Eurhinosaurus mistelgauensis Spicher, Miedema, Heijne & Klein, 2025, sp. nov.
Year: 2025
Type: other
Abstract: Eurhinosaurus mistelgauensis sp. nov. Etymology. The specific epithet is derived from Mistelgau, the locality in Bavaria where the specimens were discovered. Holotype. UMO BT 011 221.00, an almost complete skeleton (Figs 3, 6). Paratype. UMO BT 011 235.00, an almost complete skeleton (Figs 4, 7). Referred specimens. UMO BT 011 240.00, a partial snout (both premaxillae) with preserved articulated teeth and rib fragments (Fig. 5). Locality. Mistelgau, Bavaria, Germany (Fig. 1). Stratigraphic horizon. Jurensismergel Formation (Upper Toarcian), Haugia variabilis Zone, Vitiosa Subzone (UMO BT 011 235.00), and Jurensismergel Formation (Upper Toarcian), Grammoceras thouarsense Zone and Subzone (UMO BT 011 221.00 and UMO BT 011 240.00) (Fig. 2). Diagnosis. Eurhinosaurus species with the combination of the following autopomorphic characters: basioccipital with the ventral extracondylar area (ECA) greatly extending anteroposteriorly and absence of ventral protrusion so that the extracondylar area is not visible in posterior view (no dorsoventral orientation of the extracondylar area); ventral extracondylar area slightly concave; absence of basioccipital peg; prominent basioccipital condyle forming the entire posterior surface of the basioccipital; markedly thickened and robust ribs that are round in cross-section, lacking a longitudinal groove along the shaft, particularly in the dorsal region. Description. Skull Orbit and sclerotic ring. The internal orbit is partially preserved in UMO BT 011 235.00 (Figs 4, 7). The orbit is approximately 14 centimeters in diameter (Suppl. material 1: table S 1). The orbit is extremely large compared to the size of the skull (Figs 4, 7). The orbit is surrounded by the jugal ventrally, the lacrimal anteriorly, the prefrontal anterodorsally, the postfrontal dorsally, and the postorbital posteriorly (Fig. 7). Some bony material visible in the orbital region can tentatively be attributed to fragments of sclerotic plates (Fig. 7). Premaxilla. The premaxilla is a paired bone preserved in all three specimens (Figs 3, 4, 5, 6, 7; Suppl. material 3: fig. S 2). In UMO BT 011 235.00 and UMO BT 011 221.00, it is heavily damaged and fragmentary (Figs 3, 4, 6, 7). In UMO BT 011 235.00, solely the posterior portions of both premaxillae are preserved. The right premaxilla is articulated and visible in medial view. A small portion of the left premaxilla partially covering the right premaxilla is visible in lateral view and is slightly shifted upwards. In UMO BT 011 221.00, a large portion of the right premaxilla is preserved in medial view. However, the anterior and posterior ends are missing. In the same specimen, a small portion of the left premaxilla is preserved in lateral view. The premaxillae are disarticulated in UMO BT 011 221.00. In UMO BT 011 240.00, the premaxillae, exposed in both lateral (left element) and medial (right element) views, are well-preserved and articulated (Fig. 5). The most visible element, the left premaxilla, measures approximately 63 centimeters as preserved (the posterior portion is broken). (Suppl. material 1: table S 1). The premaxilla is an extremely elongated, straight, and slender bone forming most of the snout (anterior to the narial opening). The posterior portion of the premaxilla is dorsoventrally wide but narrows gradually towards its anterior tip (Figs 3, 5, 6). In UMO BT 011 221.00, the right premaxilla preserved in medial view, shows a medial flange parallel to the lateral wall (corresponding to the ventral margin of the premaxilla) along the entire length of the premaxilla (Fig. 6; Suppl. material 3: fig. S 2). The medial shelf and lateral wall of the premaxilla form a shallow alveolar groove, in which the teeth insert when in articulation. No individual alveoli are observable in the premaxilla. Laterally, the premaxilla carries a longitudinal groove extending over its entire length: the fossa premaxillaris (Fig. 5), like already observed in known Eurhinosaurus specimens (e. g., von Huene 1922, 1928; Maisch 2022). The fossa premaxillaris is discontinuous anteriorly and alternates between external exposure with small open pits and intraosseous pathways (Fig. 5). As mentioned above, premaxillae articulated to the rest of the skull are uniquely preserved in UMO BT 011 235.00, but the posterior portion of the bone is too damaged to identify the exact contact with the maxilla and nasal (Fig. 7). However, the right premaxilla, visible in medial view in specimen UMO BT 011 240.00, preserves a clearly defined facet for the nasal, located on the posterior mediodorsal surface of the bone (Fig. 5). In addition to this posterior mediodorsal contact with the nasal, the premaxilla also articulates posteroventrally with the maxilla (Fig. 7). Both premaxillae contact each other medially along most of their length, as also observed in UMO BT 011 240.00 (Fig. 5). In this specimen, the medial suture accounts for approximately 64 % of the preserved premaxillary length, while the nasal facet comprises the remaining ~ 36 %. However, the posterior-most region of the premaxilla is absent, precluding a complete assessment of the nasal facet’s full extent. Since the anterior margin of the rounded nasal opening is not preserved and the overall nasal region is heavily damaged, the contribution of the premaxilla’s posterior end to the anterior margin of the narial opening is not visible in UMO BT 011 235.00 (Fig. 7). Maxilla. The maxillae are disarticulated in UMO BT 011 221.00 and articulated in UMO BT 011 235.00 (Figs 3, 4, 6, 7; Suppl. material 3: fig. S 2). In UMO BT 011 221.00, the left maxilla is exposed in lateral view, and in UMO BT 011 235.00, the right maxilla is visible in medial view. In UMO BT 011 235.00 specifically, despite being articulated, the maxilla is strongly damaged. In lateral view, the maxilla has an anteroposteriorly elongated outline (Fig. 6). Both posterior and anterior portions of the maxilla narrow towards the respective ends. In UMO BT 011 221.00, on the anterior projection of the maxilla, there is an elongated and deep groove laterally that faces dorsally, into the direction of the suture with the premaxilla (Suppl. material 3: fig. S 2). The limits of the anterior end and dorsal suture of the maxilla are not visible, and the posterior suture is uncertain in UMO BT 011 235.00. Anteriorly and anterodorsally, the maxilla contacts the premaxilla (Fig. 7). In medial view, the posterior extension of the maxilla runs under the lacrimal so that it contacts the latter posterodorsally. Also in medial view, the posterior end of the maxilla contacts the jugal along a short contact (Fig. 7). In UMO BT 011 235.00, due to the heavily damaged region of the narial opening, it is uncertain whether the dorsal portion of the maxilla contributes to the ventral margin of the narial opening in medial view. In the maxilla of UMO BT 011 221.00, the anteroposterior extent of the facets for the premaxilla and the jugal indicates that these do not contact one another. This suggests that the dorsal surface of the maxilla at its midpoint, between the premaxilla and jugal facets, contributed to the ventral margin of the narial opening in lateral view. The alveolar groove of the maxilla is not visible in either specimen and since no teeth are found articulated in the maxilla, it remains unknown how many teeth the maxilla bears. Jugal. The left jugal is completely preserved in medial view in UMO BT 011 235.00 but disarticulated (Figs 4, 7), while the right jugal is preserved in medial view and partially articulated to the skull (Fig. 7). The right jugal is heavily damaged in UMO BT 011 235.00 and its posterior portion is missing. In UMO BT 011 221.00, two fragments of bones are tentatively identified as anteriorly incomplete jugals (Fig. 6; Suppl. material 3: fig. S 3). However, based on its general morphology, the bone fragment identified by us as left jugal may also represent the left postorbital (Fig. 6; Suppl. material 3: fig. S 3). Nevertheless, the fragment cannot be assigned to either element with certainty. The fragment identified as a right jugal is also incomplete posteriorly in UMO BT 011 221.00. In the same specimen, both jugals are preserved in lateral view. The jugal is a long and curved bone that forms the ventral mid-orbital margin when in articulation, extending posterodorsally beyond the orbit (Fig. 7). The anterior ramus of the jugal is thin and tapers towards its anterior process (Fig. 7). The anterior end of the jugal contacts the posterodorsal end of the maxilla anteroventrally and the lacrimal anterodorsally (Fig. 7). Based on the jugal facet of the maxilla of UMO BT 011 221.00, the contact between the jugal and the maxilla was shorter than the one between the maxilla and the premaxilla (Suppl. material 3: fig. S 2). The posterodorsal ramus ends in a broad dorsal facet that articulates with the descending process of the postorbital (Fig. 7). The postorbital facet of the jugal presents numerous thick ridges and grooves on its lateral surface (Fig. 7). In UMO BT 011 221.00, the jugals are more angular than in UMO BT 011 235.00 (Suppl. material 3: fig. S 4). The postorbital facet is also smaller in lateral view, as preserved in UMO BT 011 221.00, than in medial view, as preserved in UMO BT 011 235.00 (Fig. 6; Suppl. material 3: fig. S 3). The overall shape and posterodorsal ridges are very reminiscent of Argovisaurus (Miedema et al. 2024). Lacrimal. Lacrimals are solely preserved in UMO BT 011 235.00 (Figs 4, 7; Suppl. material 3: fig. S 3). The left lacrimal is disarticulated and preserved in lateral view (Fig. 4). The right lacrimal is part of the skull bones that are preserved in articulation and is exposed in medial view (Fig. 7). The lacrimal is thin and has a triangular shape (Suppl. material 3: fig. S 3). The lacrimal forms the anteroventral margin of the orbit (Fig. 7). Its dorsal process contacts the nasal and prefrontal and forms the posteroventral margin
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7083287563
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