Abichites stoyanowi

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 : 94

Abichites stoyanowi (Kiparisova in Voinova et al., 1947)

Fig. 59 ; Table 33

Kashmirites ? stoyanowi Kiparisova in Voinova et al., 1947: 149, pl. 35 fig. 1.

Xenodiscus radians – Stoyanow 1910: 86, pl. 9 fig. 5.

Xenodiscus sp. indet. Stoyanow 1910: 87, pl. 9 fig. 6.

Abichites stoyanowi – Shevyrev 1965: 179, pl. 24 figs 2–3; 1968: 94, pl. 3 fig. 5, pl. 4 fig. 2. — Korn in Ghaderi et al. 2014: text-fig. 7h. — Korn & Ghaderi in Korn et al. 2016: 881, text-fig. 38.

Diagnosis

Species of Abichites with conch reaching 70 mm dm. Subadult stage with circular, weakly compressed whorl profile (ww/wh =0.75–1.00) and rounded venter; 16–20 moderately weak ribs per volution. Adult stage with quadrate and weakly compressed whorl profile (ww/wh =0.90–1.00), flat venter and subangular to angular ventrolateral shoulder; altogether 12–14 sharp concavo-convex ribs per half volution on flanks. Prongs of external lobe simple or bifid; 6–11 notches of E, A and L lobes.

Material examined

IRAN • 1 specimen; Esfahan Province, Baghuk Mountain 1 section ; Hambast Formation; MB.C.30073 • 2 specimens; Esfahan Province, Baghuk Mountain C section ; Hambast Formation; MB.C.30074 to MB.C.30075 • 3 specimens; Esfahan Province, Baghuk Mountain E section ; Hambast Formation; MB.C.30076 to MB.C.30078 • 1 specimen; Esfahan Province, Baghuk Mountain F section ; Hambast Formation; MB.C.30079 • 2 specimens; Esfahan Province, Baghuk Mountain G section ; Hambast Formation; MB.C.30080 to MB.C.30081 • 1 specimen; Esfahan Province, Baghuk Mountain H section ; Hambast Formation; MB.C.30082 .

Description

Specimen MB.C.30078 has 62 mm conch diameter and is rather well-preserved with the last half volution belonging to the body chamber ( Fig. 59A ). This has a subtrapezoidal, weakly compressed whorl profile (ww/wh =0.90) with a broadly rounded umbilical margin, weakly concave converging flanks, an angular ventrolateral shoulder and a weakly concave venter. Two stages of the ornament are visible; the subadult stage has coarse node-like ribs on the flank, which in the adult stage become increasingly weaker and more numerous (15 per half volution at the beginning of the body chamber).

The suture line of specimen MB.C.30078 has a large external lobe with weakly diverging flanks and unsubdivided lanceolate prongs. The inverted U-shaped ventrolateral saddle is dorsally inclined and is followed by the pouched adventive lobe that has a very oblique base subdivided into three very shallow blunt notches. In contrast, the three notches of the parallel-sided lateral lobe are pointed denticles ( Fig. 59E ).

The two smaller specimens MB.C.30074 (31 mm dm; Fig. 59D ) and MB.C.30081 (34 mm dm; Fig. 59B ) have similar conch shapes and proportions; they differ in the somewhat weaker sculpture.

Remarks

Abichites stoyanowi differs from A. abichi , which is another similar species with moderately coarse sculpture, in the much weaker ribs. Abichites subtrapezoidalis has a similar whorl profile, but only very weak riblets around the umbilicus on the adult body chamber.

Stratigraphic range

Upper part of the Hambast Formation; 0.80 to 0.05 m below the extinction horizon ( Abichites stoyanowi Zone to lowest part of the Arasella minuta Zone ).

Figures

Fig. 59. Abichites stoyanowi (Kiparisova, 1947). A. Lateral and dorsal view, specimen MB.C.30078, section G, -0.40 m. B. Lateral and dorsal view, specimen MB.C.30081, section G, -0.05 m. C. Lateral and dorsal view, specimen MB.C.30079, section F, -0.75 m. D. Lateral and dorsal view, specimen MB.C.30074, section C, -0.50 m. E. Suture line, specimen MB.C.30078, at 7.2 mm ww, 7.4 mm wh. F. Whorl profile proportions. Abbreviations: see Material and methods. Scale bar units =1 mm.