Ozarkodina derenjalensis, Männik & Miller & Hairapetian, 2015

Männik, Peep, Miller, C. Giles & Hairapetian, Vachik, 2015, A new early Silurian prioniodontid conodont with three P elements from Iran and associated species, Acta Palaeontologica Polonica 60 (3), pp. 733-746 : 741

Ozarkodina derenjalensis sp. nov.

Fig. 5A–I, K.

2013 Ozarkodina sp. nov. (aff. Ozarkodina sp. C Mabillard and Aldridge, 1983); Männik et al. 2013: 10, fig. 4o, P 1 element.

Etymology: After the Derenjal Mountains in the East Central Iran.

Holotype: NHMUK PM X 3640 , P 1 element (Fig. 5A).

Type locality: A section located about 65 km north-west of Tabas, on the eastern side of the Dahaneh-e-Kolut Gorge in the Derenjal Mountains, East Central Iran; Hill B, uppermost Unit 6 (sample S12).

Type horizon: Distomodus staurognathoides Conodont Zone , Aeroni- an?, Llandovery, Silurian.

Material.— 48 specimens: P 1 element, 29; P 2, 11; M, 2; S 3–4, 4; S 1–2, 1; S 0, 1.

Diagnosis.—P 1 element carminate with distinct inclined cusp and gap or lower denticle located just to anterior. On all elements basal cavity relatively small and round, narrow inverted zone on blades of mature specimens.

Description.—P 1 element (Fig. 5A, E, F): Carminate, blade straight, elongate with lower edge straight or nearly straight. Cusp broad and low, posteriorly inclined, slightly to posterior of mid-length of blade; gap or lower denticle just to anterior. Anterior blade higher than posterior, bearing six to seven broad, erect denticles. Posterior blade with up to six posteriorly inclined denticles, generally less prominent than those of anterior, but on smaller specimens are almost same size. Denticles less fused on juvenile (Fig. 5E 1, E 2) and more completely fused on mature specimens (Fig. 5A 1, A 2, F 1). Basal cavity shallow, almost symmetrical and rounded on mature specimens (Fig. 5A 3, F 2); more tapered to anterior and posterior on smaller specimens (Fig. 5E 3). Cavity widest below lowest denticle just anterior of cusp and extends as a narrow groove below blades with narrow inverted zone better developed to posterior but can be on both blades of larger specimens.

P 2 element (Fig. 5B, C, G): Angulate, blade high, straight and strongly arched. Cusp prominent, posteriorly inclined, with sharp edges and lenticular section. Denticles laterally compressed, relatively short, fused at least until upper third of height, and generally decrease steadily in size distally on both processes. Upper parts of all denticles (including cusp) slightly inwardly curved. Lateral faces smooth, with weak thickening mid-blade on larger specimens creating a lenticular cross-section. Basal cavity small, slightly flared and deepest below cusp; almost symmetrical and rounded on mature specimens (Fig. 5C) but tapers to anterior and posterior on smaller specimens. Below processes cavity continues as narrow groove and becomes inverted on posterior blade of larger specimens (Fig. 5C).

M element (Fig. 5D): Bipennate. Cusp broken in both elements available. Preserved part of cusp asymmetrically lenticular in section; outer lateral face gently convex, inner lateral face strongly convex.Anterior process with one or two denticles. Posterior process very gently curved, bears at least six fused denticles. Cavity flared slightly inwards at base of cusp to produce small lip, continues as narrow groove below posterior process with well-developed inverted basal cavity.

S 3–4 element (Fig. 5I): Bipennate with laterally compressed, posteriorly inclined cusp. Preserved part of posterior process in specimens available straight, bearing fused?, compressed, posteriorly inclined denticles. Anterior process curving strongly downwards and slightly inwards, bearing up to eight compressed denticles. Basal cavity shallow and narrow, slightly flared beneath cusp, and continues as narrow groove below processes. Away from cusp, below posterior process, basal cavity becomes inverted.

S 1–2 element (Fig. 5H): Digyrate, cusp posteriorly inclined with ridge on inner surface producing elongated triangular section. Processes form an angle of about 90°. Anterior process with about four relatively wide, discrete, compressed and inwardly curved denticles. Posterior process bears up to eight slender denticles that are fused at least in their lower parts. Basal cavity flared more strongly on inner side below ridge on cusp; below processes cavity continues as narrow groove.

S 0 element (Fig. 5K): Alate, with a cusp lenticular in section with sharp lateral edges. Posterior face of cusp with wide prominent axial ridge at preserved part of base. Lateral processes slightly curved to posterior and directed quite steeply downwards making an angle of about 90º. Both processes bear at least six compressed, relatively discrete short denticles. Basal cavity flared below posterior ridge on cusp and continues below processes as narrow groove; cavity inverted below processes near base of cusp. Basal body fills cavity in single specimen available.

Remarks.—P 1 elements of the apparatus identified here as Ozarkodina derenjalensis sp. nov. bear some similarity to those described by Mabillard and Aldridge (1983: pl. 3: 9, 10) as Ozarkodina sp. C . However, our specimens differ by having shorter and higher blades and less prominent cusps. Based on the illustrated specimens of Ozarkodina sp. C the inverted basal cavity also appears to be absent on the Mabillard and Aldridge (1983) specimens.

Stratigraphic and geographic range.—Aeronia–Telychian (Llandovery, Silurian); Iran.