Pleuropholis germinalis, Olive & Taverne & Brito, 2022

Olive, Sébastien, Taverne, Louis & Brito, Paulo M., 2022, Pleuropholis germinalis n. sp., a new Pleuropholidae (Neopterygii, Teleostei) from the Early Cretaceous of Bernissart, Belgium, Geodiversitas 44 (17), pp. 505-514 : 508-510

Pleuropholis germinalis n. sp.

( Figs 2-5 )

urn:lsid:zoobank.org:act:0E3ABDB0-1F72-4ADF-A1D4-68AFE8CF1B0C

Pleuropholis sp. indet. – Traquair 1911: 45, pl. IX, figs 1-3.

DIAGNOSIS. — Small sized actinopterygian (SL of roughly 64 mm) with the dorsal fin located posteriorly and at the same level as the anal fin. Species of Pleuropholis with the following unique combination of characters: robust preopercle with the horizontal limb as wide and high as the vertical limb; preopercle with the posterior edge entirely smooth; preopercle canal placed at equal distance from the dorsal and ventral borders of the horizontal branch (autapomorphy of P. germinalis n. sp.); short and upturned maxilla; dentary with leptolepid notch in its median-dorsal part; quadrato-mandibular articulation lying anteriorly to the orbital margin; smooth posterior border of flank scales.

HOLOTYPE. — IRSNB P.1236 and 1235 (part and counterpart; Figs 2 , 3 ).

PARATYPE. — IRSNB P.1234 ( Fig. 4 ).

OTHER SPECIMENS. — IRSNB Vert-01680-00651 ( Fig. 5 ).

ETYMOLOGY. — The specific name refers to the novel of Emile Zola, Germinal. The novel focuses on the coalmine work and the harsh conditions of miners. Without miners, fossils from Bernissart would have never been extracted and this specific assignment consequently honors them.

TYPE LOCALITY AND HORIZON. — Bernissart, Province of Hainaut, Belgium. Sainte-Barbe Clays Formation, uppermost Barremian to lowermost Aptian ( Yans et al. 2006, 2012; Dejax et al. 2007).

DESCRIPTION

With a standard length of approximately 64 mm (specimen IRSNB P.1234, Fig. 4 ), this is a small sized actinopterygian, although one of the largest within Pleuropholidae .

The highest part of the fish is located in the mid-length of the body ( Fig. 3 ). The head, from the anterior part of the rostral to the posterior part of the opercle, is roughly one fourth of the standard length. The dorsal fin is situated well posteriorly, at the same level as the anal fin. The dermal bones and the scales are covered with ganoin.

Skull

The skull is fragmented in all specimens exhibiting it. The skull roof is preserved in right lateral view on specimen IRSNB P.1236 ( Fig. 2 ) and is partially preserved in left lateral view, where it is somewhat distorted, in IRSNB P.1234 ( Fig. 4 ). Regarding IRSNB vert-01680-00651 ( Fig. 5 ), only the posterior part of the skull, in lateral view, is preserved. The following description of the skull is therefore mainly based on specimen IRSNB P.1236 ( Fig. 2 ).

The rostral is not well preserved in any of the specimens and its posterior suture with the nasals is not clearly discernible. The nasals are longer than wide, located anteriorly to the frontals. Frontals are the longest bones of the skull roof. Like in other species of teleosts (e.g. Pleuropholis, Ichthyokentema, Siemensichthys Arratia, 2000 , Eurycormus Wagner, 1863 , and Gondwanapleuropholis Brito & Gallo, 2002 ) the frontals are broad, and do not display the anterior narrowing found in more advanced teleosts ( Arratia 2000; Brito & Gallo 2002). The parietals ( Fig. 2 ) are subrectangular, slightly longer than wide and their length represents approximately two thirds of the length of the frontals. The extrascapulars are located posteriorly to the parietals and are barely distinguishable in the available material. Only the impression of the right dermopterotic is present in the specimen IRSNB P.1236 ( Fig. 2 ). The dermopterotic is a subrectangular bone, that widens in its posterior part.

The circumorbital series, as well as the posterior cheek region, are not well preserved in any of our specimens. The circumorbital series is formed by at least four infraorbitals, the dermosphenotic, and at least two supraorbitals. The infraorbital series is very fragmented in the specimen IRSNB P.1236 ( Fig. 2 ). The dermosphenotic is in contact with the dorsal edge of the most posterior infraorbital; it is a somewhat rectangular bone that participates in the posterodorsal corner of the orbit, below the frontal and the dermopterotic.

The preopercle is a “L-shaped” robust bone in which the horizontal limb is as wide and high as the vertical limb. These limbs are placed perpendicular to each other ( Fig. 2 ). The posterior edge of the preopercle is totally smooth ( Figs 2 ; 5 ). The preopercular canal is placed at equal distance from the dorsal and ventral borders of the horizontal limb of the preopercle ( Figs 2 ; 5 ). The opercular series is formed by a slightly deeper than wide opercle, a subtriangular subopercle, and an interopercle (incomplete on IRSNB P.01236).

The maxilla is upturned, rather narrow and short, but badly preserved ( Fig. 2 ). The oral margin of the maxilla is not preserved here. The single supramaxilla is a moderately large bone placed posteriorly to the maxilla and along the anterior margin of the orbit ( Fig. 2 ). No premaxilla is preserved in the available specimens.

Dentary and angular are exposed laterally. The dentary is a short stout subsquare bone that increases in height posteriorly. The dentary presents, in its median-dorsal part, a leptolepid notch, like in P. decastroi Bravi, 1988 , from the Early Cretaceous of Italy ( Taverne & Capasso 2019). The dentary is traversed by the mandibular sensory canal, which extends along its ventral border. Posteriorly, the dentary sutures with the angular that is partially exposed in IRSNB P.1236 and forms the posterior corner of the lower jaw ( Fig. 2 ). Other bones of the lower jaw are not exposed in the specimens studied here. No teeth have been observed in the available material.

Vertebral column

Only few vertebral elements of the abdominal region are exposed where some scales are displaced or lost ( Fig. 4 ).

Paired girdles and fins

Some elements of the pectoral girdle are preserved as fragmented elements, impressions in the matrix, or are hidden by the presence of displaced scales ( Figs 2-4 ). The cleithrum is a robust bone located ventrally to the short and small supracleithrum. It is smooth, and anteriorly underlies the subopercle. Fragmented and displaced elements of the putative ventral branch of the cleithrum are found in IRSNB P.1236 ( Fig. 2 ). The pectoral fin is positioned close to the ventral margin of the body and below the large scales of the body flank in IRSNB P.1234 ( Fig. 4 ). At least nine rays are preserved. In IRSNB P.1235, a pelvic fin is preserved, in which roughly seven rays are preserved ( Fig. 3 ). No bones of the pelvic girdle are exposed in any of the studied specimens.

Dorsal and anal fins

The dorsal fin ( Figs 3 ; 4 ) counts at least 9 dorsal fin rays on IRSNB P.1235 ( Fig. 3 ) whereas the anal fin ( Fig. 4 ) displays at least 11 fin rays. The anterior margin of the anal fin displays at least 7 fringing fulcra. Elongated pterygiophores, supporting the anal fin, are observed anteriorly.

Caudal fin

The caudal pedicle is slender and covered with rhombic caudal scales( Figs 4 ; 5 ).The caudal endoskeleton is covered by scales and not visible for analysis. Although the posterior tip of the caudal fin is not preserved, the caudal fin is almost complete in IRSNB P.1234 ( Fig. 4 ). The caudal fin is hemiheterocercal and includes at least 19 evenly segmented rays. On the dorsal margin of the caudal fin, there are at least 4 dorsal caudal fulcra. The ventral margin of the caudal fin is preserved in none of the specimens.

Scales

The scales are thick and of ganoid type ( Figs 2-5 ). Those along the flank are rectangular in shape, 5-6 times deeper B Cl than long, with anterior and posterior borders being slightly curved. The entire posterior border of all flank scales is smooth. Dorsally to the flank scale row, two rows of rhomboidal scales are observed. The most dorsal scales, anterior to the dorsal fin, could potentially be pair scute-like elements. However, the preservation of this feature is not good enough to be conclusive. Ventrally to the flank scale row, at least two scale rows (probably three) are present. Scales are relatively small and rhomboidal. The lateral line is not observable through the body flank scales; pores or thickenings revealing the course of branch of the lateral line system are not observable probably due to a lack of preservation.

Figures

FIG. 2. — Skeleton of Pleuropholis germinalis n. sp., IRSNB P.01236, holotype: A, photograph; B, close-up on the head whitened with ammonium chloride;C, line drawing reconstruction. Scale bars: A, 1 cm; B, C, 0.5 cm.

FIG. 3. — Skeleton of Pleuropholis germinalis n. sp., IRSNB P.01235, holotype, counterpart of IRSNB P.01236: A, photograph; B, line drawing close-up on the dorsal fin; C, line drawing close-up on the pelvic fin. Scale bars: A, 0.5 cm; B, C, 0.25 cm.

FIG. 4. — Skeleton of Pleuropholis germinalis n.sp., IRSNB P.01234,paratype:A, photograph;B, line drawing of the vertebral skeleton and of fins.Scale bars:1 cm.

FIG. 5. — Photograph of the skeleton of Pleuropholis germinalis n. sp. with a close-up on the preopercle, IRSNB vert.01680-0065. Scale bars: A, 1 cm; B, 2 mm.