrically formed, particularly in its anterior section.

The characteristic features of the parabasisphenoid relevant to taxonomy were developed by Maisch and Matzke (1997, 2000), Maxwell (2010), and Fischer et al. (2011b). Some of these characters are utilized in Suppl. material 1: table SS1 to compare the parabasisphenoid of UMO BT011237.00 with those of other Temnodontosaurus specimens.

Extended basipterygoid processes similar to UMO BT 011237.00 have been documented in Temnodontosaurus platyodon (Fig. 17A; Godefroit 1993). Temnodontosaurus cf. trigonodon (Fig. 17E) exhibits markedly convex processes, as described by Maisch (2002). Comparable morphology is observed in parabasisphenoid of Temnodontosaurus sp. (Fig. 17G).

Projecting impressions of trabecular cartilages are recognizable in the here compared specimen of Temnodontosaurus zetlandicus (Fig. 17B), Temnodontosaurus trigonodon (Fig. 17F) and in UMO BT 011237.00 (Fig. 17H).

Unlike in UMO BT 011237.00 (Fig. 17H), in Temnodontosaurus platyodon (Fig. 17A), Temnodontosaurus trigonodon (Fig. 17C) and Temnodontosaurus sp. (Fig. 17G), the posterior margin of the basisphenoid is more or less deeply notched.

The medial margins of the pterygoid facets are straight in Temnodontosaurus zetlandicus similar to UMO BT 011237.00 (Fig. 17B, H). They are curved in Temnodontosaurus trigonodon (Fig. 17 D, F) and tentatively in Temnodontosaurus cf. trigonodon (Fig. 17E).

Unlike UMO BT 011237.00 all compared specimens exhibit paired internal carotid foramina. The shape of the basal plate of the parasphenoid varies from extended in UMO BT 011237.00, Temnodontosaurus trigonodon and Temnodontosaurus sp. (Figs 17C, 17G, 17H) to narrow in Temnodontosaurus cf. trigonodon (Fig. 17E) and tentatively Temnodontosaurus zetlandicus (Fig. 17B). The sagittal posterior parasphenoid is constricted around the internal carotid foramen in Temnodontosaurus platyodon and Temnodontosaurus trigonodon (Figs 17A, 17C, 17D, 17F). In some specimens of Temnodontosaurus trigonodon (Fig. 17D, F) and in the juvenile specimen Temnodontosaurus cf. trigonodon (Fig. 17E) it extends to the posterior margin of the basisphenoid. However, in Temnodontosaurus platyodon (Fig. 17A), Temnodontosaurus trigonodon (Fig. 17C) and Temnodontosaurus sp. (Fig. 17G), it does not reach this margin. In the described specimen (Fig. 17H), it terminates anterior to the internal carotid foramen; only a small projection of the parasphenoid extends posteriorly (Fig. 16B).

Orbit and scleral plates. A total of 20 partially fragmentary scleral plates are preserved, four of which are located within the skull slab. Two fragments exhibit an articulation of two scleral elements each, while a third scleral plate remains attached in a dislocated position in one of the pieces. Additionally, twelve isolated scleral plates were recovered from the surrounding sediment.

The elements to be described all belong to the corneal area of the scleral ring (sensu Moon and Kirton 2016). This means that the orbital areas of the plates have broken off. This breakage of the plates at this point has two causes: a) the small thickness of the corneal plates at their edge of the orbital area (less than 2 mm), b) the curvature of the plates at this point.

The shape of the plates is variable: most of them, when viewed externally, resemble a tall trapezium (with an approximate base-to-height ratio of 4:7), where the base side forms the transition to the orbital part of the scleral ring, while the parallel opposite narrow side forms the inner margin. However, there are also plates that are much narrower or wider. There are also plates that do not reach the inner margin (Fig. 19C).

In longitudinal section, the scleral plates have a slightly convex shape externally, extending over the entire bone; internally, the surface is initially convex, becoming concave (s-shaped) toward the orbital area (Fig. 19A). The scleral plates reach their thickest point (10–12 mm) about 2.5 cm from the inner margin. They become thinnest at the transitions between the corneal and orbital areas of each plate, where the bone measures less than 2 mm in thickness and bends medially. The bone structure inside the plates is spongy in the central, thicker area and exhibits a cortex on both the external and internal surfaces.

The articulation with the neighbouring plates is highly plastic (Romer 1956; Kirton 1983; Moon and Kirton 2016): the plates connect via a type of tongue and groove system. There are three types of plates: overlapping on both sides, overlapping on the right side only, overlapping on the left side only. It necessarily follows that that a fourth type, with plates overlapped on both sides, must also exist.

On the external surface (Figs 18, 19A), a progressively finer system of grooves radiates from a central point at the transition zone between the corneal and orbital areas, extending to both the edges and the inner margin of each plate. At the inner margin, the fine channels terminate in a comb-like grooved, sharp edge. The inner margin itself appears finely toothed. Additionally, there are a few significantly wider and deeper channels per plate in the same radiating direction, but these do not reach the inner margin.

The internal surface (Fig. 19B) is notably smoother and, on the portion of the bone near the corneal/orbital transition, partially covered by several thin bone laminae. Where the laminae are absent, the radiating structure described above, originating from a centre, is also visible, but less pronounced. On the side facing the inner margin, a finely branched system of grooves is also evident. In contrast to the side directed toward the orbital area, the groove system here branches more distinctly and forms a tiny polygonal pattern toward the edge of the inner margin.

Mandible. The specimen was embedded ventrally, prepared from the ventral side, and is viewed ventrally in the following description. The osteological remains of the mandible include the paired dentary, surangular, angular, and splenial, as well as an isolated articular (Fig. 20).

Both mandibular rami are tilted slightly outward in situ, so the mandible still appears connected at the symphysis, but the dental grooves point slightly outward. The long gently curving mandibular bones are clearly demarcated from each other. Compared to most Temnodontosaurus trigonodon and Temnodontosaurus platyodon specimens, which exhibit a wide range of skull morphologies (with some, such as the holotype PKB 1, having relatively more robust proportions; Bennion et al. 2023), the mandible of UMO BT 011237.00 appears relatively delicate and narrow anteriorly. The length of the lower jaw is 149 cm on the left and 147 cm on the right. The length of the mandibular symphysis is 65 cm.

The left mandible exhibits a relatively clean fracture 79 cm from the tip of the snout. The absence of callus formation and the in situ position of all left jaw bones suggest that the fracture occurred shortly before or after death. However, the encrustation by stromatolites on the bones and their fracture surfaces, which were removed during preparation, indicate that the break did not result from tectonic stress or improper salvage but occurred before the animal was embedded. Therefore, the break must have occurred shortly before or after death and embedding.

Dentary. The dentaries form the tip of the snout in the lower jaw and externally enclose the splenials, angulars, and surangulars in a half-shell. The dentaries extend about two thirds of the lower jaw length. The right dentary is broken off, 100 cm, the left one 79 cm from the snout tip. The original length of the dentaries may have been about 111 cm (reconstructed based on corresponding structures on the surangular). At their posterior ends, the dentaries cover the surangulars as narrow, cross-sectionally sickle-shaped sheets of bone.

On the lateral surface, the dentary fossa extends as a groove a few millimeters wide and deep reaching to the tip of the snout. It begins about 80 cm posterior to the tip of the dentary. From the dentary fossa, further groove-like depressions of the neurovascular groove system split off, branching several times towards the tip (Fig. 21).

50 cm before the tip of the dentary, the dentary fossa disappears and appears only in the form of narrow, elongated openings, from which the furrows described above branch off (Fig. 21). The distances between the openings become shorter and shorter toward the tip of the dentary. Similarly, in Temnodontosaurus platyodon (Godefroit 1993), the external surface of the dentary is densely perforated by numerous foramina on its anterior portion.

Connections exist between the dentary fossa and the intraosseous canal running inside the dentary as observed in the cross-section of the rostrum of Temnodontosaurus sp. (UMO BT011238.00) (Fig. 22). These connections are also described by Serafini et al. (2022) for both the premaxilla and the dentary for a platypterygiid ichthyosaur and supported by CT scans by Lomax et al. (2019) for Protoichthyosaurus prostaxalis.

Splenial. The splenials are articulated and can therefore only be described in ventral view: they become visible about 23 cm posterior to the tip of the mandible and extend posteriorly to a point approximately 29 cm anterior to the posterior end of the left angular; the right angular is pathologically altered (Pardo-Pérez et al. 2018) and therefore not suitable for measurement (Fig. 20). A gaping area at the posterior end of the symphysis reveals an 8 cm wide and 1.5 cm high rugose area on the medial surface of the splenials (Fig. 23A1), which forms the close interlocking symphyseal contact. In this region the splenials appear ventrally thickened and protruding (Fig. 23D) similar to the Cretaceous Pervushovisaurus spp. (Fischer 2016).

Further posteriorly, the splenials form the medial wall of the mandibular rami. Laterally, the splenials contact the dentary anteriorly and the angular posteriorly. The posterior end of the splenial tapers to a point; anteriorly the splenial bifurcates into a dorsal and a ventral process, with the ventral one being considerably longer. This is evidenced by two fragments, broken off before or during embedding, found in isolation, representing the dorsal processes of the splenials. Each fragment exhibits a dorsomedial region approximately 6 cm in length and 1 cm in width, characterized by a rugose surface texture. This feature suggests direct dorsal contact or, at the very least, a connection via connective tissue at the posterior end of the mandibular symphysis (Fig. 23B, C). The ventrally oriented parts remain articulated with the mandible (Fig. 23A).

The splenials form the posterior portion of the mandibular symphysis (Fig. 20), with the total symphyseal length measuring 65 cm and the splenial contributing 42 cm. Fig. 24 and Table 2 compare the proportion of splenial involvement in the symphysis across various Temnodontosaurus trigonodon specimens and UMO BT 011237.00. In UMO BT 011237.00, the splenial contributes 65%. Among the five compared specimens, this proportion ranges from 62% to 74% (Table 2, Fig. 26), contrasting with the broader range of 10% to 91% reported by Bennion et al. (2023).

Angular, prearticular. The angulars are articulated medially with the splenials and dorsolaterally with the surangulars (Fig. 25A, B, C). The right angular ends laterally 8 cm anterior to the posterior end of the surangular in a club-shaped growth with callus formation (Fig. 25B, C), in the centre of which there is a funnel-shaped deep opening running posteriorly (Fig. 25B), a pathology interpreted by Pardo-Pérez et al. (2018) as the result from an abscess of a post-traumatic infection. Medially, the dorsal, spoon-shaped prearticular protrudes by 6 cm (Fig. 25B, C). 13 cm anterior to its posterior end, the angular exhibits a dome-shaped bulge, described by Pardo-Pérez et al. (2018) as a reactive bone crest.

Surangular. The surangulars are articulated ventrolaterally with the angulars (Fig. 25A–C) and anteriorly with the dentaries (Fig. 24). Both surangulars are visible over a length of approximately 70 cm and are anteriorly overlapped by the dentary (visible only on the right surangular, as the left dentary is broken), forming the dorsal margin of the posterior mandible (Fig. 20).

13 cm from the posterior end, the surangular is partially overlapped ventrally by the angular. Anteriorly, this flat connection changes and the surangular bears a recessed facet for the angular (Fig. 25A). From half of their visible length, the surangulars are increasingly enclosed laterally and dorsally by the dentaries.

At the posterior end of the left surangular, there is a prominent ridge about 6 cm long running horizontally (Fig. 25A), the muscle insertion point of the depressor mandibulae muscle (McGowan 1973). A rugose surface about 4 cm wide and 3 cm high above this ridge also indicates an insertion of the depressor mandibulae muscle (McGowan 1973; Kear 2005). In the further anterior course, there is first a small and then a larger foramen at about the same height, from which the surangular fossa arises (Fig. 25A). The surangular fossa (Fig. 25A) starts out clearly deepened and steep-walled, flattening out anteriorly and disappearing after 20 cm. A connection to the dentary fossa is not visible. Overall, the surangular has a rather smooth bone surface. In the dorsal area, the bone is broken off horizontally.

Articular. The presumed right articular is poorly preserved and was recovered isolated in the area of the right mandibular joint; the left articular is missing. The poor state of preservation does not allow an exact delimitation of the articulation facets.

The articular, originally likely oval, has its greatest thickness anteriorly near the glenoid facet and is generally convex on the medial surface and weakly concave on the lateral surface, similar to the articular of Temnodontosaurus platyodon, which is also oval in shape and exhibits a slightly concave lateral surface (Godefroit 1993). The medial surface (Fig. 25D, E) is partially heavily eroded, with some bone surface remaining only in a slightly concave central area. A facet for the prearticular (McGowan 1973) is tentatively identifiable. The glenoid facet (Fig. 25D) is also heavily eroded, with only a tiny area of original bone surface visible.

The lateral view (Fig. 25E) reveals the articular surface for the surangular. Here the bone surface is better preserved and shows a rugose surface, with a protrusive bulge in the centre. In the anterior region, the articular is eroded.

Hyoids. Viewed ventrally, the paired hyoids lie on the pterygoids, with the right one complete and the left one missing its posterior end. (Fig. 26A). The anterior ends are flattened, broadened and concave (Fig. 26C). In contrast, the posterior ends are more round-oval. The left hyoid, which is broken off, shows a tubular shape (Fig. 26B). Both hyoids, especially the left one, are collapsed in the central region. This indicates that the bones were hollow, at least in the middle. However, it cannot be determined whether the hyoids were completely hollow or if the pronounced collapsed appearance is caused by compression of the bony trabeculae.

Dentition. A total of 101 teeth are preserved, 21 of which are still in their original position in the right dentary. 80 teeth were recovered in isolation from the sediment surrounding the fossil. Assuming about 100 teeth in the upper jaw and 80 teeth in the lower jaw (Temnodontosaurus trigonodon, UMO BT 011233.00), more than half of all teeth of the examined specimen are present.

The tooth crowns, coated with an extremely thin enamel layer, are approximately round in cross section. Between the end of the enamel coating on the crown and the cementum coating on the root is a narrow and relatively smooth zone, the collar zone, which is part of the root (Maxwell et al. 2012a) (Fig. 27A). In this zone, the dentine is smooth and unfolded, and an extremely thin, smooth layer of cementum (Maxwell et al. 2012a) can be found. Within the crown and the collar zone, some teeth exhibit one to several shallow circumferential constrictions and bulges (Fig. 27A). These have been interpreted as pathologies of uncertain origin elsewhere in the literature (see Lomax et al. 2025; Maxwell et al. 2022).

The teeth exhibit more or less distinct lingual curvature (Fig. 27A, F). The root of the tooth is notably thickened and longitudinally grooved from halfway down the tooth, tapering again toward the slightly flattened basal end. The roots exhibit a cross-section that ranges from round to rounded rectangular (Fig. 27A). The enamel has a thickness of 0.1–0.2 mm, based on a crown diameter of 5 mm. The slightly ridged appearing surface of the enamel consists of irregular longitudinal, sometimes tapering more or less rounded wavy ridgelets (Bennion et al. 2023) (Fig. 27B), subordinate ridges can also be observed.

The teeth are usually weakly bicarinate, but tricarinate teeth are also present. In a replacement tooth, the finely granulated to serrated carina, which is described for Temnodontosaurus trigonodon by Bennion et al. (2023) is clearly visible (Fig. 27C, D). According to Bennion et al. (2023), these are false denticles formed by ridgelets interacting with the carinal keel, resulting in a jagged, uneven outline of the carina (Bennion et al. 2023). The tip of the cutting edge consists of a finely grained apical carina, which extends to the tip of the tooth (Fig. 27D).

Overall, the teeth can be assigned to morphotypes D (discontinuous ridgelets, false denticles, jagged uneven carina) and E (slight lingual curvature, more or less continuous ridges towards the apex) based on Bennion et al. (2023), as are most of the Temnodontosaurus trigonodon specimens. However, transitions between the two morphotypes are also observed, leading us to suggest that morphotypes D and E may represent parts of a continuum, as Bennion et al. (2023) acknowledged.

All teeth except for three apparently not-yet functional very small replacement teeth exhibit smooth convex wear at the tips, some wear facets show concentrically arranged, differently coloured rings (Fig. 27A, E). The smooth, polished abrasions are so extensive that a third of the crown is missing on some teeth. Lateral wear facets of the teeth due to occlusion, as well as chipped or broken teeth, are also observed (Fig. 27F).

Tooth replacement: The root becomes progressively encased in an increasingly thick layer of cementum as the tooth ages (Fig. 28: 5–9). Then the cementum progressively covers both the apical foramen (Fig. 27A) and the sides of the root. The cementum fills the longitudinal furrows of the folded dentin, even reversing the relief by forming shallow ridges above the furrows (Fig. 27G). According to Maxwell et al. (2012a), this is fibrous cellular cementum, with the fibrous layers being the thickest and the fibers concentrated in the gaps formed by the folded dentin. Directly beneath the collar zone, a noticeable thickening of cementum is visible, especially in older teeth with resorption pits resulting in an almost rectangular cross-section of the root (Fig. 27A, 30, tooth 12–17). This condition has also been documented among members of the Platypterygiidae (Maxwell and Caldwell 2006; Fischer 2012; Fischer et al. 2012; Fischer et al. 2014; Fischer 2016; Maxwell 2012a; Serafini et al. 2022). The accumulation of external cellular cementum is likewise observed in Early Jurassic genera such as Temnodontosaurus (Fraas 1891; Maxwell 2012a; this study).

Thirty-eight teeth show clear signs of various stages of resorption, evidenced by basal, lingually oriented resorption pits, ranging from minimal extension to almost complete dissolution of the tooth root (Fig. 28: 10–17). This phenomenon was already described by Fraas (1891: 20–22). Resorption is also observed in seemingly healthy and minimally worn teeth.

Vertebral column. Atlas-axis complex, vertebrae, ribs, and their articulation. 21 presacral centra are present, which are highly disarticulated, especially in the pectoral girdle region (Fig. 29A).

The atlas and axis are recognizable as individual bones but are co-ossified, as described for adult specimens of Temnodontosaurus (Fraas 1913; Maisch and Matzke 2000; Martin et al. 2012) and regarded as a synapomorphy of Neoichthyosauria (Maisch and Matzke 2000). The third cervical centrum lies nearly in its original position and is only slightly tilted (Fig. 29B1).

The atlas, being the longest vertebral centrum, exhibits a slightly concave anterior surface, which, in the living animal, formed the articulation between the skull and the vertebral column via the convex occipital condyle of the basioccipital. Ventrally, the facets for the atlantal and the axial intercentra are visible (Fig. 29B1). The facet for the atlantal intercentrum shows a structure of sharp ridges and intervening grooves (width of grooves 2–3 mm) reminiscent of the karst phenomenon Karren (Fig. 29B1). Similar structures are also found laterally on the atlas-axis complex, on the dorsal side of the intercentrum, and on the facet for the neural arch of the presumed fourth cervical centrum adjacent to the atlas-axis complex. However, the surfaces of these structures are smooth and not porous, as would be expected for weathering features. Presumably, this relief serves as an attachment site for the cartilage connection between the bones.

Additionally, there are two distinct vertical deep notches in the facet for the atlantal intercentrum, the origin of which remains unknown. Laterally, parapophyses are visible in the atlas-axis complex and in the third cervical centrum, as well as a weakly developed diapophysis in the atlas-axis complex (Fig. 29B1). The facet for the axial intercentrum is divided into two depressions by the suture between atlas and axis, with a deeper depression on the atlas and a shallower depression on the axis. An intercentrum, presumably the atlantal intercentrum, is preserved in isolation (Fig. 29C). The neural arch of the atlas has a flattened flank with no discernible neural spine (Fig. 29B1, B2). The right and left halves of the atlantal neural arch are fused, in contrast to their separation observed in Stenopterygius, the juvenile Temnodontosaurus cf. trigonodon specimen MB.R. 2878.3 (Maxwell, pers. comm., 2024), Ichthyosaurus communis (McGowan 1974), Hauffiopteryx altera (Maxwell and Cortés 2020), Argovisaurus martafernandezi (Miedema et al. 2024) and Ophthalmosaurus icenicus (Moon and Kirton 2016).

The second and third neural arches have distinct paired pre- and postzygapophyses; therefore, the atlantal neural arch also has paired postzygapophyses (Fig. 29B). All cervical and dorsal neural arches of this specimen are robustly built and possess short, strong neural spines that are pointed oval in cross section. At least the pre- and postzygapophyses of the first five neural arches are clearly paired, contrary to the thesis in Maisch and Matzke (2000) that in all post-Triassic ichthyosaurs, including Temnodontosaurus, the zygapophyses of the entire vertebral column are simple, unpaired structures.

Nine other neural arches from the thoracic region exhibit unpaired zygapophyses. Two neural arches illustrate the transition from paired to unpaired zygapophyses: In these neural arches (Fig. 30B), the zygapophyses are still clearly separated by a fine gap. The neural spines are inclined posteriorly, with the surfaces of the pre- and postzygapophyses oriented at the same angle (Fig. 30D). In Temnodontosaurus azerguensis the post-zygapophyses are paired in all cervical neural arches (Martin et al. 2012).

On the trunk slab, 17 additional presacral centra are present with 14 of them nearly articulated, while three vertebral centra cannot be precisely assigned. The apophyses for the articulation of the ribs are clearly convex, visible in 14 presacral centra, with the diapophyses located laterally on the centra (approximately in the centre between the anterior and posterior margins of the centrum). The parapophyses are positioned close to the anterior margin of the vertebral centra (Fig. 30A).

Sixty-six postflexural centra, lacking caudal rib facets (Fig. 31), were isolated approximately 5 m away from the partial skeleton in the sediment. The centra are highly oval in anterior and posterior view and exhibit four weakly pronounced processes ventrally, likely ligamentous attachement points, located at the posterior and anterior margins (Fig. 31B). Of these, two diagonally opposite processes are more pronounced, while the other two are less developed. Some of the articular surfaces of the postflexural vertebrae have a wrinkled bone texture (Fig. 31C).

There are numerous dorsal ribs on the trunk slab, which were all broken into several pieces before sedimentation. Broken rib fragments were also found in the sediment. The rib fragments are weathered or have been attacked by scavengers at least at one end.

In cross section, the ribs are oval to kidney-shaped. Cross-sections in the shape of an “8” also sometimes occur, but this impression could be enhanced by collapse of the medullary bone tissue. The rib heads are unicipital, but show two articulation facets connected with each other (Fig. 32) as generally in the non-thunnosaurian neoichthyosaurians Temnodontosaurus, Leptonectes, Eurhinosaurus and Suevoleviathan (Maisch and Matzke 2000). The two facets meet at an obtuse angle.

The fact that the two apophyses of the vertebral centrum are not vertically aligned, but rather the parapophysis is shifted to the anterior margin (Fig. 30A, Fig. 32B, C, D), results in the rib head being inclined. Due to the slightly posterior orientation of the facets of the rib head, the rib initially points posteriorly in its proximal region (Fig. 32B, C).

The rib is slightly anteriorly concave in the proximal region (Fig. 32B, C, E1,3). The concavity disappears and reappears on the posterior surface of the rib Fig. 32B, C, D, E2,3). Distally there is a torsion of the rib by 30° in a clockwise direction towards anterior (Fig. 32E3). Due to this torsion and the curvature of the rib, after a few centimeters the rib points increasingly downwards and the concave side posteriorly.

There are three pathologically altered ribs with rib heads: one on the trunk slab, two isolated. According to Pardo-Pérez et al. (2018), these broken ribs, located a few centimeters from the rib head, show a rugose, widened hollow shape that has formed a callus at the distal end of the broken bone indicating the presence of a pseudoarthrosis. The same phenomenon is described by Huene (1931b) for Temnodontosaurus nuertingensis and for Temnodontosaurus trigonodon (Huene 1930).

Pectoral girdle. Clavicle. The two clavicles are located on the trunk slab. They have the shape of a slightly twisted boomerang bent lengthwise. The right clavicle is 37 cm, the left 31 cm long, with the medial end obscured and the distal end not preserved (Fig. 33A).

In cross-section, the clavicles are L-shaped in the middle third, and the distal and medial ends are flattened. The two medial ends of the clavicles are longitudinally furrowed in ventral view. The medial end of the right clavicle is curved toward the middle of the body for the last 4 cm.

Starting from the medial end, both clavicles taper as they extend laterally and form posterior bulges. Dorsally, a narrow ridge bifurcates, replacing the posterior bulge along its course (Fig. 33C, D). Shortly after the bifurcation, the two branches enclose a drop-shaped, deep pit approximately 2.5 cm in length, which is tentatively identified as a facet for the proximal anterior end of the scapula (Maxwell, pers. comm., 2024; see also Swaby and Lomax 2020 for Temnodontosaurus trigonodon, fig. 6B). At the distal end, another facet for the scapula is visible (Fig. 33C, D).

Approximately 14 cm from the medial end of the left clavicle, there are fine grooves on the posterior bulge extending over a length of 12 cm. These grooves run almost perpendicular to the bulge and appear to radiate from a point located approximately 14 cm posteriorly. Further, less pronounced grooves run at the distal end at an angle of approximately 30° to the other grooves. In the area of these grooves, the bone surface is altered (Fig. 33B): instead of the otherwise longitudinal bone structure, the surface is ornamented with fine waves. While the surface between the grooves has a fine relief, it is smoothly polished in the grooves, but the waved structure of the layer can still be recognized. Parallel to the grooves, wall-like structures are visible, which are only fractions of a millimeter wide. The grooved structures could indicate a connection of the bone with attached ligaments (Hildebrand and Goslov 2003).

The shape of the right clavicle corresponds to that of the left, although it is wider and flatter in the central area. It also has weakly pronounced groove structures. An interclavicle is not preserved.

Coracoid. The coracoids are embedded on the trunk slab in an almost natural position. They are two flat, massive bone plates (left coracoid: width: 16 cm, length: 18 cm) with rounded corners (Fig. 34).

Left coracoid: Parallel to the medial and lateral margins, the coracoid is broadly saddle-shaped. The anteromedial process (Fischer et al. 2011b) is covered by two vertebral centra. The anterior notch (McGowan and Motani 2003) is relatively broad, beginning at about the midpoint of the anterior margin of the coracoid and extending in the shape of a flat arc to the facet for the scapula. The glenoid contribution and the intercoracoid facet are approximately equal in length. The intercoracoid facets (McGowan and Motani 2003) are straight, similar to those of Temnodontosaurus nuertingensis (Huene 1931b) and Temnodontosaurus platyodon (Huene 1922). Compared to the holotype of Temnodontosaurus trigonodon (PB1) (Theodori 1854, pl. II), the posterior margin of the coracoid is more rounded. Unlike in UMO BT 011237.00, the length of the glenoid contribution in the holotype is shorter than the intercoracoid facet.

The right coracoid is severely pathologically altered: according to Pardo-Pérez et al. (2018), these bone modifications were caused by trauma and subsequent infection. The right coracoid is inflated in its central area to a thickness of approximately 11 cm (left coracoid: approximately 2 cm). The structure of the bone surface, especially in the marginal area to the glenoid contribution, is porous to honeycombed. The anterior notch is still recognizable but is clearly reduced in size compared to the left one.

Scapula. The right scapula (length: 21 cm) is located on the trunk slab (Fig. 33) and, like the coracoid and humerus, exhibits a pathologically altered bone structure in the region of the glenoid contribution. A few centimeters in front of the glenoid contribution, the bone appears inflated. Here, the bone structure is also honeycombed. The pathologies in the right pectoral girdle of the described specimen are, according to Pardo-Pérez et al. (2018), most likely the result of an infection that developed following trauma. The distal portion of the scapula shows no apparent pathological alterations and exhibits a flat morphology. With respect to its original position, the scapula is tilted approximately 45° anteriorly, and we are now looking at the more curved posterior edge and the glenoid contribution. The lateral end of the right scapula is broken off.

The ratio of scapula length to humerus length is ~1.33 when comparing the right scapula to the right humerus, and ~1.23 when comparing the right scapula to the left humerus. For comparison, the ratio in Temnodontosaurus crassimanus is ~0.68 (Swaby and Lomax 2020). Because the right humerus is pathologically altered while the left humerus appears unaffected, the latter value (~1.23) may better approximate the original anatomical proportions.

Forefin. The bones of the left forefin were removed using the stroke of a single excavator bucket and could therefore only be recovered from the excavated material. The arrangement of the carpal, metacarpal, and phalangeal bones is therefore at least partially uncertain. The bone elements of the right forefin could be recovered from the sediment, but they were disarticulated, so their exact arrangement remains uncertain. It is certain, however, that the right forefin is less complete than the left one.

In general, the arrangement of the carpal, metacarpal, and phalangeal bones (Fig. 35A) is based on the articulation of the forefin in SMNS 50000 (Swaby and Lomax 2020, fig. 7C), but the arrangement of the radius, ulna, radiale, intermedium, and ulnare can be considered certain. The bone elements of the right forefin are overall dorsoventral thicker than those of the left fin. This could be due to different compaction, but also to pathology in the right pectoral girdle.

Humerus. Left humerus: The humerus, a massive and compact bone, has a constricted shaft in dorsal and ventral views (Fig. 36A, B, D). The proximal end is club-shaped and thickened but proximally flattened. The proximal dorsal region is not preserved. The flattened proximal end shows a coarse pitted surface indicating a strong layer of cartilage in the glenohumeral joint. The deltopectoral crest is indicated in the ventral view at the narrowest part of the bone, but since the proximal part is not preserved and has been supplemented, no statement can be made about its extent. Although the left humerus is incompletely preserved, the measurements refer only to the original bone; even so, the distal end (13.4 cm) is clearly broader than the proximal end (9.3 cm).

On the anterior surface, a laterally and distally sharply defined tongue-shaped surface (width: 1.7–1.8 cm, length: 4.5–5 cm) with a smooth, flattened texture extends from the middle of the shaft distally. The edge facing the dorsal side is significantly higher than the one facing the ventral side and forms a sharp ridge. (Fig. 36C). A similar morphology is observable on the right humerus of Temnodontosaurus sp. UMO BT011239.00 (Fig. 36F) and on the left humerus of Temnodontosaurus trigonodon specimen SMNS 50000 (Swaby and Lomax 2020, fig. 8B; McGowan and Motani 2003, pl. 6) and MHH 'B08'.

The facets for radius and ulna are located on the distal humerus (Fig. 36E). Viewed ventrally (and also dorsally), they form an angle of about 136° (Fig. 38A). Both facets are bounded by a distinctly offset rim surrounding the slightly concave, pitted-rough inner region of the facets (Fig. 36E). The facet for the ulna is slightly deflected proximally on its posterior side.

The surface of the radial facet forms a narrow ridge in the horizontal plane of the humerus. This ridge is also found on the radius and ulna, as well as on almost all major carpal, metacarpal, and phalangeal elements. This may represent a compression artifact, supported by the findings of Maxwell et al. (2014), which document the collapse of internal trabecular structures in a tibia of Stenopterygius cf. uniter and in a metacarpal II of Temnodontosaurus trigonodon (SMNS 50329) under dorsoventral compaction (Maxwell et al. 2014, fig. 2C).

In ventral view (Fig. 36B), an oval, funnel-shaped pit (width: 2 cm, length: 4 cm) is noticeable in the centre of the humeral shaft. The fact that the bone’s surface texture becomes coarser and rougher at the edges of the pit indicates that the pit could not have formed post-mortem. In addition, the same pit is also present in the right humerus, although there it is more cavernous due to pathological alterations. A similar pit is observable in specimen SMNS 50000, left humerus (McGowan and Motani 2003, pl. 6) and SMNS 50004. Starting from the pit, a trough runs to the distal edge of the humerus, which tapers to a groove at the distal end between the facets for radius and ulna (Fig. 36D) (see also Theodori 1854; Huene 1931b). The groove clearly separates the two facets on the distal side as it continues, but it is lost after a few cm on the convex dorsal side of the bone.

Right humerus: The right humerus is significantly broadened compared to the left (see Table 3, Fig. 36A). This is most obvious at the proximal end and along the shaft. The pathologically induced rugose texture (Pardo-Pérez et al. 2018) is most evident along the shaft. The weakly concave radial facet is deflected proximally on its anterior side at an angle of approximately 75°. The distal end of the right humerus (15.5 cm) is distinctly broader than the proximal end (12.2 cm; Fig. 36A).

The morphology differs from the humeral morphology of Temnodontosaurus azerguensis, in which the humerus is more elongated. The length-to-midshaft width ratio of 2.87 (Martin et al. 2012) differs significantly from the ratio of 2.2 observed in the non-pathological humerus of the described specimen (Table 3).

Radius and ulna. Left forefin: The broadly oval radius is slightly concave both dorsally and ventrally. The bone is thickened proximally and distally, reaching nearly the thickness of the radial facet of the humerus proximally. In anterior, posterior, proximal and distal view, the radius appears wrinkled and pitted (indicating cartilage attachment), with a more or less horizontal ridge in proximal and distal view, corresponding with the ridge of the radial facet of the humerus, perhaps a compression artifact (Maxwell 2024, pers. com.). The anterior leading edge is relatively flat and without a notch. The proximal posterior margin of the radius bears a narrow groove, which is present ventrally and dorsally (Fig. 36D) as in SMNS 50000 and SMNS 15950 (Swaby 2020, fig. 28C, D).

The left ulna is much smaller in relation to the radius and appears to be pentagonal. The dorsal and ventral surfaces are shallowly concave, as a result of compression artifacts caused by trabecular collapse in the more spongy centre of the bone (Maxwell 2025; pers. com.). Distally and proximally, the ulna is thickened and flattens toward the posterior edge. The proximal and distal surfaces, especially the proximal surface that articulates with the humerus, display a wrinkled, pitted texture, with a pronounced horizontally running ridge, similar to the radius. On the anterior margin, there is a 6 mm deep notch proximally (Fig. 36D). Together with the posterior radial groove, a very small foramen interosseum is formed. An anterior notch in the ulna was observed in Temnodontosaurus platyodon and Temnodontosaurus trigonodon (McGowan 1996; Swaby 2020)

Right forefin: The radius and ulna are almost in articulation with the humerus on the trunk slab. They correspond in shape and size to those of the left forefin; the ulna appears somewhat inflated proximally, and the anterior notch discussed above is preserved in a rudimentary form.

Carpals, metacarpals, phalanges. The ulnare is smaller than the intermedium, a diagnostic feature of the genus Temnodontosaurus (McGowan and Motani 2003; Swaby and Lomax 2020). The left radiale is not notched, but the presumed right one is. All more distal elements of the leading edges of both forefins are notched. In the most distal elements, the notches nearly close (Fig. 35B1, 2).

Notching along most elements of the leading edge is a diagnostic feature of Temnodontosaurus trigonodon (Maisch 1998a). In contrast, in Temnodontosaurus platyodon, notching is limited to the radius and the first one to three succeeding elements (McGowan and Motani 2003; Weedon and Chapman 2022). Temnodontosaurus crassimanus possesses notching in at least five leading-edge elements (Swaby and Lomax 2020), in Temnodontosaurus azerguensis, only the anterior edges of the radius, radiale, and first carpal are distinctly notched (Martin et al. 2012).

Although the arrangement of the carpal, metacarpal, and phalangeal bones was based on size, shape, and thickness in the third digit (middle row) dcIII, mcIII, and ph1III appear to have narrow indentations at the midpoints of the distal and/or proximal edges (Fig. 35C), as is also evident in Temnodontosaurus trigonodon (SMNS 50000, Swaby and Lomax 2020, fig. 7C and GPIT-PV-30011, Stöhr and Werneburg 2023, pl. 1C). The shape of the fin elements ranges from five- to six-cornered proximally to oval and round distally. The accessory ossicles (Maxwell 2012) are round oval. The proximal fin elements have a strongly wrinkled structure on their articular surfaces, in which a horizontally running, also wrinkled elevation is usually recognizable between the wrinkled dorsal and ventral edges; this may represent a compression artifact (see the description of the humeral facets above).

Gastroliths. During preparation, four rounded pieces of quartz gravel were discovered in the area of the vertebral column. Two are located about 20 cm behind the coracoids in the anterior thoracic region on the trunk slab (Fig. 37A), two became detached during preparation and are now present in isolation (Fig. 37B). The maximum diameter of the gravel varies between 2 and 3.5 cm.

Due to the position and characteristics of the quartz gravel, we assume they are geogastroliths (Wings 2007). According to the classification of Pettijohn (1973), they are to be regarded as rounded and show a few sickle-shaped punch marks (Fig. 37C).