Stambergichthys macrodens, Barták & Ivanov & Tihlaříková & Olbert & Neděla, 2024

Barták, Pavel, Ivanov, Martin, Tihlaříková, Eva, Olbert, Martin & Neděla, Vilém, 2024, New, large actinopterygian fishes from the upper Carboniferous of Nýřany, Czech Republic, Acta Palaeontologica Polonica 69 (3), pp. 501-522 : 504-511

Stambergichthys macrodens sp. nov.

Figs. 2–5 , 6A .

ZooBankLSID: urn:lsid:zoobank.org:act:

Etymology: From Greek μακρóς (makrós), meaning “long” or “large”, and Latin dens, i.e., “tooth”; in reference to the conspicuous teeth of the holotype.

Holotype: ÚGV PAL00174 , an isolated right mandible with teeth exposed in medial view ( Fig. 2A 1 ).

Type locality: Nýřany , coal mine 13 km southwest of Pilsen, Czech Republic.

Type horizon: Main Nýřany Coal Seam , Nýřany Member, Kladno Formation, Pilsen Basin. A volcanic ash bed located ca. 85 m above the base of the Nýřany Member has been 206 Pb/ 238 U dated to 307.05 Ma ± 0.16 Ma, corresponding to the latest Moscovian stage (Asturian substage) of the Middle Pennsylvanian ( Opluštil et al. 2016).

Diagnosis.—A large actinopterygian fish (estimated total length 600–700 mm) distinguished from all other early actinopterygians by the following unique combination of characters: well-developed posterodorsal process of mandible; external dermal sculpture consists of anastomosing ridges and grooves; single row of large, smooth, homodont, cone-like teeth with bulbous bases; monocuspid marginal tooth apices lateromedially compressed and distinctly curved medially; subtle mesial cutting edge without serration restricted to apical portion of teeth.

Stambergichthys macrodens gen. et sp. nov. differs from Acrolepis sedgwicki Agassiz, 1833 , in more densely arranged teeth larger in size, and from Acropholis stensioei Aldinger, 1937 , and Plegmolepis kochi Aldinger, 1937 , by larger and more robust teeth fewer in number. Stambergichthys macrodens gen. et sp. nov. differs from Acrolepis gigas ( Frič, 1877) by more widely rounded posteroventral part of the mandible, deeper middle portion of the mandible, angular not extending far anteriorly, and by the presence of anastomosing ridges and grooves on the dentary external surface. Stambergichthys macrodens gen. et sp. nov. differs from Brazilichthys macrognathus Cox & Hutchinson, 1991 , Progyrolepis speciosus Frič, 1875 ), Progyrolepis heyleri Poplin, 1999 , Usclasichthys macrodens Heyler, 1977 , Zaborichthys fragmentalis Štamberg, 1989 , and NMMNH P-77557 (the unnamed large actinopterygian from Tinajas Member, New Mexico; Harris and Lucas 2017) by homodont dentition arranged in a single row close together, with slightly bulbous bases and medially recurved, flattened tooth tips. It further differs from Progyrolepis speciosus , Progyrolepis heyleri , and U. macrodens by smooth surface of marginal teeth, and from Z. fragmentalis by well-developed posterodorsal process of mandible. Stambergichthys macrodens gen. et sp. nov. differs from Brachydegma caelatum Dunkle, 1939 , by more closely spaced teeth with bulbous bases, which extend far posteriorly to the base of the posterodorsal process.

Description.— Mandible: The holotype of Stambergichthys macrodens gen. et sp. nov. consists of the isolated right mandible with teeth, exposed in the rock matrix in medial view Fig. 2A 1 ). The preserved portion of the mandibular ramus measures 52 mm and it is incomplete anteriorly. Most of its posterior part is present in the form of mineralized bone tissue, although the small portion corresponding to the posterodorsal process is preserved as an imprint of the lateral surface ( Fig. 2A 1 ). The mandibular ramus is disrupted by the numerous cracks, some of which are obliquely directed and resulted in both the dorsoventral and mediolateral displacement within the jaw fragment. Similarly, the bone medial surface of the mandible is damaged in the anterior region and along the ventral margin of most of the teeth, resulting in the exposure of the internal structures of the dentary ( Fig. 2A 1 , A 3 ). The general form of the mandible is boomerang-like, with the posteroventral border of the jaw smoothly curved dorsally to form a distinct posterodorsal process of quadrangular shape, which is elevated above the marginal dentition of the mandible. The preserved portion of the mandible is markedly deep in the central part, and gradually tapers in both the anterior and posterior directions.

The majority of the lower jaw is formed by the dentary. It forms the entire anterior region of the jaw laterally and extends posteriorly slightly behind the level of the marginal teeth, where it contacts the angular and surangular, although the sutures cannot be clearly observed ( Figs. 2A 1 –A 3 , 6A ). The lateral surface of the dentary, imaged through the µCT, reveals the presence of a sculpture consisting of a system of elongate, anastomosing ridges and grooves ( Fig. 2A 2 ). The ornamentation extends along the entire length of the dentary and is confined to its central part, being absent in the ventral, as well as dorsal regions. It is currently unclear, to what degree this feature is affected by the taphonomy and the µCT processing, or whether the sculpture distribution represents a natural condition. The medial surface of the dentary is deeply excavated and smooth for most of its extent ( Fig. 2A 1 , A 3 ). It has a prominent medial wall just ventral to the tooth row, of which surface is damaged and exposes the internal structures of the dentary, including the vascularised bone tissue (bone of attachment), as well as a set of thin canals partly filled with a white aluminosilicate secondary mineralization. These canals are interpreted here as a part of the mandibular neurovascular system innerving the teeth and the mandible (see below). The narrow Meckelian groove is partly preserved in the anteroventral portion of the dentary, extending more posteriorly to form a large Meckelian fossa bordered dorsally by a prominent medial wall of the bone. The angular forms the caudal border of the mandibular posterodorsal process, and constricts the lateral extent of the dentary, although the exact boundary between the two bones is unclear ( Figs. 2A 2 , A 3 , 6A ). The lateral extent of the angular on the posterodorsal process of the mandible is apparent from the imprint of its lateral dermal sculpture, consisting of thin and relatively densely arranged ridges ( Figs. 2A 1 ). The angular is confined to the posterior border of the process and is extended anteriorly in the dorsal region, while ventrally it has a subquadrangular shape ( Figs. 2A 2 , 6A ). The smooth lateral surface anterior to the angular in posterodorsal part of the bone probably corresponds to the surangular, and represents the area of overlap with the posterior region of the maxillary postorbital plate ( Figs. 2A 1 , A 2 , 6A ).

Dentition: The marginal dentition is implanted in shallow depressions of the acrodont form and consists of a single row of large, conical teeth ( Fig. 2A 4 ). There is no evidence on the presence of a set of smaller lateral teeth common in many other early actinopterygians ( Poplin and Heyler 1993). In addition to the nine more or less complete marginal teeth, seven more tooth positions are present in the preserved portion of the mandibular ramus, making the total count no less than sixteen teeth in the lower jaw of S. macrodens gen. et sp. nov. The teeth are homodont and set close together; the distance between the two adjacent tooth positions is only 0.8 mm. The largest teeth are 3.5 mm high and 2 mm long on the base. The dimensions of the marginal dentition are relatively constant throughout the length of the jaw, and only minor size decreasing is perceptible in the posterior region of the tooth row. The proportions of the teeth are relatively large in comparison to the dorsoventral depth of the jaw ramus, which reaches about 2.5 to 3.5 times of their apico-basal height. The general form of the teeth is cone-like and resembles the large laniary teeth of other Palaeozoic predatory actinopterygians ( Fig. 3A 1 –A 13; Poplin 1999; Štamberg 2018, 2020). The teeth are set perpendicular to the mandibular ramus and are upright along their entire height. The base is suboval in the cross section and slightly bulbous both mediolaterally and mesiodistally. A subtle mesial cutting edge with no serration is confined to the medially curved upper-most part of the tooth crown as a result of the lateral tooth compression ( Fig. 3A 3 –A 5 , A 12, A 13). The surface of the teeth is smooth throughout their height and shows no presence of ridges or microsculpture in a form of tubercles and protuberances seen in some other actinopterygian forms ( Richter 1983; Poplin 1999; Štamberg 2018, 2020). The smooth enameloid layer is present in the specimen and occupies about 40% of the tooth height in the apical part ( Fig. 3A 1 , A 2 , A 6 –A 11). Its bright surface forms a sharp transition between it and the collar enamel of the tooth shaft, and can be seen as a very thin, superficial layer in the µCT transversal and axial slices of the teeth ( Figs. 3A 15, 4A 6; Germain et al. 2016). The internal structure of the marginal dentition, uncovered by the µCT, shows the presence of a large pulp cavity surrounded by a moderately thick layer of the dentine ( Figs. 3A 15, 4A 1 –A 5). In the cross section, this dentine layer displays the presence of a simple form of plicidentine, which is restricted to the very base of the teeth and cannot be observed in any form (e.g., grooves and ridges) on the external surface of the implanted teeth. The individual dentine folds are not ramified and do not extend to the centre of the large pulp cavity of the teeth. This simple form of the dentine infolding corresponds well to the simplexodont type of plicidentine reported recently in some actinopterygian and sarcopterygian fishes ( Meunier et al. 2015a, b).

Neurovascular system: The X-ray µCT imaging techniques revealed inside the mandibular ramus of S. macrodens gen. et sp. nov. the presence of a slender bony canal, located immediately below the marginal dentition, which is interpreted here as a passage for the mandibular branch of the trigeminal nerve (V, ramus mandibularis trigemini; Figs. 2A 1 , A 3, 3A 14 –A 16, 5). The continuity of the mandibular canal has been disrupted by the numerous fractures and short displacements that occur in the dentary of the specimen. The descending branch of the mandibular nerve, coming from the trigeminal ganglion, probably entered the mandibular ramus of S. macrodens gen. et sp. nov. in its posterior region, as reported in some extant lower actinopterygians ( Allis 1922; Piotrowski and Northcutt 1996). The posterior-most portion of the preserved part of the mandibular canal splits into four or five subparallel branches which more anteriorly, at the level of the posterior-most teeth, pass into the lateral ramus of the mandibular canal. The lateral ramus alters in morphology from nodular to rod-like along its course, and is accompanied by the subparallel medial ramus in the posterior part of the mandible, which retains the form of a simple bar throughout its length. Both rami merge at the level of the tenth posterior-most tooth position to form a single main ramus that passes into the more anterior portion of the mandible. Its form is well exposed in the longitudinal section at the medial surface of the dentary due to the breakage of the bone ( Figs. 2A 1 , A 3 , 5A 4 ). Both rami of the mandibular canal posteriorly, as well as a single main ramus anteriorly, split into several branches towards the dentary teeth to form a dental plexus, through which the nerves and blood vessels passed, supplying the pulp cavities. In the anterior portion of the jaw fragment, a robust branch of the mandibular neurovascular canal extends posterolaterally from its main trunk and terminates in several smaller branches leading to the pores on the lateral surface of the dentary which might have innerved the external surface of the mandible. No mandibular sensory canal of the lateral line system ( Leuzinger et al. 2020) could be clearly observed in the dentary of S. macrodens gen. et sp. nov., although a few narrow, elongate, parallel canaliculi present in the more ventral position of the jaw ramus might be related to the cephalic sensory system.

Remarks.—The fragmentary nature of the type specimen of S. macrodens gen. et sp. nov. merits detailed account of its actinopterygian characteristics before the taxonomic assignment at the specific level and comparison to other taxa can be addressed. The thin enameloid layer confined to the apical portion of the teeth represents the only actinopterygian synapomorphy present in the holotype of S. macrodens gen. et sp. nov. ( Ørvig 1978b; Patterson 1982). Although a number of other characteristics of the jaw fragment have a wider distribution among the early osteichthyians, all of these features occur to varying degrees in early actinopterygians, further supporting its attribution to this group. These include (i) simplexodont plicidentine at the tooth base, (ii) mandibular ramus dorsoventrally deep in posterior part, (iii) smoothly curved posteroventral margin of mandible, (iv) prominent posterodorsal process of quadrangular shape, (v) laterally flattened mandibular ramus, (vi) external dermal sculpture formed by elongated ridges and grooves.

A thin enameloid layer is clearly present in the dentition of S. macrodens gen. et sp. nov. ( Figs. 3A 1 , A 2 , A 15, 4A 6) and, unlike chondrichthyans where the enameloid covers most of the tooth shaft (e.g., Jambura et al. 2019), it is confined to the apical portion of the teeth, forming the characteristic acrodin caps of actinopterygians. Furthermore, the simplexodont form of plicidentine is present at the base of the marginal teeth, which is now known to be widely distributed among the various actinopterygian forms (see Viviani et al. 2022 for the recent summary), although not necessarily confined to them ( Meunier et al. 2015b). The marginal teeth arranged in two series have been interpreted to represent a plesiomorphic condition for the actinopterygians, with the large, cone-like teeth placed medially in respect to the diminutive lateral dentition ( Poplin and Heyler 1993; Lund and Poplin 1997). Although this characteristic indeed frequently occurs in the Palaeozoic forms, the presence of a single marginal tooth row present in S. macrodens gen. et sp. nov. does not preclude its attribution to Actinopterygii, as it is currently known from many other early actinopterygian genera (e.g., Dunkle 1939; Lund 2000; Poplin and Lund 2000; Hamel 2005; Štamberg 2016; Stack et al. 2021; Argyriou et al. 2022), and is considered to represent an apomorphic state of this group ( Lund and Poplin 1997). The mandible of S. macrodens gen. et sp. nov. is deepest in its posterior part in front of the posterodorsal process, and it gradually narrows both anteriorly and posterodorsally along the smoothly curved ventral margin of the bone ( Figs. 2 , 6A ). The same general form of the lower jaw can be seen in many Palaeozoic actinopterygians, and the resemblance is especially evident in taxa such as Paratarrasius hibbardi Lund & Melton, 1982 , “ Elonichthys ” hypsilepis Hay, 1900 , Progyrolepis heyleri , Eurynotus crenatus Agassiz, 1835 , and Brachydegma caelatum , in which the pronounced posterodorsal process is well exposed ( Lund and Melton 1982; Schultze and Bardack 1987; Poplin 1999; Štamberg 2018; Friedman et al. 2019; Argyriou et al. 2022). Moreover, the mandible is markedly flattened mediolaterally, as present in early osteichthyians ( Botella et al. 2007; Zhu et al. 2009), as well as sarcopterygian (e.g., Jeffery 2002; Porro et al. 2015a) and actinopterygian fishes (e.g., Arratia and Cloutier 1996; Giles et al. 2015; Figueroa et al. 2019), but absent in early tetrapods ( Ahlberg and Clack 1998; Porro et al. 2015b). In early actinopterygians, the form of dermal sculpture on the external surface of the jaws and skull roof varies most commonly from the granular to ridged, both capped with a ganoine layer ( Ørvig 1978a, b). The ridges may be relatively coarse and pronounced (e.g., Lund 2000; Mickle et al. 2009), or rather fine and vermicular, as in Progyrolepis ( Štamberg 1991, 2018; Poplin 1999). Although the presence of the ganoine cannot be readily confirmed in the mandible of S. macrodens gen. et sp. nov., the dermal sculpture on the dentary conforms to the first pattern, whereas the second condition is present on the external surface of the angular ( Fig. 2A 1 ). All the characteristics discussed above therefore indicate that the holotype of S. macrodens gen. et sp. nov. represents an actinopterygian fish.

The mandible of S. macrodens gen. et sp. nov. is in general form similar to that of other large-bodied predatory genera like Brazilichthys macrognathus ( Cox and Hutchinson 1991; Figueroa et al. 2019; Figueroa and Andrews 2023), Brachydegma caelatum ( Dunkle 1939; Argyriou et al. 2022), Rastrolepis riojaensis López-Arbarello et al., 2006 , and acrolepids ( Aldinger 1937; Gardiner 1963; Štamberg 1991, 2018; Poplin 1999; López-Arbarello et al. 2010), having elongated mandibular ramus tapering anteriorly, and the pronounced posterior articulating region elevated above the marginal tooth row. The well-preserved mandibles from the lower Permian of France and Brazil reveal that the prominent posterodorsal region of the lower jaw in Progyrolepis heyleri and Brazilichthys macrognathus consists of both angular and surangular, whereas the dentary is posteriorly rounded and is not involved in its construction ( Štamberg 2018; Figueroa and Andrews 2023). Although the sutures are difficult to be traced in S. macrodens gen. et sp. nov., the congruent arrangement of these elements can also be assumed for this region ( Fig. 6A ).

The preserved portion of the jaw fragment of S. macrodens gen. et sp. nov. measures 52 mm. However, the mandible is clearly incomplete anteriorly, and we assume that about one-quarter to one-third of the lower jaw might be missing ( Fig. 6A ). If this estimation is correct, then the complete mandible of the specimen could have reached about 70–80 mm in length. Based on the similarly sized lower jaws, Štamberg (1991) and Poplin (1999) estimated the total body length of Progyrolepis at about 600–700 mm. Although no information on body proportions, such as the ratio of skull length to total body length, are available in S. macrodens gen. et sp. nov., we assume the estimated length of the specimen could be roughly similar to that of Progyrolepis speciosus and Progyrolepis heyleri . In the Permo-Carboniferous continental basins of the Czech Republic, several actinopterygian species reaching a size comparable to S. macrodens gen. et sp. nov. are known, including Acrolepis gigas , Progyrolepis speciosus , and Zaborichthys fragmentalis , the material all of which was first hand re-examined for comparison purposes. The lectotype of Acrolepis gigas is an almost complete specimen preserved as part and counterpart in a large siderite concretion, which includes, among others, the skull and mandible, and measures 1250 mm in total length ( Štamberg 1991). The mandible of A. gigas shows the general plesiomorphic morphology shared with similar actinopterygians of reasonable size, but is much larger compared to that of S. macrodens gen. et sp. nov., reaching a total length of at least 120 mm ( Fig. 6B ; Štamberg 2006). The mandibular ramus is very slender and straight anterior to the posterodorsal process in this species, whereas in S. macrodens gen. et sp. nov. it is deep and has broadly rounded dorsal and ventral margins. Unlike the massive, far anteriorly projecting angular of A. gigas , the bone appears to be relatively narrow and restricted to the posterior border of the posterodorsal process in S. macrodens gen. et sp. nov., with no evidence on its anterior extension in a manner seen in the former. Moreover, the external dermal sculpture is only apparent on the angular of A. gigas , where it is formed by the elongate parallel ridges, whereas the dentary seems to lack the well-developed anastomosing ridges and grooves present in S. macrodens gen. et sp. nov., although this may partly result from its poor preservation. Fritsch’s (1895: pl. 130) illustration of the specimen shows details of the lower jaw, as well as dentition, which resembles in general morphology to S. macrodens gen. et sp. nov. An inspection of the specimen by one of the authors PB) showed that the structures formerly interpreted as teeth are formed by the coarse depressions of irregular shape and distribution near the dorsal margin of the mandible, and these are only present on the counterpart slab. We consider these structures to be of inorganic origin as irregularities on the surface of the matrix, and agree with Štamberg (1991) that teeth are not preserved. In Progyrolepis speciosus , the morphology of the jaw and especially the form and arrangement of the dentition are very distinct from S. macrodens gen. et sp. nov., consisting about 11–12 well spaced, large laniaries with abruptly tapering apical parts and no medial curvature, accompanied by the series of much smaller and more numerous lateral teeth ( Štamberg 1991, 2020). The type specimen of Zaborichthys fragmentalis is represented by the scattered skeletal remains of a moderately large individual, the mandible of which would have probably not exceeded a total length of 50 mm ( Štamberg 1991). It differs from S. macrodens gen. et sp. nov. in morphology of the posterior part of the mandible, which is much more robust and lacks a well-developed posterodorsal process. Štamberg (1991, 2013) referred to Z. fragmentalis an isolated right maxilla with teeth (CGS YA1355; erroneously designated as lower jaw). The well-preserved marginal dentition of this specimen consists of two types of teeth arranged in two rows, thus differing from a single row of stout and homodont teeth of S. macrodens gen. et sp. nov.

The exceptionally well-preserved marginal dentition of the newly described species enables a detailed comparison of its morphology and arrangement with other early actinopterygians possessing a single row of teeth in the jaws. The homodont conical teeth arranged in a row close to each other and having bulbous bases, present in S. macrodens gen.et sp. nov., exhibit a resemblance with the dentition of Acrolepis sedgwicki , as well as some other acrolepid specimens described by Schaumberg (1996) from the upper Permian marine deposits of Germany (Kupferschiefer) and England (Marl-Slate). Since the mandibular dentition has not yet been described in the literature for Acrolepis sedgwicki , the comparison with this species is limited here to the upper jaw dentition, despite minor differences between the teeth of the maxilla and mandible might have existed. The reported marginal teeth of Acrolepis sedgwicki have conical to bulbous shape and are arranged in a row close to each other, similar to S. macrodens gen. et sp. nov. However, the teeth present in Acrolepis sedgwicki appear to be smaller relative to the depth of the jaw and have different proportions. The tooth height/longitudinal diameter ratio in the largest teeth of Acrolepis sedgwicki reaches 2.2–2.3 (based on Schaumberg 1996) while in S. macrodens gen. et sp. nov. the same parameter ranges from 1.6 to 1.8. Similarly, the ratio corresponding to the distance between adjacent tooth positions/tooth longitudinal diameter varies from 0.6 to 1.3 in Acrolepis sedgwicki , indicating that the tooth spacing is greater relative to S. macrodens gen. et sp. nov., in which the ratio is only 0.2–0.3. The indeterminate acrolepid mandibles described by Schaumberg (1996: figs. 3, 8) can also be readily distinguished from S. macrodens gen. et sp. nov. based on their diminutive dentition relative to the mandibular depth and the higher tooth number in the lower jaw. The knowledge on the morphology and arrangement of marginal teeth in other acrolepids is limited. López-Arbarello et al. (2010) demonstrated that family Acrolepidae as established by Aldinger (1937) is doubtful, and restricted the content of the group to only a few genera, among which a considerable dental variability appears to be present. For instance, the dentition of Acropholis stensioei and Plegmolepis kochi is very small relative to the depth of the jaw ( Aldinger 1937), contrasting with the large marginal teeth of S. macrodens gen. et sp. nov., although details of the dentition cannot be compared until a redescription of these taxa is made. On the other hand, Challaia elongata ( Cabrera, 1944) , Watsonichthys pectinatus ( Traquair, 1877) , Progyrolepis speciosus , and Progyrolepis heyleri display very large conical laniaries accompanied by teeth of much smaller size ( Gardiner 1963; Štamberg 1991, 2018; López-Arbarello et al. 2006, 2010), which are clearly distinct from the homodont dentition of S. macrodens gen. et sp. nov. Apart from the acrolepids, the dentition of S. macrodens gen. et sp. nov. resembles that of Brachydegma caelatum , in which the large conical teeth of equal size and shape show medially recurved apical tips ( Dunkle 1939; Argyriou et al. 2022). However, the teeth of the latter are much higher relative to the mandibular depth and are more widely spaced. Indeed, the tooth height/mandibular height ratio at the jaw mid-length corresponds to 0.6 in Brachydegma caelatum , whereas in S. macrodens gen. et sp. nov. it reaches only about 0.3. Similarly, the ratio of the distance between adjacent tooth positions and the tooth longitudinal diameter on the base is much higher (0.6) in Brachydegma caelatum compared to S. macrodens gen. et sp. nov. (0.2–0.3). Moreover, the dentition of Brachydegma caelatum is confined to anterior two-thirds of the lower jaw ( Dunkle 1939) whereas in S. macrodens gen. et sp. nov. the tooth row extends far posteriorly to the base of the posterodorsal process, and the teeth in the former lack a bulbous base. Although much smaller in body length, the dentition similar to S. macrodens gen. et sp. nov. can also be found in Igornichthys bohemicus Štamberg, 2016 , from the lower Permian of the Czech Republic, in which a single row of straight, homodont, conical teeth with smooth shaft is present ( Štamberg 2016, 2020). However, the well-preserved teeth of this species are markedly pointed apically and show neither a medial curvature nor a mesial cutting edge resulting from the compression of the tooth tip, which are present in S. macrodens gen. et sp. nov. Another early actinopterygian fish with a single tooth row, Wendyichthys dicksoni Lund & Poplin, 1997 , from the lower Carboniferous of Montana, shows a peculiar anterior inclination of the tooth shafts along the dentary length ( Lund and Poplin 1997), thus markedly differ from the upright dentition of S. macrodens gen. et sp. nov. Therefore, based on the comparisons presented above, it can be concluded that none of the known Permo-Carboniferous actinopterygian species match the unique tooth morphology described in S. macrodens gen. et sp. nov.

Stratigraphic and geographic range.— Type horizon and locality only.

Figures

Fig. 2. The actinopterygian fish Stambergichthys macrodens gen.et sp. nov.from Moscovian, Middle Pennsylvanian,Nýřany Member, Kladno Formation, Nýřany, Czech Republic. The right mandible of the holotype, ÚGV PAL00174, as preserved in medial view (A1). µCT surface model of the mandible in lateral (A2), medial (A3), and dorsal (A4) views. The green colour in A3 and A4 represents the sedimentary infill of neurovascular mandibular canal. Dashed lines with arrows indicate fractures where displacement has occurred.

Fig. 3. The actinopterygian fish Stambergichthys macrodens gen. et sp. nov. from Moscovian, Middle Pennsylvanian, Nýřany Member, Kladno Formation, Nýřany, Czech Republic. Marginal dentition and transversal sections of the right mandible of the holotype, ÚGV PAL00174. Photographs of the marginal teeth in medial view (A1, A2). Anterior-most preserved tooth showing apically restricted cutting edge in mesial view (A3, A4, A5). Close up images from A-ESEM showing apical portion of the marginal teeth in medial view (A6,A7, A8). Morphology of the well-preserved anterior marginal teeth from A-ESEM in medial view (A9, A10, A11). 3D model of the third anterior-most preserved tooth displayed through the confocal microscopy showing mesial cutting edge (A12,A13). Transversal sections through the mandibular ramus (A14,A15, A16). Interpretative drawing of the mandible showing the course of slices and details of the teeth depicted in other figures (A17).Abbreviations:ct, cutting edge; en, enameloid;mc, mandibular neurovascular canal; mcb,mandibular neurovascu- lar canal branch; Mg, Meckelian groove; pc, pulp cavity; pmcb, posterior mandibular neurovascular canal branches.Scale bars for A12 and A13 not available.

Fig.4. The actinopterygian fish Stambergichthys macrodens gen. et sp. nov. from Moscovian, Middle Pennsylvanian, Nýřany Member,Kladno Formation, Nýřany, Czech Republic. Cross section through marginal dentition of the holotype, ÚGV PAL00174, showing the morphology and distribution of plici- dentine. A. µCT axial slices at different levels of marginal teeth (A1, A2, A3). Interpretative drawings of cross sections at the base (A4), in the middle (A5) and close to apical tip (A6) of a single tooth. Interpretative drawing of the specimen showing the course of slices in other figures (A7). B. Phylogenetic diagram showing distribution and morphology of plicidentine in marginal teeth of selected extinct and extant actinopterygian fishes. Abbreviations: de, dentine; df, dentine fold; en, enameloid; pc, pulp cavity; vb, vascularised bone (bone of attachment).

Fig. 5. The actinopterygian fish Stambergichthys macrodens gen. et sp. nov. from Moscovian, Middle Pennsylvanian, Nýřany Member, Kladno Formation, Nýřany, Czech Republic. Neurovascular system in the right mandible of the holotype, ÚGV PAL00174, displayed through the µCT.The mandible in medial (A1), lateral (A2), and dorsolateral (A3) views. Reconstruction of the mandibular neurovascular system in lateral view (A4). Green colour represents the canals of mandibular neurovascular system, yellow colour marks the position of lateral pores.Abbreviations: dp, dental plexus; mcb, mandibular neurovas- cular canal branch; mr, mandibular canal ramus; pca, parallel canaliculi; pmcb, posterior mandibular neurovascular canal branches.

Fig. 6. The comparison of the mandible of actinopterygian fishes (A) Stambergichthys macrodens gen. et sp. nov. (Moscovian, Middle Pennsylvanian, Nýřany Member,KladnoFormation,Nýřany,Czech Republic) and (B) Acrolepis gigas (Frič, 1877) (Gzhelian, Upper Pennsylvanian, Mšec Member, Slaný Formation, Žilov, Czech Republic). A. ÚGV PAL00174, holotype, the reconstruction of the right mandible (reversed) in lateral view. B. NMP M125, lectotype, the photography of the left mandible in lateral view.

Fig. 1. A. The stratigraphic position of the actinopterygian material described in present study. The stratigraphic scheme is modified from Martínek et al. 2017). B. Permo-Carboniferous continental basins of the Czech Republic with marked location of Nýřany locality.