Rostropycnodus gayeti, Taverne & Capasso, 2013

Taverne, Louis & Capasso, Luigi, 2013, Gladiopycnodontidae, a new family of pycnodontiform fishes from the Late Cretaceous of Lebanon, with the description of three genera, European Journal of Taxonomy 57, pp. 1-30 : 19-26

Rostropycnodus gayeti gen. et sp. nov.

Figs 15-21

urn:lsid:zoobank.org:act:89707CF2-AF8E-450E-8D6F-16A0B02EDE93

Diagnosis

Gladiopycnodontid with a very long snout, forming a rostrum anteriorly outpacing the lower jaw level ( Fig. 18 ). Anterior tip of the rostrum formed by both the prefrontal and the premaxilla.Anterior extremity of the prefrontal bearing four small spines. Frontal bearing one long pointed horn. Dermosupraoccipital forming a nuchal process. Small lower jaw. Preopercle much larger than the exposed part of the hyomandibula-dermohyomandibula. Posttemporal articulated with the nuchal process. Hypertrophied cleithrum with a long and broad ventral branch. Short and broad pectoral spine. Two large postcleithra. Nuchal horn absent. 17 neural spines and 17 haemal spines before the epichordal and hypochordal series. Dorsal fin with 6 pterygiophores. Anal fin with a long and strong initial spine and 4 short soft rays. Caudal skeleton with 6 epichordal and 7 hypochordal elements. Last three hypochordal elements moderately broadened. Caudal fin with 21 rays and a convex posterior margin. Body entirely covered by large, tuberculated scales with a spiny anterior border.

Etymology

The species name of the new gladiopycnodontid is dedicated to Mireille Gayet (Lyon), the well known French palaeontologist, who has greatly improved our knowledge of the Late Cretaceous ichthyofauna of Lebanon.

Material examined

Holotype

Sample CLC S-608a, b, the two faces of a nearly complete specimen ( Fig. 15 ). The tip of the rostrum and the caudal fin are missing. Total length: 47.3 mm.

Paratypes

Sample CLC S-337, a complete specimen ( Fig.16 ). The body and the tail are severely crushed. Total length: 59.8 mm.

Sample CLC S-595, a nearly complete specimen ( Fig.17 ). The tip of the rostrum is missing. Total length: 58.6 mm.

Formation and locality

Marine Upper Cenomanian, Haqel, Lebanon.

Holotype morphometric data

Due to the incompleteness of the available specimens, no accurate morphological data can be provided and the reconstruction is therefore composite.

Osteology

1. The skull ( Fig. 19 )

The head, rostrum and opercular series included, is twice as long as the body. The dermal bones of the skull are ornamented with a few thin ridges and many tubercles.

The snout is elongated, forming a long rostrum that is, however, shorter than in Gladiopycnodus karami gen. et sp. nov. The preorbital length, rostrum included, represents 59.5 % of the total length of the skull. The rostrum consists of the prefrontals, the premaxillae, the mesethmoid and the parasphenoid. Only the most posterior parts of the mesethmoid and of the parasphenoid are visible. Both the prefrontal and the premaxilla form the tip of the rostrum. The long and broad prefrontal bears four small spines on its anterior tip as seen on sample CLC S-337. The upper margin of the prefrontal is ornamented with small spines. The vomer remains hidden by the premaxilla. A vomer with very small molariform teeth is present in the family, as shown in some other gladiopycnodontid genera.

The frontal and the dermosupraoccipital are the main bones of the skull roof. The frontal is short but broad. Anteriorly, it does not go beyond the orbit. The frontal bears a long pointed horn with a large basis and of which the anterior and posterior borders are spiny. The dermosupraoccipital is enlarged and forms a long and broad nuchal process. The autosphenotic, parietal and dermopterotic are rather small bones. The parietal does not bear a brush-like process. The large supratemporal is pressed against the dermosupraoccipital.

The parasphenoid is long and toothless. A well developed orbitosphenoid is articulated on the rear of the mesethmoid. The other endocranial bones of the braincase are hidden by the hyomandibuladermohyomandibula, the opercle and the hypercleithrum.

The toothless upper jaw is a part of the rostrum. The premaxilla is very long and rather narrow but, however, a little broader anteriorly than posteriorly. It is located under the prefrontal and is sutured with it all along its upper margin. The maxilla is small, considerably shorter than the premaxilla, lance headshaped and posteriorly located.

The lower jaw is small, triangular in shape and, by far, does not reach the anterior extremity of the rostrum. The short dentary bone, well visible on specimen CLC S-608, is reduced to its ventral branch. The teeth are not preserved. The other bones of the mandible are too crushed to allow adequate description.

The bones of the palatoquadrate arch are hidden by the preopercle.

A large dermosphenotic is the only part preserved of the infraorbital series.

The exposed part of the hyomandibula-dermohyomandibula is much smaller than the large preopercle that is, however, not as hypertrophied as in Gladiopycnodus karami gen. et sp. nov. The preopercle is separated from the lower margin of the fish by the cleithrum, another difference from G. karami gen. et sp. nov.. The small opercle is a deep ovoid bone with an acuminate ventral extremity. The hyoid bar

and the branchiostegal rays are not visible. A fragment of a branchial bone and a few short nail-shaped branchiospines are preserved in the orbit of specimen S-337.

2. The girdles ( Figs 18-19 )

The massive pectoral girdle is intimately associated with the skull, forming a sort of cephalo-thorax. The posttemporal is well developed and located just behind the hypercleithrum. The hypercleithrum (= supracleithrum) is a large triangular bone with some spines on its posterior border. The cleithrum is really gigantic, with a very broad dorsal branch and a very long, broad and pointed ventral branch reaching the lower jaw level. There are two large postcleithra well visible on sample CLC S-337 and located behind the cleithrum. The pectoral fin is replaced by a short but very broad spine that is partially fused with the cleithrum.

Two small pelvic bones are preserved between the cleithrum and the post-coelomic bone on specimen CLC S-595, but the fin rays are lost.

3. The axial skeleton ( Fig. 18 )

The body is fusiform. Holotype CLC S-608a, b shows a complete vertebral column. The notochord is incompletely surrounded by the neural and haemal arches, which are reduced. The neural and haemal spines are well developed. There are 17 neural spines before the epichordal series and 17 haemal spines before the hypochordal series. The first ten neural spines are thin. The seven other spines are shorter but also broader. The first three haemal spines are rather short. Their length progressively increases from the fourth to sixth one and then decreases from the seventh to the seventeenth. The neural and haemal spines are not interlocked together by interdigitating sutures. The presence of ribs is uncertain, the situs viscerum being hidden by the gigantic cleithrum.

The post-coelomic bone is moderately long, robust, extremely broad and backwardly curved. Dorsally it reaches the vertebral axis and ventrally the inferior border of the fish.

4. The dorsal and anal fins ( Fig. 20 )

The dorsal fin is short. Holotype CLC S-608b shows 6 dorsal pterygiophores, largely separated from each other. The dorsal rays are lost but, considering the spacing between the pterygiophores, they surely formed a series of isolated finlets as in Gladiopycnodus karami gen. et sp. nov.

The anal fin begins with a large and strong spine. This spine has spiny dorsal and ventral margins, an acuminate posterior tip and a very broad basis articulated on the post-coelomic bone and the first anal pterygiophore, which is much longer than the following ones. The pointed tip of the spine reaches the level of the tail but does not outpace the caudal fin as in G. karami gen. et sp. nov. Four other small anal pterygiophores, bearing four short rays, are visible on holotype CLC S-608a.

5. The caudal skeleton ( Fig. 21A )

The caudal skeleton is rather well preserved on holotype CLC S-608a, b. There are 6 epichordal elements and 7 hypochordal elements. The last three hypochordal pieces are moderately broadened. No urodermal is visible.

Paratype CLC S-595 possesses a more or less complete caudal fin, but essentially preserved as a print. There are 21 rays, but it is not possible to distinguish the procurrent from the principal rays. The fin has a convex distal border ( Poyato-Ariza & Wenz 2002: fig. 36 B).

6. Squamation ( Fig. 21B )

The body is entirely covered by large deep scales that are imbricated. Their entire surface is ornamented with well developed tubercles and their anterior border is often irregularly spiny, as clearly seen on paratype CLC S-595. The first scales of the dorsal margin of the fish are of the same type, but still larger than those on the flanks. Generally, on the other samples, only the tubercles are preserved, but not the outlines of the scales.

Two large, irregularly shaped pelvic scales are visible below the pelvic bones on paratype CLC S-595.

Figures

Fig. 15. Rostropycnodus gayeti gen. et sp. nov. Holotype CLC S-608a (above) and 608b (below).

Fig. 16. Rostropycnodus gayeti gen. et sp. nov. Paratype CLC S-337.

Fig. 17. Rostropycnodus gayeti gen. et sp. nov. Paratype CLC S-595.

Fig. 18. Rostropycnodus gayeti gen. et sp. nov., paratype CLC S-337. Reconstruction based on the three specimens. Body scales omitted.

Fig. 19. Rostropycnodus gayeti gen. et sp. nov., paratype CLC S-337 Reconstruction of the skull based on the three specimens.

Fig. 20. Rostropycnodus gayeti gen. et sp. nov. The pelvic and anal region of holotype CLC S-608 (above) and of paratype CLC S-595 (below).

Fig. 21. Rostropycnodus gayeti gen. et sp. nov. A. Caudal skeleton of holotype CLC S-608a. The arrows point on the more external procurrent rays of the caudal fin. B. Body scales of paratype CLC S-595.