Paratirolites serus 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 : 59-61

Paratirolites serus Korn & Ghaderi in Korn et al., 2016

Fig. 40 ; Table 19

Paratirolites serus Korn & Ghaderi in Korn et al., 2016: 868, text-fig. 27.

Diagnosis

Paratirolites with conch reaching 80 mm dm. Subadult stage with weakly to strongly trapezoidal, depressed whorl profile (ww/wh =1.40–1.80) and broadly rounded venter; 12–14 coarse conical ventrolateral nodes. Adult stage with circular or slightly trapezoidal, weakly to moderately depressed whorl profile (ww/wh =1.20–1.60), flattened venter and subangular to angular ventrolateral shoulder; numerous ribs on the flank. Prongs of external lobe simple; altogether 6–9 notches of E, A and L lobes.

Material examined

Holotype IRAN • East Azerbaijan, Ali Bashi N section ; Paratirolites Limestone , 0.65 m below the top; illustrated by Korn & Ghaderi in Korn et al. (2016: text-fig. 27a); MB.C.25300 .

Additional material

IRAN • 1 specimen; Esfahan Province, Baghuk Mountain C section ; Hambast Formation; MB.C.29934 • 2 specimens; Esfahan Province, Baghuk Mountain E section ; Hambast Formation; MB.C.29935 to MB.C.29936 • 1 specimen; Esfahan Province, Baghuk Mountain F section ; Hambast Formation; MB.C.29937 .

Description

Specimen MB.C.29936 has 62 mm conch diameter and is the largest available specimen ( Fig. 40A ). It is corroded but still rather well preserved and allows the study of three whorls. A little more than half a volution belongs to the body chamber. The weakly depressed whorl profile (ww/wh = 1.05) of the body chamber is trapezoidal with weakly diverging flanks and the flattened venter is separated from the flanks by a subangular ventrolateral shoulder. The sculpture changes, on the last portion of the phragmocone, from a subadult stage with 14 coarse ventrolateral nodes per volution to the adult stage with numerous weak radial ribs with weak ventrolateral nodes on the flank.

Specimen MB.C.29934 is a smaller individual with 48 mm conch diameter and is better preserved than the preceding one with half a volution of the body chamber preserved ( Fig. 40B ). It shows a weakly trapezoidal, weakly depressed body chamber whorl profile (ww/wh=1.05) with rounded ventrolateral shoulder and a broadly rounded venter, while the phragmocone has a more depressed whorl profile (ww/ wh= 1.40). The sculpture in the subadult stage has twelve coarse ventrolateral nodes, which become weaker and radially elongated on the body chamber, where they finally disappear and instead shallow radial dorsolateral ribs take place.

The suture line of specimen MB.C.29934 has an external lobe with nearly parallel flanks and unserrated, narrow lanceolate prongs. The ventrolateral saddle is weakly asymmetric and the adventive lobe is strongly asymmetric with a steep ventral flank, four little notches and an oblique dorsal side. The lateral lobe possesses only three small notches ( Fig. 40D ).

Remarks

Paratirolites serus is the stratigraphically youngest species of the genus in the Baghuk Mountain sections. It differs from the other by its small conch size and the simple suture line with unsubdivided prongs of the external lobe.

Subadult specimens of P. serus resemble some stratigraphically older species such as P. kittli and particularly P. vediensis . Paratirolites serus differs from these in the smaller conch diameter (40 mm maximum phragmocone diameter in contrast to 70–80 mm in P. kittli and P. vediensis ) and a simpler suture line with unsubdivided prongs of the external lobe.

Stratigraphic range

Upper part of the Hambast Formation; 0.75 to 0.60 m below the extinction horizon ( Abichites stoyanowi Zone ).

Figures

Fig. 40. Paratirolites serus Korn & Ghaderi, 2016. A. Lateral and dorsal view, specimen MB.C.29936, section E, float. B. Lateral and dorsal view, specimen MB.C.29934, section C, -0.60 m. C. Lateral and dorsal view, specimen MB.C.29937, section F, -0.75 m. D. Suture line, specimen MB.C.29934, at 16.0 mm ww, 10.3 mm wh. E. Whorl profile proportions. Abbreviations: see Material and methods. Scale bar units= 1 mm.