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Permonautilus abichi

Year: 2025
Type: article
Abstract: Permonautilus abichi (Kruglov, 1928) Figs 46–48; Table 28 Coloceras Abichi Kruglov, 1928: 89. Permonautilus Abichi – Kruglov 1933: 187. Permonautilus (Alexandronautilus) abichi – Shimansky 1962: 162, pl. 4 figs 4–5. Permonautilus abichi – Shimansky 1965a: 41. — Gliwa et al. 2020: text-fig. 17f. Nautilus excentricus – Abich 1878: 16, pl. 1 fig. 4. Nautilus concavus – Abich 1878: 18, pl. 3 figs 3–4. Nautilus cornutus – von Arthaber 1900: 211, pl. 18 fig. 1. Liroceras sp. indet. – Teichert & Kummel 1973: 424, pl. 3 figs 11–12. ? Nautilus propinquus Abich, 1878: 16, pl. 3 fig. 6. Diagnosis Species of Permonautilus with thickly pachyconic to thinly globular, subinvolute conch (ww/dm = 0.75– 0.90; uw/dm ~0.20), moderately depressed whorl profile (ww/wh= 1.70–2.00) and very high coiling rate (WER = 2.25–2.35) at a conch diameter of 40–80 mm. Whorl profile with broadly arched venter and flanks, broadly rounded umbilical margin, convex umbilical wall and moderately wide imprint zone (IZR ~ 0.20). Without sculpture. Suture line nearly straight. Material examined IRAN – East Azerbaijan • 1 specimen; Ali Bashi N; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2018; Korn et al. leg.; illustrated in Fig. 46; MB.C.32074 • 1 specimen; Ali Bashi 4; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2018; Ghaderi leg.; illustrated in Fig. 47A–C; MB.C.32075 • 1 specimen; same data as for preceding; 2011; Korn et al. leg.; illustrated in Fig. 47D; MB.C.32076 • 1 specimen; Ali Bashi 4; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2018; Ghaderi leg.; MB.C.32085 • 5 specimens; same data as for preceding; 2010; Korn et al. leg.; MB.C.32086 to MB.C.32090 • 1 specimen; same data as for preceding; 2002; Weyer leg.; MB.C.32091 • 1 specimen; Ali Bashi N; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2018; Korn et al. leg.; MB.C.32092 • 2 specimens; Zal; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2013; Korn et al. leg.; MB.C.32093, MB.C.32094 • 2 specimens; Ali Bashi; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); illustrated in Fig. 48A–B; GLM #GH1003, GLM #GH1001. – West Azerbaijan • 1 specimen; Aras Valley; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2018; Ghaderi leg.; illustrated in Fig. 47E–F; MB.C.32077 • 1 specimen; same data as for preceding; illustrated in Fig. 47G–H; MB.C.29351 • 5 specimens; same data as for preceding; MB.C.32078 to MB.C.32082 • 1 specimen; Aras Valley; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2011; Korn et al. leg.; MB.C.32083 • 1 specimen; same data as for preceding; 2018; Korn et al. leg.; MB.C.32084. Description Specimen MB.C.32074 is probably a fully mature individual. It has a conch diameter of 134 mm and possesses the main criterion for adulthood, which are the umbilical shell processes (Fig. 46B). Although the specimen is slightly crushed ventrally, it is possible to obtain the main measurements of the conch. The conch is pachyconic in the terminal stage and the umbilicus is rather narrow (ww/dm = 0.74; uw/dm = 0.14). The whorl profile suffered from deformation, but the symmetry of the specimen suggests that the venter was probably concave near the terminal aperture. On both sides of the specimen there are remnants of lateral umbilical processes, hemispherical in section and about 22 mm in diameter. As they are broken it is impossible to determine their original length. The shell remains appear smooth but show traces of fine growth lines, which are almost straight in their course across the flank. The septa are crowded at the end of the phragmocone at a conch diameter of about 94 mm; the suture line has an almost straight course (Fig. 46C). The smaller specimens show that intraspecific variation in conch geometry is rather limited. Specimen MB.C.32075 may serve as a characteristic example (Fig. 47A–B). It is a fragment with a conch diameter of 56 mm and has a globular and subinvolute shape (ww/dm= 0.88; uw/dm =0.19) with a moderately depressed whorl profile (ww/wh= 1.95) and a very high coiling rate (WER = 2.26). However, the specimen differs from the others in that it is the only individual to show remnants of a coarse ornament, visible only in a small area as impressions on the internal mould. It appears that the specimen has rather coarse growth lines, spaced about one millimetre apart, with a rather shallow and wide sinus extending across the venter. The suture line is almost straight (Fig. 47C). Specimens MB.C.29351 (34 mm dm; Fig. 47G) and MB.C.32077 (51 mm dm; Fig. 47F) give an impression of the ontogenetic development of the conch, in which no major changes can be seen. The conch is thinly globular (ww/dm=0.95 and 0.88 respectively) and the whorl width is approximately twice the whorl height. Specimen MB.C.32076 (78 mm dm; Fig. 47D) has a similar morphology but is slenderer (ww/dm =0.75). In this specimen the septa of two consecutive whorls can be seen. They show a displaced siphuncle with a diameter of 0.15 of the aperture height. A characteristic visible in nearly all the specimens is the presence of a midventral longitudinal line on the internal mould, being produced by a thin internal groove in the shell. The character was already figured by Abich (1878: pl. 3 fig. 3) and described under the species “ Nautilus concavus ”. Remarks Abich (1878) described the following species, which may belong to Permonautilus abichi: • “ Nautilus excentricus Eichwald ”. – The fully chambered specimen with a conch diameter of 30 mm described and illustrated by Abich (1878: pl. 1 fig. 4) has an almost spherical shape with a rather wide umbilicus (uw/dm =0.40). Flanks and venter are broadly rounded. The suture line is almost straight but forms a shallow lobe on the venter. • “ Nautilus propinquus, nov. form.”. – Abich (1878: pl. 3 fig. 6) described and illustrated only a small, chambered specimen with a conch diameter of about 20 mm. It shows a narrowly umbilicate conch with a clear umbilical margin and apparently broadly rounded flank and venter. The suture line is almost straight. This specimen is probably not suitable to characterise a species. • “ Nautilus concavus Sowerby ”. – Abich (1878: pl. 3 figs 3–4) illustrated two fragments with about 50 mm and a conch diameter of 40 mm, respectively. The smaller specimen is better preserved and shows the whorl profile of an inner whorl. At a diameter of 16 mm, the conch is globular (ww/ dm= 1.03) with a very narrow umbilicus (uw/dm= 0.10) and a depressed whorl profile (ww/wh = 1.90). The whorl profile shows a shallow dorsal inflexion. Already von Arthaber (1900) suggested that it is not clear whether the three species described by Abich (1878), “ Nautilus excentricus ”, “ Nautilus propinquus ” and “ Nautilus concavus ”, belong to one single species. He synonymised these three species with the Middle Permian Nautilus cornutus Golovkinsky, 1869 from the Volga Basin of Russia. In a revision of this occurrence, Kruglov (1928) discussed “ Nautilus excentricus ” of Abich and gave it the new name “ Coloceras Abichi ”. Kruglov (1933) later placed this species in his new genus Permonautilus. Shimansky (1962c) then used this species to found the new subgenus Permonautilus (Alexandronautilus), which should be distinguished from the nominal genus by the presence of thin transverse ribs. In a later account (Shimansky 1965a), however, he did not use this anymore. Barskov et al. (2014), when revising the Middle Permian cephalopods of the Volga-Ural region, also did not use the subgenus. Instead, they separated the genus Permonautilus and their new genus Nemdoceras from the Liroceratidae, for which they introduced the new family Permonautilidae that is characterised by their spiny umbilical projections. The presence of umbilical shell processes in the material from Julfa was already suggested by von Arthaber (1900: 212), but the specimen he cited (von Arthaber 1900: pl. 18 fig. 1) is probably too small to have developed such projections. The large specimen MB.C.32074 now allows us to clearly assign the material to Permonautilus. Our material differs from the species from the Volga-Ural region mainly by the narrower umbilicus (uw/dm is about 0.15, in contrast to 0.20–0.30 in the species from the Volga). Teichert & Kummel (1973) did not list Permonautilus among their collection from Ali Bashi, although Shimansky (1965a) mentioned 28 specimens in his collection from the neighbouring sites north of the Aras River, meaning that it is a commonly occurring genus. It is most likely that the material attributed to Liroceras sp. indet. by Teichert & Kummel (1973) in fact belongs to Permonautilus.
DOI: 10.5281/zenodo.17258205
Language: English
Subfield: Paleontology
Open Access status: gold
OpenAlex ID: W7084622886
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