Paratirolites lanceolobatus 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 : 34-36

Paratirolites lanceolobatus Korn & Hairapetian sp. nov.

urn:lsid:zoobank.org:act:EA9569C5-F88F-4487-A528-878A60FB4CE1

Fig. 25 ; Table 10

Diagnosis

Species of Paratirolites with conch reaching 90 mm dm. Subadult stage with weakly trapezoidal, weakly depressed whorl profile (ww/wh =1.10–1.30) and broadly rounded venter; about 12 radial ribs ending in coarse conical ventrolateral nodes per volution. Adult stage with rectangular and weakly compressed whorl profile (ww/wh = 0.85–1.00), flattened, weakly tectiform venter and subangular ventrolateral shoulder; numerous rounded ventrolateral nodes. Prongs of external lobe lanceolate and usually unsubdivided; altogether 11–15 notches of E, A and L lobes.

Etymology

From the Latin’ lancea ’, meaning ‘lance’, because of the lanceolate prongs of the external lobe.

Material examined

Holotype IRAN • Esfahan Province, Baghuk Mountain B section ; Hambast Formation; illustrated in Fig. 25A ; MB.C.29769 .

Paratypes IRAN • 18 specimens; Esfahan Province, Baghuk Mountain 1 section ; Hambast Formation; MB.C.29751 to MB.C.29768 • 3 specimens; Esfahan Province, Baghuk Mountain E section ; Hambast Formation; MB.C.29770 to MB.C.29772 • 1 specimen; Esfahan Province, Baghuk Mountain G section ; Hambast Formation; MB.C.29773 • 2 specimens; Esfahan Province, Baghuk Mountain ; Hambast Formation; MB.C.29774 to MB.C.29775 .

Description

Holotype MB.C.29769 is a comparatively well-preserved individual with 73 mm conch diameter; a little more than half of the last whorl belongs to the partly corroded body chamber. The last two and a half whorls of the phragmocone are better preserved ( Fig. 25A ). The beginning of the terminal body chamber is at 50 mm diameter; it is well identifiable by the crowding of two septa. This boundary is not identical with spontaneous changes in conch shape and sculpture. At the beginning of the body chamber, the whorl profile is trapezoidal with a flattened, broadly rounded venter; at the end, the whorl profile is slightly trapezoidal with weakly diverging flanks. The rounded, weakly tectiform venter is delimited from the flanks by rounded ventrolateral shoulders. The sculpture shows three ontogenetic stages: (1) The inner whorls (up to 10 mm dm) appear to be smooth without ribs or nodes. (2) The intermediate stage (between 10 and 50 mm dm) shows radial ribs that end in coarse conical ventrolateral nodes (12 per volution in the smaller growth stage and more densely arranged in the larger stage), which weaken at the beginning of the body chamber. (3) The main portion of the body chamber shows smoothening of the sculpture.

The suture line of holotype MB.C.29769 possesses a parallel-sided external lobe with very narrow, lanceolate non-serrated prongs. The ventrolateral saddle is rather narrow (much narrower than the external lobe) and weakly inflated; it is followed by a rather broad, drop-shaped adventive lobe that is multiply serrated, a wide and broadly rounded lateral saddle and a V-shaped, weakly serrated lateral lobe ( Fig. 25E ).

The smaller paratype MB.C.29770 with 55 mm conch diameter resembles the holotype in conch proportions and sculpture, but appears to enter the adult growth stage at a smaller conch diameter with a maximum phragmocone diameter of 38 mm ( Fig. 25C ). Very coarse ventrolateral nodes are present in an interval of about 270 degrees of the phragmocone. The suture line of this specimen also shows nonserrated prongs of the external lobe.

Suture lines of the further two paratypes MB.C.29751 and MB.C.29757 (both at about 11 mm whorl height) demonstrate, when compared with the holotype, the variability within the Material examined

Common to all three specimens are the simple prongs of the external lobe, which in the paratypes MB.C.29751 and MB.C.29757 is less deep as the adventive lobe. All three specimens show an asymmetric adventive lobe that appears to be dorsally inclined ( Fig. 25E–G ).

Remarks

The new species shows some similarities to species of the genus Dzhulfites , particularly in the reduced depth of the external and lateral lobes. It may thus represent a link between the two genera. The low stratigraphic position at the base of the Paratirolites Limestone supports this hypothesis.

Paratirolites lanceolobatus sp. nov. differs in the non-serrated prongs of the external lobe from most of the other species of the genus. Similar species are the Transcaucasian P. trapezoidalis and P. birunii , but both possess an adult body chamber with numerous small nodes at the angular ventrolateral shoulder. Paratirolites robustus sp. nov. is the most similar of the Central Iranian species but differs in the wider whorl profile (ww/wh= 1.20 at 70 mm dm) from P. lanceolobatus sp. nov. (ww/wh =0.85). Furthermore, P. robustus sp. nov. has bifid prongs of the external lobe.

Stratigraphic range

Upper part of the Hambast Formation; 3.85 to 2.80 m below the extinction horizon ( Paratirolites lanceolobatus Zone to lower part of the Paratirolites kittli Zone ).

Figures

Fig. 25 (next page). Paratirolites lanceolobatus Korn & Hairapetian sp. nov. A–E. Lateral and dorsal views. A. Holotype MB.C.29769, section B, float. B. Paratype MB.C.29751, section 1, float. C. Paratype MB.C.29770, section E, -3.30 m. D. Paratype MB.C.29752, section A, float. E–H. Suture lines. E. Holotype MB.C.29769, at 13.5 mm wh. F. Paratype MB.C.29751, at 11.2 mm wh. G. Paratype MB.C.29757, at 11.2 mm wh. H. Paratype MB.C.29770, at 11.1 mm wh. I. Whorl profile proportions. Abbreviations: see Material and methods. Scale bar units=1 mm.