Perledovatus nothosomoides ( Deecke, 1889 ) López-Arbarello & Brocke, 2024

López-Arbarello, Adriana & Brocke, Rainer, 2024, New generic name for a small Triassic ray-finned fish from Perledo (Italy), Swiss Journal of Palaeontology (30) 143 (1), pp. 1-12 : 3-7

publication ID	https://doi.org/10.1186/s13358-024-00325-6
persistent identifier	https://treatment.plazi.org/id/AE5C87EC-FFE0-7A35-FCDB-FCEBFD2EFE8C
treatment provided by	Felipe
scientific name	Perledovatus nothosomoides ( Deecke, 1889 )
status	comb. nov.

Treatment

Species Perledovatus nothosomoides ( Deecke, 1889) new comb.

1889 Allolepidotus nothosomoides n. sp. —Deecke: p. 118–119, pl. 6: Fig. 9.

1910 Allolepidotus nothosomoides Deecke —De Alessandri: p. 116–118, pl. 8: Fig. 7.

2001 Allolepidotus nothosomoides —Lombardo: p. 350.

Holotype

SMF P1237 About SMF a, b. ( Fig. 2 View Fig ). Te holotype is a complete and rather well-preserved specimen in right lateral view. Unfortunately, it has been damaged and the squamation in the second half of the body and parts of the caudal fin are now lost (compare Fig. 2 View Fig with pl. 6, Fig. 9 in Deecke, 1889).

Type locality and horizon

Perledo, Italy. Perledo Member of the Perledo-Varenna Formation; upper Ladinian, Middle Triassic ( Gaetani et al., 1992).

Diagnosis

Small neopterygian fish characterized by the following combination of characters: bones of the skull and pectoral girdle densely ornamented with tubercles; small parietals contacting at midline; large dermopterotic, almost twice the size of the parietal, approximately trapezoidal, deepest posteriorly; supraorbital bones present; suborbital bones present; maxilla long, almost reaching posterior end of lower jaw; maxilla with almost straight ventral border, fully garnished with small conical teeth, and concave posterior border, but without postmaxillary process; moderately large median gular, also strongly ornamented; quadratomandibular articulation well behind the orbit; comma-shaped preopercle almost vertically oriented; very inclined interopercle; opercle much larger than subopercle; oval body shape with large, nearly circular head; BD/SL = 0.44; HL/SL = 0.35; OL/HL = 0.29; dorsal fin emarginate with distinctly long marginal ray; caudal fin deeply forked with equally large dorsal and ventral lobes, with broadly acute distal ends; dorsal fin originates slightly behind insertion of pelvic fins and ends approximately at origin of anal fin; PreD/SL = 0.56, PreV/ SL = 0.52, PreA/SL= 0.70; (PreD-PreV)/SL = 0.04; (PreA-PreD)/SL = 0.15; complete series of distinctly large scutes between dorsal and caudal fins, and between anal and caudal fins; scales in anterior two thirds of the body with serrated posterior borders; middle flank scales deeper than long, up to 2.3 depth/length ratio; ventral flank scales between pectoral and pelvic fins quadrangular; 38 scales along the lateral line, vertical row at dorsal fin origin with 17 scales (7 + 1 + 9); 9 scales in marginal row of axial lobe. Pterygial formula: (D18 / V5 A15 C33) T38.

Remarks Te original description of SMF P1237 by Deecke (1889) is quite complete, and after direct study of the specimen, the senior author (ALA) has been able to verify most of the characters described by him. Deecke was not able to trace the boundaries of the individual cranial bones and did not describe them, but he did describe details of the postcranium, which are now lost but appear to be accurate given the remains still in the rock. Recent preparation of the specimen has revealed more detailed anatomical information, making it possible to complete the description.

Description

Specimen SMF P1237 is a medium-sized fish with oval body shape, broad caudal peduncle and deeply forked and evenly lobed caudal fin ( Fig. 2 View Fig ). Although large, the head is relatively short. Its length represents ~ 35% of the standard length, but its depth is larger than its length, equal to the body depth close to the end of the dorsal fin and represents ~ 83% of the maximal body depth approximately midway between the skull and the dorsal fin. Te maximal body depth is close to half of the standard length. Te profile of the head is strongly curved, and the round orbit is large and very close to the forehead edge. Te longitudinal diameter of the orbit reaches almost a third of the head length and the preorbital distance is only ~ 18% of the head length.

Te exposed dermal bones in the skull and pectoral girdle are strongly ornamented with densely arranged fine tubercles; there is no evidence of ganoin on them ( Fig. 3 View Fig ). Tis ornamentation extends on a few scales around the dorsal midline immediately behind the skull. Te bones in the snout are imperfectly preserved, but a small rectangular rostral is visible; it is traversed by a median groove corresponding to the ethmoidal commissure. Te presence of a post rostral is unlikely, but it cannot be excluded with certainty. Te nasals seem to be long and slender, but are poorly preserved. Te frontal broadens in posterior direction, following the curvature of the orbit, and narrows towards the midline at the suture with the dermopterotic. Te proportions of the bone can be estimated only roughly, the maximal length to width ratio being approximately three. Te parietal is relatively small and almost quadrangular, with a width to length ratio of 0.85; the ratio between the parietal length and the frontal length is ~ 0.27. Te trapezoidal dermopterotic is large, approximately as long as it is wide, with almost parallel medial and lateral borders, perpendicular posterior bor- der, and posteriorly inclined anterior border. Its posterior and ventral borders are nearly equally long and perpendicular; they form a small, posteriorly directed posteroventral process. Te lateral border of the dermopterotic is ~ 1.5 times the length of the dorsal border or the length of the parietal. In the back of the skull are two extrascapular bones. Te lateral extrascapular is almost quadrangular and the medial extrascapular is subtriangular, narrowing towards and reaching the dorsal midline. Te posterior limits of the posttemporal are unclear, but the bone is relatively large and reaches the dorsal midline.

Te circumorbital series includes the antorbital, lacrimal, two subinfraorbitals, the jugal, two postinfraorbitals, the dermosphenotic, and three supraorbitals ( Fig. 3 View Fig ). Te antorbital and lacrimal are very poorly preserved and their shape is only roughly estimated. Te antorbital apparently has approximately equally large vertical and horizontal portions. Te lacrimal is larger than the subinfraorbitals, but smaller than the jugal. It is almost rectangular, more than twice as long as it is high, with an excavated concave dorsal border. Te subinfraorbitals are rectangular, with the anterior one slightly longer than deep, and the posterior subinfraorbital nearly twice as long as it is high, and twice as long as the length of the anterior subinfraorbital. Te jugal is quite large, and subtrapezoidal in shape, expanding posteriorly, almost reaching the preopercle. It has almost straight dorsal and anterior borders, irregularly convex posterior border, and slightly concave ventral and orbital borders. Numerous ridges on the surface of the jugal and irregular indentations of its posterior border indicate intensive branching of the infraorbital canal. Te ventral postinfraorbital is very badly preserved and its shape can be reconstructed only roughly. Te dorsal postinfraorbital is trapezoidal, narrowing dorsally, somewhat deeper than it is long. Te infraorbital sensory canal is indicated close to the orbital border of the infraorbital bones, except in the lacrimal and antorbital, and several ridges and pores indicate the presence of numerous branches, especially in the jugal and subinfraorbitals. Sensory lines are not clearly discernible in the lacrimal and antorbital, except for a portion of the infraorbital canal in the posterior part of the lacrimal and several large openings in the lacrimal and antorbital.

Te dermosphenotic is tightly bound to the dermopterotic and frontal and rigidly incorporated into the skull roof ( Fig. 3 View Fig ). Its shape is subtriangular, narrowest ventrally, with divergent posterior and anterior borders; the latter is longer than the former and follows the curvature of the orbit. Te dorsal and orbital borders are approximately equally long. Anterior to the dermosphenotic, three supraorbitals complete the dorsal rim of the orbit. Te posterior supraorbital is the largest in the series. Te dermosphenotic and supraorbitals show the same ornamentation of densely arranged tubercles as present in the skull roofing bones.

Te area between the postinfraorbitals, jugal and opercle is covered by what appears to be a single large suborbital bone, which covers the anterior margin of the dorsal portion of the preopercle ( Fig. 3 View Fig ). Dorsal and ventral to this large suborbital, several partially preserved bones are interpreted as additional suborbitals; their precise number and shape cannot be determined. Between the large suborbital and the dermosphenotic is a small bone which might represent a dermal sphenotic ossification or, more likely, an additional small suborbital.

Te preopercle is comma shaped and almost vertically oriented; its precise shape cannot be reconstructed

( Fig. 3 View Fig ). Te opercle is approximately rectangular with oblique ventral border. It is deeper than it is long, and much larger than the subopercle. Te maximal length of the opercle, at its ventral border, is ~ 60% of its maximal depth at the anterior border. Te maximal depth of the subopercle, excluding the ascending process, is ~ 25% of that of the opercle. Te interopercle is elongated in a posterodorsal to anteroventral direction at an angle of approximately − 55° to the longitudinal axis of the fish. Tere appears to be a separate small bone, an anteopercle or a dermohyal, between the anterodorsal corner of the opercle and the dorsal end of the preopercle, but this should be confirmed with better preserved specimens.

Te gape is large ( Fig. 3 View Fig ). Te quadrato-mandibular articulation is well behind the orbit and both jaws are long and robust. Te premaxilla is only partially exposed, anterior to the maxilla and medioventral to the antorbital and rostral. Te long maxilla extends far beyond the posterior rim of the orbit, its length represents ~ 57% of the head length and ~ 64% of the lower jaw length. Te shape of the maxillary blade in lateral view is quite irregular. Te ratio between the maxillary maximal depth, at its posterior border, and the maxillary length is ~ 0.20. Te ventral border is almost straight in the anterior third, convex in the middle and slightly concave in the posterior third. Tiny conical teeth are scattered along the ventral margin of the maxilla, which was probably completely toothed. Te maxillary posterior border is gently sinuous, concave in the middle, but there is no postmaxilary process. Te dorsal border is almost straight in the anterior half, and it is concave in the posterior half, where it accommodates the relatively large supramaxilla. Te supramaxilla is approximately oval, slightly narrowing anteriorly, with a depth to length ratio of ~ 0.33. Te length of the supramaxilla represents ~ 38% of the length of the maxilla.

Te lower jaw is incompletely exposed in lateral view; the dentary, angular and surangular are visible ( Fig. 3 View Fig ). Te dentary is very long, approximately as long as the maxilla, with a more or less rectangular, uniformly deep anterior half. Te dentary symphysis is rather deep. As exposed, the depth of the anterior end of the dentary represents ~ 15% of the lower jaw length. Te ascending ramus of the dentary forming the coronoid process is hidden by the maxilla. Te posterior border of the dentary, which sutures to the angular, is irregularly zigzag. Te dorsal half of the dentary is smooth, but the ventral portion is strongly ornamented with densely arranged short ridges and small tubercles. Te mandibular sensory canal is indicated by a series of relatively large openings aligned parallel and close to the ventral border of the dentary. Dentary teeth are not preserved, but their presence cannot be excluded. Te angular completes the lower jaw posteroventrally. Its surface is ornamented with densely arranged tubercles. Te surangular is only little exposed, mostly hidden by the maxilla.

Tere is a moderately large median gular, which is also strongly ornamented with densely arranged tubercles

( Fig. 3 View Fig ). Te shape of the bone is somewhat ovoid, with maximal width at midlength, narrowing anteriorly to a deeply convex anterior border. Te posterior border is straight. Te length of the gular is ~ 38% of the length of the lower jaw. As preserved, the width to length ratio of the gular is 0,41, but the actual bone was probably somewhat wider. As usual, the gular is followed posteriorly, at both sides of the skull, by the series of branchiostegal bones. Although the most anterior branchiostegals are certainly plate-like and relatively broad, the preservation is not sufficient to establish their precise shape or number.

Te dermal bones of the pectoral girdle, supracleithrum, cleithrum and postcleithra, present the same ornamentation of densely arranged tubercles as in most of the skull bones ( Fig. 3 View Fig ). Te supracleithrum is dorsoventrally elongated; its exposed surface has a depth to length ratio of ~ 3. Te lateral line enters the bone at approximately the middle of the posterior border. A series of short longitudinal ridges arranged parallel to each other along the posterior margin of the bone projects beyond the bony plate so that the posterior border of the supracleithrum is serrated, as is the case of the scales. Te cleithrum is relatively large, but it is poorly preserved, and no details can be described. Similarly, the presence of at least two postcleithra is evident, but they are badly preserved. Te only well-preserved feature is their posterior borders, which show an ornamentation similar to the one described for the posterior border of the supracleithrum.

Te pectoral fins are incompletely preserved, but they were likely small and placed low in the flank, almost at the same level of the pelvic fins ( Fig. 2 View Fig ). Te leading edge is garnished with fringing fulcra. At least one pair of small basal fulcra is present. Te pelvic fins are also incompletely preserved, only the presence of basal (two or three pairs) and fringing fulcra like those on the pectoral fin can be described ( Fig. 4 View Fig ).

Te dorsal fin is deeply emarginate and has a distinctly long anterior marginal ray ( Fig. 4a View Fig ). Te fin starts almost directly above the pelvics and reaches to the beginning of the anal fin, which has the appearance of the dorsal except for the unusual length of the first ray and its posterior profile is only slightly concave. Deecke counted 12 dorsal and anal fin rays, but he did not distinguish between fin rays and fulcra, so at least some of the basal fulcra are probably included in his counts. As preserved today, there are only nine dorsal and anal fin rays. Te dorsal fin has five basal fulcra, the first of them is tiny and unpaired, and numerous (more than 20) fringing fulcra. Te first fringing fulcra have very broad bases and following fulcra become very slen- der distally. Te anal fin has three basal fulcra and the most posterior one is comparatively smaller than the last dorsal basal fulcrum ( Fig. 4b View Fig ). Te fringing fulcra on the anal fin also become slenderer distally, but the anterior elements are not as large as the corresponding elements on the dorsal fin. Sixteen fringing fulcra are preserved on the marginal anal fin ray, but they were certainly a few more.

Deecke reported a total of 20 caudal fin rays. Te caudal fin was better preserved at that time ( Deecke, 1889: pl. 35, Fig. 9; Fig. 2 View Fig ). Presently, there is evidence for 11 rays below and probably nine rays above the lateral line, corresponding to the ventral and dorsal lobes, respectively. Te dorsal margin of the fin is not preserved, the ventral margin is incomplete, but a group of small but relatively strong fringing fulcra are preserved. Te series of dorsal caudal fulcra is also incomplete; the preserved elements are relatively large. Tree ventral basal fulcra are poorly preserved, but seem to be the complete set of these elements.

Te squamation consists of 38 (Deecke counted 35) vertical rows of scales along the lateral line ( Fig. 2 View Fig ). Te scales immediately behind the opercle are higher than long; those of the lateral line have a height to length ratio of 2.2–2.3. Te scales become shallower in dorsal, posterior and ventral direction, but only in the posterior caudal peduncle and in the ventrum, between the pectoral and pelvic fins, both masses are equal and the scales are square. Te posterior margin of all scales is serrated, all over the body, but the serrations are more numerous in the anterior half of the body and are restricted to the ventral half of the scale towards the caudal peduncle. Deecke described a complete series of median strong hexagonal shields between the dorsal and caudal fins and in front of the anal fin. However, only imperfect remains of these scutes are left in the specimen today. Te lateral line runs from the middle posterior edge of the supracleithrum, descending from the upper third of the body to the middle of the tail. Te lateral line scales are characterized by a round bulge in the middle of the posterior margin. Some of them are pierced by relatively large foramina. Tere are 17 scales in the vertical row at the origin of the dorsal fin, with one scale pierced by the lateral line, seven above and nine below it. Te axial lobe is relatively large, including nine quadrangular scales forming its single marginal row and four inverted rows of scales.