Leptolepis jaegeri Agassiz 1832
Creators: name: Konwert, Martin
name: Stumpf, Sebastian
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Salmoniformes
Leptolepidae
Leptolepis
Leptolepis jaegeri

description: Leptolepis jaegeri Agassiz, 1832
Figures 7 A–C; 8A–C; 9A, B; 10A, B; 11; Plates 1D; 2E; 3D; 4A–C
Synonyms:
Leptolepis Jaegeri Agassiz, 1832: p. 146
Leptolepis Jaegeri Agassiz, 1833 –1844 (vol. 2): p. 13 Leptolepis jaegeri Woodward, 1895: p. 505
Liassolepis bronni (nomen nudum) Jaekel, 1929: fig. 3 Leptolepis coryphaenoides (in part) Wenz, 1968: figs. 92A, 95A Leptolepis jaegeri Nybelin, 1974: figs. 9, 10A–C; pls. XII, XIII fig. 3 Leptolepis bronni Ansorge & Obst, 2015: fig. 15C
Material. NRM P 6483a, b (neotype) from Holzmaden; GG 431/1 isolated head with pectoral girdle, preserved in 3D, from Dobbertin; GG 431/6 isolated head with pectoral girdle, from Grimmen; GG 431/9a isolated head preserved in 3D prepared from left side, from Grimmen, acid prepared specimen; GG431/9b same individual as GG 431/9a, right side of the head in lateral view; GG 431/10 almost complete, juvenile specimen from Grimmen; GG 431/15 incomplete head from Grimmen; GG 431/16 isolated head from Grimmen.
Geographical distribution. Zell, Holzmaden (Baden-Württemberg, Germany); Dobbertin, Grimmen (Mecklenburg-Western Pomerania, Germany); Le Cain (Normandy, France);?Dumbleton (Gloucestershire, Great Britain) (data from Agassiz 1832; Nybelin 1974; this paper).
Stratigraphical distribution. Lower Jurassic, Toarcian, at least Harpoceras falciferum Zone, Harpoceras exaratum Subzone.
Description. General description: Small, slender teleost, maximal known head-length 22 mm. Pelvic fins placed at about 50% of standard length, origin of dorsal fin slightly posterior to pelvic fin. Anal fin placed at about 70% of standard length. Body covered with cycloid scales.
Cranial bones (Figs. 7 A, B; 8A–C; 9A, B; 10A, B; Pls. 1D; 2E; 3D; 4A–C): The mesethmoid is well preserved in GG 431/9a, the anterodorsal margin of this bone is short. The ventral lamella of the mesethmoid extends posterior from the lateral and point to the anterior tip of the lateral etmoids. The anterior tip of the lateral wing of the mesethmoid is in contact to the anteromedial tip of the bone, forming a mesethmoidal foramen. The nasal bones are small. They articulate with the parietal laterally. The posterior portion of the nasal bone is mainly formed by the tube-like ossification of the supraorbital sensory canal, whereas it is triangular in its anterior portion. The parietals form most of the skull roof. They are narrow and elongate in their anterior part. The suture between both parietals is smooth. The parietals articulate with the mesethmoid anteriorly; the nasal bones, supraorbital and dermosphenotic laterally; the pterotic posterolaterally; and the postparietal posterodorsally. The postparietal bones seem to be subrectangular. The anterior and middle pit lines are present in the posterior portion of the bone. The pterotic forms most of the lateral aspect of the skull roof. Its exact outline remains unknown, because of poor preservation. The middle pit line was observed on the right pterotic of GG 431/1. The narrow lateral ethmoids are well preserved in GG 431/9a, b. They articulate with the parietals and do not reach the parasphenoid ventrally. A short anteroventral process points to the posteroventral lamella of the mesethmoid. The parasphenoid is elongate and narrow. It articulates with the vomer anteriorly, the entopterygoid ventrally and with endocranial bones posterodorsally. A tooth plate is fused to the parasphenoid slightly anterior to the ascending processes of the parasphenoid, at the ventral margin of the bone. At least six teeth are present at the right margin of the plate, some more are medially placed. The teeth are comparatively large, conical and point posteroventrally. The short vomer articulates with the parasphenoid ventral to the mesethmoid. The vomer bears at least seven, comparatively large, conical teeth. The vomerine teeth are arranged in two rows and point posteroventrally. The orbitosphenoid is preserved in GG 431/9a. It is located dorsal to the orbit and does not exceed anteriorly or ventrally. Posteriorly, the orbitosphenoid sutures with the pterosphenoid, which forms the medial aspect of the posterodorsal margin of the orbit. The extrascapula is preserved in GG 431/1 and GG 431/16, but the state of preservation is poor in both specimens. In specimen GG 4321/9a, some bones of the braincase are preserved. The prootic forms most of the lateral and anteroventral aspects of the braincase, it sutures with the basioccipital posteroventrally, with the pterosphenoid and basisphenoid anteriorly, and with exoccipital posteriorly. The articulation of the prootic with the parasphenoid remains unknown because of poor preservation. The prootic-exoccipital suture runs vertical and is almost straight. The exoccipital forms the posterolateral and posterior aspects of the braincase, it sutures the basioccipital ventrally. The exocciptal-basioccipital suture is clearly visible in the anterior portion of the anteroventral portion of the exoccipital but was not observed in the posterior part of the bone. This may indicate a fusion of both bones, late in ontogeny. The basioccipital forms the ventral and the posteroventral part of the posterior braincase. The epiotic forms the posterodorsal and most probably, a part of the posterior aspect of the braincase. The autosphenotic and pterotic are not preserved in GG 431/9a.
Hyoid arch (Fig. 8 A, 9B): The posterior ceratohyal preserved in GG 431/9b, but most of the bone is covered so its shape remains unknown. The groove for the afferent hyoidean artery runs close to dorsal margin of the bone. A small facet, probably for the articulation of the interhyal, is present on the posterodorsal margin of the posterior ceratohyal. The anterior ceratohyal is fenestrated, the groove for the afferent hyoidean artery is continuous with the fenestra and leaves the bone at its anterior margin. Most of the dorsal hypohyal is covered by the ventral hypohyal, the shape and size of the bone remains unknown. The anterodorsal tip of the dorsal hypohyal bears two small depressions anteriorly. The ventral hypohyal is a massive, subrectangular bone. A deep groove for the afferent hyoidean artery is present. It runs in anteriorly, but turns ventrally at about the center of the bone. The afferent hyoidean artery pierced the bone and exited it at its medial side. An elongate bone, which is probably the displaced urohyal, lies dorsal to the anterior ceratohyal in GG 431/9b. Several very small, conical teeth are present on the complete surface of the bone. A broad bone is present anterior to the hypohyals, this is either the basihyal or a basihyal tooth plate. Its anterodorsal surface is sparsely covered with conical teeth. The size of the teeth varies. The teeth near the medial and lateral margins of the bone are larger than those in the center of the bone. Some branchiostegal rays are preserved in both lateral sides of GG 431/1 and in GG 431/15. They are long and seem to broaden in posterior direction.
Palatoquadrate arch (Figs. 8 A, B; 9A, B; 10A, B; Pls. 3D; 4B, C): The metapterygoid is almost completely preserved in GG 431/9a, it is large and subrectangular. The ventral margin of the bone seems to be slightly convex. The anterior portion of the bone is directed medially to meet the entopterygoid. The processus basalis forms the anterodorsal tip of the bone. The processus metapterygoideus lateralis is short but well defined. It arises from the anterodorsal margin of the metapterygoid and points dorsally. The quadrate is triangular, the posterodorsal margin is broad and slightly concave. The posteroventral process of the quadrate is narrow and much longer than the main body of the quadrate. The symplectic is elongate, it is narrow in its anterior portion and broadens posteriorly. The entopterygoid is large, it forms most of the ventral margin of the orbit. Several small teeth are present on the medial side of the entopterygoid. The ectopterygoid is elongate and narrow, it bears an articulation facet for the autopalatine anteriorly. The lateral surface of the bone is edentulous, but teeth may be present at its medial side. The autopalatine is large, it is as deep as the ectopterygiod. The posterior part of the bone is directed posterodorsally. The autopalatine seems to articulate with the ectopterygoid.
Upper jaw (Figs. 7 A–C; 8A, B; 9A, B; 10A, B; Pls. 3D; 4A–C): The upper jaw consists of premaxilla, maxilla and two supramaxillae. The premaxilla is large (in comparison with L. coryphaenoides) and bears a high ascending process. A single row of comparatively large, conical teeth is present on the oral margin of the bone. In specimen GG 431/1 at least 11 teeth are present on the right premaxilla. The maxilla is the largest bone of the upper jaw. It is long and reaches to the center of the quadrate. The maxilla is convex ventrally and concave dorsally. The articular process is well defined and resembles the length of the premaxilla, it is narrow and directed anteromedially. A prominent bony ridge is present along the lateral side of the anterior portion of the maxilla. The posterior part of the bone is smooth. Fifty-six conical teeth are preserved along the ventral margin of the left maxilla of GG 431/1 and 60 in GG 431/15, but several teeth are missing in both specimens. The former number of teeth must have been about 70. The teeth in the anterior part of the maxilla are slightly larger than these in the posterior part of the bone. The supramaxillae large. The anterior supramaxilla is fusiform with a sharp anterior tip. The posterior supramaxilla is slightly larger than the anterior one. A long, spine-like anterodorsal process arises from the center of the bone. It articulates with the dorsal margin of the anterior supramaxilla. The lateral surface of the posterior supramaxilla is ornamented with several longitudinal grooves and bony ridges.
Lower jaw (Figs. 7 A, B, 8, B; 9A, B; 10 A, B; Pls. 3D; 4A–C): The lateral aspect of the lower jaw is formed by the dentary and angular. Most of the ventral margin of the lower jaw is formed by the dentary. The oral margin of the dentary ascends gently in direction of the coronoid process. In GG 431/1, GG 431/9a and GG 431/16, the oral margin of the dentary possess a low, broad dorsal process. The “leptolepid” notch is present just anterior to the coronoid process, it is deep and narrow. The high and heavily ossified coronoid process is placed at about 50% of the length of the dentary. The dorsal margin of the bone is formed by the coronoid process and a long posteriodorsal process. The posterodorsal tip of the dentary almost reaches the quadrate. A single row of at least 12 comparatively large teeth are present at the oral margin of the dentary. The dentary teeth are conical and slightly curved in posterior direction. In GG 431/16, the dentary teeth posterior to the process on the oral margin of the dentary are thin and straight. The angular inserts in the space between the posterodorsal process and the ventral margin of the dentary. The lateral aspect of the bone is formed by a thin sheet of bone. The ventral portion of the angular is heavily ornamented with several grooves and ridges. The state of fusion of angular, articular and retroarticular remains unknown.
Orbital bones (Figs. 8 A–C; 9A, B; 10A, B; Pls. 1D; 3D; 4B, C): Two supraorbital bones are present. The anterior supraorbital is narrow and elongate and bears a sharp anterior tip. Anteriorly, the bone almost reaches infraorbital 1. The posterior supraorbital bone is preserved in GG 431/16. It is elongate, but much smaller than the anterior supraorbital. A very small, slightly dislocated bone is present in the olfactory region of GG 431/9b. It is flat and carries a sensory canal. In order to its shape and position, the bone is identified as the antorbital bone. Infraorbital 1 is a large bone, its anterior margin is deeper than the posterior margin. Infraorbital 2 is narrow and elongate, not much broader than its part of the infraorbital sensory canal. Infraorbital 3 is the largest bone of the series. It is rectangular and about as twice as broad as deep; its posterior margin reaches the preopercle. The ventral part of infraorbital 4 overlaps the anterodorsal part of infraorbital 3, it is about as broad as deep. Infraorbital 5 is subrectangular and about as large as infraorbital 4. The dermosphenotic is preserved in GG 431/8b and GG 431/ 16. It is large and articulates with infraorbital 5 ventrally. Its anteroventral margin is concave and the dorsal and posterior margins are convex. The anterior margin of the suborbital is covered by the infraorbitals 3 to 5, and its posterior margin overlaps the dorsal part of the preopercle. A notch is present in the posterior margin of the bone. An “accessory” suborbital bone is absent. The anterior and posterior sclerotic bones are preserved in GG 431/16. Both bones are semi-circular and apparently have formed a complete ring around the eye.
Opercular bones (Figs. 7 A, B; 8A, B; 9A, B; 10 A, B; Pls. 2E; 4A–C): The opercle, subopercle, interopercle and preopercle are preserved. The opercle is the largest bone of the series. It is is trapezoidal shaped. The anterior, ventral, and posterior margins are straight. The dorsal margin is medially directed and seems to be slightly convex. The anterior margin is formed by a bony ridge. The suborbital is large, its depth is about 2/3 of the opercle. It is evidently broader than the opercle. The ventral and posterior margins of the subopercle are convex. The preopercle is composed of a dorsal and a ventral limb, which form an angle of about 110°. The bone is expands in ventrally and posteriorly. Thus, it is deeper and broader than in other species of the genus. The dorsal limb narrows dorsally, its dorsal-most part is covered by the suborbital. There is no notch in the posterior margin of the preopercle. A small anterior process in the anterior margin of the preopercle is present in GG 431/1, GG 431/8b, GG 431/9a, and GG 431/15. The process is absent in NRM P 6483a and GG 431/16. A suprapreopercle was not observed. Most of the interopercle is covered by the preopercle, it seems to be as long and as deep as the ventral limb of the preopercle.
Sensory canal system (Figs. 7 A, B; 8A–C; 9A, B; 10A, B; Pls. 1D; 2E; 4B, C): All sensory canals run bone enclosed on the surface of the bones, with exception of the mandibular canal. The supraorbital runs along the parietals. Anteriorly, it continues on the nasal bones. Posteriorly, the infraorbital canal reaches up to the center of the postparietal, where it is continuous with the anterior pit line. The canal does not give off any tubules, but at least three pores are present in the dorsal surface of the posterior part of the canal of GG 431/1. The anterior pit line is continuous with the posterior opening of the supraorbital sensory canal, it is short and meets the posterior and middle pit lines near the posterior margin of the postparietal. The posterior pit line is short and runs medially. It ends close to the suture of both postparietals. The middle pit line is continuous with the posterior pit line. Which runs in laterally and reaches on the pterotic, where it runs in ventrally. Its length remains unknown due to poor preservation. The anterior-most part of the infraorbital canal was observed in the antorbital in GG 431/9b, the possible presence of tubules remains unknown. The infraorbital canal runs close to the dorsal margin of infraorbital 1. Five tubules are present in infraorbital 1, they end close to the ventral margin of the bone. There is no evidence of tubules leaving the canal in infraorbital 2. The canal continues near the anterodorsal and anterior margins of the infraorbitals 3 to 5. The canal gives off two to three tubules in infraorbital 3. A single tubule is bifurcate in infraorbital 3 in GG 431/8. Two or three short tubules are present in infraorbital 4. Tubules are absent in infraorbital 5 of GG 431/16, but a single tubule is present in the bone in GG 431/8. The infraorbital canal continues in the dermosphenotic where it splits in the anterior and posterior branch. The anterior branch seems to end at the anterior margin of the bone. Two tubules are present in the dermosphenotic of GG 431/8b and at least one in GG 431/16. The tubules are dorsally directed and seem to reach the dorsal margin of the bone. The posterior branch is short and is continuous with the otic canal. The opening of the canal is placed on the medial side of the dermosphenotic, in its posterior portion. The otic canal is poorly preserved in all specimens, it runs close to the ventral margin of the pterotic. The supratemporal canal is preserved in GG 431/16, it runs close to the anterior margin of the extrascapula and gives off at least three tubules. The posttemporal canal run close to the ventral margin of the posttemporal. A single, very short, dorsally directed tubule is present in GG 431/1. The canal continues in the supracleithrum where it runs posteroventrally. It leaves the bone at its posterior margin. The mandibular canal is best preserved in GG 431/9b. It runs within the bone close to the ventral margin of the dentary. Five pores are present in the mandibular canal, they are arranged with almost equal distances to each other. The canal continues within the ventral part of the angular. The posterior opening seems to be at the medial side of the bone. The preopercular canal runs close to the dorsal and anterior margins of the preopercle. The canal gives off 11 to 13 unbranched tubules. They run posteroventrally and posteriorly. With exception of the dorsal-most one or two tubules, these are directed posterodorsally. The distal tips of the tubules are broader than their proximal portions. Most of the tubules are very long and reach the ventral or posterior margins of the bone, or end very close to the margins of the preopercle. In specimen GG 431/9a and GG 431/15, the distal parts of some tubules in the ventral limb of the preopercle overlap the distal part of the subsequent tubule. The trunk canal is not preserved.
Vertebral column and associated bones (Pl. 4A–C): The total number of vertebrae as well as the numbers of abdominal and caudal vertebrae remain unknown due to poor preservation. The autocentra are longer than high, and are slightly constricted in the middle. The surface of the autocentra is smooth, without any ornamentation. In anterior/posterior view the autocentra are thin and ring-like, and do not or just slightly constrict the notochord. The parapophyses are fused to the centra ventrally. They are subtriangular and as long as their centra. A short process is present at the lateral margin of each parapophysis. The ribs are poorly preserved in the examined specimens. They are thin, slightly curved, and seem to end close to the ventral margin of the body. A single supraneural bone is preserved in GG 431/10. The bone is thin, elongate and seems to be straight. The number of supraneurals remains unknown. The abdominal neural arches are not fused to their centra in the juvenile specimen GG 431/10. The condition is unknown in adult individuals. Both halves of the abdominal neural spines are separate, whereas the caudal neural spines are fused. The hemal arches and spines are poorly preserved so not much is known about these bones.
Pectoral girdle and fin (Fig. 1A, Pl. 4A–C): The pectoral girdle is poor preserved in all examined specimens. The posttemporal, supracleithrum and cleithrum are preserved. The posttemporal consists of a well ossified dorsal limb and a thin ventral limb, which mainly carries the posttemporal canal. Most of the supracleithrum is covered by the opercle, the bone is comparatively broad and elongate. The cleithrum is composed of a narrow dorsal limb, which is oriented vertically; and a ventral, almost horizontal limb. The anterior tip of the ventral limb bends ventrally. A narrow, and elongate postcleithrum articulates with the cleithrum along its posterior margin, it is assumed to be the first postcleithrum. Other postcleithra are not preserved. Seventeen pectoral fin rays are preserved in GG 431/6, the first one is evidently broader than the others. The fin rays are segmented, and at least some of them are branched in their very distal portions.
Pelvic fin (Pl. 4A): The pelvic fin is placed at about 55% of standard length. The preservation of the pelvic girdle and fin in NRM P 6483 a, b and GG 431/10 is too poor to give a description.
Dorsal fin (Pl. 4A): The dorsal fin is placed at about 57% of standard length. The numbers of the pterygiophores and lepidotrichia remain unknown due to poor preservation. In NRM P 6483b (neotype), the first pterygiophore is formed of three processes which point anteroventrally. At least the two anterior processes are connected by a thin ossifiation.
Anal fin (Pl. 4A): The anal fin is poorly preserved in GG 431/10. It is placed at about 73% of standard length. The fin consists of at least one precurrent and ten principal lepidotrichia. The precurrent ray is significantly shorter than the principal rays. All principal anal rays are segmented and branched in their distal portions. The number and shape of the pterygiophores remains unknown.
Caudal skeleton and fin (Fig. 11, Pl. 4A): The description of the caudal skeleton is based in GG 431/10, a juvenile specimen. The ural and preural autocentra are poorly preserved. The fragments of the autocentra show that they were thin with smooth surfaces. The neural and hemal arches are not fused to the respective autocentra. At least the neural arches of preural centra 1 to 3 bear a sharp anterior process at their bases. The neural spine of preural centrum 3 is long, it ends close to the dorsal margin of the body. The neural spines form and angle of about 40° with the dorsal margin of the vertebra. The neural spine of preural vertebra 2 is not preserved. The neural spine of the first preural verebra is short, about as half as long as the spine of preural vertebra 3. The hemal spines of preural vertebrae 1 and 2 bear short anterior processes. Two ural vertebrae are present, both are poorly preserved so their exact shapes remain unknown. The first ural centrum is longer than the preural centra and supports two hypurals. Two neural spines are present in ural centrum 1+2. The anterior one is about as long as the neural spine of preural vertebra 1, whereas the posterior spine of ural centrum 1+2 is evidently shorter. The second ural centrum is evidently smaller than ural centrum 1+2. Nine hypurals are present. The first one is the largest bone of the series and bears a spine-like anterior process. Anterior processes are absent in the other hypurals. Hypural 1 and 2 are not fused at their bases. The hypurals decrease in size posteriorly. Three epurals are present. They are thin and elongate. The dorsal tips of the epurals are covered by the epaxial basal fulcra, so their length remain unknown. Seven uroneurals are present, all are elongate and the first three are slightly sigmoidal shaped. The anterior tip of the first uroneural is broken, so its length remains unknown. The first three uroneurals reach at least the anterior margin of the first ural centrum. Uroneurals 1 and 2 bear a thin membranous outgrowth at their anterodorsal margins. A single, plate-like dorsal caudal scute is present. The ventral caudal scute is incompletely preserved, so its size and shape remain unknown. Eight epaxial basal fulcra are present. The anterior ones are short, but their length increases posteriorly. An elongate fringing fulcrum is preserved in GG 431/10. The total number of fringing fulcra in the dorsal lobe remains unknown due to poor preservation. Fringing fulcra are absent in the ventral lobe of the caudal fin. There are 10+9 principal caudal rays. A short dorsal process is present in the proximal segment of principal ray 8. The proximal portion of the first segment of principal ray 10 is dorsally and ventrally expanded. Eight precurrent fin rays are present in the ventral lobe of the caudal fin. Six of them are segmented. The segmentation of all fin rays is straight or slightly sigmoidal. 'Urodermals' are not preserved.
Squamation (Pl. 4A): The body is covered with thin cycloid scales. Most of them show circular or oval outlines. In GG 431/10 the scales in the anterolateral part of the body are larger than the other scales. They are about as twice as high than broad, but also show circuli. The scales are devoid of ganoine.
Identification: The above described specimens are comparible with Leptolepis jaegeri sensu Nybelin (1974), particular based on the shapes of premaxilla, dentary, preopercle, and the presence of comparatively large, conical teeth on maxilla, premaxilla and dentary. The holotype of L. jaegeri is lost (Nybelin 1974; Maxwell, pers. comm.). Therefore, Nybelin (1974) designated NRM P 6483a, b as neotype. However, the neotype is poorly preserved and the assignment to L. jaegeri is apparently only based on “Its larger size and the locality (…)” (Nybelin 1974: 64). In the initial description L. jaegeri is described as: “Broader, larger, with larger scales.” (than L. “ bronni ”) (Agassiz 1832: 146, translated). The shape of the scales in the neotype is unknown due to the poor state of preservation of the specimen. Comparatively large scales were observed in the anterior part of the body of specimen GG 431/10. Thus, Nybelin´s assignment is most probably correct.
description: Published as part of 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), pp. 249-296 in Zootaxa 4243 (2) on pages 266-275, DOI: 10.11646/zootaxa.4243.2.2, http://zenodo.org/record/399081