Paratirolites trapezoidalis Shevyrev, 1965

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 : 47-49

Paratirolites trapezoidalis Shevyrev, 1965

Fig. 32 ; Table 15

Paratirolites trapezoidalis Shevyrev, 1965: 177 , pl. 24 fig. 1.

Paratirolites trapezoidalis – Shevyrev 1968: 92, pl. 4 fig. 1. — Korn in Ghaderi et al. 2014: text-fig. 7e. — Korn & Ghaderi in Korn et al. 2016: 858, text-fig. 16.

Diagnosis

Species of Paratirolites with conch reaching 120 mm dm. Subadult stage with trapezoidal, depressed whorl profile (ww/wh= 1.40–1.60) and flattened, slightly tectiform venter; 10–15 coarse ribs, which end in coarse conical ventrolateral nodes, per volution. Adult stage with strongly trapezoidal and weakly depressed whorl profile (ww/wh =1.00–1.40), flattened venter and angular ventrolateral shoulder; weak straight riblets and numerous small ventrolateral nodes. Prongs of external lobe usually unsubdivided, rarely trifid; altogether 12–19 notches of E, A and L lobes.

Type material

Holotype AZERBAIJAN • Nakhichevan Province, Dorasham 2 section ; Paratirolites Limestone ; illustrated by Shevyrev (1965: pl. 24 fig. 1); PIN 1252/129 .

Material examined

IRAN • 1 specimen; Esfahan Province, Baghuk Mountain C section ; Hambast Formation; MB.C.29843 • 2 specimens; Esfahan Province, Baghuk Mountain E section ; Hambast Formation; MB.C.29844 to MB.C.29845 • 3 specimens; Esfahan Province, Baghuk Mountain ; Hambast Formation; MB.C.29846 to MB.C.29848 .

Description

Specimen MB.C.29844 is a moderately well-preserved individual of 71 mm conch diameter and allows the study of one and a half whorls ( Fig. 32B ). The last segment of 210 degrees belongs to the body chamber, which has a weakly depressed trapezoidal whorl profile (ww/wh =1.05) with weakly concave flanks and a nearly flat venter and an angular ventrolateral shoulder. The sculpture of the subadult stage consists of conical and coarse, spiny ventrolateral nodes, 13 on the last phragmocone volution. The nodes become significantly weaker and more numerous on the body chamber, where about 16 of them are present on half a volution.

Specimen MB.C.29844 allows only the study of the suture line on the venter. The external lobe is narrow and parallel-sided with non-serrated, narrow lanceolate prongs. The ventrolateral saddle is very asymmetric and dorsally inclined and the asymmetric adventive lobe has an oblique base that is serrated by six small notches ( Fig. 32C ). specimen MB.C.29845 ( Fig. 32A ) is similar in conch shape and sculpture but possesses a suture line with trifid prongs of the external lobe.

Remarks

Paratirolites vediensis has a similar conch shape, but differs from P. trapezoidalis in the stronger ventrolateral nodes in the adult stage. P. coronatus has an even wider whorl profile (ww/wh = 1.60–1.80 in P. coronatus but only 1.40 in P. trapezoidalis ); the species has also less coarse but more numerous ventrolateral nodes in the subadult stage (15 in P. coronatus but only 10 in P. trapezoidalis ).

Stratigraphic range

Upper part of the Hambast Formation; 3.05 to 2.80 m below the extinction horizon ( Paratirolites kittli Zone ).

Figures

Fig. 32. Paratirolites trapezoidalis Shevyrev, 1965. A–B. Lateral and dorsal views. A. Specimen MB.C.29845, section E, -2.80 m. B. Specimen MB.C.29844, section E, float. C. Suture line of specimen MB.C.29844, at 13.3 mm wh. Abbreviation: see Material and methods. Scale bar units =1 mm.