Paratirolites aduncus 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 : 52-57

Paratirolites aduncus Korn & Hairapetian sp. nov.

urn:lsid:zoobank.org:act:86D671DC-3110-45AE-A379-2543EA8DEDD0

Figs 35–37 ; Table 17

Diagnosis

Species of Paratirolites with conch reaching 125 mm dm. Subadult stage with circular or weakly depressed whorl profile (ww/wh = 1.00–1.30) and rounded venter; about 10 very coarse conical ventrolateral nodes per volution. Adult stage with weakly trapezoidal and weakly compressed whorl profile (ww/wh =0.75–0.90), flattened tectiform venter and subangular ventrolateral shoulder; about 10 hook-shaped ventrolateral nodes per half volution. Prongs of external lobe usually bifid but rarely trifid or multiply serrated; altogether 11–17 notches of E, A and L lobes.

Etymology

From the Latin ‘ aduncus ’, meaning ‘incurved’, because of the curved ventrolateral nodes.

Material examined

Holotype IRAN • Esfahan Province, Baghuk Mountain B section ; Hambast Formation; illustrated in Fig. 35A ; MB.C.29894 .

Paratypes IRAN • 9 specimens; Esfahan Province, Baghuk Mountain 1 section ; Hambast Formation; MB.C.29880 to MB.C.29888 • 5 specimens; Esfahan Province, Baghuk Mountain A section ; Hambast Formation; MB.C.29889 to MB.C.29893 • 1 specimen; Esfahan Province, Baghuk Mountain B section ; Hambast Formation; MB.C.29895 • 5 specimens; Esfahan Province, Baghuk Mountain C section ; Hambast Formation; MB.C.29896 to MB.C.29900 • 17 specimens; Esfahan Province, Baghuk Mountain E section ; Hambast Formation; MB.C.29901 to MB.C.29917 • 1 specimen; Esfahan Province, Baghuk Mountain F section ; Hambast Formation; MB.C.29918 • 8 specimens; Esfahan Province, Baghuk Mountain G section ; Hambast Formation; MB.C.29919 to MB.C.29926 • 1 specimen; Esfahan Province, Baghuk Mountain H section ; Hambast Formation; MB.C.29927 • 3 specimens; Esfahan Province, Baghuk Mountain ; Hambast Formation; MB.C.29928 to MB.C.29930 .

Description

Holotype MB.C.29894 ( Fig. 35A ) is a fairly well-preserved specimen with 80 mm conch diameter. It shows, at a conch diameter of 60 mm, three closely approximated septa, after which the terminal body chamber begins with a sudden weakening of the ventrolateral nodes. While these nodes are coarse and conical on the phragmocone, they almost spontaneously become elongated and hook-shaped on the body chamber.

The suture line of holotype MB.C.29894 shows a deep, parallel-sided external lobe with prongs multiply serrated asymmetrically ( Fig. 35C ). The ventrolateral saddle is nearly symmetric and inverted U-shaped, it is followed by an adventive lobe and a lateral lobe with six little notches each. Both lobes are semicircular at the base and slightly asymmetric.

Paratype MB.C.29880 has 83 mm conch diameter; half of the last volution belongs to the body chamber ( Fig. 35B ). It largely agrees, in conch shape and sculpture, with the holotype. The specimen allows for the study of two whorls, on which transformations in conch shape and sculpture can be observed. The phragmocone has a nearly circular whorl profile (ww/wh about 1.15 at 60 mm conch diameter) with nine coarse conical ventrolateral nodes on its last volution, which sometimes are developed as sharp spines. On the body chamber, the transformation into a weakly trapezoidal whorl profile can be observed; here the slightly concave flanks diverge towards the subangular ventrolateral shoulder that separates the flank from the flattened, weakly tectiform venter. On the body chamber occurs also a change in the sculpture towards more numerous (about 10 per half whorl) short ribs, which are restricted to the outer flank and ventrally end in hook-shaped, sharp nodes.

Paratype MB.C.29900 is a specimen of 104 mm conch diameter. It has a fairly well-preserved phragmocone but a weathered body chamber, of which a little more than half a volution is preserved ( Fig. 36A ). The shape of the body chamber whorl profile had to be reconstructed; it shows a trapezoidal shape with weakly diverging flanks, a rounded ventrolateral shoulder and a flattened tectiform venter. One volution earlier, the whorl profile is strongly trapezoidal with flat, diverging flanks and a flattened, broadly rounded venter. The sculpture is coarse on the phragmocone and weakens in strength significantly on the body chamber. The last volution of the phragmocone has 15 conical, spiny ventrolateral nodes, which are first very coarse and conical but later elongate, weaker and more closely spaced. On the body chamber, weak and rounded ribs with concave course are visible on the outer flank.

The suture line of paratype MB.C.29900 shows a parallel-sided external lobe with parallel-sided prongs that are divided by four small notches. The very narrow ventrolateral saddle is weakly inclined towards the umbilicus. Following is a very asymmetric, weakly pouched adventive lobe with eight notches,

which are already climbing up the ventral side. The weakly inflated, asymmetric lateral saddle is low and the asymmetric lateral lobe with steep dorsal flank possesses five notches ( Fig. 36B ).

Remarks

Paratirolites aduncus sp. nov. differs from the other species of the genus in the presence of the hookshaped ventrolateral nodes of the adult stage.

Stratigraphic range

Upper part of the Hambast Formation; 2.65 to 1.15 m below the extinction horizon ( Paratirolites kittli Zone to Lutites profundus Zone ).

Figures

Fig. 35 (preceding page). Paratirolites aduncus Korn & Hairapetian sp. nov. A–B. Lateral and dorsal views.A. Holotype MB.C.29894, section B, float. B. Paratype MB.C.29880, section 1, -1.60 m.C. Suture line of holotype MB.C.29894, at 17.3 mm wh. D. Whorl profile proportions. Abbreviation: see Material and methods. Scale bar units =1 mm.

Fig. 36. Paratirolites aduncus Korn & Hairapetian sp. nov. A. Lateral and dorsal view, paratype MB.C.29900, section C, -2.45 m. B. Suture line, paratype MB.C.29900, at 30 mm ww, 16.0 mm wh. Abbreviations: see Material and methods. Scale bar units=1 mm.

Fig. 37. Paratirolites aduncus Korn & Hairapetian sp. nov. A. Paratype MB.C.29922, section G, float. B. Paratype MB.C.29884, section 1, float. Scale bar units =1 mm.