Pseudopholidoctenus germanicus, Arratia & Schultze, 2024

Arratia, Gloria & Schultze, Hans-Peter, 2024, The oldest teleosts (Teleosteomorpha): their early taxonomic, phenotypic, and ecological diversification during the Triassic, Fossil Record 27 (1), pp. 29-53 : 29

publication ID	https://dx.doi.org/10.3897/fr.27.115970
publication LSID	lsid:zoobank.org:pub:AB28819E-2917-4A05-ACD5-ACDB2617580F
persistent identifier	https://treatment.plazi.org/id/CC8072F4-A28E-42EA-91D9-3D45809E1BBD
taxon LSID	lsid:zoobank.org:act:CC8072F4-A28E-42EA-91D9-3D45809E1BBD
treatment provided by	by Pensoft
scientific name	Pseudopholidoctenus germanicus
status	sp. nov.

Treatment

Pseudopholidoctenus germanicus sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6

Pholidoctenus 2021 Pholidoctenus sp. Schultze and Kriwet: p. 321, fig. 11.

Diagnosis.

(Based on a unique combination of characters among stem teleosts. Autapomorphies are identified with an asterisk [*].) Small fish of about 55 mm total length. Skull roof bones covered by small tubercles and ridges of different sizes. The length of the nasal region is about 30% of the midorbital width (Table 1 View Table 1 ). The length of the postorbital region is about 50% of the orbital region length [*]. Deep opercle about five times deeper than the subopercle. Suture between opercle and subopercle slightly oblique. Ventral limb of cleithrum straight and narrow, lacking a posterior expansion at the confluence of both limbs. With a series of large scales or scutes, almost square-shaped, preceding the epaxial lobe of the caudal fin [*]. Less than 18 principal caudal rays present [*]. No hypaxial procurrent rays present [*]. Scales covered with a smooth layer of ganoine. Posterior margin of the scales with a few conspicuous acute projections or serrae.

Derivatio nominis.

The name refers to the similarity of the skull roof and serrations on bones and scales to the genus Pholidoctenus from the Norian of Italy.

Type material.

Holotype. MB. f. 18641, a well-preserved skull roof including sensory cephalic cranial system.

Paratypes. MB. f. 19904, almost complete specimen (missing the anterior part of the head and distal tips of the caudal fin rays), relatively well preserved considering the hardness of the rock and problems cleaning the surface of bones without destroying them. MB. f. 19905 and 19906, skull roofs.

Provenience.

Opencast mine in Rüdersdorf, 25 km east of the center of Berlin, Germany.

Age.

Lower Middle Triassic, lower Anisian (middle Muschelkalk).

Description.

This is a small species of about 55 mm total length and about 36 mm SL. Specimen MB. f. 19904, with the body and squamation preserved in situ, is a rare one in a locality where the fishes are usually preserved as disarticulated bones (Fig. 2 View Figure 2 ). The anterior part of the head is missing, and since the body is slightly bent, it is not possible to estimate its body shape accurately; possibly, it was oblong, and the peduncle depth seems to be half of the predorsal depth. The pectoral fins are missing, and the pelvic fins are incompletely preserved. The dorsal fin is placed at about half the length of the fish, and the anal is placed posteriorly, very close to the ventral margin of the caudal fin.

Skull roof. The nicely preserved skull roof (8.3 mm long and 7.5 mm wide at the postorbital region) has all dermal bones fused into a large plate (Fig. 3 View Figure 3 ), with the exception of the rostral and nasal bones that are not preserved. The skull roof plate is almost triangular, being narrow anteriorly at the so-called triangular nasal region and expanding posteriad, reaching its maximum width at the supratemporotabular [= dermopterotic] level and ending in a straight line (Fig. 3 View Figure 3 ). A posterior process is absent in the posterior margin of the supratemporotabular region. The skull roof looks like a flat plate having a straight profile. Most of the skull roof is formed by the orbital region whose length is about 62% of the total length of the skull roof. The small triangular nasal region is short, and its length is about 11% of the skull roof length (Table 1 View Table 1 ). The lateral margins of the nasal region would articulate with the nasal bones that are not preserved, but considering the oblique position of both sutures for the nasal bones, it is assumed here that the rostral bone had an anterior position in front of the nasals. The orbital region is narrower than the postorbital region, with the width at its mid-region being ca. 33% of the postorbital region width (Table 1 View Table 1 ).

The skull roof (Fig. 3 View Figure 3 ) does not show obvious sutures, but there is a slight median overgrowth in the region where both parietals [= frontals] would fuse, a tenuous, incomplete suture where both postparietals [= parietals] would meet, and a tenuous suture separating the short and small right supratemporotabular [= dermopterotic]. According to this interpretation, the parietal region would be the largest component of the skull roof, forming the whole orbital region and extending into the postorbital region. There is no process at the lateral margin at the confluence of the nasal and orbital regions of the plate. The lateral margin of the plate, at the supratemporotabular region, shows an invagination that may be occupied by the dorsal margin of the suborbital or an accessory suborbital, as in Pholidoctenus serianus ( Zambelli 1977; Arratia 2013) and Ph. sanpellegrinensis ( Arratia 2017). There is no evidence of a supraoccipital bone and/or epiotics at the posterior region of the plate.

The preorbital region of the skull roof plate that is formed by the fusion of both parietals occupies a significant part of the plate (Table 1 View Table 1 ). In contrast, the anteriormost narrow orbital region is about 30% of the postorbital region. This gives the skull roof characteristic proportions and shape (see section "Morphological comparisons and taxonomic assignments"). The anterior nasal region of the plate is triangular-shaped, and acting as sutural margins for the nasal bones, an interpretation based on other pholidophorids and teleosteomorphs with the bones in situ. Following such an outline and by comparisons with Pholidoctenus serianus and Ph. sanpellegrinensis , it is hypothesized here that both nasals were medially sutured in part of their medial contact surfaces. The posterolateral corner of the orbital region is the area corresponding to the autosphenotic or sphenotic, which in this case, is fused to the parietal laterally and supratemporotabular [= dermopterotic] posteriorly.

The surface of the skull roof is covered by a thin layer of smooth ganoine; small tubercles and ridges covering the whole skull roof are observed under high magnification.

The supraorbital sensory canal (Fig. 3B View Figure 3 ) is visible (on both sides) through the bone, with few small pores, irregularly placed and opening on the surface directly on the trajectory of the canal. The supraorbital sensory canal extends posteriad, ending in the postparietal branch, just anterior to the middle pitline. The supraorbital canal, nicely preserved, shows that there is not a lateral connection with the infraorbital canal, neither with the otic canal whose trajectory (and pores) is partially visible in the right supratemporotabular region of the plate. Three pitlines (Fig. 3B View Figure 3 ) are clearly visible on the postorbital region. The longest one is the middle pitline that extends from near the mid-region of the plate to the lateral margin of the supratemporotabular region. The short anterior pitline is placed in continuation of the postparietal branch, and the posterior pitline, equally short, extends near the posterior margin of the skull roof plate.

Circumorbital bones and suborbital region. Only the posterior part of the circumorbital ring is preserved (Fig. 4 View Figure 4 ) and includes the dermosphenotic and two partially preserved dorsoposterior infraorbitals that probably correspond to infraorbitals 4 and 5. The suborbital region, placed between the dorsoposterior infraorbitals anteriorly and the opercle and preopercle posteriorly, is unclear. It could include one large suborbital or two suborbitals.

Opercular bones. The opercle and subopercle, and a small fragment of the preopercle (Fig. 4 View Figure 4 ) are preserved. The opercle is a large bone, almost five times deeper than the subopercle. It is almost oval-shaped dorsally, expanding slightly at its mid-region and suturing with the subopercle throughout a slightly oblique suture. One small serration is preserved at the posterior margin.

The small subopercle has an oval-shaped ventral contour; its short anterodorsal process is at the confluence of the preopercle, opercle, and subopercle. The three opercular bones have smooth exposed surfaces. The posterior section of three narrow branchiostegal bones are preserved below the subopercle.

Paired girdles and fins. A section of a stout, long and narrow lower arm of the cleithrum (Fig. 4 View Figure 4 ) is preserved; the angle of the lower arm is characteristically shaped and implies that the upper section of the cleithrum was short. An elongate and moderately broad supracleithrum is posterior to the opercle and dorsal part of the cleithrum. The trajectory of the lateral line canal is not visible. Three approximately rectangular-shaped elements, scale-like, are positioned posterior to the supracleithrum and cleithrum and are interpreted here as postcleithra. Postcleithra 2 and 3 are slightly displaced and partially covering each other. There is no information on other pectoral girdle bones or pectoral rays.

The pelvic basipterygium is covered by scales so that information is not available, and the fin is represented by a few, incomplete preserved pelvic rays.

Dorsal and anal fin. An incompletely preserved dorsal fin (Fig. 5 View Figure 5 ) is placed slightly anterior to the mid-length of the body trunk, slightly posterior to the incompletely preserved pelvic rays, and it does not oppose the anal fin (Fig. 2 View Figure 2 ). A broad, slightly oval and short scute precedes four paired basal fulcra that are leaf-like and are followed by at least nine dorsal rays, seven with broken bases and two that are displaced. An elongate and broad fringing fulcrum is placed between the last basal fulcrum and the first principal ray, and it is followed by a series of elongated fringing fulcra that decrease in size distally. The first principal ray, only segmented and not branched, has a long base; the following principal rays have also long bases that become thinner posteriad. The bases of the dorsal rays are surrounded by enlarged, thick scales (Fig. 5 View Figure 5 ).

Remains of anal rays (Fig. 6 View Figure 6 ) are preserved posteriorly in the body. Remnants of five anal rays, incompletely preserved, almost reach the anterior margin of the hypaxial lobe of the caudal fin.

Caudal fin. The fin lacks its middle-posterior part; it seems to be hemiheterocercal, with an abbreviated dorsal scaly lobe (Fig. 6 View Figure 6 ). Preceding the dorso-anterior margin of the fin is a series of scutes that apparently were in continuation with the posterior part of the dorsal fin, which is missing. The series of scutes is in continuation with three basal fulcra that are lanceolate in shape with their median posterior margin bifurcated. An incomplete series of elongate fringing fulcra follows. The fin seems to have few principal rays; 14 rays are preserved, and apparently there are not more; their segmentation is mainly straight. The number of principal rays is fewer than in the Italian genus Pholidoctenus with 18 to 22 principal rays ( Arratia 2013, 2017). Remains of one hypaxial basal fulcrum is preserved; this fulcrum is followed by a series of elongate fringing fulcra. According to the preservation, procurrent rays are absent in the hypaxial lobe of the caudal fin, which is another major difference with species of Pholidoctenus .

Scales and scutes. Ganoid scales of lepisosteid-type of different sizes and shapes cover the body. Most scales of the dorsal and ventral rows of the flank are rhombic, rectangular or even square-shaped, with a variable number of small serrations at their posterior margin. Apparently, the three main rows of the flank, just posterior to the upper half of the opercle, are deeper and larger than other posterior scales (Fig. 2 View Figure 2 ). The scales decrease in size posteriad and have different shapes, but they are not preserved well enough for a detailed description.

The scales at the posterior region of the dorsal margin anterior to the dorsal fin seem to be enlarged in comparison to dorsolateral scales (Figs 2 View Figure 2 , 5 View Figure 5 ). The median scales placed posterior to the dorsal fin are incompletely preserved, but there are at least four large, square-shaped scales preceding the epaxial basal fulcra (Fig. 6 View Figure 6 ).

Teleosteomorpha Arratia, 2001