Jafarirhynchus alatus, Popov & Hairapetian & Pour & Modzalevskaya, 2015

Popov, Leonid E., Hairapetian, Vachik, Pour, Mansoureh Ghobadi & Modzalevskaya, Tatiana L., 2015, A new, unusual rhynchonellide brachiopod with a strophic shell from the Silurian of Iran, Acta Palaeontologica Polonica 60 (3), pp. 747-754 : 749-750

Jafarirhynchus alatus sp. nov.

Figs. 2 , 3A–C ; Table 1.

Etymology: After the alate shape of the shell.

Type material: Holotype: AEU1500, a pair of conjoined valves. Paratypes: AEU1501, 1501–1510, NMW 2011.11 G.400–456, CNIGR136 /12600, total 62 articulated shells and four ventral valves from sample K-33/1 .

Type locality: Boghu Mountains about 25 km south-west of the town of Kashmar, Iran .

Type horizon: Sample K-33/1, lower–middle Telychian, Llandovery, Silurian.

Measurements (in mm): Paratype AEU1501, Lv = 14.0, Ld = 12.3, W = 25.6, T = 10.0, SLw = 7.6, SLt = 8.3; AEU1503, Lv = 17.6, Ld = 15.6, W = 28.1, T = 13.6, SLw = 9.9, SLt = 9.4.

Diagnosis.—As for the genus.

Description.—Shell variably asymmetrical, strophic, dorsibiconvex, strongly alate, transverse, subtriangular in outline about three-fifths as long as wide, with maximum width at or slightly anterior to hinge line, and two-thirds as thick as long. Cardinal extremities slightly rounded. Lateral commissures almost straight, converging anteriorly. Anterior commissure strongly bisulcate. Ventral valve gently convex with a sulcus originating at the umbo and strongly deepening anterior to mid-length, bearing a single rib. Ventral interarea, planar, almost orthocline, with a broad, triangular delthyrium completely covered by the medially merged deltidial plates. Lateral profile of dorsal valve strongly convex with maximum height between mid-length and the anterior valve margin or at the anterior margin. Median fold with steep lateral slopes originating at the umbo, bearing two strong, high ribs, occupying about one-third maximum valve width at the anterior margin. Radial ornament of 17–22 strong, tubular ribs separated by interspaces of equal size. Two prominent subangular ribs on the dorsal median fold and a pair of subangular ribs on the flanks of ventral sulcus about twice as high and wide as other ribs. Concentric ornament of fine, regularly spaced concentric lamellae, becoming more prominent and densely crowded close the anterior margin of the mature individuals.

Ventral interior with strong, oblique teeth supported by the short, strongly thickened dental plates. Ventral muscle field strongly impressed with adductor scars completely enclosed by larger diductor scars. Strongly thickened pedicle callist mainly occupying the floor of the small delthyrial cavity. Dorsal interior with massive hinge plates and a small septalium supported by a strongly thickened, short median septum. Cardinal process septiform. Crura faint, radulifer, gently curved dorsolaterally. No calcified brachial supports.

Stratigraphic and geographic range.—Niur Formation, Aeronian, Llandowery, Silurian, Central Iran.

Figures

Fig. 2. Rhynchonellide brachiopod Jafarirhynchus alatus gen. et sp. nov. from Llandovery, Telychian, Niur Formation, sample K33/1, Boghu Mountains, CNIGR136/12600. A. Transverse serial sections (L = 18.4; W = 23.2; T = 10.5). B. Sagittal section of the shell. C. Dorsal valve interior. Numbers indicate distance in mm from the tip of the ventral umbo.

Fig. 3. Rhynchonellide brachiopod Jafarirhynchus alatus gen. et sp. nov. (A–C) and spiriferide Striispirifer? ocissimus Popov, Modzalevskaya, and Ghobadi Pour in Hairapetian et al., 2012 (D, E) from Niur Formation, Telychian, Llandovery, Silurian, sample K33/1, Boghu Mountains. A. AEU1500, holotype, a pair of conjoined valves, in dorsal (A 1), ventral (A 2), lateral (A 3), and anterior (A 4) views, enlarged ventral interarea (A 5). B. AEU1501, a pair of conjoined valves, in anterior (B 1), ventral (B 2), dorsal (B 3), and lateral (B 4) views of a strongly asymmetrical specimen. C. AEU1502, dorsal view of a pair of conjoined valves (C 1), enlarged surface ornament (C 2). D. AEU1511, a pair of conjoined valves, in ventral (D 1), lateral (D 2), and dorsal (D 3) views. E. AEU1512, ventral valve exterior. Scale bars 2 mm.