Proleptolepis

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 : 256

Proleptolepis -like

Figure 3 , Plate 1C

Material. MV 202612, fragmentary head preserved in medial view.

Geographical distribution. Former clay pit of Grimmen, Mecklenburg-Western Pomerania, Germany.

Stratigraphic distribution. Lower Jurassic, lower Toarcian “Green Series”, Harpoceras falciferum Zone , Harpoceras exaratum Subzone.

Description. Opercular series ( Fig. 3 ; Pl. 1C): The opercle, subopercle, propercle, and interopercle are preserved in the specimen. The opercle is poorly preserved. Its anterior margin is formed by a well-ossified ridge. The broad and deep subopercle is very large. The overall size seems to be equal to the size of the opercle, or it was slightly larger. The anterodorsal and anterior margins of the subopercle are straight, whereas the ventral and posterior margins are convex. The dorsal part of the preopercle is not preserved, but its mold allows to evaluate its outline. The bone is formed by a dorsal, vertical oriented, and a ventral, horizontal oriented limb; both limbs form an angle of about 120°. Anteriorly, at the confluence of both limbs there is a broad, convex process. Although the ventral margin of the bone is covered by the interopercle, the exposed part suggests the ventral limb of the preopercle to be very deep. In the posterior margin of the bone, at about the confluence of both limbs, a deep, sharp notch is present. The fragments and the molds interopercle suggest that it was large and triangular. Its length exceeds the length of the ventral limb of the preopercle. The ventral and posterior margins of the bone form an angle of about 90°.

Infraorbital 3 and suborbital ( Fig. 3 ; Pl. 1C): Anteriorly to the preopercle, there are fragments of a canal bearing, dermal bone. In order to the large size and the position of these remains, they are identified as belonging to infraorbital 3. Between the posterior margin of infraorbital 3 and the impression of the preopercle, there are two bone fragments. According to their position, these fragments are interpreted as remains of a suborbital bone.

Sensory canal system ( Fig. 3 ; Pl. 1C): The infraorbital sensory canal is only known from a single, trifurcated tubule in the remains of infraorbital 3. The preopercular canal runs close to the anterior respectively dorsal margins of the bone. Its canal gives off at least 10 unbranched tubules. Some more might be covered by the interopercle. The dorsal part of the canal gives off a single, posteriorly directed, long tubule. This seems to end at or close to the posterior margin of the preopercle. Two short and thin tubules are present at the confluence of both limbs, an additional short tubule is directed anteriorly.

Identification: The shape of the preopercle and the large size of the subopercle prevent an assignment to any species of Leptolepis . A large subopercle is found in Longileptolepis wiedenrothi , Proleptolepis furcata and P. megalops . As described above, MV 202612 bears a deep notch in the posterior margin of the preopercle. A shallow notch is present in Longileptolepis wiedenrothi ( Arratia & Thies 2001) and some species of Leptolepis (see below). A deep notch in the posterior margin of the preopercle, similar to the described specimen, is only present in Proleptolepis . Thus, MV 202612 indicates closest morphological resemblance to Proleptolepis . However, given the incomplete nature of the specimen it is here considered as an indeterminate Leptolepidae until more material is available.

Figures

FIGURE 3. Proleptolepis - like (MV 202612) from Grimmen. Line drawing of cranial bones in medial view. Dashed lines indicate moulds. Abbreviations: iop, interopercle; io 3, infraorbital 3; io. c, infraorbital sensory canal; op, opercle; pop, preopercle; pop. c, preopercular sensory canal; sop, subopercle; suo, suborbital.