Alibashites ferdowsii Korn & Ghaderi, 2016

Korn, Dieter, Hairapetian, Vachik, Ghaderi, Abbas, Leda, Lucyna, Schobben, Martin & Akbari, Amir, 2021, The Changhsingian (Late Permian) ammonoids from Baghuk Mountain (Central Iran), European Journal of Taxonomy 776, pp. 1-106 : 73-76

Alibashites ferdowsii Korn & Ghaderi in Korn et al., 2016

Figs 48–49 ; Table 24

Alibashites ferdowsii Korn & Ghaderi in Korn et al., 2016: 871, text-fig. 30.

Diagnosis

Species of Alibashites with conch reaching 100 mm dm. Subadult stage with circular to subtrapezoidal, weakly depressed whorl profile (ww/wh =1.25–1.50) and broadly rounded venter; 10–12 very coarse ventrolateral nodes. Adult stage with subtrapezoidal and weakly depressed whorl profile (ww/wh =1.20– 1.50) with converging flanks, almost flat venter and angular ventrolateral shoulder; sharp ribs on flanks, forming short dorsolateral nodes and stronger ventrolateral nodes. Prongs of external lobe variable in shape, bifid to multiply serrated; altogether 15–18 notches of E, A and L lobes.

Material examined

Holotype IRAN • West Azerbaijan, Aras Valley section ; Paratirolites Limestone ; illustrated by Korn & Ghaderi in Korn et al. (2016: text-fig. 30a); MB.C.25327 .

Additional material

IRAN • 6 specimens; Esfahan Province, Baghuk Mountain 1 section ; Hambast Formation; MB.C.29976 to MB.C.29978 • 1 specimen; Esfahan Province, Baghuk Mountain B section ; Hambast Formation; MB.C.29979 • 7 specimens; Esfahan Province, Baghuk Mountain C section ; Hambast Formation; MB.C.29980 to MB.C.29986 • 2 specimens; Esfahan Province, Baghuk Mountain E section ; Hambast Formation; MB.C.29987 to MB.C.29988 • 2 specimens; Esfahan Province, Baghuk Mountain G section ; Hambast Formation; MB.C.29989 to MB.C.29990 .

Description

Specimen MB.C.29974 is the largest available specimen with 59 mm conch diameter ( Fig. 48A ). Slightly less than half of a volution belongs to the body chamber. The profile of the aperture is characterised by a broadly rounded umbilical margin, weakly concave flanks, an angular ventrolateral shoulder and a broadly rounded but somehow flattened venter. The whorl profile in this stage is weakly depressed with a ww/wh ratio of 1.35. One volution earlier, the venter is more rounded and the flanks are widely curved, producing a depressed oval whorl profile. The sculpture changes from the subadult stage with coarse ventrolateral nodes per volution into the body chamber sculpture with sharp dorsolateral ribs, which are connected by low and rounded folds with weak ventrolateral nodes.

The suture line of specimen MB.C.29974 is characterised by a Y-shaped external lobe, of which the prongs are subdivided by four small notches of varying depth. The ventrolateral saddle is strikingly

asymmetric and dorsally inclined. It is followed by the asymmetric adventive lobe with seven small notches, the asymmetric parabolic lateral saddle and a lateral lobe with three notches ( Fig. 49A ).

Specimen MB.C.29987 is a specimen with 51 mm conch diameter. Its profile is subtrapezoidal at the aperture; it shows a convex and oblique umbilical wall and is widest in the dorsolateral portion of the flank and weakly concave in the outer flank area ( Fig. 48C ). The flattened venter is separated from the flank by an angular ventrolateral shoulder. One whorl earlier is the whorl profile trapezoidal with a rounded ventrolateral shoulder and a broadly rounded venter. The sculpture on the phragmocone consists of twelve coarse conical nodes; on the body chamber these nodes become weaker and are connected with elongate rounded dorsolateral ribs by shallow, rounded folds.

The suture line shows a slightly pouched external lobe with lanceolate, unsubdivided prongs. The ventrolateral saddle is turned U-shaped with nearly parallel flanks. Both flanks of the adventive lobe stand parallel, but its base is oblique and serrated into six little notches ( Fig. 49D ).

Remarks

The specimens from Baghuk Mountain are morphologically very similar to the material from the type area, and the sizes of the specimens are nearly identical. Differences occur in the degree of sutural subdivision; while the prongs of the external lobe in the material from Julfa are secondarily subdivided (two, three or four notches), many of the specimens from Baghuk Mountain show non-subdivided lanceolate prongs.

Alibashites ferdowsii shows an intermediate morphological position between the genera Paratirolites and Abichites . Characteristic for Paratirolites is the intermediate growth stage with trapezoidal whorl profile with the prominent conical ventrolateral nodes; similar to Abichites is the flat venter in the adult stage. The intermediate position of A. ferdowsii is also visible in the suture line; on the one side is the more complex external lobe in Paratirolites (with serrated prongs of the external lobe), and on the other side is Abichites (with a trend towards unserrated prongs of the external lobe).

Stratigraphic range

Upper part of the Hambast Formation; 2.25 to 0.70 m below the extinction horizon ( Alibashites ferdowsii Zone to lower part of the Abichites stoyanowi Zone ).

Figures

Fig. 48. Alibashites ferdowsii Korn & Ghaderi, 2016.A. Lateral and dorsal view, specimen MB.C.29974, section 1, -1.60 m. B. Lateral and dorsal view, specimen MB.C.29990, section G, float. C. Lateral and dorsal view, specimen MB.C.29987, section E, float. D. Lateral and dorsal view, specimen MB.C.29980, section C, -1.15 m. E. Lateral and dorsal view, specimen MB.C.29979, section B, float. F. Whorl profile proportions. Scale bar units=1 mm.

Fig. 49. Alibashites ferdowsii Korn & Ghaderi, 2016, suture lines. A. MB.C.29974, at 12.8 mm wh. B. MB.C.29980, at 10.9 mm wh. C. MB.C.29979, at 14.0 mm ww, 10.4 mm wh. D. MB.C.29987, at 10.3 mm wh. Abbreviations: see Material and methods. Scale bar units=1 mm.