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

ABSTRACT 
 A new actinopterygian species from lacustrine Lower Permian deposits of the Krkonoše Piedmont Basin (Bohemian Massif, Czech Republic) is assigned to the genus Igornichthys Heyler, 1972. Present study of this new species reveals several anatomical structures that markedly advance our knowledge and make the generic diagnosis of Igornichthys more precise. Characters that include sharply pointed spines on the scales, a supraorbital sensory canal continuing from the frontal on to the dermopterotic, a maxilla with the maxillary plate protruding at a ventro-posteriorly angle, dentition forming a single row of similar conical teeth, and an oblong operculum are diagnostic of the new species. Igornichthys is placed within Igornichthyidae Heyler, 1977 together with Igornella Heyler, 1969, Setlikia Štamberg & Zajíc, 1994 and Commentrya Sauvage, 1888 from the Stephanian and Lower Permian of the French Massif central and the Bohemian Massif. Analysis of the anatomical features of Igornichthys and other members of Igornichthyidae demonstrates clear differences from other actinopterygians occurring in the lacustrine basins of the Carboniferous and Lower Permian. The occurrence of very closely related species within Igornichthys and genera included in Igornichthyidae and Amblypteridae Romer, 1945, documents an extensive interconnection among the lacustrine basins of the French Massif central, the Saar Nahe Basin and the Bohemian Massif in the Late Carboniferous and particularly in the Early Permian.


INTRODUCTION
Actinopterygian fish of the genus Igornichthys Heyler, 1972 from the Lower Permian of the Autun Basin (French Massif central) were discussed by Heyler (1969Heyler ( , 1972. These actinopterygians, along with specimens of the genus Igornella Heyler, 1969 from the same deposits of the Autun Basin, were assigned by Heyler (1972) to the proximity of Aeduellidae. The course of the supraorbital canal is consistent with that in Aeduellidae Heyler, 1969, that was given as support for his assignment. However, conspicuous differences in the maxilla, teeth, parietal and the type of the sculpture of the scales are similar to the Triassic genus Brookvalia Wade, 1933, andHeyler (1977) subsequently placed Igornichthyidae within the new order Brookvaliiformes Heyler, 1977. According to Heyler (2000, the family Igornichthyidae includes: Igornichthys doubingeri Heyler, 1972 andIgornella comblei Heyler, 1969 from the Lower Permian of the Autun Basin, Igornella montcellensis Heyler & Poplin, 1994 from the Stephanian of Montceau-les-Mines, and Commentrya traquairi Sauvage, 1888 from the Stephanian of Commentry. Štamberg & Zajíc (1994) included Setlikia bohemica Štamberg & Zajíc, 1994 from the Upper Carboniferous of the Kladno-Rakovník Basin (Bohemian Massif ) as a species and genus within the family Igornichthyidae. Recent extensive study of Lower Permian deposits of the Krkonoše Piedmont Basin (Bohemian Massif ) provided the author of this paper with abundant new actinopterygian material including a juvenile specimen of Igornichthys. The anatomical characters of this specimen significantly extends our knowledge of this genus and an analysis comparing the anatomical characters of Carboniferous and Permian actinopterygians from the Bohemian Massif, Saar Basin and French Massif central is now possible.

GEOLOGICAL CONTEXT
The intramontane Krkonoše Piedmont Basin occupies the north-eastern region of the Bohemian Massif. The area of the basin is more than 1100 km 2 , and the maximum thickness of the volcano-sedimentary basin fill in its central part is nearly 1800 m. The basin was formed as a part of a system of basins that opened in the Bohemian Massif during the late phases of the Variscan orogeny. Deposition within the basin started during the Westphalian D (Moscovian), and continued to the Early Permian (Sakmarian). The youngest units (Saxonian to Triassic) are preserved only in the eastern part of the basin (Trutnov-Náchod subbasin) (Prouza & Tásler 2001). The Lower Permian filling is represented by the Vrchlabí Formation (Asselian) along with the important fossiliferous Rudník Member. The Rudník Member represents on average a 40-60 m thick succession of lacustrine grey mudstone with layers of black claystone, carbonate, sandstone and conglomerate. Present outcrops indicate the east-west extent of the Rudník Member is more than 30 km in length, and has a surface area of approximately 300-500 km 2 , although it could be much larger, on the order of 1000 km 2 (Martínek et al. 2006).
The occurrence of actinopterygians, and other vertebrates, is restricted to a lacustrine bituminous gray-black calcareous claystone, which outcrops in one or two beds in numerous localities along the northern border of the Krkonoše Piedmont Basin between the villages Semily and Rudník, and repeatedly in the short strip between villages Košťálov and Kundratice. The most common species in all of the studied Rudník Member localities is Paramblypterus rohani (Heckel, 1861) of the family Amblypteridae Romer, 1945. Neslovicella elongata Štamberg, 2010, a member of the Aeduellidae is rarer than Paramblypterus rohani. The small predatory actinopterygian Letovichthys Štamberg, 2007 is rare and known only from a total of five specimens. An isolated occurrence of another small predatory actinopterygian, Igornichthys, comes from a single locality, Příkrý "Hoňkův creek".

METHODS
The descriptive terminology used in this paper conforms to that adopted by Grande & Bemis (1998) with observations, drawings, measurement methods and some terms after Štamberg (2007). The descriptions of the fin structures correspond with that of Arratia (2008). An SEM Hitachi S-3700N was used for the study and documentation of suitable scales and tooth microsculpture. remArks Heyler (1977) erected the family Igornichthyidae in his text but did not include a diagnosis. The here given diagnosis was compiled and based primarily on Heyler (1969,1977  genus: "Maxillaire à plaque postérieure assez forte, se courbant vers le bas en arrière ; mandibule forte, non élevée à l'arrière ; opercule et sous-opercule assez étroits ; préopercule de forme imprécise, mais courbant en avant en sa partie supérieure ; rayons branchiostèges étroits et nombreux ; corps allongé, pelvienne s'attachant vers la 9 e rangée d'écailles ; écailles portant une ornementation très particulière formée d'une ou deux pointes dirigées postérieurement et un peu vers le bas, plaquées sur la surface de l'écaille". Heyler (1969) unfortunately neglected to designate a type species, but resolved this situation when he designated Igornichthys doubingeri Heyler, 1972 as the type species of the genus Igornichthys Heyler, 1972. According to the International Code of Zoological nomenclature (ICZN: art. 11.9.3) this is considered an unavailable name, and the genus Igornichthys became valid after the designation of the type species in 1972. Heyler (1969) thus provided a diagnosis of the genus Igornichthys only from the characters of I. doubingeri. The current author is convinced that the new species from the Bohemian Massif belongs to the genus Igornichthys, but differs in some characters from the type species. 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 trav- A new actinopterygian species from the Krkonoše Piedmont Basin (Czech Republic) erses 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. 9A-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.

DISCUSSION
The new species exhibits characters of the genus Igornichthys. The most important of these are the typical scale sculpture, a supraorbital sensory canal that traverses from the frontal to the dermopterotic, a maxilla with a large maxillary plate that is postero-ventrad prolonged to a processus and marginal conical teeth. Igornichthys is presently known as: I. doubingeri (Heyler, 1972)   A new actinopterygian species from the Krkonoše Piedmont Basin (Czech Republic) ornichthys. This new species demonstrates some characters previously described by Heyler (1969), but also adds new information regarding the skull roof including the course of the supraorbital canal. The course of the supraorbital canal in I. bohemicus n. sp. confirms its affinity with Igornella (Heyler, 1969), Setlikia (Štamberg & Zajíc, 1994) and Commentrya (Blot, 1966). Igornichthys bohemicus n. sp. is erected by the author based on the dentition, position and the shape of the operculum, and the origin of the pelvic fin, which are distinct from I. doubingeri. Heyler (1969) described I. doubingeri as showing an alternation of large and smaller teeth on the jaws. Igornichthys bohemicus n. sp., in contrast, has marginal teeth that are of equal shape and size. Unlike those in I. doubingeri, the teeth of I. bohemicus n. sp. are arranged in a single row. Interestingly, both species of Igornichthys represent subadult specimens that are from 50-80 mm in total length, and the long ray segments and an absence of dichotomisation in these structures support this conclusion. Igornichthys combines some anatomical features that are separately seen in several actinopterygian families of the Carboniferous and Permian basins of the French Massif central, Bohemian Massif and Saar Nahe Basin. The skull roof bones in Igornichthys are noticeably similar to those of other actinopterygians. The dermosphenotic in Igornichthys is narrow and long (Fig. 10D). It carries the angle of the infraorbital sensory canal and according to the definition of Poplin (2004) belongs to a group of actinopterygians with one dermosphenotic that extends over the orbit. The dermosphenotic is prolonged over the orbit, and its shape and position is similar to Aeduellidae (Fig. 10A, B) (Heyler 1969;Poplin & Dutheil 2005;Štamberg 2007, 2010 and Commentrya traquairi Sauvage, 1888(Blot 1966. It conforms in position and shape with Letovichthys tuberculatus Štamberg, 2007 from the Bohemian Massif. However, it differs in absence of infraorbital canal dichotomization, which is known in L. tuberculatus. Conversely, other species of the family Igornichthyidae, Ig-ornella comblei and Setlikia bohemica, have another ventral dermosphenotic (infraorbital after Štamberg & Zajíc 1994;supraorbital? after Heyler 1969) between the dermosphenotic and the orbit. The position and shape of the dermosphenotic is quite distinct in Amblypteridae. It is triangular in shape and separated from the orbit by the infraorbital and nasal (Blot 1966;Heyler 1969;Dietze 1999Dietze , 2000Štamberg 1976, 2013.
The course of the supraorbital canal is another important character in Carboniferous and Permian actinopterygians. It generally traverses the frontal and passes to the parietal in most actinopterygians (Amblypteridae, Elonichthyidae, Rhabdolepidae, and others). The supraorbital canal in Igornichthys, and other taxa within Igornichthyidae including Commentrya, passes from the frontal to the dermopterotic. The same course of the supraorbital canal is observed in Aeduellidae (Heyler 1969;Poplin & Dutheil 2005;Štamberg 2007, 2010 and also in Commentrya traquairi (Blot, 1966) that is a taxon of the Igonichthyidae. The shape of the maxilla and the type of dentition is another important feature of Permo-Carboniferous actinopterygians. The maxilla of Igornichthys has a distinctive maxillary plate with a prominent postero-ventral angle. This characteristic is also present in taxa belonging to Elonichthyidae Aldinger, 1937and Rhabdolepidae Gardiner, 1963of the Saar Basin and Bohemian Massif (Gardiner 1963Schindler 1993Schindler , 2007Štamberg 1991, 2010. Amblypterids also have a well-developed maxillary plate but the plate is deeper and without a prominent postero-ventral angle (Heyler 1969;Štamberg 1976;Dietze 1999Dietze , 2000. Aeduellids have a maxillary plate of triangular shape (Heyler 1969(Heyler , 1991Štamberg 2007, 2010. The dentition in Carboniferous and Permian actinopterygians shows morphological variation. The marginal teeth in aeduellids and amblypterids form as very small tubular teeth that are closely set and form a narrow brush on the jaws (Blot 1966, Poplin & Heyler 1993. Igornichthys bohemicus n. sp. has small, but strongly conical, marginal teeth in one row. Igornichthys doubingeri has similar teeth which were described by Heyler (1969) as alternating with much smaller ones. Genus Letovichthys from the Lower Permian of the Bohemian Massif has teeth in two rows. The teeth in the inner row are large and sharply pointed, and those in the outer row are small and numerous. These tooth rows are seen also in Meisenheimichthys Schindler, 1993 from the Saar Nahe Basin (Schindler 1993(Schindler , 2007 and the large carnivore Progyrolepis (Fritsch, 1895) from the Bohemian Massif (Štamberg 1991) and Buxières-les-Mines (Poplin 1999). The ratio of tooth height to the depth of the skull in front of the opercular series provides a somewhat precise appraisal of the relative size of the teeth (Poplin & Heyler 1993). The ratio found in I. bohemicus n. sp. is 40, which is about the same as Letovichthys tuberculatus from the Bohemian Massif. The stout laniary teeth in Progyrolepis speciosus (Frič, 1875) differ in having a ratio of 20.
The operculum of Igornichthys is closely similar in shape to that of amblypterids. It is not exceedingly deep or anteriorly bent as that of aeduellids, but is oblong and dorsally rounded with a straight ventral rim. Ventrally it is not as narrow as the operculum in Meisenheimichthys from the Saar Basin (Schindler 2007) or in Progyrolepis speciosus (Frič, 1876) and "Elonichthys" krejcii (Fritsch, 1895) from the Bohemian Massif (Štamberg 1991).
The discovery of microsculpture in some scales and segments of the lepidotrichia in Igornichthys bohemicus n. sp. is another important character. These small tubercles are typical for ganoine surface (Schultze 2016), and they have been observed on the scales of Mesozoic and Recent holostean and polypterids. Arrangement and shape of the microtubercles could be diagnostic feature for determination of isolated scales of Permo-Carboniferous actinopterygians, as already Meunier et al. (1986) The relationship between Igornichthys and Igornella deserves special consideration. Heyler (1969) described the new genus and species Igornella comblei together with Igornichthys from the same deposits of the Autun Basin. The holotype and other specimens of Igornella comblei well demonstrate the rostral region and the skull roof, and partially the opercular region. The jaws and branchiostegal rays are presently unknown in comparison with I. doubingeri. By contrast the skull roof and rostral region are presently unknown in I. doubingeri. The additional description of another species Igornella montcellensis (Heyler & Poplin, 1994) did not complete our knowledge in this respect. What is presently known is that the genera Igornichthys and Igornella have the same sculpture on the scales. Heyler (1969,2000) has already known that these genera are not clearly separated. I. bohemicus n. sp. shows new data about the skull roof and documents a correspondence in the course of the supraorbital canal with Igornella comblei. Although Igornichthys and Igornella show several important features in common, it is not possible to synonymize them for the following reasons: Igornella comblei has an infraorbital (ventral dermosphenotic after Poplin 2004) between the orbit and the dermosphenotic, which is missing in I. bohemicus n. sp.; and the operculum of Igornichthys is 1.7 × deeper than long, whereas it is only slightly deeper in comparison to its length in Igornella comblei. A similar situation exists between I. bohemicus n. sp. and Setlikia bohemica (Fig. 10C) from the Bohemian Massif. S. bohemica shows similarity in its rostral region to Igornella comblei by having a skull roof with a triangular parietal and a supraorbital canal that traverses from the frontal to the dermopterotic and the second dermosphenotic. This species certainly belongs to Igornichthyidae, although information about the upper jaw, dentition and squamation are unfortunately missing.
The present discussion presents evidence that the anatomical characters of the Igornichthyidae differ substantially from the Amblypteridae, Aeduellidae, Elonichthyidae that occupied basins of the French Massif central, Saar Nahe Basin and Bohemian Massif in the Late Carboniferous and Early Permian. Representatives of Igornichthyidae have a set of characters that are known separately in other families, namely: supraorbital canals that transverse from the frontal to the dermopterotic; maxilla with a large maxillary plate of oblong shape and a postero-ventral angle; small but strong conical teeth fixed to the jaws; operculum of oblong shape that does not narrow ventrad or dorsad; and the sculpture on the scales form one or two large spines pointing posteriad and slightly downwards.