Progyrolepis heyleri POPLIN , 1999

Štamberg, Stanislav, 2018, Actinopterygians Of The Permian Locality Buxières-Les-Mines (Bourbon- L’Archambault Basin, France) And Their Relationship To Other Early Actinopterygians, Fossil Imprint 74 (3 - 4), pp. 245-291 : 248-270

Progyrolepis heyleri POPLIN, 1999

Text-figs 4–24

1999 Progyrolepis heyleri n. sp.; Poplin, p. 148–154, figs 1–6. 2000 Progyrolepis heyleri ; Steyer et al., pl. I, fig. C.

2016b Progyrolepis heyleri POPLIN, 1999 ; Štamberg, figs 5–7.

D i a g n o s i s. After Poplin (1999; here completed). Large carnivorous fish reaching 70 cm in total length with maxillaries and mandibles reaching 10 cm in length. The maxillary plate is trapezoidal in shape and lowers anteriorly than posteriorly, and longer than the narrow anterior suborbital part of the maxilla. The maxillary plate bears outstanding sculpture formed by vermicularly curved ridges; tubercles prevail along the ventral border and on the anterior suborbital part of the maxilla. The plate is without sculpture anteriorly, and it is overlapped by the very large jugal. Similarly, the smooth dorsal border of the narrow suborbital part of the maxilla is overlapped by the lachrymal. The anterior border of the maxillary plate is relatively steep and in adult specimens makes an angle of about 70° with the denticulated inferior margin of the maxilla. Laniary conical teeth are large and the ratio of tooth height to head depth at the front of the opercular series is about 22. The teeth have an acrodin apex and fine microsculpture formed by tiny protuberances distributed over the surface of the tooth around the acrodin apex. The elliptical protuberances are proximodistally elongated, separated from each other and only rarely in contact. The hyomandibula, conspicuously anteriorly

Frfr Fr Fr infs Dsph

Dpt

Pa

b

inclined, consists of two clearly distinct arms forming an angle of 151–157°. The dorsoanterior arm is the wider. The processus opercularis is well developed. The preoperculum is without sculpture anteriorly, inclined in an anterior direction and forms an angle of 15° with the anteroposterior axis of the body. The operculum is oblong in shape and does not narrow ventrally. The narrow antoperculum borders the dorsal third of the anterior border of the operculum. The suboperculum is of quadrilateral shape projecting anteriorly as in dorsal as ventral directions. The anterior border of the supracleithrum is straight in its dorsal two thirds, but the ventral one third is conspicuously concave and considerably narrowed. Stout rhomboidal shaped scales bear conspicuous sculpture formed by ridges diagonally traversing across the scale to terminate in denticulation posteriorly.

D e s c r i p t i o n. Body form. The referred skeletal and body fragments represent a carnivorous species reaching up to 70 cm in total body length. The slender body is covered with sculptured scales and the skull length is approximately 20 % the total body length.

Rostral part and skull roof. The rostral area has a convex outline in an anterior direction as demonstrated by specimen BX 11.11.97. However, the individual bones of the rostral region are not satisfactorily preserved in any of the other studied specimens. Although the bones of the skull roof are mostly isolated, partial complexes of the frontal, parietal, dermosphenotic and dermopterotic are preserved (D 11.11.95.7; D 08.02.98.50; MHK 82834). The frontal ( Text-figs 4 , 5 ) is oblong in shape and elongated in an anteroposterior direction, with length 2.5 times the width. The interfrontal suture is significantly curved and forms two processes which fit into depressions on the opposite frontal bone. The lateral edge of the frontal lacks processes, and

contacts the dermosphenotic and dermopterotic slightly in the posterior region. The frontal is posteriorly adjacent to the parietal which is 2.5 times shorter than the frontal, and is slightly elongated in an anteroposterior direction (Textfig. 4). Similar to Elonichthys germari GIEBEL, 1848, the total width of the posterior part of the median part of the

skull roof (i.e. right and left parietals) is clearly smaller than the width of the anterior part (i.e. right and left frontals) ( Schindler 2018a). The triangular dermosphenotic borders the frontal laterally. The oblong dermopterotic borders the posterior region of the frontal and entire lateral edge of the parietal laterally ( Text-fig. 4 ). The border between the

dermosphenotic and dermopterotic is located anteriad to the border between the frontal and the parietal. Some fishes of the family Elonichthyidae ALDINGER, 1937 have the dermosphenotic-dermopterotic borderline posteriorly to the contact between the frontal and the parietal, as illustrated by Schindler (2018b) in Rhabdolepis macropterus ( BRONN, 1829) and Štamberg (2010a) in Elonichthys krejcii ( FRITSCH, 1895) or the dermosphenotic-dermopterotic borderline is almost anteriad to the borderline between the frontal-parietal as figured by Schindler (2017, 2018a) in Elonichthys fritschi FRIEDRICH, 1878 and Elonichthys germari GIEBEL, 1848.

a b

The exposed part of the skull roof bones are covered by

conspicuous sculpture. The sculpture on the anterior half of the frontal consists of tubercles or very short ridges. The well-

developed ridges prevail in the posterior half of the bone, and

they diverge radially from the radiation centre of the frontal

which lies approximately at equal distance from the anterior

and posterior borders of the bone. A narrow strip of the frontal anterior margin is overlapped by the posterior part of the postrostral ( Text-fig. 5 ). The young specimen MHK 82834 exhibits two small bones inserted between the anterior part of the right and left frontals. These two bones are bordered by the right and left frontals, and they are characterised by different sculpture on the frontals in this area ( Text-fig. 4 ). They are not developed in any other studied skull roof, and I believe these bones are formed from fragmentation of the frontals, and they developed only by chance in this young specimen. This is distinct from the arrangement of small bones in the centre line of the anterior region of the parietals (frontals in the sense used herein) in Cheirolepis canadensis WHITEAVES, 1881 which were described as posterior postrostrals by Arratia and Cloutier (1996).

Significant sculpture consisting of short ridges and tubercles also covers other bones in the skull roof ( Text-fig. 4 ), and completely conceals the pores of the sensory canals. Sculpture on these bones is also well developed in young specimens.

The same shape and sculpture of the skull roof bones is demonstrated in the specimen BUX 4a figured by Heyler (1984: fig. 8b) and Heyler and Poplin (1990: fig. 5). The figured specimen shows the frontals, parietals and left dermosphenotic of triangular shape, but not the postrostral as is stated in the associated explanations of Heyler (1984) and Heyler and Poplin (1990).

Parasphenoid. The isolated parasphenoid in specimen D 07.11.95.10 exhibits a three lobed bone ( Text-fig. 6 ). The anterior lobe creates the middle corpus parasphenoidis which extends in a postero-lateral direction as paired processus ascendens posterior. The centre of ossification is situated in the posterior third of the corpus parasphenoidis, and it lies at the intersection of the axes of these lobes. The

a b

corpus parasphenoidis tapers significantly and narrows in a forward direction. On the contrary it extends smoothly backwards to become the paired processus ascendens posterior which narrows distally, and forms an angle of 68° with the corpus parasphenoidis. The posterior border of the corpus parasphenoidis is slightly convex but it does not extend posteriorly. Granulation in the posterior region of the bone in the counterparts of D 07.11.95.10 indicates dentition on the ventral surface of the corpus parasphenoidis ( Text-fig. 6 ). The shape of the parasphenoid, including the angle of the processus ascendens direction is similar to the parasphenoid of Elonichthys crassidens GIEBEL, 1848 (personal observation).

Palatoquadrate and dermal bones of the cheek. The palatoquadrate is ossified as a single bone and its division into the pars quadratum, pars metapterygoidea and pars autopalatina is only arbitrary because the suturing of these individual parts is unclear. The palatoquadrate ( Text-figs 7 , 17 ) is conspicuously thickened in the pars quadratum area and on the posteroventral edge two condyles were developed for articulation of the palatoquadrate with the lower jaw. There is neither a hole or processes on the pars metapterygoidea as figured by Pearson and Westoll (1979) in Cheirolepis traili AGASSIZ, 1835, Watson (1928: fig. 7) in Nematoptychius greennocki ( TRAQUAIR, 1866), Gardiner (1984: figs 56, 58) in Mimipiscis toombsi ( GARDINER and BARTRAM, 1977) and Moythomasia durgaringa GARDINER and BARTRAM, 1977, or Nielsen (1942: fig. 35) in Pteronisculus magnus ( NIELSEN, 1942). The medial surface of the palatoquadrate in the pars metapterygoidea exhibits a small groove (spig) which traverses arcuately close to the dorsal margin of the bone ( Text-fig. 7 ). This groove may represent a similar structure in Pteronisculus magnus as described by Nielsen (1942: fig. 36) or Mimipiscis toombsi and Moythomasia durgaringa figured by Gardiner (1984: figs 56, 58). Gardiner (1984) assumed it was the lateral surface of the ventral end of the spiracular diverticulum. Three dermal bones are associated with the medial side of the palatoquadrate. Laterally the palatoquadrate is covered by the maxilla, quadratojugal and partly by the preoperculum.

The ectopterygoid is an anteroposteriorly elongated bone (BX 12.05.98.5; D 08.02.98.10.4/4; D 14.03.97.10; D 14.03.98.19.6/6) which covers the medial side of the palatoquadrate posteroventrally ( Text-figs 7 –9). It extends from the most posterior part of the palatoquadrate where it has a vertical position and binds to the palatoquadrate at the location of the adductor fossa. Immediately anteriorly to the adductor opening is the ectopterygoid bend and it forms a ventral horizontal lamina where the vertical lamina continues in an anterior direction. The vertical lamina is deepest midlength and conspicuously narrower anteriorly. The horizontal lamina (Text-fig. 9) sutures laterally with the horizontal lamina of the maxilla. The ectopterygoid bears small teeth covering the entire medial surface of the bone.The teeth on the horizontal lamina are sharply pointed (Text-fig. 9b), identical in size with the smaller marginal teeth forming the outer row on the jaw. The teeth covering the dorsal region of the medial surface are much smaller. The ectopterygoid is bordered dorsally by the dermometapterygoid.

The dermometapterygoid covers the medial side of the palatoquadrate in the pars metapterygoidea. Here, the dermometapterygoid is considered to be a separate bone and not just a denticulated part of the pars metapterygoidea ( Arratia and Schultze 1991). The dermometapterygoid ( Text-fig. 8 ) begins at the posterior end of the palatoquadrate, dorsally borders the ectopterygoid and narrows anteriorly, and does not reach the position from which the anterior part of the maxillary plate begins to broaden. The radiation centre of the metapterygoid lies in the posterior region of the bone near its dorso-posterion margin. The dermometapterygoid is one bone which corresponds in its shape and position with that figured by Nielsen (1942: fig. 37) in Pteronisculus aldingeri ( NIELSEN, 1942) or Gardiner (1963) in Rhabdolepis saarbrueckensis GARDINER, 1963 in contrast to Mimipiscis toombsi where there are four dermometapterygoids ( Gardiner 1984) in the pars metapterygoidea.

The entopterygoid in the sense of Arratia and Schultze (1991), covers medially a large portion of the palatal region of the pars autopalatina. The entopterygoid ( Text-figs 7 , 8 ) is posteriorly in contact with the ectopterygoid as in Mimipiscis toombsi ( Gardiner 1984) and sutured dorsoposteriorly with the dermometapterygoid. The bone is approximately triangular in outline, it is extended in an anteroposterior direction and it increases in depth posteriorly where it is in contact with the ectopterygoid and dermometapterygoid. The entopterygoid is bent laterally along its ventral margin forming the horizontal lamina which continues up to the horizontal lamina of the ectopterygoid. The horizontal lamina and medial surface of the entopterygoid are densely covered with small teeth ( Text-fig. 7 ). The centre of ossification of the entopterygoid lies on its posterior margin, and its location is different to that in Pteronisculus aldingeri and Mimipiscis toombsi where the centre of ossification of the entopterygoid lies close to the dorsal margin of the bone ( Nielsen 1942, Gardiner 1984).

hlec vlec

Tex-fig. 9. Progyrolepis heyleri POPLIN, 1999 . Left ectopterygoid in lateral view with the horizontal lamina which bears the teeth. D 08.02.98.10.4/4, Scale bars 5 mm. a – photograph, whitened. b – drawing. Abbreviations: hlec – horizontal lamina of ectopterygoig; vlec – vertical lamina of ectopterygoid.

The presence of the dermopalatinal bones is obscure. This region is not well preserved on the palatoquadrate. Specimen D 08.02.98.10.4/4 exhibits an ectopterygoid with a well-developed horizontal lamina (Text-fig. 9) reaching up to the anterior margin of the ectopterygoid.

Maxilla. The shape, sculpture, and dentition of the maxilla were considered by Poplin (1999) to be essential in the designation of the new species Progyrolepis heyleri . The newly studied material contains numerous specimens with not only a well preserved maxilla with these defining features, but also the whole palatoquadrate complex including its dermal bones. The maxillary bones from different ontogenetic stages are also preserved, ranging from the small 18 mm long maxilla representing young specimens of 140 mm total body length (D 11.11.95.7) to the 97 mm length maxilla (BX 17.10.98.2). The maxilla consists of a narrow anterior suborbital part and a conspicuously deep maxillary plate continuing backwards ( Text-figs 10 , 11 ). The maxillary plate is relatively low and long. The length of the maxilla is from 1.6 to 1.9 times that of the maxillary plate, and it is clear that the narrow suborbital part of the maxilla is shorter than the length of the maxillary plate. The juvenile specimen (D 13.04.97.6) has an anterior maxillary suborbital part that is less pronounced and slightly longer than in older specimens in comparison to the maxillary plate, with the length being almost the same as that of the maxillary plate ( Text-fig. 11b, c ). The adult specimen (D 04.10.98.5) on the contrary has a strongly pronounced anterior suborbital part which is conspicuously shorter than the length of the maxillary plate ( Text-figs 10a , 11a ). The maxillary plate is trapezoidal in shape and deeper posteriorly than anteriorly. The posterior margin is oblique, and slightly concaves ( Text-fig. 10 a–d). The maxillary plate is ventroposteriorly extended into a strongly pronounced process. The ratio of the maxillary plate length to its greatest depth, including the

a

c b d e

f

ventroposterior process, is 1.6–2.0. The anterior margin of the plate in older specimens is relatively steep compared to the denticulated inferior margin of the maxillary, and it produces an angle of 70–77° ( Text-figs 10 a–d, 11a). The anterior margin of the maxillary plate in young specimens is not so steep, and the angle is approximately 40° (Textfig. 11b, c). A conspicuous horizontal lamina (hlm) traverses

along the ventral border of the maxilla on its medial side ( Text-fig. 11b, c ). The horizontal lamina begins on the ventral margin of the maxilla, at approximately one third of the maxillary plate length. The horizontal lamina increases anteriorly in width and is stouter. The horizontal lamina bears a row of small teeth laterally and large carnivorous teeth medially. The horizontal lamina of the maxilla is medially in contact with the horizontal lamina of the ectopterygoid.

The maxilla bears outstanding sculpture on its lateral surface. The type of sculpture varies according to the position on the maxilla. The narrow anterior suborbital part of the maxilla bears tubercles and short ridges arranged predominantly in an anteroposterior direction. The maxillary plate exhibits predominantly long ridges parallel to the posterior, anterior and dorsal margins of the bone. The maxillary plate of specimen D 23.08.98.5 ( Text-fig. 10a, b ) shows the ridges parallel to the dorsal and posterior border of the maxillary plate, the ridges bend in a dorsal and

ventral direction. The ridges parallel to the dorsal margin are anteriorly bent in a ventral direction. The vertical arrangement of closely positioned ridges near to the anterior margin of the maxillary plate as described by Poplin (1999: fig. 3B) does not appear regularly. They were recorded on specimen D 11.11.95.17 ( Text-fig. 10e, f ) only, and these differences probably occur within the range of sculpture variability on the maxilla. The tubercles and ridges bear microsculpture consisting of conspicuous ridges on the top ( Poplin 1999: fig. 3E). The maxilla is characterized by large areas without sculpture. The sculpture on the anterior narrow suborbital part

a a

b c

of the maxilla is limited to the narrow ventral part of its lateral

surface, while the dorsal part of its lateral surface is without

sculpture ( Text-figs 10 a–e, 11a). This unsculptured portion

was covered by the lachrymal and partly by the jugal. More

extensive is the unsculptured anterior part of the maxillary

plate, where it has been preserved ( Text-figs 10 a–e, 11a).

This unsculptured part has a continuation on the unsculptured

anterior region of the preoperculum ( Text-fig. 11a ), and was

covered by the large jugal during the life of the animal.

Two groups of several holes representing nerve foramina

for branches of the horizontal pit line of the maxillary nerve ( Text-fig. 10c ) are situated in the transition area between

the narrow suborbital part of the maxilla and the maxillary

plate, this is also the radiation centre. The same foramina

grouping was described by Nielsen (1942: pl. 9, fig. 1) in

Pteronisculus and Gardiner (1984: fig. 66) in Moythomasia durgaringa, and they are common in many other Permian

actinopterygians. The dentition of the maxilla is well

developed along the whole ventral border of the bone

including the ventroposterior process of the maxilla.

If we compare the shape of the maxilla with that in other

actinopterygians it is clear that the postorbital maxillary plate is significantly longer than in Cheirolepis , Mimipiscis , Pteronisculus , Pygopterus nielseni or in Elonichthys krejcii. In Elonichthys germari the ratio of the postorbital plate compared to the length of the maxilla is similar to that in P. heyleri , but the maxillary plate is not so deep relative to the length (personal observation). The studied maxillary plate is, on the contrary, shorter than in Nematoptychius greenocki and Watsonichthys pectinatus ( TRAQUAIR, 1877) (personal observation). Schindler (2018b) figured the maxillary plate of Rhabdolepis macropterus which is longer than in Progyrolepis heyleri , and the anterior margin of the maxillary plate is very low, and makes an angle of 24° with the denticulated ventral margin of the maxilla. This angle in E. germari is about 45° ( Schindler 2018a), and in Elonichthys fritschi is 46° ( Schindler 2017). The shape of the maxilla in P. heyleri fully corresponds with that in Progyrolepis speciosus as figured by Fritsch (1883) and Štamberg (1991: fig. 15). A more recent revision of the upper jaws of Progyrolepis speciosus shows that the length of the maxilla represents 1.8 times the length of the maxillary plate, and the ratio of the length of the maxillary plate to the length of the narrow suborbital section is 1.1 and not 0.9 as quoted by Štamberg (1991).

Dentition. Well preserved marginal teeth in the sense of Poplin and Heyler (1993) are present on the maxilla and dentalosplenial. The same type of predatory dentition is on both the lower and upper jaws. The teeth on the jaws are arranged in two rows ( Text-figs 10 a–d, 11, 13, 14), the outer row consists of small sharply pointed teeth of variable size. The inner row is formed by 12 to 14 large conical teeth (BX 17.10.98.2) characterizing a predatory fish. The teeth on the lateral row are not all the same size, but are always 4–7 times shorter than the laniaries conical teeth on the medial row. Dentition in a young specimen can be a little different. The dentition of adult specimens also consists of two types of teeth in two rows on the maxilla. 12–14 large conical teeth form the medial row, and numerous much smaller teeth form the lateral row. The 27 mm long lower jaw of young specimen, D 09.11.96.11, bears 16 large slenderconical sharply pointed teeth of which 13 are located on the anterior 1/3 of the bone. Similarly in another specimen (D 07.11.98.4) in which the maxilla is 48 mm long, there are 15 large slender conical teeth located along the ventral margin of the maxilla. The conical teeth on the older specimens are of course larger, and they have a wider base compared to their length. Calculating the ratio of tooth height (th) to head depth (dh) in front of the opercular series in the sense of Poplin and Heyler (1993) is of only limited use in the specimen D 11.11.95.7 where the ratio of dh/th is 22. The acrodin apex of P. heyleri teeth is smooth ( Text-fig. 15c ), but the remaining part of the tooth corpus is sculptured with longitudinal ridges distributed around the periphery of the tooth. In addition, a different fine microsculpture is observable on the whole surface of the tooth, with the exception of the acrodin apex. The fine microsculpture is formed by fine protuberances distributed on the surface of the tooth ( Text-fig. 15 d–g). The elliptical protuberances are proximo-distally elongated, spaced out from each other and only occasionally touch. The same microsculpture can also be observed on the small teeth of the outer row, with less space between the protuberances. Studies of the microsculpture on the large teeth on the internal row and much smaller teeth on the outer row, demonstrate a match with the microsculpture of P. speciosus . This microsculpture is not exclusive to the teeth of Progyrolepis speciosus as described by Poplin (1999), but is also common in P. heyleri and for this, in many extinct lower actinopterygian taxa ( Richter 1983, Schindler 2018a). Dentition on the upper and lower jaws of Progyrolepis heyleri is partly similar to the dentition on the lower jaw of Usclasichthys macrodens HEYLER, 1977 from the Lodève Basin as figured by Heyler (1977). Comparing the large conical teeth of P. heyleri and Usclasichthys macrodens, the main differences are in the size of the teeth and mainly in the swollen bases which contain a spacious pulp cavity in Usclasichthys macrodens. Different tooth morphology in P. heyleri and Usclasichthys macrodens was previously mentioned by Poplin (1999) and Steyer et al. (2000). Among the P. heyleri lower jaws are specimens which are very similar in characters to those of Usclasichthys macrodens. One of them is lower jaw D 14.03.98.19 ( Text-fig 15b ) which is 8–9 cm long, and presents large conical teeth 10 mm in height and with a 5 mm wide base in which the conical laniaries are of the same height as the depth of the lower jaw at the point where the teeth are inserted. It will be important if some future finds of Usclasichthys macrodens jaws retain the characters reported in the holotype described by Heyler (1977) or if the swollen bases of the teeth with large pulp cavities were only an artefact of preservation associated with compression during the process of fossilisation.

In addition to the marginal teeth small short sharply pointed teeth were developed covering the dorsal surface of the coronoids, particularly on the lower jaw, the medioventral surface of the ectopterygoid and dermatopterygoid on the upper jaw, and the ventral surface of the parasphenoid.

The preoperculum is a long bone angled along the dorsal border of the maxilla. It is possible to distinguish two distinct regions on the preoperculum, a wider anterior region and narrow posteroventral region of the bone ( Text-fig. 11a ). The whole bone lies in an oblique position in the skull, and its posterodorsal margin forms an angle of 15° with the body axis. The anterior branch of the preoperculum is deep in the anterior area, but much less than is usual in many other palaeozoic actinopterygians. The ratio of the length of the anterior branch of the preoperculum to the depth of its anterior part is 2.5. The angle between the dorso-posterior margin of the anterior branch of the preoperculum and the posterior margin of the ventral branch of the preoperculum is around 130°. The anterior margin of the anterior branch is oblique thus the anterodorsal corner is more significantly pronounced anteriorly than the ventroanterior corner (Textfigs 11a, 20). The preoperculum borders posteriorly and dorsally the maxillary plate and the maxilla overlaps the ventral and anteroventral margin of the preoperculum. The ventral branch of the preoperculum is wedged between the maxillary plate, the operculum and the suboperculum.A large unsculptured anterior area of the preoperculum is covered by the large jugal ( Text-fig. 20 ). Conspicuous sculpture consists mainly of long ridges arranged anteroposteriorly on the anterior branch of the preoperculum, while short ridges and tubercles prevail in the ventral narrow branch. The anterior part of the preoperculum presents a sharp borderline between the sculptured and unsculptured areas ( Text-fig. 11a ). The unsculptured part of the preoperculum leads up to the unsculptured anterior part of the maxillary plate, and both bare surfaces were covered by the large jugal. The preopercular canal traverses along the dorsoposterior margin of the preoperculum from where the preoperculum bends in an anterior direction and it leaves the preoperculum on its dorsal side just before the dorsoanterior angle of the preoperculum. Traversing of the preopercular canal is partly similar to that in Mimipiscis toombsi where the preopercular canal leaves the dorsal margin earlier ( Gardiner 1984). The preopercular canal traversing along the posterior margin of the ventral branch of the preoperculum and then along the posterodorsal margin of the anterior branch of the preoperculum is well preserved in medial view in specimens D 14.03.97.12 and D14.03.97.10. Conspicuous thickening of the bone is visible where the preopercular canal passes and particularly where the bone bends. This region is also the centre of ossification of the preoperculum. Thickening of the bone in the area through which the preopercular canal passes represents the horizontal lamina ( Text-fig. 7 ) which probably reinforces cohesion of the preoperculum and palatoquadrate. The fixed connection between the preoperculum and palatoquadrate was previously figured by Nielsen (1942: fig. 35) in Pteronisculus magnus. The bend, obliqueness and the shape of the preoperculum are the conspicuous anatomical features characterizing different actinopterygian species. In Mimipiscis toombsi the dorsoanterior branch of the preoperculum is significantly shorter, connected with the significantly shorter maxillary plate ( Gardiner 1984). In Howqualepis rostridens LONG, 1988 the preoperculum is only slightly bent with the dorsoanterior branch deeper anteriorly ( Long 1988: fig. 14) but not as much as in P. heyleri . The preoperculum of Pteronisculus on the contrary

a

is more similar to that of P. heyleri , and it resembles that species both in the angle of the bend and the ratio of the antero-dorsal and ventral branches of the bone.

The jugal (D 09.11.96.3; D 10.08.95) is the largest and best preserved of the bones making up the infraorbital series. The bone forms two thirds of the posterior margin of the orbit, it is slightly concave anteriorly and strongly convex posteriorly ( Text-figs 12 , 20 ). The jugal significantly overlaps the smooth anterior area of the maxillary plate and partly also the smooth anterior area of the preoperculum. The infraorbital canal passes arcuately across the anterior half of the bone, and small channels split off from the infaorbital canal in a fan-like manner ( Text-fig. 12a ). The shape of the jugal is a distinguishing feature among the actinopterygians. An identical shape was described by Schindler (2018a) in Elonichthys germari, and Štamberg (2010a) in “ Elonichthys ” krejcii, and a similar shape was also described by Gardiner (1984: fig. 73) in Moythomasia durgaringa and Long (1988) in Mansfieldiscus sweeti ( WOODWARD, 1906). As regards the lachrymal, it is not preserved, but its presence is obvious when considering the smooth dorsal region of the suborbital part of the maxilla, the lachrymal formed the ventral border of the orbit and greatly overlapped the suborbital part of the maxilla ( Text-fig. 20 ).

Lower jaw. The lower jaw is preserved in many specimens such as D 02.03.969.9; D 04.10.98.5; D 09.11.96.9; BX 04.10.98.2; BX 08.12.97.5; BX 10.05.96.5; BX 14.01.96.1; BXM 094 etc. It is a very robust bone with the anterior portion curving in medially. The largest whole lower jaw is 10 cm long (BX 14.01.96.1), but fragments of longer jaws are known. The lower jaw is a complex of several bones. The basic axis of the lower jaw is formed of Meckel’s cartilage which is totally ossified only in the posterior part of the jaw where it protrudes dorsally as pars

b a

b

c d

articularis with distinct medial and lateral facets (Textfigs 13a, b, 14a–c). These facets articulate with the double condyle of the quadratum. The large adductor fossa for the adductor mandibularis anteriorly reaches to the facets of the pars articularis ( Text-fig. 14 a–c). Anterior ossification of the Meckelian cartilage which was observed in

a

b

gr vlpre hlpre t

d

c mc Ang De

e

Mimipiscis toombsi, Moythomasia durgaringa by Gardiner (1984), in Nematoptychius greenocki by Watson (1928) or Pteronisculus magnus by Nielsen (1942) is missing in P. heyleri . A significant groove is present where the Meckelian cartilage would have been. On the contrary in medial view

the dentary is conspicuously thickened along its dorsal and

ventral margins ( Text-fig. 15b ) as similarly figured by Long (1988) in Howqualepis rostridens. The lateral surface of the lower jaw is composed of three dermal bones, the dentary, the

angular and the supraangular, which forms the lateral wall of

the adductor fossa. The dentary is the largest bone, elongated in an anteroposterior direction, slightly deeper posteriorly,

and anteriorly it is curved medially. The dentary bears

conspicuous sculpture consisting of predominantly long

ridges which elongate in an anteroposterior direction. Short ridges in combination with tubercles are developed along the dorsal margin of the dentary and in the anterior part of the dentary. Identical sculpture was figured by Štamberg (1991) in Progyrolepis speciosus , and also is present on the type specimen of Elonichthys germari (personal observation). The sculptured part of the dentary is rounded posteriorly, and it overlaps the anterior margin of the angular ( Text-fig. 14 a–c, e). In some specimens the dentary exhibits slight differences in the sculpture. Specimen D 02.03.96.9 shows ridges bending upward from an anteroposterior direction in the posterior third of the dentary ( Text-fig. 14e ). The sculpture on the dentary of young specimens consists exclusively of long ridges regularly arranged in an anteroposterior direction ( Text-fig. 13d ).The mandibular sensory canal traversed from the anterior end along the ventral margin of the bone in a posterior direction and posteriorly it traversed to the angular. The pores of the mandibular canal are arranged in a line. In addition, there are some small pores spread over the surface of the anterior half of the dentary ( Text-fig. 13b, c ). These pores probably mediated environmental perception.

The angular continues posteriorly to the dentary (Textfigs 13a, b, 14a–c, e). The angular is much smaller than the dentary and is approximately triangular in shape with the triangle base located on the posteroventral margin of the lower jaw ( Text-fig. 14c ). The angular forms one third of the total length of the lower jaw in a posteroanterior direction similarly as in Mimipiscis toombsi or Moythomasia durgaringa ( Gardiner 1984, Choo 2011) but contrary to Pteronisculus magnus ( Nielsen 1942) or Nematoptychius greenocki ( Watson 1928) where it forms one half of the lower jaw total length. Also in Elonichthys germari the angular is extended more anteriad ( Schindler 2018a). The borderline between the dentary and the angular is clearly visible due to its distinct sculpture. The posterior region of the dentary bears long ridges arranged anteroposteriorly while the angular exhibits short ridges and tubercles (Textfigs 13a, b, 14a–c, e). The mandibular sensory canal is traceable via the holes which traverse from the dentary to the angular, close to the ventral margin of the bones and it continues along the posterior margin of the angular ( Text-figs 14 a–c, e, 20). The angular is dorsally sutured to the supraangular in an interdigitating suture and both the angular and the supraangular are devoid of sculpture in the area where the ventroposterior part of the maxilla overlaps these bones ( Text-figs 13a, b , 14 a–c). The supraangular occurs in some palaeoniscoids such as Moythomasia durgaringa, Nematoptychius greenocki, Pygopterus nielseni, Pteronisculus magnus etc. but in others it is absent, e. g. Mimipiscis toombsi ( Gardiner 1984).

The lower jaw in medial view exhibits a complex of bones. The largest of them is the prearticular, medially surrounding the space for the adductor mandibularis. The prearticular ( Text-figs 13a , 14d ) is bent dorsoventrally and forms the horizontal lamina, in front of the adductor fossa, the lamina extends to half the length of the lower jaw. The horizontal lamina laterally borders with the dentary, and it is covered by shagreen of small teeth. The teeth on the horizontal lamina of the prearticular near to the border with the dentary may be sharp and pointed similar to the small teeth on the dentary. Medially the teeth are minute or form a shagreen of small tubercles which gradually pass towards the ventral region of the prearticular which is completely smooth along its ventral margin ( Text-fig. 14d ). The ventral part of the prearticular covers the Meckelian cartilage medially. Anterior to the prearticular are four coronoids ( Text-figs 13a, b , 14 a–c). They are much smaller than the prearticular, and they overlap one another in an anteroposterior direction. The coronoids bear shagreen of small teeth similarly as in the prearticular. Progyrolepis heyleri has four short coronoids as in Mimipiscis toombsi or Moythomasia durgaringa ( Gardiner 1984: figs 92, 95), but the P. heyleri coronoids are accompanied by a long prearticular reaching half way along the length of the lower jaw. The prearticular in Pteronisculus magnus is also conspicuously elongated anteroposteriorly but only three coronoids are present ( Nielsen 1942: fig. 40).

Hyoid arch. The bones of the hyoid arch are preserved as a complex of isolated bones which compose the arch. The hyomandibula, the symplectic and the ceratohyal for certain can be recognised in the material. The hyoid arch bones are preserved in many specimens such as D 06.09.98.3; D 09.11.96.5; D 14.03.97.10; BX 12.05.98.5; BX 10.08.95 etc.

The hyomandibula is a large, stout conspicuously dorsoventrally elongated bone, angularly bent, and with a significant anterior inclination ( Text-figs 7 , 16 a–d). It consists of two clearly distinct arms forming an angle of 151–157°. The dorsoanterior arm is widest anteriorly where it is visibly compressed from the lateral and medial sides. It narrows backwards towards the point where the two arms join. The ventral arm is 10 % shorter than the dorsoanterior one, it is narrower and not lateromedially compressed. The ventral end of the ventral arm is straight, and it articulates with the symplectic. The processus opercularis is well developed in lateral view on the posterior margin of the bone in the area where it bends. The processus opercularis is formed by the hump of the round ground and points lateroposteriorly ( Text-fig. 16 a–c). A thin posterior lamina stretches along the posterior margin of the dorsal arm of the hyomanibular in a dorsal direction from the processus opercularis (Textfig. 16a, b). A conspicuous narrow groove originates at the level of the processus opercularis and traverses between the dorsal arm of the hyomandibula and the posterior lamina ( Text-fig. 16a, b ). This groove can be compared with the truncus hyoideomandibularis facialis canal figured by Nielsen (1942) in Pteronisculus magnus, by Aldinger (1937) in Pygopterus nielseni and by Štamberg (2010a) in Rhabdolepis saarbrueckensis. The processus opercularis is well preserved, andlocatedventraltotheposteriorlamina.Thisisdifferentfrom Pygopterus nielseni where the processus opercularis is figured as running dorsally to the posterior lamina ( Aldinger 1937: fig. 41A). The processus opercularis is also well developed in Rhabdolepis saarbrueckensis and on the type material of Elonichthys crassidens as figured by Štamberg (2010a: fig. 4) and Schindler (2018a: fig. 40). On some specimens, a hole is visible ventral to the processus opercularis ( Text-fig. 16a, b ). This hole may indicate the presence of a hyomandibular canal as was described by Gardiner (1984) in Mimipiscis toombsi and Moythomasia durgaringa. The presence of such a canal is not 100% clear, and a continuation of the canal on the medial side of the hyomandibular was not apparent. The shape of the hyomandibula, including the bend in the bone and the shape of the processus opercularis correspond to that figured by Schindler (1993) in Meisenheimichthys palatinus and by Štamberg (2010a) in Rhabdolepis saarbrueckensis. The

a

c d f

b

e

g

po

hyc

a b

d f c

hyomandibula of Elonichthys crassidens which was figured

by Štamberg (2010a: fig. 4B) has an angle of 158°–160° where

the bone bends is also very similar ( Schindler 2018a), but the

antero-dorsal arm is twice the length of the ventral arm.

In medial view ( Text-figs 7 , 16d ), a conspicuous wide

furrow can be seen traversing across the centre of the

hyomandibular dorsal arm. It is narrow at the point where

the bone bends and the ventral arm is extended but it does not reach the ventral end of the hyomandibula. This may be an insertion point of the musculus adductor mandibulae. This groove on the hyomandibula was previously recorded by Long (1988: fig. 21B) in Howqualepis rostridens, but he figured the groove on the antero-dorsal arm only, and not at the point of the bend.

Ceratohyal. Right and left ceratohyals are well preserved on the slab BXM 074 together with numerous scattered bones of the skull. For this reason, the medial or lateral side of the ceratohyal was identified based on an earlier description of the bone in Pygopterus nielseni, Pteronisculus aldingeri and Moythomasia durgaringa (Aldiner 1937, Nielsen 1942, Gardiner 1984). The ceratohyal is slightly mediolaterally compressed, generally of rectangular shape in lateral and medial views. It expands posteriorly, narrows slightly anteriorly, and is conspicuously narrow in the anterior 1/3 of the length ( Text-fig. 16e, f ). The anterior margin of the bone is straight, the posterior is oblique. A conspicuous groove on the lateral side ( Text-fig. 16e ) of the bone begins at the posterior end, it traverses anteriorly in the middle of the lateral surface of the bone, and bends slightly upwards where the bone constricts and leaves the bone on the dorsal margin immediately before the anterior end of the bone. The same groove was described in Moythomasia durgaringa ( Gardiner 1984: fig. 106), Pygopterus nielseni ( Aldinger 1937: fig. 41B) and others and is considered as being a groove for the afferent hyoidean artery. The identical shape in the ceratohyal and course of this groove for the afferent hyoidean artery have been recorded in Pteronisculus aldingeri (Nielsen

a

1942: fig. 43) and Progyrolepis speciosus ( Štamberg 1991: fig. 21). On the contrary, the shape of the ceratohyal differs from this bone in Moythomasia durgaringa ( Gardiner 1984: fig. 106) and Pygopterus nielseni ( Aldinger 1937: fig. 41b). In the anterior third of the bone length where the course of the groove for the afferent hyoidean artery runs, the bone is clearly ossified. In medial view, the ceratohyal exhibits ( Text-fig. 16f ) massive perichondrally ossified bone with fine grooves indicating the ossification centre again in the area of bone constriction in the anterior third of the bone s length.

The symplectic is a robust bone connecting the hyomandibula to the ceratohyal in the sense of Nielsen (1942, 1949), Poplin and Véran (1996). It has the form of a short cylinder and can be observed behind the lower and upper jaws ( Text-figs 7 , 17a ) or as an isolated bone in specimens D 09.11.96.11; D 14.03.98.19; BX 10.08.95. This short robust bone has two dorsally supporting columns terminating in facets in medial view ( Text-fig. 17a, b ). The anterior column is broader than the posterior one, with a conspicuous groove passing vertically from the dorsal margin of the bone dividing it into two halves. The symplectic is slightly constricted mid height. The ventral end of the bone is not divided and is slightly convex. There is a suggestion of articular facets on the anterior and posterior edges of the convex ventral end. The described symplectic is not well preserved, but the shape with probable articular facets on the dorsal and ventral ends indicates that the symplectic is the interconnection between the hyoid and palatoquadrate

b

c

arches. The above described symplectic varies greatly from that of Cheirolepis canadensis and “ Pygopterus ” degeeri after Véran (1988: figs 7, 8), Pteronisculus after Lehman (1952: fig. 35B) or Pteronisculus aldingeri after Nielsen (1942: fig. 42). The symplectic in Cheirolepis canadensis is of triangular shape in lateral view and in the other above mentioned species the symplectic is relatively narrow.

Opercular apparatus. The antoperculum, operculum, suboperculum and branchiostegal rays were distinguished among the dermal bones of the opercular apparatus.

The antoperculum itself was not found in the studied material. Its existence was suggested by the unsculptured anterior margin of the operculum ( Text-fig. 18a, b ) in specimen D 01.01.96.2. Based on the unsculptured anterior margin of the operculum, the triangular shape of the antoperculum can be deduced. It is dorsoventrally elongated, reaching to nearly 1/2 the length of the operculum anterior margin from its dorsal end and wedged between the operculum and preoperculum. It is clear that this bone is not attached to the hyomandibula, and must be considered to be the antoperculum in the sense of Gardiner et al. (2005).

The operculum is preserved in several specimens (D 01.01.96.2; D 17.08.96.4; BX 10.03.96). It is rectangular, conspiucuously elongated in a dorso-ventral direction, with a slightly obtuse dorsoanterior angle ( Text-figs 18 a–c, 20). It is approximately 3 times deeper than it is long and 2.5–3 times deeper than the depth of the suboperculum. The operculum is significantly inclined anteriorly to the axis of the body, at an angle of 25°–30°. The ventral corners of the operculum are rounded, and the anterior margin is straight but slightly concave. The posterior margin of the operculum is slightly convex. It is laterally sculptured by closely arranged vermicular ridges in the ventral third of the surface, the ridges being long and mostly parallel to the ventral margin of the bone. Along the anterior and posterior margins are ridges running parallel to these margins, in the central area of the surface are short vermicular ridges combined with tubercles. An unsculptured narrow area along the dorsal part of the anterior margin in specimen D01.01.96.2 was overlapped by the antoperculum. The operculum overlaps the supracleithrum posteriorly and the suboperculum ventrally.

The shape of the operculum is markedly different from the operculum of Progyrolepis speciosus as described by Štamberg (1991). The operculum of Progyrolepis speciosus is also elongated in dorso-ventral direction, but does not have a rectangular shape, the sloping of the ventro-anterior part of the bone forms a space for the triangular epipreoperculum, which in Progyrolepis heyleri is absent. These differences in the composition of the opercular apparatus can be attributed to evolution of the skull from Upper Carboniferous (Gzhelian) times when P. speciosus existed, to the occurrence of P. heyleri (Lower Permian, Asselian or Sakmarian). The shape of the operculum can also be variable to some extent as was described by Štamberg (2010a) in Rhabdolepis saarbrueckenensis in which one specimen had an operculum which was significantly narrower in the ventral direction while the neotype of R. saarbrueckenensis has a parallelogram shaped operculum ( Gardiner 1963). Similar conclusions also resulted from Schindler’s study (2018b) of Rhabdolepis macropterus which was found to also have a parallelogram shaped operculum ( Schindler 2018b: figs 2, 3) which significantly narrows ventrally ( Schindler 2018b: fig. 1). The shape and position of the operculum in Progyrolepis heyleri is similar to the parallelogram shaped operculum in Rhabdolepis macropterus. An antoperculum is also present in R. macropterus but it extends up to 4/5 of the depth of the operculum ( Schindler 2018b: figs 2, 3). The difference is in the absence of an accessory operculum in P. heyleri in contrast to its presence in R. macropterus. The operculum of P. heyleri differs significantly from that in Watsonichthys pectinatus or Cosmoptychius striatus (AGASSIZ, 1835) as described by Gardiner (1963) where the operculum distinctly narrows ventrally and an accessory operculum is present.

A suboperculum is well preserved in D 01.01.96.2; D 14.03.97.12; D 17.08.96.4. It is approximately square in shape with prolonged anteroventral corner ( Text-fig. 18a, b, d, e ). The bone is shorter in the dorsal part than in its ventral part. The suboperculum has a straight anterior border, convex posterior border, and is slightly undulating dorsally and concave ventrally. The ossification centre lies in the ventral third of the bone near to its anterior border. Sculpture is preserved only on part of the bone and consists of closely spaced vermicular ridges mostly parallel to the dorsal, posterior and ventral margins of the bone (Textfig. 18d, e). Along the dorsal border the bone is without sculpture and was overlapped by the operculum, the ventral margin of the suboperculum overlaps the dorsal margin of the first branchiostegal ray. The suboperculum touches anteriorly the ventral portion of the preoperculum, and it overlaps the ventral part of the supracleithrum and dorsal part of the cleithrum posteriorly ( Text-fig. 20 ). The shape of the suboperculum is very similar to that described ( Štamberg 1991) in Progyrolepis speciosus .

Branchiostegal rays. A complete set of branchiostegal rays was not found preserved, but several branchiostegal rays can be seen in specimens D 01.01.96.2 ( Text-fig. 18a, b ) and BX 31.07.97.1 ( Text-fig. 18f ), and isolated branchiostegal rays are preserved in D 04.10.98.5 and BX 31.10.97.1. The branchiostegal rays are anteroposteriorly elongated, but are not excessively narrow. In the posterior region they are 2.3 times deeper than in the anterior, and are rounded anteriorly and posteriorly. It can be assumed that about 10 to15 branchiostegal rays formed this part of the skull during the life of the animal. Conspicuous sculpture on the lateral surface of the branchiostegal rays consists of tubercles and short ridges vermicularly twisted. Along the ventral margin of the rays are long ridges parallel with the ventral border of the bone. Along the dorsal margin is a strip of bone without any sculpture which was overlapped by the ventral margin of the above branchiostegal ray.

Components of the branchial arches are preserved only as isolated bones, and there is no obvious relationship between them or their position on the skull.

Dermal bones of the shoulder girdle. The posttemporal, supracleithrum, cleithrum and clavicle form the dermal components of the shoulder girdle.

The posttemporal is preserved in D 08.02.98.10.4/4 and BX 04.11.97.17. The bone is oval in shape, elongated in a mediolateral direction, and slightly narrower medially ( Text-fig. 19g ). Specimen D 08.02.98.10.4/4 contains a

b

a

c e

f

fragment of the dorsal side of the bone with sculpture consisting of conspicuous ridges. The rest of the specimen shows the imprint of the ventral surface of the posttemporal

with a conspicuous lateral sensory line in the anterolateral corner. The lateral sensory line most likely passed from the lateral extrascapular and continued across the posttemporal, traversing across the dorsal side of the supracleithrum. The shape of the posttemporal corresponds to that in Progyrolepis speciosus , Elonichthys krejcii and Acrolepis gigas ( FRIČ, 1877) ( Štamberg 1991, 2010a), it differs however from the triangular posttemporal in Pteronisculus ( Nielsen 1942) and rectangular posttemporal in Mimipiscis toombsi ( Gardiner 1984).

The supracleithrum is a large oval shaped bone,

elongated in a dorso-ventral direction with a large dorsal process ( Text-fig. 19a, e ). The supracleithrum in specimen D 10.08.95 7/ 7 in Text-fig. 19e shows the bone in medial view; it is 65 mm high, including the dorsal process which is 10 mm high. The bone is longest in its dorsal third and measures 26 mm. In the ventral direction, it is slightly

narrower, and the ventral end is rounded. The posterior border of the supracleithrumm is moderately convex with a notch at the point where the lateral sensory canal traverses from the supracleithrum to the scales of the body.

The anterior border of the supracleithrum is straight in the dorsal two thirds, but in the ventral 1/3 it is conspicuously concave and is considerably narrower. The lateral sensory

canal traverses across the dorsal third of the bone and is clearly traceable from the medial as well as the lateral sides. It passes to the supracleithrum from the posttemporal on its dorsal border, immediately anteriorly to the dorsal

process on the supracleithrum. It then passes diagonally in a ventroposterior direction and traverses from the supracleithrum to the scales one third of the way down its

f

e g

posterior margin. The lateral surface of the supracleithrum exhibits conspicuous sculpture. Ridges arranged in an anteroventral direction prevail in the dorsal quarter of the bone, the rest of the bone is ornamented with long ridges running parallel to the anterior and posterior borders of the bone. These ridges bend ventrally along the ventral margin of the supracleithrum. There is no sculpture on the dorsal process of the supracleithrum which is overlapped by the posttemporal. In medial view, distinct reinforcement of the bone is visible in the location of the supracleithrum dorsal process which continues ventrally through the centre of the bone up to the ventral margin and gradually weakening. The process on the dorsal border of the supracleithrum is outstanding. This type of process, which is overlapped in its normal position by the lateral margin of the posttemporal, is common for example in Amblypteridae and Aeduellidae , but is absent in Mimipiscis toombsi ( Gardiner 1984).

The cleithrum is a dorsoventrally elongated and laterally convex bone which borders the branchial cavity posteriorly and forms support for the insertion of the pectoral fin ventroposteriorly. The cleithrum ( Text-fig. 19 b– d) in lateral view is divided into two branches, namely the dorsal branch which is almost vertical and the ventral branch which is almost horizontal. The dorsal branch is triangular in shape, twice higher than it is long and significantly elongated and tapering to the tip dorsally. A conspicuous convex edge crosses the cleithrum from its dorsal point arcuately ventroanteriorly, and the cleithrum bends medially alongside this edge. The edge forms the posterior border of the branchial cavity. During the life of the animal, this space was overlapped by the suboperculum and branchiostegal rays. The posterior border of the dorsal branch is strongly convex with a shallow notch in the ventral part of the margin at the point where the pectoral fin would be connected. A conspicuous reinforcement of the dorsal branch is visible in medial view and it passes from the dorsal tip of the cleithrum ventroanteriorly up to the ossification centre of the bone which lies at the point where the cleithrum bends, i.e. in the area of transition between the dorsal branch and ventral branch of the cleithrum. The lateral surface of the vertical branch is conspicuously ornamented with ridges and tubercles demonstrating three types of sculpture. The lateroanterior region of the bone which forms the posterior border of the branchial cavity exhibits crests arranged in a parallel fashion with minute denticulation on the top edges. The crests are not densely positioned. The edge of the dorsal branch, passing from the dorsal apex of the branch anteroventrally, on the contrary exhibits densely spaced tubercles and short ridges. The extended lateral surface of the vertical branch behind its edge, shows densely positioned long moulds which are arranged predominantly in a dorsoventral direction.

The ventral branch of the cleithrum is almost square in outline ( Text-fig. 19b, c ), and nearly horizontal. The ventral surface of the branch is conspicuously sculptured with long ridges closely positioned in an anteroposterior direction. The anterior margin of the cleithrum is without sculpture and is overlapped by the clavicle.

The clavicle is a large bone. Similarly to the cleithrum, it consists of two parts, namely the horizontally oriented ventral division and vertically oriented dorsal division (Textfig. 19h). The horizontal ventral division of the clavicle is triangular in outline in ventral view. It is relatively short in anteroposterior dimension and bluntly terminates anteriorly. The medial margin of the clavicle’s horizontal division is almost straight, not undulating, rounded posteriorly and slightly convex ventrally. The horizontal division is laterally bent dorsally and continues to the vertically orientated dorsal division. The vertical dorsal division is also triangular in outline in lateral view and forms a process dorsolaterally. There is no sculpture on the large anterodorsal surface which is smooth and covered by the branchiostegal rays.

The short wide clavicle of Progyrolepis heyleri differs significantly from the clavicle of a number of other actinopterygians. Devonian actinopterygians Mimipiscis toombsi and Moythomasia durgaringa have a clavicle with an anteriorly elongated and pointed horizontal branch ( Gardiner 1984), similarly the clavicle is significantly elongated in Cheirolepis trailli ( Pearson and Westoll 1979) .

Pectoral fin. The pectoral fin is preserved in D 12.10.95.11; D 12.10.95.8; BX 31.07.97.1; D 03.10.95.8, and they represent fins from young and adult specimens. The fin consists of at least 15 lepidotrichia which are segmented in addition to the lepidotrichia of the leading edge of the fin. The leading pectoral fin lepidotrichium is unsegmented, with small fringed fulcra on its anterior border. The fringed fulcra are firmly connected to the leading pectoral fin lepidotrichium ( Text-fig. 22a ).

Pelvic fin. The base of the pelvic fin extends over eight scale rows, and the fin consists of at least 20 lepidotrichia (D 17.09.96.4). The lepidotrichia are segmented ( Text-fig. 22b ), and some segments bear two or three grooves. The longest lepidotrichia on BX 31.05.99.49 have 15 segments.

Caudal fin. The ventral lobe of the caudal fin consists of 18 segmented lepidotrichia. These segments bear lengthwise grooves (D 14.03.38.23).

Scales. The complete shape of the body is not visible in any specimen. Numerous fragments including D 03.10.95.8; D 05.06.96(3); D 05.09.98(3); D 11.11.95.7; D 12.10.95.8; D 12.10.95.11; D 12.11.95(7); D14.03.38 (23); D 17.09.96(4); D 18.12.96(7); D 20.03.99.6; BX 03.11.98(1); BX31.05.99.49; BX 31.07.97.1 demonstrate only part of the body and the fins. Fragments of the body document a spindle shaped body extending to 70 cm of the total body length, with the head occupying 1/5 of the total body length. Below the lateral sensory line are 26 scales, between the ridge scale of the anal fin and lateral sensory line (BX 31.05.99.49), and the same row has 16 scales above the lateral sensory line. The lateral sensory line is traceable from the posterior margin of the supracleithrum up to the caudal peduncle, and the pores of the lateral sensory line are not visible on each scale in the line but more often on every third scale. The exposed side of the scale containing the pore is convex in the area in front of the pore ( Text-fig. 23c, d ). In addition to the lateral sensory line, there is another sensory line developed in the dorsal part of the anterior region of the body. The dorsal accessory sensory line is visible only on several scales and there are 11 scales between the main lateral sensory line and this dorsal accessory sensory line. The complementary dorsal sensory line is known in Howqualepis rostridens ( Long 1988). Blot (1966) described a dorsal sensory line in Paramblypterus decorus ( EGERTON, 1850) and Heyler (1969) in Aeduella blainvillei ( AGASSIZ, 1833). The body is covered with scales arranged in transverse scale rows. There are about 9 scale rows between the supracleithrum and pelvic fin base, 26 scale rows between the supracleithrum and the anal fin base, and 46 scale rows between the supracleithrum and the base of the caudal fin. There are about 50 scale rows between the supracleithrum and the line of inversion in the caudal peduncle. The shape of the scales varies depending on the location on the body, similarly as recorded in other palaeoniscoid fishes ( Text-figs 22 , 23 ). The sculpture on the exposed face of the scales changes simultaneously. The scales in the anterior part of the body along the lateral sensory line are of oblong shape, twice higher than they are long ( Text-figs 22e , 23f ). Significant ridges of ganoine traverse across the scales, and protrude at the posterior border of the scale to form serrations. There are up to 16 short spines on the posterior border of the scales. The scales located more posteriorly on the body have a rhombic shape ( Text-fig. 23a ). The scales possess diagonal ridges. The longest ridge passes diagonally from the anterodorsal corner to the posteroventral corner of the scale, and it terminates in a dental form process on the posterior margin of the scale. This is the second or third dental form process on the posterior border of the scale, counting from the ventral corner of the scale. This long ridge divides the lateral surface of the scale into the anteroventral and posterodorsal halves. The arrangement of ridges on the two halves is different. Six to seven ridges are recognizable on the anteroventral region of the scale. These ridges start at the anterior margin of the scale anastomosis posteriorly, and terminate in one or two depressions. The posterodorsal half of the scale has one or two ridges which start at the anterodorsal corner of the scale, branch posteriorly, and terminate in eight or more depressions. The scales above the pelvic fin are shallow; they are five times longer than they are deep. Long ridges pass along the ventral margin of the scales where the ridge along the ventral margin of the scale is conspicuously wide ( Text-fig. 23d, h ). Peg and socket articulation is well developed. Scales overlap each other but mutual overlapping of scales in an anteroposterior direction

is limited, being from 1/8 to 1/9.

The microsculpture on the scales is formed by micro-

tubercles arranged in the same direction as the ridges. The microtubercles have an elliptical base, are antero-posteriorly

elongated ( Text-figs 23b , 24 ), and are more elongated and

less numerous than in “ Elonichthys ” sp. ( Štamberg 2016b:

figs 8C, 9B, D). Microtubercles are typical for ganoine

a c d

g

f h

b e i a b

c

( Schultze 2016), and they are also present in Palaeozoic actinopterygians Strepheoschema fouldenensis WHITE, 1927 and Palaeoniscum freieslebeni BLAINVILLE, 1818 ( Richter 1995), Spinarichthys dispersus ( FRITSCH, 1894) ( Štamberg 2016a) and Aeduella blainvillei ( Text-fig. 34g, h ).

Several specialised scales are developed in addition to the flank scales. Three or four large ridge scales precede the base of the dorsal fin. They bear sculpture consisting of conspicuous ridges arranged in an antero-posterior direction ( Text-fig. 22f ). Large ridge scales are also developed in front of the anal fin. Closest to the anal fin is a single large scale with a conspicuous ventral ridge that forms a keel (Textfig. 22g). Posterior to this large keeled scale are large paired flat scales ( Text-fig. 22h ). The ridge scales bear numerous ridges protruding posteriorly in several serrations. Large basal fulcra cover the dorsal and ventral border of the caudal peduncle ( Text-fig. 22i ). They extend in an antero-posterior direction and bear conspicuous ridges on their exposed surface and their medial surface which is overlapped by the preceding basal fulcra.

Conclusion to Progyrolepis heyleri . The decomposed bodies, isolated bones and scales produced a large quantity of new information about Progyrolepis heyleri . Knowledge regarding the jaws which are of vital importance for designation of this species ( Poplin 1999) was greatly enhanced, including changes in the shape of the maxilla during ontogenesis. Completely new information about the construction of the palatoquadrate, dermal bones of the skull roof, opercular apparatus and the shoulder girdle was gained. Characteristics regarding the squamation were identified and described, including microsculpture on scales, and specialised scales in front of the fins. Some information was gained in regards to the bones of the rostral part of the skull, around the orbit, and the ventral portion of the operculo-gular series. A general understanding of the shape of the body was also formed. The study of the microsculpture on the teeth documents the same microsculpture in Progyrolepis heyleri as described by Fritsch (1895) in Progyrolepis speciosus , and there is no difference as proposed by Poplin (1999). Similarly, decoration on the anterior part of the maxillary plate is variable and cannot be considered a character that can discriminate Progyrolepis speciosus from Progyrolepis heyleri as assumed by Poplin (1999). The character which differentiates Progyrolepis speciosus from Progyrolepis heyleri is the shape of the operculum. It is oblong shape and there is an antoperculum in P. heyleri , whereas the operculum narrows ventrally and an epipreoperculum is present in Progyrolepis speciosus . The scales of P. heyleri are well preserved while the scales of P. speciosus are partly preserved in only one specimen, and therefore a thorough comparison of the two species is not possible as of yet.

The shape of the operculum, with a slender antoperculum limited to the dorsal border of the anterior margin of the operculum, suggests some convergence of Progyrolepis heyleri with Pygopterus nielseni, Nematoptychius greenocki and Cycloptychius . The shape of the parasphenoid and curved interfrontal suture do not fit in the original description of Pygopteridae submitted by Aldinger (1937). It is important to compare Progyrolepis heyleri with other large carnivorous fish such as Elonichthys and Rhabdolepis from European Permo-Carboniferous basins. The large jugal and form of the cheek bones figured by Schindler (2018a) in Elonichthys germari and Štamberg (1991) in “ Elonichthys ” krejcii demonstrate great similarity. In addition the border between the dermopterotic and dermosphenotic in Progyrolepis heyleri is in a more posterior location but remains anteriad to the border of the fronto-parietal. The dermosphenoticdermopterotic border in Rhabdolepis macropterus or “ Elonichthys ” krejcii is located posteriorly to the frontoparietal border ( Štamberg 2010a, Schindler 2018b). The maxilla of Rhabdolepis macropterus has a slanting anterior margin which forms an angle of 20°–29° ( Schindler 2018b) with the ventral denticulated border of the maxilla, and in Elonichthys germari this angle is 45° ( Schindler 2018a). Progyrolepis speciosus and Progyrolepis heyleri demonstrate angles of 68°–77°, and only juvenile specimens have a more oblique anterior margin and angle of around 40°. The arrangement of the dermal bones of the operculogular series in Progyrolepis heyleri differ significantly from those in Rhabdolepis macropterus or Rhabdolepis saarbrueckensis in which one or two accessory opercula are inserted between the operculum and suboperculum ( Gardiner 1963, Štamberg 2010a, Schindler 2018b) and also from those in Elonichthys germari or “ Elonichthys ” krejcii in which the operculum narrows ventrally, and additionally a very deep first branchiostegal ray follows the suboperculum ( Štamberg 2010a, Schindler 2018a).

Figures

Text-fig. 4. Progyrolepis heyleri POPLIN, 1999. The skull roof in dorsal view. MHK 82834. Scale bars 5 mm. a – photograph, whitened. b – drawing. Abbreviations: Dsph – dermosphenotic; Dpt – dermopterotic; Fr – frontal; Frfr – frontal fragments; infs – interfrontal suture; Pa – parietal.

Text-fig. 5. Progyrolepis heyleri POPLIN, 1999. Isolated right frontal in dorsal view. Specimen D 08.02.98.50. Scale bar 5 mm. a – photograph, whitened. b – drawing.

Text-fig. 6. Progyrolepis heyleri POPLIN, 1999. Parasphenoid in ventral view. D 07.11.95.10. Scale bar 5 mm. a – photograph. Granulation in the medial region of the corpus parasphenoidis and in the proximal part of the processus ascendens are the remains of the dentition on the ventral side of the parasphenoid. b – drawing.

Text-fig. 7. Progyrolepis heyleri POPLIN, 1999. Left palatomaxillary apparatus in medial view. The hyomandibula above, the entopterygoid and the ectopterygoid demonstrate shagreen-like cover with small teeth. BX 12.05.98.5, whitened. Scale bar 5 mm. Abbreviations: coqu – condyles on the quadratum; Ect – ectopterygoid; Ent – entopterygoid; Hy – hyomandibula; hlp – horizontal lamina of preoperculum; Mx – maxilla; Pq – palatoquadrate; spig – spiracular groove; Sy – symplectic.

Text-fig. 8. Progyrolepis heyleri POPLIN, 1999. Outprint of the left entopterygoid, ectopterygoid and dermometapterygoid in lateral view. D 14.03.98.19.6/6, whitened. Arrow indicates directio cranialis. Scale bar 5 mm. Abbreviations: Dmpt – dermometapterygoid;Ect– ectopterygoid;Ent–entopterygoid.

Text-fig. 10. Progyrolepis heyleri POPLIN, 1999. a, b – drawing and photograph of the left maxilla in lateral view. D 23.08.98.5. Scale bars 5 mm. c – drawing of the left maxilla in lateral view. D 06.03.96.1. Scale bar 5 mm. d – right maxilla in lateral view. BX 17.10.98.2, whitened. Scale bar 5 mm. e, f – left maxilla in lateral view with detail of the sculpture on the anterior region of the maxillary plate (f). D 11.11.95.17, whitened. Scale bars 5 mm.

Text-fig. 11. Progyrolepis heyleri POPLIN, 1999. a – set of bones of the left side of the cheek demonstrates the strong lower jaw, maxilla and preoperculum of old specimen. Large anterior regions of the preoperculum and maxilla are without sculpture, they were covered by the jugale. D 04.10.98.5. Scale bar 5 mm. b, c – photograph and drawing of the left maxilla of juvenile specimen D 13.04.97.6 with conspicuous horizontal lamina,whitened. Scale bars 5 mm. Abbreviations: Art– articulare; Aup –autopalatinum; Cor – coronoid; De – dentalospleniale; hlm – horizontal lamina of preoperculum; Mx – maxilla; Pop – preoperculum; popc – preopercular canal.

Text-fig. 12. Progyrolepis heyleri POPLIN, 1999. a – isolated jugal in medial view with conspicuous ridges fanny diverging from the radiation centre situated in the centre of the arched bend in the infraorbital canal. Specimen D 09.11.96.3, whitened. Scale bar 5 mm. Abbreviation: ioc – infraorbital canal. b – isolated jugal in medial view with infraorbital canal. The rests of the sculpture on lateral face of the bone are observable in places of lacking bone. Specimen BX 10.08.95. Scale bar 5 mm. Abbreviation: ioc – infraorbital canal.

Text-fig. 13. Progyrolepis speciosus POPLIN, 1999. a – drawing and b – photograph of the right lower jaw in lateral view. D 02.03.96.9, whitened. Scale bars 5 mm. c – right dentalosplenial in lateral view. D 17.09.96.4, whitened. Scale bar 5 mm. d – left lower jaw of a juvenile specimen. D 09.11.96.11, whitened. Scale bar 5 mm. Abbreviations: Ang – angular; artf – articular facet; Cor – coronoid; De – dentalosplenial; Pre – prearticular.

Text-fig. 14. Progyrolepis heyleri POPLIN, 1999. a – left lower jaw in dorsolateral view. BXM 094, whitened. Scale bar 5 mm. b – photograph, whitened and c – drawing of the posterior part of the left lower jaw. BXM 094. Scale bars 5 mm. d – right prearticular in medialview. D 14.03.98.19, whitened. Scale bar 5 mm. e – angular and posterior part of the dentalosplenial in lateral view. Borderline between the dentalosplenial and the angular is clearly noticeable on the basis of distinct sculpture. D 02.03.96.9, whitened. Scale bar 5 mm. Abbreviations: Ang – angular; addf – adductor fossa; artf – articular facet; Cor – coronoid; De – dentalosplenial; gr – groove on prearticular; hlpre – horizontal lamina of prearticular; mc – mandibular canal; Pre – prearticular; Sy – symplectic; sur – surangular; t – teeth; vlpre – vertical lamina of prearticular.

Text-fig. 15. Progyrolepis heyleri POPLIN, 1999. a – row oflarge conical teeth on the right lower jaw. D 17.09.96.4, whitened. Scale bar 5 mm. b – large conical teeth with wide base and spacious pulpal cavity, and conspicuous grooves on the narrow part of the teeth in the anterior part of the lower jaw. The dentary is in medial view, conspicuously thickened along its dorsal and ventral margins. D 14.03.98.19, whitened. Scale bar 5 mm. c – large conical tooth from the internal row and three much smaller teeth from the outer row of the lower jaw. Scale bar 1 mm. d, e – microsculpture formed by elliptical proximo-distally elongated protuberances on the large tooth. Scale bars 100 μm. f – three large slender teeth of the internal row and two teeth of the outer row of the lower jaw of a subadult specimen. D 13.04.97. Scale bar 400 μm. g – microsculpture formed by elliptical proximo-distally elongated protuberances on the large tooth. D 13.04.97. Scale bar 50 μm.

Text-fig. 16. Progyrolepis heyleri POPLIN, 1999. a, b – drawing and photograph of the left hyomandibula in lateral view. D 02.03.96.9, whitened. Scale bars 5 mm. c – drawing of the left hyomandibula in lateral view. D 09.11.96.5. Scale bar 5 mm. d – right hyomandibula in medial view. D 14.03.97.10, whitened. Scale bar 5 mm. e – left ceratohyal in lateral view. BXM 074. Arrow indicates directio cranialis. Scale bar 5 mm. f – right ceratohyal in medial view. BXM 074. Arrow indicates direction cranialis. Scale bar 5 mm. Abbreviations: grh – groove for truncus hyoideomandibularis facialis; hyc – hyomandibular canal; po – processus opercularis.

Text-fig. 17. Progyrolepis heyleri POPLIN, 1999. a – right palatoquadrate and symplecticum in medial view. BX 10.08.95, whitened. Scale bar 5 mm. b – right symplecticum in medial view. BX 10.08.95. Scale bar 5 mm. c – left symplecticum in lateral view. D 14.03.98.19. Scale bar 5 mm. Abbreviations: Sy – symplectic; Qu – quadrate.

Text-fig. 18. Progyrolepis heyleri POPLIN, 1999. a, b – photograph and drawing of right opercular and palatomaxillary apparatus in lateral view. D 01.01.96.2, whitened. Scale bars 5 mm. c – right operculum in lateral view. D 17.08.96.4, whitened. Arrow indicates directio cranialis. Scale bar 5 mm. d, e – photograph and drawing of the left suboperculum in lateral view. D 14.03.97.12, whitened. Arrow indicates direction cranialis. Scale bars 5 mm. f – four branchiostegal rays in lateral view. BX 31.07.97.1. Arrow indicates direction cranialis. Scale bar 5 mm. Abbreviations: Aop – antoperculum; Op – operculum; Rbr – branchiostegal rays; Sop – suboperculum.

Text-fig. 19. Progyrolepis heyleri POPLIN, 1999. Arrows indicate directio cranialis. Scale bars 5 mm. a – drawing of the left supracleithrum in lateral view. BX 07.09.97. b, c – photograph and drawing of the left cleithrum in lateral view. BX 03.06.97.1, whitened. d – right cleithrum in medial view. BX 04.11.97.1, whitened. e – right supracleithrum in medial view. D 10.08.95.7/7, whitened. f – drawing of the right suboperculum in lateral view. MHK 82828. g – left posttemporal in dorsal view. D 08.02.98.10.4/4, whitened. h – left clavicle in medial view. BX 04.11.97.1, whitened.

Text-fig. 20. Progyrolepis heyleri POPLIN, 1999. Restoration of the skull in lateral view. Bones that are not clearly retained on the skull are marked with dashed lines. Scale bar represents 10 mm. Abbreviations: Ang – angular; Aop – antoperculum; Cl – cleithrum; De – dentalosplenial; Dsph – dermosphenotic; Dpt – dermopterotic; Ext – extrascapular; Fr – frontal; Gul – gular lateral; ioc – infraorbital canal; Ju – jugale; La – lachrymal; lsc – lateral sensory canal; mc – mandibular canal; Mx – maxilla; Na – nasal; Op – operculum; Pa – parietal; Pop – preoperculum; popc – preopercular canal; Pt – posttemporal; Ptr – postrostral; Rbr – branchiostegal ray; Sbo – suborbital; Scl – supracleithrum; Sop – suboperculum.

Text-fig. 21. Progyrolepis heyleri POPLIN, 1999. a, b – photograph and drawing of the fragment of the haemal arche of the axial skeleton. BX 10.08.95, whitened. Scale bar 5 mm. Abbreviations: ha – haemal arch; hs – haemal spine.

Text-fig. 22. Progyrolepis heyleri POPLIN, 1999. Scale bars 5 mm. Arrows indicate directio cranialis. Whitened. a – lepidotrichia from the anterior border of the pectoral fin. D 03.10.95.8. b – pelvic fin. BX 31.05.99.49. c – the scales from the area between the pelvic and anal fins. D 18.12.96. d – the scales from the area below the lateral sensory line above the pelvic fin. BX 03.11.98.1. e – the scales from the anterior region of the body above the lateral sensory line. D 05.09.98. f – ridge scales in front of the dorsal fin base. BX 03.11.98.1. g – single ridge scale conspicuously convex forming a keel in front of the anal fin. D 14.03.97. h – flat paired ridge scale in front of the anal fin. BXM 80. i – large basal fulcra from the dorsal rim of the caudal peduncle. D 12.11.95.7.

Text-fig. 23. Progyrolepis heyleri POPLIN, 1999. a – a scale from the middle part of the lateral side of the body with conspicuous ridges arranged diagonally across the scale. MHK 82831, whitened. Scale bar 1 mm. b – small tubercles which form the microsculpture on the scale have elliptical base, antero-posteriorly elongated, and are arranged diagonally in the same direction as the ridges on Text-fig. 23a. MHK 82831. Scale bars 100 μm. c, d – photograph and drawing of a scale with a pore of the lateral sensory line. D 08.02.98.10.4/4, whitened. Scale bar 1 mm. e – drawing of a scale from the middle part of the lateral side of the body. D 04.11.95.10. Scale bar 1 mm. f – drawing of a scale from the anterior region of the body above the lateral sensory line. D 05.09.98. Scale bar 1 mm. g – drawing of a scale from the lateral side of the body between the lateral sensory line and the base of the pelvic fin. D 18.13.96.7. Scale bar 1 mm. h – drawing of a scale from the abdominal region of the body in front of the pelvic fin. BX 31.05.99.49. Scale bar 1 mm. i – large basal fulcra from the dorsal rim of the caudal peduncle. BX 28.01.99.8. Scale bar 5 mm.

Text-fig. 24. Progyrolepis heyleri POPLIN, 1999. Scales from the dorsal part of the body which exhibit ridges arranged diagonally across the scale plus microtubercles. MHK 82829. a – whole scales. The frame marks the view at b of this Text-fig. Scale bar 1 mm. b – sector of the surface with some ridges and microtubercles. Scale bar 100 μm. The frame marks the view at c. c – sector of the surface with microtubercles slightly extended diagonally. Scale bar 50 μm.

Text-fig. 34. Aeduella blainvillei (AGASSIZ, 1833). a – ridge scales in front of the dorsal fin of a juvenile specimen (total length of the body 38 mm). D 03.11.96.14. Scale bar 1 mm. b – ridge scales in front of the dorsal fin of a juvenile specimen (total length of the body 40 mm). D 26.11.95.7. Scale bar 5 mm. c – ridge scales in front of the dorsal fin of a subadult specimen (total length of the body 80 mm). D 07.06.98.10. Scale bar 5 mm. d – ridge scales in front of the dorsal fin of an adult specimen (total length of the body 145 mm). MHK 82809. Scale bar 5 mm. e – part of the dorsal lobe of the caudal fin. MHK 82809, whitened. Scale bar 5 mm. f – part of the ventral lobe of the caudal fin with fringing fulcra along its anterior edge. MHK 82809, whitened. Scale bar 5 mm. g – microtubercles on a scale from the lateral side of the body. Microtubercles on this and the following snaps have a round shape, and are arranged in rows. MHK 82790. Scale bar 50 μm. h – Microtubercles on a scale from the lateral side of the body. MHK 82805. Scale bar 50 μm.