Monophyllum galalaensis, El-Desouky & Herbig & Kora, 2023

El-Desouky, Heba, Herbig, Hans-Georg & Kora, Mahmoud, 2023, Kasimovian (late Pennsylvanian) cornute rugose corals from Egypt: taxonomy, facies and palaeogeography of a cool-water fauna from northern Gondwana, Swiss Journal of Palaeontology (32) 142 (1), pp. 1-39 : 18-19

Monophyllum galalaensis n. sp.

( Fig. 9A 1–A 82 , B 1–B 6 , 12B ).

Derivation of the name: From the type locality (eastern cliffs of the Northern Galala Plateau ) .

Holotype: Specimen RAh 9; collected from the basal shales of the lower member of the Aheimer Formation and illustrated in Fig. 9A 1–A 82 . Six transverse thin-sections are available.

Material: Paratypes are represented by five partly preserved corallites (RAh 13, RAh 41, RAh 52, RAh 80 and RAh 92); collected from the lower shales of the Aheimer Formation. Te internal structures of these corallites are diagenetically altered. Eighteen transverse thin-sections are available, four of them belonging to RAh (13) are extremely altered by diagenesis and thus excluded from illustrations.

Type locality: Eastern cliffs of the Northern Galala plateau (Lat. 29° 28 ′ 01 ″ N and Long. 32° 27 ′ 38 ″ E) ,

northern Eastern Desert, western side of the Gulf of Suez, Egypt.

Type horizon: Basal shales of the lower member of the Aheimer Formation; Upper Pennsylvanian (Kasimovian).

Diagnosis: Monophyllum having maximum n:d ratio 24:11. Major septa meet in the corallite axis forming a stereocolumn; they retreat near the calice floor, forming a small free axial area occupied only by the incipient columella resulting from the elongated counter septum. Cardinal septum moderately shortened from early maturity.

Description: External characters: Corallites are ceratoid, about 2.2– 3 cm long. Calyx and apex are not preserved in the holotype ( Fig. 9A 1 ) but preserved in most of the paratype specimens ( Fig. 9B 1 ). When preserved, calyx is deep and laterally compressed. A remarkably long counter septum that forms an incipient columella with its end can be detected on its floor ( Fig. 9A 2 ). Delicate growth lines and distinct septal furrows are visible in the good preserved external wall ( Fig. 9A 1–A 2 ).

Internal characters: Te young stages of ontogeny are described from the paratype specimen ( Fig. 9B 2–B 3 ), where the apical part is well-preserved. In the earliest ontogenetically preserved section (nepionic stage) of the paratype RAh (13) only 3 protosepta can be traced in about 1 mm diameter ( Fig. 9B 2 ). Te subsequent section records the early neanic stage ( Fig. 9B 3 ), where there are 14 major septa in 2.5 mm diameter, all meet near the corallite axis with their thick inner ends. Te subsequent neanic growth stages of the paratype have n:d of 19–22: 5–6.7 mm. Tese sections are not suitable for illustration as stated before.

Te two earliest preserved ontogenetic sections of the holotype have 21–22 septa in 6–6.5 mm diameter

( Fig. 9A 3–A 4 ). In this stage major septa are thick, except for the cardinal septum. Te counter septum is slightly thicker than the others and is longer. Septa are pinnately to sub-radial arranged and meet in the centre to form a stereocolumn. Minor septa are mostly missing. In the successively youngest sections ( Fig. 9A 5–7 , B 4 ), major septa count 23–24 in 8–10.5 mm diameter. Tey are joined with their thickened axial ends to form a dense axial column, with a narrower free axial area. Te counter septum is the longest and exceeds all the majors in the axial stereocolumn with a rhopaloid thickened end. Cardinal septum thins towards the axis ( Fig. 9A 5 ), immediately becoming short, situated within a triangular, adaxial open cardinal fossula, which is located on the concave side of the corallite ( Fig. 9A 6–7 ). Alar fossulae are not visible. In the last mature sections, below the calice floor

( Fig. 9A 81 , 2 , B 5 ), and within the calice ( Fig. 9B 6 ), major septa are a little withdrawn from the axis and a narrow free axial area is developed that disappears in the lower, less mature sections. Tey are radially arranged. Minor septa are underdeveloped and form small triangular spikes at the inner wall. However, the long rhopaloid counter septum, incipient columella, and the short cardinal septum in the triangular fossula are still developed. Te arrangement of the major septa changes from radial to pseudo-radial and then pinnate when going down towards the successively older parts of the corallite.

Discussion: Te species discussed differs from the Upper Moscovian type species Monophyllum sokolovi Fomichev, 1953 in the strong elongation of the counter septum up to the calice floor, forming an incipient columella. Monophyllum parvum Fomichev, 1953 differs in its smaller n:d ratio ( Fig. 12B ). Te current species differs from M. cassum Fedorowski, 1987 by its larger n:d ratio (24:11.5 vs. 22:9.3). In addition, M. cassum shows withdrawing of major septa from the corallite axis already in the late neanic/early ephebic stage, while this happens in the late ephebic stage near or at the calice floor in the Egyptian species. Te formation of a stereocolumn is missing in M. cassum .

Figures

Fig. 9 A Monophyllum galalaensis n. sp. (Holotype specimen, Rah 9). A1 Lateral external view of the corallite, positions of thin-sections indicated in A1. A2 A calice view of the paratype specimen (RAh 41), with eroded rim, shows an elongated counter septum that form a columella (arrow). A3–A5 Successive transverse thin-sections of the neanic stage,showing the pseudo-radial to pinnate arrangement of major septa, a long thin ended cardinal septum, and a longer counter septum with a swollen end in a dense stereocolumn. A6–7 Two successive mature sections, showing a short cardinal septum. A81, 2 Transverse thin-section in the late mature stage below the calice,showing radially arranged major septa that retreat a little leaving a narrow free axial area occupied by the elongated part of the counter septum. Note, A82 is a redrawing of section A81. Paratype specimen (RAh 13). External alar view of the corallite,positions of thin-sections are indicated in white lines. B2 Nepionic stage.B3 Early neanic stage. B4–5 Two partly compressed successive mature sections (ephebic stage), show a distinctly long counter septum.B6 Last mature section—more or less in the calice—showing a detached columella that is separated from the long counter septum. Black dots indicate the positions of cardinal septum (below), counter septum (above) and the two alar septa

Fig. 1 Geological map of the eastern cliffs of the Northern Galala Plateau, modified after Abdallah and El Adindani (1965)

Fig. 8 A Lytvolasma paraaucta n. sp. A1 Lateral external view of the holotype specimen (RAh 54). Note that, calice is compressed due to compaction.A2 Transverse thin-section in the immature part, showing major septa with irregular zaphrentoid arrangement.A3 Transverse thin section in the early mature part of the corallite, showing radially arranged major septa with rhopaloid ends. A4 Laterally compressed section in the calice base,showing a deformed fossula. A5 Transverse thin-section in the compressed calice, with calcareous mud filling. B1 Lateral external view of the paratype specimen (RAh 19). B2–B5 Successive transverse thin-sections from the immature part near the apex (B2) to the last mature part in the calice (B5)

Fig. 6 A Actinophrentis crassithecata n. sp.: (Holotype specimen RAh (57). A1 External view showing a thick walled, slightly curved corallite with septal furrows ornamenting the external wall. Position of thin-sections indicated. A2 Transverse thin-section near the non-preserved apical part, shows thick major septa meeting in the centre and adaxially thinning cardinal septum. A3 Transverse thin-section in the middle part of the corallite, shows major septa meeting in the centre and noticeable fossular breaks. A4 Last adult transverse thin section just below the calice shows septa withdrawn a little from the centre.A5 Details of the external wall of A3. B1, B2 External lateral views of the specimen RAh (11) showing a thick walled,slightly curved corallite with septal furrows and concentric growth lines on the external wall. C Lytvolasma cf. canadense Fedorowski and Bamber,2001, specimen RAh (66). C1, C2 Transverse thin-section in the middle mature part of the corallite, shows a short cardinal septum and a long counter septum with a rhopaloid axial end. C3 Transverse thin-section in the calice, shows a long counter septum. Scale bars: 2.5 mm, except A2–A5: 2 mm. Black dots indicate the positions of cardinal septum (below), counter septum (above) and the two alar septa

Fig. 12 Relation between number of major septa and coralla alar diameters for: A Lytvolasma paraaucta n. sp.,L aucta Fedorowski,1987, L. asymetrica Soshkina, 1925 described by Chwieduk (2013), L. canadense Fedorowski and Bamber, 2001 and the current studied L. cf. canadense Fedorowski and Bamber, 2001. B Monophyllum galalaensis n. sp. and M. parvum Fomichev, 1953. C Rotiphyllum exile de Groot, 1963. D Zaphrentites cf. parallela (Carruthers,1910) and Zaphrentites sp

Fig. 2 A Lithostratigraphic succession of the Aheimer Formation studied along the eastern cliffs of the Northern Galala Plateau after Kora and Mansour (1992). B Enlargement of the mudstone dominated basal shale part of the lower member of the Aheimer Formation studied herein (see also Fig. 3A)

Fig. 3 Field aspects of the Aheimer Formation; A General view of the studied succession of the lower member exposed in a faulted block to the north of Porto Sukhna; the shales mudstones close to the base (rectangle) are interbedded with thin, hard dolomitic bands. B Close up view on of the lower fossiliferous shale mudstone beds of A. C, D Close-up view on of two rugose corals entombed in the shale mudstone beds.E Close-up view on of a rugose coral species with diagenetically compressed calyx. Note strong ferrugination of corallite and surrounding matrix within the fossiliferous shale. F Fossiliferous shales mudstone with thin bands of ferruginous dolomitic limestone and secondary evaporite veinlets; Cr = crinoidal stems. G Crinoid columnals (Cr) and rugose corals (RC) are embedded in the shale mudstone. H Close-up view on of a spiriferid valve shell within the shale (arrow). Diameter of coins in C–E, G: 25 mm

Fig. 4 Effects of diagenesis on some coral specimens: A Thin-section in the calice of the specimen RAh (44) shows a completely compressed calice filled with fossiliferous mud. B Thin-section below the calice of the Bothrophyllum okense (RAh 37) shows beginning of compression and breakage of septa. C Thin-section below the calice of the specimen RAh (79), shows completely broken and altered septa, probable outer dissepimentarium and axial structure, filled with ferruginous mud. D Thin-section of a completely compressed specimen RAh (200) shows high alteration,breakage and ferrugination of skeletal elements.E Thin-section in the early mature part of the Actinophrentis crassithecata n. sp.(RAh 11), shows ferrugination affects a large part of the interior skeleton. F Mature thin-section of Rotiphyllum exile (RAh 29), shows ferrugination and dolomitization of skeletal elements.G, H Thin-sections of mature part of the specimen (RAh 81) in G and the immature part of the specimen RAh (99) in H show extensive dolomitization and ferrugination of the internal skeletal elements

Fig. 5 Internal morphological characters of the non-dissepimented rugose corals referred to in the systematic descriptions, after Denayer and Hoşgör (2014). A Transverse section. B Longitudinal section

Fig. 7 Lytvolasma aheimerensis n. sp. A External view of the specimen RA (2), showing a straight corallite with partly eroded calice and non-preserved apical part, positions of thin-sections indicated.B–D Successive transverse thin-sections in the early preserved growth stages, shows very thick major septa joining together near the centre.The cardinal septum is deformed in D. E–G Successive thin-sections in the early mature stages show the formation of a stereozone with a free axial area,shortening of the cardinal septum with maturity and the longest counter septum with a rhopaloid end. H–I Two transverse thin-sections below the calice, deformed due to rejuvenation in H and lateral compaction in I. Scale bars: 2.5 mm, except A: 5 mm. Black dots indicate the positions of cardinal septum (below), counter septum (above) and the two alar septa