Paratirolites robustus Korn & Hairapetian, 2021

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 : 36-40

Paratirolites robustus Korn & Hairapetian sp. nov.

urn:lsid:zoobank.org:act:10C9CACF-9ED4-4E61-8140-FDBB70154F87

Figs 26–27 ; Table 11

Diagnosis

Species of Paratirolites with conch reaching 120 mm dm. Subadult stage with trapezoidal, weakly depressed whorl profile (ww/wh =1.30–1.50) and rounded venter; 8–12 coarse, radially elongated midflank nodes per volution. Adult stage with trapezoidal and weakly depressed whorl profile

(ww/wh =1.00–1.10), flattened, tectiform venter and angular ventrolateral shoulder; numerous weak ribs on flank. Prongs of external lobe simple to trifid; altogether 12–17 notches of E, A and L lobes.

Etymology

From the Latin ‘ robustus ’, meaning ‘robust’, because of the coarse ribs.

Material examined

Holotype IRAN • Esfahan Province, Baghuk Mountain E section ; Hambast Formation, 2.95 m below top; illustrated in Fig. 26A ; MB.C.29778 .

Paratypes IRAN • 2 specimens; Esfahan Province, Baghuk Mountain E section ; Hambast Formation; MB.C.29776 to MB.C.29777 • 1 specimen; Esfahan Province, Baghuk Mountain E section ; Hambast Formation; MB.C.29779 • 1 specimen; Esfahan Province, Baghuk Mountain G section ; Hambast Formation; MB.C.29780 • 4 specimens; Esfahan Province, Baghuk Mountain ; Hambast Formation; MB.C.29781 to MB.C.29784 .

Description

Holotype MB.C.29778 has 80 mm conch diameter and consists of a rather well-preserved phragmocone and a more or less strongly weathered body chamber ( Fig. 26A ). Septal crowding indicates that the maximum phragmocone diameter is 48 mm. The conch shape changes during growth; there is a strongly trapezoidal whorl profile of the phragmocone and a weakly trapezoidal profile of the body chamber. The sculpture of the phragmocone shows 12 conical nodes, which are circular and symmetric in section in the penultimate whorl but become asymmetric and radially elongated towards the end of the phragmocone.

The suture line of holotype MB.C.29778 has a Y-shaped external lobe, in which the prongs are weakly serrated including two notches. The adventive lobe is asymmetric and ventrally inclined with nearly parallel flanks and asymmetric notching. It is dorsolaterally followed by an asymmetric lateral saddle and a nearly symmetric lateral lobe with seven small notches ( Fig. 27A ).

The slightly smaller paratype MB.C.29782 (73 mm dm) is very similar in conch shape and suture line. The penultimate whorl has eight coarse conical nodes, which transform, at the end of the phragmocone, into weakly curved elongated nodes ( Fig. 26B ). The suture line has an external lobe with weakly diverging

flanks, an asymmetric ventrolateral saddle and a weakly asymmetric, strongly notched adventive lobe with nearly flat base and parallel flanks ( Fig. 27B ).

Remarks

Paratirolites robustus sp. nov. differs from the most similar of the Central Iranian species P. lanceolobatus sp. nov. in the stouter whorl profile (ww/wh = 1.20 in P. robustus sp. nov. at 70 mm conch diameter and only 0.85 in P. lanceolobatus ). Furthermore, P. lanceolobatus sp. nov. has non-serrated prongs of the parallel-sided external lobe. Paratirolites robustus sp. nov. differs from P. vediensis in the rounded venter and from P. kittli in the radially elongated nodes of the subadult stage and the presence of weak radial ribs of the body chamber.

Stratigraphic range

Upper part of the Hambast Formation; 3.20 to 2.90 m below the extinction horizon (uppermost part of the Paratirolites lanceolobatus Zone to Paratirolites kittli Zone ).

Figures

Fig. 26. Paratirolites robustus Korn & Hairapetian sp. nov., lateral and dorsal views. A. Holotype MB.C.29778, section E, -2.95 m. B. Paratype MB.C.29782, float. Scale bar units =1 mm.

Fig. 27. Paratirolites robustus Korn & Hairapetian sp. nov. A. Suture line, holotype MB.C.29778, at 14.2 mm wh. B. Suture line, paratype MB.C.29782, at 13.2 mm wh. C. Whorl profile proportions. Abbreviations: see Material and methods. Scale bar units=1 mm.