Progyrolepis heyleri POPLIN , 1999

Štamberg, Stanislav & Steyer, Jean-Sébastien, 2021, New Actinopterygians From The Permian Of The Brive Basin, And The Ichthyofaunas Of The French Massif Central, Fossil Imprint 77 (1), pp. 145-165 : 154-160

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Progyrolepis heyleri POPLIN , 1999


Progyrolepis heyleri POPLIN, 1999

Text-figs 7–10 View Text-fig View Text-fig View Text-fig View Text-fig

D i a g n o s i s. See Štamberg (2018).

M a t e r i a l. Forty specimens are described here: GMC 1–11, 22, 25, 29, 38, 41–43, 54–57, 60–62, 74–75, 77, 81–84, 86, 92, 97, 101, 115–116, 125, 127, 130 and G 123. They correspond to body portions, isolated bones and disarticulated skull bones. They represent juvenile specimens of 50–60 mm of total body length (e.g., GMC 11, GMC 83) and adult specimens with a lower jaw length of 90 mm (e.g., GMC 1, GMC 130, G 123).

D e s c r i p t i o n. Skull roof. The skull roof is clearly visible in GMC 56 which the frontal, parietal, dermopterotic and dermosphenotic bones are preserved ( Text-fig. 7a, b View Text-fig ). The frontal is very elongated, three times longer than it is wide. Its anterior edge is convex and rounded. Its lateral border has no processes. It makes contact with the dermosphenotic along most of its lateral edge and slightly with the dermopterotic in its posterior region. The interfrontal suture forms a significant process. Traces of the supraorbital canal are visible on both frontals. The supraorbital canal runs along the frontal, from its anterior border posteriorly to its lateral edge. It does not run close to the lateral edge of the frontal, as in many Palaeozoic actinopterygians, but extends to about one-third of the width of the bone from its lateral edge ( Text-fig. 7a, b View Text-fig ). The sculpture on the exposed surface of the frontal is very conspicuous, and consists of very short ridges anteroposteriorly oriented. The ossification centre of the bone lies at equal distance between its anterior and posterior borders where the supraorbital canal runs. The shape of the parietal cannot be determinate accurately because its contact with the dermopterotic is covered by ornamentation, and its posterior region is missing. The supraorbital canal runs from the frontal to the parietal on which its anterior pit line is preserved. The sculpture on the parietal is similar to that of the frontal. The dermosphenotic is narrow and triangular; pointing anteriorly and slightly widening posteriorly. It borders the frontal laterally and the dermopterotic posteriorly. The dermosphenotic-dermopterotic borderline is displaced posteriorly but it is slightly anterior to, and aligned with, the fronto-parietal borderline. The dermopterotic is slightly elongated with traces of the infraorbital canal laterally.

An isolated right frontal is visible in dorsal view on GMC 81 ( Text-fig. 9d View Text-fig ), it is twice longer than wide but widens posteriorly. Its medial edge forms a smooth narrow strip on which the left frontal was overlapping. The interfrontal suture forms a small but conspicuous process which maintained both right and left frontals. The dorsal sculpture of the frontal consists of conspicuous short ridges posteriorly and tubercles anteriorly. The intersection of the ridges and tubercles marks the region of the radiation centre where the supraorbital sensory canal runs at the level of the interfrontal suture process. The supraorbital canal is not well preserved on the dorsal surface of the frontal but its posterior opening is visible at the level of a posterior notch of the bone.

The shape of the frontal, a curved interfrontal suture forming a large process, ornamentation composed of short anteroposterior ridges, and a dermopterotic-dermosphenotic borderline not extending beyond the frontal-parietal borderline are typical characters of Progyrolepis heyleri , also known from the Permian of Buxières-les-Mines ( Štamberg 2018).

Parasphenoid. The bone is visible in dorsal view on GMC 84 ( Text-fig. 7c, d View Text-fig ), the corpus parasphenoidis stretches anteroposteriorly. It narrows anteriorly and terminates semicircularly posteriorly. Its ossification centre is located at the level of the bucco-hypophysial foramen, in the posterior third of the corpus parasphenoidis. A significant convex medial part extends from this ossification centre to the anterior edge of the bone, and along its medial part, passes grooves where the parabasal canal continues. The paired processus ascendens posterior extend laterally in the posterior third of the corpus parasphenoidis, at an angle of 60°. This angle of 60°, together with the shape of the parasphenoid, is similar to the angle of 68° detected in Progyrolepis heyleri from Buxières-les-Mines ( Štamberg 2018).

Preoperculum. It is partly preserved on G 123 where it appears as an elongated bone, bent along the posterior and dorsal borders of the maxilla ( Text-fig. 9c View Text-fig ). Dorsally, its posterior region is smooth and narrow whereas its anterior region is widened and ornamented by elongated ridges. Its anterior branch is deep and concave anteriorly. Its anterodorsal corner is more pronounced anteriorly than its anteroventral corner.

Maxilla. This bone can be observed on both juvenile (e.g., GMC 60, GMC 83; Text-fig. 8b View Text-fig ) and adult (e.g., G 123; Text-fig. 9c View Text-fig ) specimens and has a length from 60 to 80 mm. It consists of a narrow anterior suborbital region and a long deep maxillary plate. In juvenile and larger specimens (e.g., GMC 43; Text-fig. 8a View Text-fig ), the length of the maxillary plate is about half that of the bone and its height twice that of the bone. This maxillary plate extends posteroventrally as a strong process. In GMC 83, the maxilla is visible in medial view with a distinct horizontal lamina forming a ventral maxillary edge ( Text-fig. 8b View Text-fig ). This horizontal lamina extends from the anterior extremity of the maxilla to one third of the maxillary plate length. The maxillary plate of the adult specimen G 123 exhibits ornamentation composed of numerous tubercles along posterior margin of the plate. These long ridges turn into vermicular ridges towards the centre of the maxillary plate. Dorsally, the maxillary plate also bears long ridges arranged anteroposteriorly. The apices of the tubercles and ridges bear microsculpture consisting of ridges similar to those in Progyrolepis heyleri ( Poplin 1999, Štamberg 2018). The sculpture is missing on the dorsal part of the anterior suborbital region of the bone and on the anterior part of the maxillary plate because they were overlapped by the large jugal and the narrow lacrymal. The angle between the anterior margin of the maxillary plate and the denticulate ventral margin of the maxilla is about 35° in the juvenile specimens GMC 43 and GMC 75. It is extrapolated to between 45° and 50° in the adult specimen G 123 where the anterior margin of the maxillary is not well preserved.

Lower jaw. This is a robust element of the skull. The dentalosplenial is preserved in the juvenile specimens GMC 43 and GMC 83 ( Text-fig. 8a, b View Text-fig ) and in the adults GMC 1 (Textfig. 9a, b) and GMC 130 together with a poorly preserved pars articularis posteriorly. In juveniles, the exposed lateral surface of the dentalosplenial bears sculpture composed of long ridges parallel to the ventral edge of the bone. In adults, short ridges and tubercles are visible along the ventral edge and anterior region of the bone, whereas its posterior region bears long ridges running parallel to the ventral edge.

Dentition. On both the dentalosplenial and maxilla, the teeth are arranged in two rows; the outer row consisting of numerous small and sharply pointed teeth and the inner row of large conical teeth. The juvenile GMC 83 has 12–14 large conical teeth in its inner row. These large conical teeth are thinner than those of the adults and are sometimes (e.g., GMC 42) not regularly spaced. On the maxilla of the adult G 123 ( Text-fig. 9c View Text-fig ), the large conical teeth are 3.8–7.5 mm high and 1.9–3.2 mm wide (= height/width ratio of 2–2.3). The highest teeth are in the anterior region of the maxilla, their height then decreases posteriorly and the shortest ones are on the ventral edge of the maxillary plate. The maxilla carries large conical teeth along the ventral edge of the posterior region of the maxillary plate. On the lower jaw, the inner row is composed of the same large conical teeth which are regularly spaced ( Text-fig. 9a, b View Text-fig ). This dentition is consistent with that of Progyrolepis heyleri from the Bourbon-l’Archambault Basin ( Poplin 1999, Štamberg 2018). Similarly the microsculpture formed by fine protuberances of elliptical shape ( Text-fig. 10i, k View Text-fig ) covering the whole surface of the tooth, in addition to the acrodin apex, is the same as in Progyrolepis heyleri described by Štamberg (2018: text-fig. 15d, e, g) and in Briveichthys chantepieorum gen. et sp. nov. The elliptical protuberances are proximo-distally elongated, they have an outer sharp edge, and it is assumed that these fine edges facilitated the penetration of the tooth into the meat tissue.

Jugal. It is preserved in medial view on GMC 7 where it is oval, slightly elongated dorsoventrally, and it forms the posterior edge of the orbit ( Text-fig. 8e View Text-fig ). It covered the anterior part of the maxillary plate during the animal’s lifetime. The infraorbital canal has an arcuate shape on the anterior half of the bone. On the lateral surface of the jugal its ornamented negative imprint is exposed. Ventrally, the ornamentation consists of a long ridge parallel to the ventral branch of the infraorbital canal. Posteriorly and dorsally, it consists of short ridges vermicularly arranged. This large jugal is similar to that of Progyrolepis heyleri from Bourbon-l’Archambault ( Štamberg 2018), Elonichthys germari ( Schindler 2018) , E. krejcii ( FRITSCH, 1895) ( Štamberg 2010) , Moythomasia durgaringa ( Gardiner 1984) or Mansfieldiscus sweeti ( Long 1988) .

Hyoid arch. The hyomandibula and the ceratohyal are visible in G 123. The hyomandibula is a large, stout bone which consists of two clearly distinct arms forming an angle of 150° ( Text-fig. 9c View Text-fig ). The anterodorsal arm is widest anteriorly. In lateral view, the well-developed processus opercularis, visible at the level of the maximum curvature of the bone, faces backwards. In medial view, the right ceratohyal is robust, slightly curved and mediolaterally compressed ( Text-fig. 9c View Text-fig ). The shape of the bone is exactly the same as in Progyrolepis heyleri ( Štamberg 2018: textfig. 16e, f).

Branchial arch. Long and thin branchial bones are preserved in GMC 75, G 123 and other specimens, but not in their original positions. The ceratobranchials are recognizable by their slightly widened extremities (Textfig. 9c).

Operculum. It is preserved in G 123, GMC 9, GMC 10, GMC 11, GMC 75. It is rectangular, with rounded corners and very deep (about three times deeper than long). Its anterodorsal corner slightly protrudes anteriorly. Its outer surface is sculptured by closely arranged vermicular ridges ( Text-fig. 9e View Text-fig ). The suboperculum, sub-square in shape, is preserved in GMC 1 and GMC 116. Its anteroventral and anterodorsal corners protrude, the latter terminating as a pointed projection ( Text-figs 5f View Text-fig , 9b View Text-fig ). The ossification centre lies in the ventral third of the bone, near its anterior border. Several branchiostegal rays are preserved in a number of specimens but their original location cannot be determinated.

The shape and vermicular sculpture of the operculum and suboperculum are identical to those of Progyrolepis heyleri . This operculum differs significantly from that of Progyrolepis speciosus ( Štamberg 1991) and of Briveichthys chantepieorum gen. et sp. nov. by its sculpture. However, the suboperculum shows significantly protruding anterodorsal and anteroventral corners in both Progyrolepis heyleri and Progyrolepis speciosus ( Štamberg 1991, 2018).

Dermal bones of the pectoral girdle. The posttemporal, preserved in dorsal view on GMC 74, is isolated: it is oval and wide. It shows a prominent process at about the middle of its anterior edge. It is ornamented, and the ornamentation consists of conspicuous ridges vermicularly arranged on most of its dorsal surface, and short ridges and tubercles in its medial region. The anterior margin of the posttemporal, including the process, is smooth and was probably overlapped by extrascapular bones.

The supracleithrum (GMC 38, GMC 115) is very high, with a large process on its dorsal edge. This bone narrows ventrally. Its posterior edge is slightly concave. It is ornamented on its lateral surface and partly on its ventral surface by prominent long ridges arranged in a dorsoventral direction. The lateral sensory canal traverses diagonally across the dorsal third of the bone and traverses from the supracleithrum to the scales one third of the way down its posterior margin.

The cleithrum is laterally divided into dorsal and ventral branches (GMC 130, G 123). The dorsal branch is large and triangular. It narrows conspicuously, dorsally, and ends acutely. It is 2.5 times deeper than the ventral branch which is nearly horizontal. This dorsal branch is also subdivided by a prominent ridge which separates its anterior region, which forms part of the branchial cavity margin, from its posterior region, exposed posteriorly to the opercular bone series during the life of the animal.

Axial skeleton. The axial skeleton is not fully preserved, in adult specimens, it is represented by arcuate ventral and dorsal elements. The ventral elements (GMC 25) are represented by dorsally forked haemal arches that continue ventrally as a pointed haemal spine ( Text-fig. 8c, d View Text-fig ). Haemal arches are highly arched and firmly integrated into the unit surrounding the haemal canal. These haemal arches and spines are very similar in shape to those of Progyrolepis heyleri ( Štamberg 2018: text-fig. 21). The dorsal arcuate element (G 123) is represented by a basic neural arch element, and two slender spines, right and left, protrude from the neural arch (Textfig. 9c). It is not clear whether these arches were fused. Two slender spines, right and left, protrude from the neural arch. These spines are closely adjacent or lie together along their entire length. Some fragments are also visible; they were determined according to axial fragments also observed in Pygopterus nielseni ( Aldinger 1937) , Pteronisculus ( Nielsen 1942) and Mimipiscis toombsi ( CHOO, 2011) ( Gardiner 1984) . In posteroventral view, the ventral arcuate elements are V-shaped as in Pygopteus nielseni ( Aldinger 1937: fig. 43) but not in Mimipiscis toombsi or Pteronisculus where they are semicircular.

The location of the ventral and dorsal arcuate elements is deduced from the description of the axial skeleton of Amia calva ( Grande and Bemis 1998) . According to its shape, the dorsal arch may originate from the axial skeleton in the transitional region between the abdomen and the caudal part. The tightly attached paired spines show the place on the axial skeleton where the transition between paired and median neural spines takes place. The ventral haemal arch with haemal spine probably had an initial location in the caudal region of the axial skeleton, as evidenced by the shape of the haemal arch and the opening of the haemal canal ( Grande and Bemis 1998).

Fins. The pectoral fins of the juvenile specimens GMC 55 and GMC 61 consist of 17 lepidotricha. The leading pectoral fin lepidotrichium is unsegmented, with small fringed fulcra firmly connected to the anterior edge of the lepidotrichium. The following two or three lepidotrichia are not segmented in the proximal third of their length. The other lepidotrichia are articulated at their base. The dorsal fin consists of 30–35 segmented lepidotrichia (GMC 82), and the base of the dorsal fin ( Text-fig. 10c View Text-fig ) extends over 9–10 scale rows (GMC 11, GMC 82). The leading edge of the fin is protected by fulcral scales. The segments of the lepidotrichia are long and narrow because they belong to juvenile specimens (see below). The anal fin is triangular with the fulcral scales protecting the leading edge of the fin (GMC 55). The caudal fin of the juvenile specimen GMC 41 has a large ventral lobe and a relatively long dorsal lobe (1.4 times longer than the ventral lobe). These dorsal and ventral lobes form an angle of 16° (GMC 55) to 20° (GMC 41) with the horizontal. The dorsal edge of the dorsal lobe on GMC 55 is protected by numerous fulcral scales ( Text-fig. 10a View Text-fig ). These fulcral scales are quite upright, narrow and densely set.

The segments of the lepidotrichia are narrow and long in juvenile specimens, whereas they are very stout, wide and short in adults where they are found only isolated. Their width may be one third greater than their length. These segments also have, in their anterior half, conspicuous ridges arranged slightly obliquely across the segment of the lepidotrichium. The posterior half of the segment, in lateral view, is smooth and concave. The resulting depression allows the segment to articulate with the following lepidotrichium. The basal segment of the lepidotrichium ( Text-fig. 10g View Text-fig ) is not articulated (GMC 101). An unsegmented basal part of a lepidotrichium was also figured by Long (1988: fig. 33D) in Howqualepis rostridens . Here, the complete shape of the body is not visible. The best-preserved specimen, the juvenile GMC 11, displays most of its body with well positioned fins (Text fig. 10c). The base of the anal fin begins at the level of the dorsal fin mid-length. The tilt between the vertical scale row and the horizontal plane, just before the anal fin, is 52°.

On the specimens examined, the scales are scattered on the mid-lateral side and abdominal region. They are rhombic, with conspicuous peg and socket articulation and thick diagonal ridges on their external side. The longest ridge passes diagonally from the anterodorsal to the posteroventral corner of the scale, and terminates in a denticle-shaped process on the posterior margin of the scale ( Text-fig. 10d View Text-fig ). This denticle-shaped process is the third on the posterior border of the scale. The long ridge divides the lateral surface of the scale into anteroventral and posterodorsal halves. The posterodorsal ridges are short, they may join together posteriorly and protrude from the posterior edge as toothlike projections. The entire posterior edge of the scale carries tooth-like projections, 2/3 of them are on the posterodorsal half of the scale. The ridges of the anteroventral half of the scale are longer, they join together and terminate in two or three tooth-like projections posteriorly. The anterior 20–25 % of the surface of the scale is smooth and was covered by the preceding scales. The dorsal margin of the scales also has a smooth narrow strip. On G 123, the ridges of the scales bear a microsculpture which consists of microtubercles arranged in the same direction as the ridges ( Text-fig. 10d, e, f View Text-fig ). The base of the microtubercles is either circular or anteroposteriorly elliptical. These microtubercles are similar to those of Progyrolepis heyleri from Buxièresles-Mines ( Štamberg 2018).

Some specialised scales have also been observed on GMC 55, such as a single large scale with a conspicuous ventral ridge that forms a keel lying in front of the anal fin. On G 123, isolated large basal fulcra ( Text-fig. 10b View Text-fig ) lie on the dorsal edge of the caudal peduncle. They extend in an anteroposterior direction and are 4.5 times longer than wide. Their medial part shows a deep anteroposterior groove in which the preceding basal fulcrum fits. This groove is smooth but the conspicuous ridges are visible laterally to the groove. These ridges run postertolaterally from the medial line and they anastomose.

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