Leptolepis coryphaenoides ( Bronn, 1830 )

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 : 258-262

Leptolepis coryphaenoides ( Bronn, 1830)

Figures 4 A, B, 6; Plates 2A–C, 3A, B

Synonyms:

Cyprinus coryphaenoides Bronn, 1830 : pl. 1.

Leptolepis Bronnii Agassiz, 1832: p. 146 .

Leptolepis bronnii Quenstedt, 1858 : pl. 33 figs. 8–11.

Leptolepis bronni Rayner, 1937 (in part): figs. 1–14.

Leptolepis coryphaenoides Nybelin, 1962 : fig. 1A.

Leptolepis coryphaenoides Nybelin, 1963 : fig. 9.

Leptolepis coryphaenoides Wenz, 1968 (in part): figs. 79–107, pls. XL–XLVIII. Leptolepis coryphaenoides Patterson, 1968 (in part): figs. 9 A–C. Leptolepis coryphaenoides Nybelin, 1974 : figs. 4A–B; 5A–K; 6A–L; 7D–G; 8; pls. VI–X; XI, figs. 1, 4–5. Leptolepis coryphaenoides Patterson, 1975 (in part): figs. 58, 89–91, 127, 128A, 132B, 144. Leptolepis coryphaenoides Taverne, 1975 : fig. 1.

Leptolepis coryphaenoides Nybelin, 1976 : pl. 1, fig. 4–5.

Leptolepis coryphaeniodes Tintori, 1977 : figs. 1–4.

Leptolepis coryphaenoides Patterson & Rosen, 1977 : figs. 32B–C, 33C. Leptolepis coryphaenoides Schultze & Arratia, 1989 : fig. 6A. Leptolepis coryphaenoides Arratia & Schultze, 1990 : fig. 10A–E. Leptolepis coryphaenoides Arratia, 1994 : pl. 7 figs. A–B.

Leptolepis coryphaenoides Wild, 1994 : fig. 85.

Leptolepis coryphaenoides Arratia & Lambers, 1996 : fig. 14C. Leptolepis coryphaenoides Arratia, 1996a : fig. 1D.

Leptolepis coryphaenoides Arratia, 1996b : figs. 5A, 6B.

Leptolepis coryphaenoides Arratia, 1997 : figs. 76A, B, 82A, 83B, 88B, 89A–C, 90A. Leptolepis coryphaenoides Delsate, 1997 : pl. 1, 3A–B.

Leptolepis coryphaenoides Arratia, 1999 : fig. 13.

Leptolepis coryphaenoides Kriwet, 2001 : fig. 4.7H.

Leptolepis normandica Arratia & Thies, 2001 : fig. 12B.

Leptolepis coryphaenoides Arratia & Thies, 2001 : fig. 12D. Leptolepis coryphaenoides Bean, 2006 : figs. 9H–I, 19A.

Leptolepis normandica Bean, 2006 : fig. 18A.

Leptolepis coryphaenoides Arratia & Herzog, 2007 : fig. 7C. Leptolepis coryphaenoides Arratia, 2008 : fig. 7B, 22.

Leptolepis coryphaenoides Arratia, 2009 : fig. 14A.

Leptolepis coryphaenoides Arratia & Hikuroa, 2010 : figs. 7A–D. Leptolepis coryphaenoides Arratia, 2013 : figs. 97D, 99A, 100A–B. Leptolepis coryphaenoides Schultze & Arratia, 2013 : figs. 5B, 9A, B, 21B. Leptolepis coryphaenoides Arratia & Schultze, 2015 : fig. 768A. Leptolepis coryphaenoides Arratia, 2015 : figs. 4A, C, 10C, 11D, 15C.

Material. GG 431/3 slightly disarticulated, incomplete head, from Dobbertin; GG 431/7 subadult, almost complete specimen, missing most of the caudal fin, from Grimmen; NRM P 6091 (cast of MNH P. 23834) fragmentary head, from Dobbertin; GG 431/19 isolated head with pectoral girdle, from Grimmen; GG 431/20 incomplete head, from Dobbertin.

Geographical distribution. Neudingen, Holzmaden, Zell, Boll (Baden-Württemberg, Germany) ; Dobbertin, Grimmen (Mecklenburg-Western Pomerania, Germany) ; Curcy (Normandy, France), Dumbleton, Gretton, Ilminster (England, Great Britain); Bergamo (Lombardy, Italy) (data from Wenz 1968; Tintori 1977; Nybelin 1974; this paper).

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

Description. Cranial bones ( Figs. 4 A, B; Pl. 2A): A short part of the mesethmoid was observed in GG 431/7, most of it is covered by infraorbital 1. The parietals form most of the skull roof. They are poorly preserved in GG 431/7 but the remnants show that they were narrow anteriorly but broader in its posterior portion. The postparietals are not preserved. In GG 431/7 the pterotic is subrectangular, with a smooth surface. The pit lines were not observed. The extrascapula seems to be semicircular, with a straight anterior margin.

Upper jaw ( Figs. 4 A, B, 5; Pls. 2A, 3A, B): The upper jaw consists of maxilla, premaxilla and two supramaxillae. The triangular premaxilla is very small and elongate, with the ascending process being low and narrow. A single row of very small teeth is present along the oral margin of the premaxilla. The maxilla is the largest bone of the upper jaw. It is moderately long and deep. Its posterior margin reaches the center of the quadrate. The ventral margin is convex, especially its posteroventral margin shows a strong curvature. A single row of miniscule teeth is present on the ventral margin of the maxilla. A well-ossified ridge is present along the lateral margin of the bone. In GG 431/3 several small longitudinal grooves are present on the lateral surface of the maxilla. These were not observed in GG 431/7 but this might due to the fact that GG 431/7 is a subadult specimen and thus, the bone might not be fully developed. Most of the dorsal margin of the maxilla is covered by the supramaxillae. The anterior supramaxilla is elongate, with a sharp anterior tip. A low ridge is present along the lateral margin of the bone. The main body of the posterior supramaxilla is somewhat triangular in GG 431/7 but ovoid in GG 431/3. A long, spine-like anterior process emerges from about the center of the bone. The anterior tip of the process is covered by the first infraorbital in both specimens, so its length is unknown. The posterior supramaxilla shows an ornamentation of several grooves, running parallel to the dorsal and ventral margins of the bone.

Lower jaw ( Figs. 4 A, B; Pl. 3A): Most of the lower jaw is covered by the maxilla in the examined specimens. The dentary forms most of the ventral margin of the lower jaw. The oral margin ascends with an angle of about 40° in respect to the ventral margin of the dentary. Two very small teeth are preserved on the dentary of GG 431/7. The ventral margin of the dentary is slightly convex and the mandibular sensory canal runs close the ventral margin of the bone. Posterodorsally, the dentary articulates with the angular. The exposed part of the angular shows a distinct ornamentation of grooves and ridges.

Circumorbital bones ( Figs. 4 A, B, 5; Pl. 2C): The circumorbital series is incomplete in all examined specimens. The large and elongate infraorbital 1 is subtriangular, with its anterior margin deeper than the posterior margin. Infraorbital 2 is very thin, mainly carrying the infraorbital sensory canal. It is slightly shorter than infraorbital 1. Infraorbital 3 is the largest bone of the series. It is subrectangular with a concave anteroventral and convex dorsal and posterior margins. Infraorbitals 4 and 5 are preserved in NRM P 6091. Both are of equal size and shape. They are small and subrectangular. The ventral part of the dermosphenotic is preserved in NRM P 6091 but its exact shape remains unknown. A single suborbital is present between infraorbitals 3 to 5, dermosphenotic, the preopercle and the opercle. It is elongate and bears a well-marked notch in its posterior margin. The ventral part of the thin and delicate anterior sclerotic bone is preserved in GG 431/7. The anterior part of the anterior supraorbital was observed in GG 431/7. It is thin and elongate. A very small, poorly ossified bone lies laterally to the anterodorsal tip of infraorbital 1 and the anterior tip of the parietal of GG 431/7, which might be a remnant of the antorbital.

Hyoid- and palatoquadrate arches ( Figs. 4 A, B; Pl. 2A): The dorsal part of the hyomandibula is exposed in GG 431/7 and the complete bone in GG 431/3. Anteriorly, it bears a thin lamella, and well-marked opercular and preopercular processes posteriorly. The main body of the quadrate is triangular. It bears a well-defined condyle for the articulation with the lower jaw. The posteroventral process of the quadrate is elongated; its posterior part is broken in GG 431/3 and covered by the preopercle in GG 431/7. Thus, its length remains unknown, but it is at least as long as the main body of the quadrate. The symplectic was not observed. The ventral part of the metapterygoid is exposed in GG 431/7. Its dorsal portion is covered by infraorbital 3 and its ventral margin is less broad than its dorsal part, as well as the dorsal part of the quadrate. An elongate, chondral bone lies ventrally to the preopercle in GG 431/7. This bone was identified as posterior ceratohyal. The number of the branchiostegal rays remains unknown due to poor preservation, but the more posterior ones seem to be longer and much broader than the anterior ones.

Opercular bones ( Figs. 4 A, B, 5; Pl. 2A–C): From the opercular series the opercle, subopercle, preopercle, and interopercle are preserved in the specimens. A suprapreopercle (see Nybelin 1962, 1974) is absent in specimen GG 431/7. The condition remains unknown in the other specimens. The opercle is the largest bone of the series. A well ossified ridge is present along its anterior margin. Several fine growth lines are running parallel to the ventral posterior and dorsal margins of the bone. The anterior, ventral and posterior margins of the bone are straight, whereas the dorsal margin is convex. Contrary to the descriptions of Nybelin (1962, 1974), the anterior and posterior margins are not parallel. This is also true for specimen NRM P 6091 (MNH P 23834 in Nybelin 1974) which was assigned to L. coryphaenoides . The subopercle is slightly broader than the opercle but less deep. Several fine growth-lines are present parallel to the ventral and posterior margins of the bone. The preopercle is L-shaped. The ventral and dorsal limbs form an angle of a 110° with each other. The dorsal-most part of the dorsal limb of the preopercle is well preserved in GG 431/7. It seems to be only formed by the tube-like ossification of the preopercular sensory canal, and reaches the otic sensory canal dorsally. In GG 431/3, there is an indistinct notch in the posterior margin of the preopercle. Most of the interopercle is covered by the preopercle in both specimens, so not much is known about this bone.

Sensory canal system ( Figs. 4 A, B, 5; Pl. 2A–C): Only the cephalic sensory canals are known. The trunk canal is not preserved in the examined specimens. All sensory canals are running in tube-like ossifications. A short, poorly preserved part of the supraorbital canal is preserved on the posterior part of the parietal of GG 431/7. Its shape remains unknown. The infraorbital canal runs along the center of infraorbital 1. The canal is not preserved in GG 431/3 but impressions on the surface of the bone indicate the presence of at least four tubules, which seem to end close to the ventral margin of the infraorbital 1. The canal continues in the dorsal margin of infraorbital 2, no tubules were observed. On infraorbital 3, the canal runs near the anterior margin of the bone. It gives off two to four tubules which end at about the center of the bone. These are not branched in the juvenile specimen GG 431/7, but strongly branched in NRM P 6091 and GG 431/19. In NRM P 6091 and GG 431/19, the canal continues close to the anterior margins of infraorbitals 4 and 5. The canal gives off one to two tubules in infraorbital 4 and one in in infraorbital 5. All tubules in infraorbitals 4 and 5 are unbranched, posteriorly directed and close to the posterior margins of the respective bones. The canal on the dermosphenotic is only known from NRM P 6091. In this bone the canal seems to trifurcate. The anterior, dorsal directed part of the canal is undoubtely the anterodorsal branch of the canal. One of the posteriorly, respectively posterodorsally directed “branches” must be a tubule, the other the true posterior branch. A decision cannot be made on the basis of specimen NRM P 6091 because of the defective state of the dermosphenotic. Nybelin (1974:40) interpreted the ventral one as a posterior directed tubule, since he observed an equivalent tubule in another specimen (BMNH 19642). Thus, we follow Nybelin’s interpretation. The mandibular canal is well preserved in GG 431/3. It runs near the ventral margin of the dentary. Three pores are present on the ventral margin of the canal. The canal continues in the ventral part of the angular, the posterior opening is not visible. It is probably placed at the medial side of the bone. The preopercular canal runs close to the dorsal/anterior margin of the preopercle. In GG 431/3 it gives off at least 11 tubules (on the left preopercle), some of them are very broad and at least six of them are branched up to four times. The very broad tubules might be the result of fusion of adjacent tubules. All tubules end close to the ventral or posterior margin of the preopercle. In GG 431/7 the preopercular canal gives off 10 tubules, only two of them are branched. The preopercular canal reaches the otic canal dorsally. The otic canal runs along the dorsolateral margin of the pterotic, a single, dorsally directed, short tubule is present. Posteriorly, the otic canal is continuous with the supraoccipital canal. This runs close to the anterior margin of the extrascapula. The number of tubules and the continuation with the posttemporal canal is unknown because of poor preservation. The canals in the posttemporal and supracleithrum are not preserved.

Vertebral column and associated bones (Pl. 2A): The following description is based on GG 431/7, a subadult specimen. Bones of the vertebral column can change their shape and often fuse with other bones during ontogeny. For descriptions of adult individuals of Leptolepis see e.g., Rayner (1937), Wenz (1968), Nybelin (1962, 1974), Arratia (1991, 1997), and Arratia & Hikuroa (2010). The total number of vertebrae, as well as the number of abdominal and caudal vertebrae are unknown, because the anteriormost vertebrae are covered by the opercle, others are covered by scales. The autocentra are slightly longer than broad, each being slightly constricted in its middle part. Their surface is smooth, without any ornamentation. The parapophyses are fused to their respective centrum, they are subtriangular in shape and are as long as their centra. Both halves of the abdominal neural spines are unfused but are fused in the caudal region. The ribs are thin, at least the anterior ribs seem to reach the ventral margin of the abdomen. Thin, elongate epineural processes are associated with the anterior abdominal neural arches. Epipleural bones seem to be absent. All neural arches seem to be unfused with their respective centrum in GG 431/7. Arratia (1991, 1997) described the abdominal neural arches as to be unfused, but the caudal neural arches as fused to their centra in L. coryphaenoides . Therefore, the herein observed unfused caudal neural arches of GG 431/7 are interpreted as an ontogenetic condition. The last six neural spines and the last five hemal spines are distally expanded. The neural spines are thin, their length remain unknown.

Pectoral girdle and fin ( Figs. 4 A, 5; Pl. 2A): The pectoral girdle is complete in GG 431/7, but many of the bones are poorly preserved. Most of the posttemporal is covered by the opercle, so its shape is unknown. This is also true for the supracleithrum that seems to be elongate. The dorsal limb of the cleithrum is covered by the subopercle, the ventral limb is directed anteroventrally. Its anterior tip and its posterior margin are bent in medial direction. Several fine grooves run parallel to the margins of the cleithrum, which seem to be growth lines. Postcleithrum 1 is an elongate bone, that seems to articulate with the supracleithrum dorsally and overlaps the postcleitrum 2 ventrally. Postcleithrum 2 is broad and seems to be triangular. The dorsal part of postcleithrum 3 is covered by the left pectoral fin. Its ventral part is triangular. The pectoral fin is located close to the ventral margin of the body. The following description is based on the right pectoral fin of GG 431/7. Sixteen pectoral fin rays are present. Most of them are segmented and branched in their distal portions. Two, maybe three small, elongate scales seem to be associated with the last pectoral fin ray. There are four poorly preserved proximal radials. Three are elongate, the fourth is short and about twice as broad as the others. The anterior part of the coracoid is narrow and elongate. Anteriorly it reaches the anteroventral tip of the cleithrum. The posterior part of the coracoid is about as twice as broad as the anterior portion. A small part of the scapula is exposed in GG 431/7, but most of it is covered by the cleithrum, so its shape remains unknown.

Pelvic girdle and fin (Pl. 2A): The pelvic fin is placed at about 50% of standard length. The basipterygium is triangular, with a strongly ossified ridge along its lateral edge. Eleven fin rays plus an elongate pelvic splint are present. The distal portions of the pelvic fins are poorly preserved, but at least some of the lepidotrichia are segmented distally.

Dorsal and anal fin (Pl. 2A): Both, the dorsal and anal fins are poorly preserved. The dorsal fin consists of at least 11 fin rays. The number of precurrent rays is unknown. At least ten fin rays are present in the anal fin, the first three are precurrent rays. Fulcra are absent in the dorsal and anal fins.

Squamation (Pl. 2A): Several comparatively large cycloid scales are preserved in GG 431/7. Their shape is circular in the dorsal part of the abdominal region, but some scales in the ventral part of the abdomen show an oval outline. However, all scales show complete circuli.

Remark: Nybelin (1974: pl. IX, fig. 3) figured a cast of a fragmentary head of a L. coryphaenoides from the Dobbertin Lagerstätte with the collection number MNH P 23834. This cast was found in the collection of the Naturhistoriska Riksmuseet in Stockholm, but with the different collection number NRM P 6091. The labels indicate that the collection number MNH P 23834 refers to the original specimen.

Identification: The above described specimens share the presence of branched tubules in the preopercular canal. Nybelin (1974) listed three species of Leptolepis which possess branched tubules in the preopercular sensory canal, L. coryphaenoides ( Bronn, 1830) , L. saltviciensis Simpson, 1855 and L. autissiodorensis Sauvage, 1892 . Nybelin (1974) also points out that L. saltviciensis might represents juvenile stages of L. autissiodorensis . The preopercles of L. saltviciensis and L. autissiodorensis are almost equal in shape. They are less broad and more crescentic than in L. coryphaenoides . Furthermore, the tubules in the preopercular canal are shorter, the number of tubules is higher and fewer branched tubules are present in L. saltviciensis and L. autissiodorenis . The herein described specimens GG 431/3, GG 431/19, GG 431/20 and NRM P 6091 have relatively broad preopercles and relatively low numbers of tubules in the preopercular canal. Therefore, they are assigned to L. coryphaenoides . This assignment is also supported by the presence of miniscule teeth on the maxilla and premaxilla, as well as the presence of a small premaxilla in GG 431/3, as described in L. coryphaenoides by Nybelin (1974). Specimen GG 431/7 shows a comparatively narrow preopercle, as described in L. saltviciensis and L. autissiodorensis ( Nybelin 1974) . Otherwise, GG 431/7 is considered as a juvenile and the preopercle might not be fully developed. The specimen differs to L. autissiodorensis in the low number of tubules in the preopercular canal of 10 (more than 22 in L. autissiodorensis ). The miniscule teeth on maxilla, premaxilla and dentary, as well as the small premaxilla of GG 431/7 are consistent with referral to L. coryphaenoides . Thus, GG 431/7 is also assigned to L. coryphaenoides .

Figures

FIGURE 4. Leptolepis coryphaenoides. Line drawings of cranial bones. A GG 431 / 7, juvenile specimen from Grimmen. B GG 431 / 3, adult specimen from Dobbertin. Abbreviations: ang, angular; ant, antorbital; a. smx, anterior supramaxilla; br, branchiostegal rays; cl, cleithrum; de, dentary; exs, extrascapula; gu?, gular plate?; iop, interopercle; io 1, infraorbital 1; io 2, infraorbital 2; io 3, infraorbital 3; l. pop, left preopercle; pmx, premaxilla; pt, pterotic; ptt, posttemporal; hym, hyomandibula; md. c, mandibular sensory canal; met, mesethmoid; mtg, metapterygoid; mx, maxilla; op, opercle; op. pr, opercular process of hyomandibula; pa, parietal bone; pcl 1, postcleithrum 1; pcl 2, postcleithrum 2; pop, preopercle; pop. pr, preopercular process of hyomandibula; p. cer, posterior ceratohyal; p. smx, posterior supramaxilla; qu, quadrate; r. pop, right preopercle; scl, supracleithrum; sob, supraorbital bone; sop, subopercle.