Palaeoscyllium formosum Wagner 1857

†Palaeoscyllium formosumWagner, 1857 Figs 1, 2 Holotype. The specimen SNSB-BSPG AS I 1365 (see Fig. 2) from the Upper Jurassic of the Solnhofen Archipelago in southern Germany, preserving only the postcranial skeleton but completely lacking the head (both cranium and dentition are missing). The holotype was originally described by Wagner (1857: 291) and subsequently figured by him (see Wagner 1861: pl. 5, fig. 2; Wagner 1862: pl. 2, fig. 2; see also Fig. 1). Referred specimens. Only the holotype (SNSB-BSPG AS I 1365). Nomenclatural remarks. Wagner (1857: 291) undoubtedly established the type species † Palaeoscyllium formosum in accordance with the requirements reported in the ICZN (1999: art. 12) and, consequently, it must be considered as ‘ available’ (i. e., exist for the purposes of zoological nomenclature; see also Notton et al. 2011). Furthermore, the name-bearing type material of the species (holotype, catalogue number: SNSB-BSPG AS I 1365) provides a set of species-specific characters (see also the Amended diagnosis section, below). This set of unambiguous morphological features represents an “ objective standard of reference ”, making the name both valid and applicable for taxonomic purposes (see ICZN 1999: art. 61; see also Notton et al. 2011). According to the ICZN (1999: art. 42.3, 43, 67), the name-bearing type of a genus (or subgenus) is its nominal taxon, called its “ type species ” (see also ICZN 1999: Glossary), and its application is determined with reference to such nominal species. Therefore, the validity here confirmed for the type species † P. formosum also applies to the genus name † Palaeoscyllium. After the original establishment by Wagner (1857), von der Marck (1863: 67, pl. 8, figs 6–9) erroneously re-introduced the genus † ‘ Palaeoscyllium ’ with a different type species, † ‘ P. ’ decheni (see also Cappetta 2012: 290). However, Marck’s genus name is preoccupied by † Palaeoscyllium Wagner, 1857 (see ICZN 1999: art. 23; see also Cappetta 2012). According to the “ Principle of Homonymy ” (see ICZN 1999: art. 52), the name of each taxon must be unique. † Palaeoscyllium von der Marck, 1863 is thus a junior homonym of † Palaeoscyllium Wagner, 1857 and, although available, must not be used as a valid name for taxonomic purposes (see ICZN 1999: Glossary and “ Principle 5 ” of the Introduction). Consequently, the species † ‘ P. ’ decheni, together with the material assigned to it (see Bertling 2018: fig. 44.5), should be moved to a different genus (see also Cappetta 2012: 289). Müller (1989: text-fig. 12, pl 15, fig. 1) moved † ‘ P. ’ decheni to the genus † Paratriakis Herman, 1977 based on morphological similarities between the teeth associated to the skeleton (holotype) of † ‘ Palaeoscyllium ’ decheni and those used by Herman (1977: pl. 12, figs 5, 6) to establish the taxon † Paratriakis bettrechiensis (type species of † Paratriakis) and those assigned to † Palaeotriakis curtirostris Davis, 1887 (ex † Paratriakis curtirostris). Amended diagnosis (after Wagner 1862: 289; asterisks indicate species-specific characters). A fusiform shark with short, rounded, triangular paired and unpaired fins. The pectoral fin is anterior to the dorsal fin and well separated from the pelvic fin. The pelvic fin originates approximately at the midpoint of the dorsal fin with a straight anterior margin and wide base *. Both dorsal fins have a convex anterior margin, but they slightly differ in proportions, with the second dorsal fin being narrower and higher than the first one. The anal fin originates posterior to the anterior margin of the second dorsal fin and is well separated from the caudal fin *. The anal fin is wide with a straight anterior margin that is longer than the posterior one. The caudal fin is markedly heterocercal with a shallow, angular posterior notch that separates the upper lobe from the lower one *. The lower lobe is triangular and well developed, but shorter than the upper one. The radial elements of the pelvic and dorsal fins are slender and not reaching the distal margins. The vertebrae are fully mineralized. The caudal vertebrae have short epichordal radials and hypochordal processes. Dermal denticles (placoid scales) have a small base, short peduncle, and inclined crown. Denticle morphology varies from arrow-shaped with ridges to oval without ornamentations, depending on the position across the body. Pointed arrow-shaped denticles characterize the head region and the dorsal fins. Pelvic and caudal fins have rounded arrow-shaped denticles. The anal fin is characterized by oval denticles, which are the only ones lacking ridges. Locality, horizon, and age. The type specimen, SNSB-BSPG AS I 1365, comes most likely from the Hybonoticeras hybonotum zone of the lower Tithonian of the Upper Jurassic (compare Schweigert 2015) of the Solnhofen area Archipelago in Bavaria (southern Germany; see also Villalobos-Segura et al. 2023). The specimen most likely was recovered from one of the stone quarries in the vicinity of the village of Solnhofen. Re-description of the holotype. SNSB-BSPG AS I 1365 (Fig. 2) is an incompletely articulated skeleton embedded in a limestone slab in lateral view. The postcranial outline and a few skeletal remains are clearly recognizable, while all skeletal and soft body elements of the head are missing. Its general body shape is elongated and fusiform, tapering posteriorly. Only one of each paired fin (pectoral and pelvic) is preserved (see Fig. 2 A). Although the proximal portion of the pectoral fin (Fig. 2 B, p 1 f) is not visible (not fully preserved or covered by matrix), its distal potion is wide and rounded. The latter is placed anteriorly to the first dorsal fin. The pelvic and both dorsal fins are triangular with round apices (Fig. 2 A). The pelvic fin (Fig. 2 B, p 2 f) originates in line with the midpoint of the dorsal fin and the distance between the pectoral and pelvic fins is around 78 mm. The complete outline of the pelvic fin has a wide base and a straight anterior margin. Both dorsal fins are similar in shape with an anterior margin slightly curved (Fig. 2 A). The first dorsal fin (Fig. 2 B, d 1 f; length: 63 mm; height: 36 mm) is wider than the second one (Fig. 2 B, d 2 f; length = 48 mm; height = 36 mm). The anal fin (Fig. 2 B, af) originates at the midpoint of the second dorsal fin and is well separated from the caudal fin. The anal fin is asymmetric with a wide base (length = 44 mm) and a straight anterior margin (42 mm) that is longer than the posterior one (23 mm). The caudal fin (Fig. 2 B, caf) is short and asymmetrical with the upper lobe longer than the lower one, which is triangular, and the vertebral column continues into the upper lobe (heterocercal). The two caudal lobes are wide and divided by a shallow, angular posterior notch (Fig. 2 B, pn) forming an obtuse angle of about 146 °. The heterocercal angle of the caudal fin is ca. 23 °, while the hypocercal angle is ca. 40 °. Although the upper postventral margin of the upper caudal lobe is slightly damaged in some areas, it has a regular outline with no obvious discontinuities running from the posterior notch to the posterior tip (Fig. 2 B, pt). The posterior tip is large and rounded. Concerning the skeletal elements of SNSB-BSPG AS I 1365 (Fig. 2 A, B), all structures of the neurocranium and splanchnocranium are not preserved, while some post-cranial cartilaginous remains are recognizable. Those include most of the vertebral column and portions of basal and radial elements of the pelvic, dorsal, anal, and caudal fins. Overall, traces of at least 98 fully mineralized vertebrae are clearly observable (Fig. 2 B, vc). The anterior-most vertebrae are missing, while those at the level of the first dorsal and caudal fins are poorly preserved. The pectoral and pelvic girdles, as well as the skeletal elements of the pectoral and pelvic fins, are not preserved. Although partially covered in skin, some basal and radial elements of the pelvic fin are clearly recognizable. For the unpaired fins, only the radials (Fig. 2 B, rd) are preserved. In the proximal region of the caudal fin, hypochordal processes (Fig. 2 B, hcp) are recognizable directly ventral to the vertebrae, while short epichordal radials (Fig. 2 B, ecr) are barely visible only towards the tail end. All radial elements are slender and limited to the proximal region of the fins; no segmentation is observed, possibly because of their poor state of preservation. In addition, patches of skin are recognizable on the tip and external margins of the fins (see Fig. 2 B). Different morphologies are recognizable in the twenty-three dermal denticles detached from different regions of SNSB-BSPG AS I 1365 (Fig. 2 C, D), which can be grouped into three different morphotypes (here named α, β, and γ). All denticles of SNSB-BSPG AS I 1365 (Fig. 2 C, D) have a single plane of symmetry (antero-posterior) and a short peduncle, which is wider than its height and connected to the crown in the centre with a posterior obtuse angle (see Fig. 2 C, D). The crown is larger than the base protruding over it all around. Morphotype α (Fig. 2 D) has an arrow-shaped crown with a rounded, anterior margin and a single-vertex posterior side; the marginal micro-texture is smooth on all sides. The anterior edge is scalloped with three bulges (one central, two lateral) separated by two deep notches. The vertex consists of a rounded cusp protruding posteriorly from the denticle crown. Two slender, straight ridges start at the anterior margin of each bulge and converge towards the posterior vertex. Often, each ridge running along the central bulge is further paired in double ridges that can fuse posteriorly. Double ridges rarely occur on the lateral bulges. All ridges are equally marked and well defined, while the rest of the crown surface is relatively smooth, without a recognizable secondary texture. Morphotype β (Fig. 2 D) is almost identical to the previous morphotype but diffe