Leptolepis normandica Nybelin, 1962

Konwert, Martin & Stumpf, Sebastian, 2017, Exceptionally preserved Leptolepidae (Actinopterygii, Teleostei) from the late Early Jurassic Fossil-Lagerstätten of Grimmen and Dobbertin (Mecklenburg-Western Pomerania, Germany), Zootaxa 4243 (2), pp. 249-296 : 263-266

Leptolepis normandica Nybelin, 1962

Figure 6 ; Plates 1E, 2D, 3C

Synonyms:

Leptolepis concentricus Egerton, 1849 (in part): p.35.

Leptolepis pachystetus Sauvage, 1874 : pl. VII, figs. 2, 3. Leptolepis bronni Woodward, 1895: p. 504 .

Leptolepis normandica Nybelin, 1962 : fig. 1B.

Leptolepis normandica Nybelin, 1963 : fig. 10.

Leptolepis coryphaenoides Wenz, 1968 (in part): figs. 91, 92B, 94A, pl. XLII, XLIII fig. C. Leptolepis normandica Nybelin, 1974 : figs. 1A, B; 2; 3 A–C; 7A–C; pls. I–IV; V figs. 1–5; IX figs. 2, 3; XXX fig. 1. Leptolepis normandica Nybelin, 1976 : pl. 1, fig 3.

Leptolepis normandica Delsate, 1997 : figs. 1–5; pl. 1, figs. 1, 4A–C; pl. 2, figs. 5–9. Leptolepis normandica Arratia, 1984 : fig. 7E.

Leptolepis coryphaenoides Arratia & Thies, 2001 : fig. 12C. Leptolepis normandica Bean, 2006 : figs. 9E–G.

Leptolepis coryphaenoides Bean, 2006 : fig 18B.

Leptolepis bronni Ansorge & Obst, 2015 : fig. 15B.

Material. GG 431/2a, b, articulated head with pectoral girdle and few abdominal vertebrae, preserved in part and counterpart. The specimen is associated with four insect wings, including the holotypes of Protorhyphus stigmaticus Handlirsch, 1920 and Parablattula reticulata Handlirsch, 1920 .

Geographical distribution. Curcy, May (Normandy, France) ; Dumbleton, Alderton (Gloucestershire, England) ; Dobbertin (Mecklenburg-Western Pomerania, Germany) ; Barscharage (Luxembourg); ?Holzmaden (Baden-Württemberg, Germany) (data from Wenz 1968; Nybelin 1962, 1974; Delsate 1997; this paper).

Stratigraphical distribution. Lower Jurassic, Toarcian, at least Harpoceras falciferum Zone.

Description. Cranial bones ( Fig. 6 ; Pl. 1E): Most of the cranial bones are poorly or not preserved. Most of the cranial roof is formed by the parietal. It is narrow and elongate in its anterior portion. The posterior portion is damaged. It seems to have been much broader than the anterior part. Anteriorly, the parietal articulates with the mesethmoid. Remnants of the postparietal, pterotic and endocranial bones are preserved but are uninformative. The mesethmoid is short, but the lateral wing is large. It extends in anterolateral and posterolateral directions. The posterior part of the lateral wing is covered by infraorbital 1, so its posterior length is unknown. The nasal bone lies slightly dislocated below the supraorbital. The exposed part of this bone is its posterior portion, which is thin and tube-like, mainly carrying the supraorbital sensory canal. The lateral ethmoid is narrow, elongate, and poorly ossified.

Upper jaw ( Fig. 6 ; Pl. 3 C): The upper jaw consists of premaxilla, maxilla and two supramaxillae. The premaxilla is small. It bears a well marked, broad ascending process. A single row of at least eleven, long, but very narrow teeth are present on the oral margin of the premaxilla. The maxilla is the largest bone of the upper jaw. It is long, reaching the posterodorsal margin of the quadrate. The bone is convex ventrally and concave dorsally. A well ossified ridge is present along the lateral margin of the bone. An elongate groove is present on the lateral surface, running parallel to the ridge. Some short grooves are running diagonal to the dorsally and ventral margins of the maxilla at about the center of the bone. The dorsal margin of the maxilla bears an elongate surface for the articulation of the supramaxillae. A single row of several small, needle-like teeth is present along the ventral margin of the maxilla. Each tooth is associated with a small groove. The ventral portions of both supramaxillae are broken and their dorsal margins are covered by infraorbital bones. Thus, the exact shapes of both bones are unknown. The anterior supramaxilla seems to have been elongated, with a sharp anterior tip. The remaining part of the posterior supramaxilla indicates a more or less trapezoidal shape, an anterior process seems to arise from the anteroventral portion of the bone and extands anterodorsally. Its length remains unknown. The surface of the posterior supramaxilla is strongly ornamented. The ornamentation consists of several grooves, running more or less parallel to the ventral margin of the bone and some low tubercles.

Lower jaw ( Fig. 6 ; Pl. 3C): The lower jaw is formed laterally by the dentary and angular. Most of both bones is covered by bones of the upper jaw. Most of the ventral margin of the lower jaw is formed by the dentary. The oral margin ascends with an angle of about 30° in respect to the ventral margin of the bone. Four very small teeth were observed on the oral margin. The exposed part of the angular is poorly preserved in the specimen, so not much is known about it.

Palatoquadrate and hyoid arches ( Fig. 6 ): The quadrate and a small portion of the entopterygoid are the only exposed bones of the palatoquadrate arch in the specimen. The main body of the quadrate seems to be triangular, as in the other species of Leptolepis . The posteroventral process of the quadrate is longer than the main body, but its posterior part is covered by the preopercle, so its length remains unknown. Some poorly preserved branchiostegals are present ventral to the interopercle, these seem to be elongate and laterally flattened.

Orbital bones ( Fig. 6 ; Pl. 1E): The orbital bones are nearly completely preserved, lacking only the posterior supraorbital, the dermosphenotic, and the antorbital. The anterior portion of the anterior supraorbital is preserved in the specimen. It shows a sharp anterior tip and is sharp angled along its lateral margin. The second supraorbital is not preserved. Both sclerotics are preserved. Both are semicircular shaped, and at least the posterior is very broad. They have probably surrounded the eye completely. Infraorbital 1 is subrectangular, with its anterior part being deeper than the posterior margin. Infraorbital 2 is about as long as infraorbital 1, but thin, just a little bit broader than the infraorbital sensory canal. Infraorbital 3 is the largest bone of the infraorbital series. Posteriorly, it reaches the preopercle. It is convex at its ventral and concave at its posterior margins. The dorsal margin of infraorbital 3 is partly overlapped by infraorbital 4. Infraorbital 4 is subrectangular, with a convex ventral margin, which overlaps infraorbital 3. The ventral margin of infraorbital 5 is straight, and as broad as the dorsal margin of infraorbital 4. The bone narrows in dorsal direction. The dorsal margin of the bone is not preserved. One suborbital is present whereas an “accessory” suborbital (see Nybelin 1974) is absent. The bone covers the space between the infraorbitals and the opercle and preopercle. The anterior margin of the bone is covered by infraorbitals 3 to 5. The posterior margin of the suborbital bears a distinct notch. A small notch is also present in the dorsal margin, probably for the passage of the preopercular sensory canal.

Opercular bones ( Fig. 6 ; Pl. 1E): The opercular series consists of opercle, subopercle, preopercle and interopercle. The opercle is the largest bone of the series. Its anterior, ventral and posterior margins are straight, but it is convex and bent in medial direction dorsally. Some fine growth lines were observed. The subopercle is about as half as deep as the opercle, but slightly broader. Its posteroventral margin is convex. The preopercle is L-shaped, with a long dorsal and a shorter ventral limb, both form an angle of about 110°. The posterior margin of the preopercle shows a vague notch. In the anterior margin, near the confluence of both limbs, the preopercle bears an anterior process. A suprapreopercle, as described by Nybelin (1974), was not observed. It is either absent or completely covered by the suborbital. Most of the interopercle is covered by the preopercle, so its exact shape is unknown. Its ventral margin is as long as the ventral limb of the preopercle.

Sensory canal system ( Fig. 6 ; Pl. 2D): The sensory canal system is known from the mandibular, preopercular, infraorbital, and a very short portion of the supraorbital canal. All preserved parts are enclosed by bone. All tubules are unbranched. The mandibular canal runs close to the ventral margin of the dentary. The canal is poorly preserved and does not allow a proper description. The preopercular canal runs close to the dorsal margin of the ventral limb and along the center of the dorsal limb of the preopercle. It gives off twelve tubules, nine of them are present in the ventral limb. These tubule increase in length posteriorly, and point in posteroventral direction. The tubules in the ventral limb end close to the ventral margin of the bone or reach the margin. At the confluence of dorsal and ventral limb, two tubules, pointing in posterior and posterventral directions are present. These are much shorter than the preceding ones and do not reach the posterior margin of the preopercle. A very short, anteriorly directed tubule is also present at the confluence of both limbs. A single tubule is present in the ventral part of the dorsal limb. This points in posterodorsal direction and does not reach the posterior margin of the preopercle. The infraorbital canal runs close to the dorsal, or anterior margin of the infraorbital bones. The infraorbital canal is not preserved in infraorbital 1, but impressions on the bone show its position. The canal gives off at least four tubules, which apparently have reached the ventral margin of the bone. The canal continues close to the center of infraorbital 2. It gives off four tubules in infraorbital 3, which are directed posteroventrally. The first one is much shorter than the other tubules. Two tubules are present in infraorbital 4, they point posteriorly. The ventral one is long, ending close to the posterior margin of the bone; the dorsal tubule is evidently shorter. The infraorbital canal does not seem to give off any tubules in infraorbital 5.

Vertebral column and associated bones (Pl. 1F): Seven abdominal vertebrae are exposed in the specimen, but it is assumed that few others are covered by the opercle. The autocentra are slightly longer than broad, each being slightly constricted in its middle part. Their surface is smooth, without ornamentation. The parapophyses are large, about as broad as their respective centrum. The parapopyses are fused to the autocentra lateroventrally and bear a short, very thin process at its lateroventral margin. The processes point posteroventrally. Ribs are not preserved. The neural arches are not fused to their centra. Each arch bears a thin epineural process, which is directed posteriorly. The epineural processes are united with the neural arches also by thin bony lamellae. These lamellae exceed in anterior and dorsal direction and form a small anterodorsal process. The neural spines are thin and form an angle of about 45° with the vertebral column. Supraneural bones are not preserved.

Pectoral girdle and fin ( Fig. 6 ; Pl. 1E): The preserved bones of the pectoral girdle are: cleithrum, supracleitrum, and two postcleithra. The cleitrum is composed of two limbs, a vertical dorsal and a horizontal ventral one. The dorsal limb seems to be longer than the ventral one. Several fine grooves and ridges, running parallel to the posterior margin of the bone are present. These seem to be growth lines. The elongate supracleithrum is hardly damaged. A long and narrow bone is present posterior to the cleithrum. This bone is identified as postcleithrum 1. A second postcleithrum is present ventrally to postcleithrum 1. This element is incompletely preserved, so that its shape remains unknown. Several lepidotrichia of the pectoral fin (probably originating from both fins) lie ventrally and posteriorly to the cleithrum, they are poorly preserved. At least some rays are segmented.

Remark: Nybelin (1974) pointed out that L. normandica Nybelin, 1962 might be identical with L. pachystetus Sauvage, 1873 . This assumption is based on the relatively low number of unbranched tubules in the preopercular sensory canal and a similar shaped opercle in both species. Due to Sauvage’s insufficient description and the loss of the holotype of L. pachystetus the identity of both species cannot be confirmed (see Nybelin 1974). The herein examined specimens of Leptolepidae sp. 1, Proleptolepis -like, Leptolepis sp. 1 and L. jaegeri , do also have a relatively low number of unbranched tubules in the preopercular sensory canal, but differ from L. normandica in other characters. This shows that the number and shape of the tubules cannot be used as sole character for the identification of the species. Furthermore, we disagree with Nybelin’s (1962, 1974) interpretation of the shape of the opercle in L. normandica (see below). For these reasons, we retain the use of the name L. normandica , following the nomenclature of Nybelin (1962, 1974).

Figures

FIGURE 6. Leptolepis normandica (GG 431 / 2 a) from Dobbertin. Line drawing of head in lateral view. Abbreviations: ang, angular; a. sc, anterior sclerotic; a. smx, anterior supramaxilla; br, branchiostegal rays; de, dentary; iop, interopercle; io 1, infraorbital 1; io 5, infraorbital 5; let, lateral ethmoid; met, mesethmoid; mx, maxilla; na, nasal bone; op, opercle; pa, parietal bone; pmx, premaxilla; pop, preopercle; p. sc, posterior sclerotic; p. smx, posterior supramaxilla; qu, quadrate; sob, supraorbital bone; sop, subopercle; suo, suborbital.