Igornichthys bohemicus, Štamberg, 2016

Štamberg, Stanislav, 2016, A new actinopterygian species of Igornichthys Heyler, 1972 from the Permian of the Krkonoše Piedmont Basin (Bohemian Massif, Czech Republic), and its relationship to the actinopterygians of other European Permo- Carboniferous basins, Geodiversitas 38 (4), pp. 475-488 : 478-480

Igornichthys bohemicus n. sp.

(Figs 1-10)

Igornichthys sp. – Štamberg 1994: 21, fig. 2; 2013: 167, 168.

HOLOTYPE. — Specimen MHK 30866 (part and fragment of the counterpart) with relatively well preserved bones of the head and anterior region of the trunk. The holotype is deposited in the Museum of Eastern Bohemia in Hradec Králové.

ETYMOLOGY. — Bohemicus, -a, um (Lat.); after the region of the Czech Republic.

MATERIAL EXAMINED. — Holotype only.

TYPE LOCALITY. — Rybnice “Hoňkův creek”, 50°36’59.47N, 15°23’08.80E, Semily District, Krkonoše Piedmont Basin, Czech Republic.

STRATIGRAPHIC HORIZON AND AGE. — Rudník Member, Vrchlabí Formation, Asselian, Early Permian.

DIAGNOSIS. — Supraorbital canal traverses from the frontal to the dermopterotic. Large orbit with thin sclerotic bones. Demosphenotic narrow and elongated. One row of straight, conical marginal teeth of uniform shape and size. Dorsally convex operculum with rounded edges and a straight ventral border. The deep of the operculum is 1.7 × that of the length. There are 12 scale rows anterior to the origin of the pelvic fin. Anterior margins of the pelvic and anal fins are “protected” by fulcra of the procurrent rays. Terminal segments of rays together with fringing fulcra are forming the leading edge. Lepidotrichia of the pectoral fin are unsegmented.

DESCRIPTION

The referred holotype specimen of the new species of Igornichthys represents a small subadult that is approximately 50 mm in total length. The overall specimen is reasonably well preserved including jaws with teeth, bones of the skull roof, operculum and dermal bones of the shoulder girdle. The trunk shows well the squamation and also the structure of the pectoral, pelvic and anal fins. The posterior part of the body is missing.

Body form

The body is fusiform and only slightly convex in the anterior portion ( Fig. 3A ). The skull length represents c. 1⁄5 of the total length of the body.

Head

The head contains a conspicuously large orbit with a length that equals one third of the entire head. There are fragments of three sclerotic bones which are gently bent and narrower on their distal ends (Figs 1; 2; 3B). Complete sclerotic ring that probably consists of four sclerotic bones. The dorso-ventrad elongated nasal is sculptured with tubercles and borders the orbit anteriorly. The nasal is dorso-posteriad in contact with dermosphenotic and frontal, and separates the orbit from the frontal. A narrow lacrymal borders the ventral rim of the orbit. The bones between the posterior maxillary plate and the orbit are not clearly visible. The dermosphenotic borders the orbit dorsally. It is antero-posteriad elongated, anteriorly narrow and broadens gradually posteriad. The infraorbital sensory canal is preserved over a short distant only, it traverses from the dermopterotic to the dermosphenotic. It is bent at a 90° angle, and appears to continue posterior to the orbit. The dermopterotic is wider and shorter than the dermosphenotic. It is placed posteriorly and in line with it. The frontal is the largest skull roof bone that is seen. It is laterally bordered with the demosphenotic, and the posterior part of the lateral margin of the frontal is in contact with dermopterotic. A conspicuous supraorbital sensory canal passes from the anterior margin of the frontal along the lateral margin of the bone, and slightly bends when laterally traversing to the dermopterotic. The interfrontal suture is not clear. A parietal that is twice as short as the frontal, is seen only in incomplete outline. The jaws are well preserved. The maxilla has a narrow and long anterior part that markedly elevates posteriad. The posterior part forms a maxillary plate of oblong shape with a downwardly protruding postero-ventral angle. The maxilla represents 2.4 × the length of the maxillary plate. The depth of the maxillary plate including the postero-ventral angle represents 3 × the length of the maxilla. The lower jaw is strong, anteriorly narrow and posteriorly moderately elevated. Dentition on the upper and lower jaws forms a single row of straight, conical teeth of equal size and shape. The teeth have a relatively wide base, and their height is twice that of the base. Tooth surfaces are smooth ( Fig. 6 ). The teeth are in a single row, and interlock when the jaws are closed. There are 24-27 marginal teeth along each half of the jaw. The height of the teeth compared to the depth of the skull in front of the opercular series ( Poplin & Heyler 1993) yields a ratio of 40. The palatal bones are provided with small and sharply pointed teeth, several of which are preserved.A parasphenoid fragment is preserved that shows a strong lateral ascending process in the dorsal part of the orbit. The ventral surface of the processus cultriformis was likely tooth-bearing, as evidenced by a number of circular broken bases (Fig. 1). Circular broken bases of the teeth demonstrate much smaller teeth than are on the jaws. The preoperculum is partially preserved; it is anteriorly bent along the dorso-posterior rim of the maxillary. A portion of the preopercular canal extends along the posterior margin of the preoperculum. The operculum is oblong in shape, and its depth is 1.7 × that of the length. The axis of the operculum ( Štamberg 2007) is inclined at an angle of about 50°. The operculum is rounded in the dorsal region, and the ventral margin is straight with rounded corners. The suboperculum is unknown, and fragments of three narrow branchiostegal rays posterior to the lower jaw indicate that there were several branchiostegal rays in the operculo-gular apparatus. There is an outline of a large post-temporal that extends onto the dorsal rim of the operculum. The extrascapular bones are unknown. The supracleithrum is dorso-ventrad elongated, and is taller than the operculum. The ventral region of the supracleithrum reaches the cleithrum. A lateral sensory canal traverses across the dorsal region of the supracleithrum diagonally. The cleithrum is strong and broadly exposed laterally. The cleithrum and the operculum are mutually shifted during fossilization (Figs 1; 3). Acute dorsal end of the supracleithrum reached the ventral border of the operculum beyond the life of the animal ( Fig. 4 ).

Fins

The pectoral fin is preserved showing unsegmented lepidotrichia along the entire length. The lepidotrichia are not dichotomically branched in the distal portion. The leading edge of the pectoral fin shows a terminal section of six procurrent rays. A partially preserved, small, pelvic fin is proximally placed slightly closer to the origin of the anal fin than to the pectoral. There are 12 scale rows anterior to the origin of the pelvic fin and 23 scale rows anterior to the origin of the anal fin. The anal fin is triangular in shape. The lepidotrichia of the pelvic and anal fins are segmented along their entire length. These segments are narrow and very long, which indicates that this is subadult specimen.

The rays of the anal fin have no more than eight segments. The leading edges of both fins show protective terminal segments of rays together with less numerous fringing fulcra ( Fig. 9E, F ). Some segments show a very fine microsculpture on their ganoine surface. The basal segments of the anal fin have ridges that are short, fine and linearly arranged ( Fig. 9D ).

Squamation

The scales and their sculpture show important characteristic features. The surfaces of the scales have conspicuous spines. The spines in the central region of the scales generally have a wide base, and are pointed posteriad and slightly downwards. Each scale shows only a single spine ( Figs 7A, B, D, E ; Fig. 8A ), although two spines do occur on scales in the rows ventral to the lateral line scales behind the head ( Fig. 3B ), and in the fifth and twentieth rows ( Figs 7C ; 8B ). All trunk scales including those from the lateral sides, ventral sides and the posterior region of the body are equipped with the spines. The spines are absent only from the scales of the lateral sensory line. It is not clear if they were present or absent from behind the anal fin as these scales are not preserved. The surface of the spines is distinct from that of the surrounding scale surface. The scale surfaces are rough, which indicates bone tissue. The spine surfaces are covered with a thickened ganoin layer that bears fine ridges. These ridges are linearly arranged, oriented parallel to the axis of the spine, and set 4 µm apart ( Fig. 7F ). The microsculpture was partially removed in the course of fossilization. There are 12 vertical scale rows between the supracleithrum and the origin of the pelvic fin. There are roughly 23 scale rows between supracleithrum and the origin of the anal fin. Eight horizontal scale rows are below and five horizontal scale rows are above the lateral line in the level of the begin of the pelvic fin.

There is a fragment of a ventral scute at the lower peduncle in front of the caudal fin. It contains a flat ridge on its surface that shows a thickened ganoine layer with well-preserved microsculpture. The microsculpture is formed by short ridges that are linearly arranged. These ridges are 4.5 µm apart, and show a gentle flabelliform fork ( Fig. 9 A-C). The remainder of the scute has a rough surface indicative of bone. The above observations suggest the ganoine is limited to the spines only.

Figures

FIG. 3. — Igornichthys bohemicus n. sp., holotype MHK 30866: A, left view of the whole specimen; B, detail of the skull in left lateral view. Scale bars: 5 mm.

FIG. 6. — Igornichthys bohemicus n. sp., holotype MHK 30866:A, general view of the teeth of upper and lower jaws; B, detail of the teeth of the upper and lower jaws, which interlock, when the jaws are closed; C, detail of the teeth of the anterior region of the lower jaw; D, detail of the teeth of the lower jaw. Scale bars: A, B, 500 µm; C, D, 100 µm.

FIG. 4. — Igornichthys bohemicus n. sp.,reconstruction of the skull in left lateral view. The outlines of the bones, which are ill-defined, are marked with dashed lines. Abbreviations: see Methods. Scale bar: 5 mm.

FIG. 9. — Igornichthys bohemicus n. sp., holotype MHK 30866: A-C, ventral scute from the caudal peduncle, which shows the sculpture of flat ridges on its surface (A) and microsculpture formed by short ridges and tubercles that are linearly arranged (B, C); D, basal segments of the anal fin with fine microsculpture on their surface; E, the leading edge of the anal fin with fulcral scales; F, detail of the fulcral scale on the leading edge of the anal fin. Scale bars: A, E, F, 500 µm; B, C, D, 100 µm.

FIG. 7. — Igornichthys bohemicus n. sp., holotype MHK 30866, scales on the left lateral side of the body: A, scales from rows 23-27 with conspicuous spines; B, detail of the scales from rows 25-27 with single spine; C, scales with two spines; D, detail of the scale with single spine in medial view; E, detail of the scale from row 27 with microsculpture of spines, whereas the surrounding scale surface is rough, which indicates bony surface; F, detail of the microsculpture on the spine of the previous scale. Scale bars: A, B, C, 500 µm; D, E, F, 100 µm.

FIG. 8. — Igornichthys bohemicus n. sp., holotype MHK 30866: A, scales with one spine sharply pointing in posterior direction and slightly downwards on each scale; B, scale with two sharply pointed tubercles. Scale bars: 1 mm.