Eoconulus subquadratus, Hansen & Holmer, 2011

Hansen, Jesper & Holmer, Lars E., 2011, Taxonomy and biostratigraphy of Ordovician brachiopods from northeastern Ny Friesland, Spitsbergen 3076, Zootaxa 3076 (1), pp. 1-122 : 77-80

Eoconulus subquadratus sp. nov.

Pl. 21, Figs. 2 –15, Table 27

Derivation of name. Latin ‘ sub ’ and ‘ quadratus ’, subquadrate; refers to the rounded quadratic outline.

Plate 21

Biernatia sp.

Valhallfonna Formation, Profilbekken Member, 26 m above base. Coll. J. Hansen, 04.08.2008, sample JH-184. 1. TSGF16943, interior of damaged ventral valve.

Eoconulus subquadratus sp. nov.

Valhallfonna Formation, Olenidsletta Member.

2–3. TSGF16860 , paratype, dorsal valve exterior, oblique anterolateral view. 94 m above base. Coll. J. Hansen, 21.07.2008, sample JH-52 .

4–5. TSGF16853 , paratype, dorsal valve exterior, oblique lateral view. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH-45 .

6–7. TSGF16861 , holotype, dorsal valve exterior, oblique lateral view. 94 m above base. Coll. J. Hansen, 21.07.2008, sample JH-52 .

8–9. TSGF16859 , paratype, dorsal valve exterior and larval shell. 94 m above base. Coll. J. Hansen, 21.07.2008, sample JH-52. 10 . TSGF16856 , paratype, dorsal valve exterior. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH-45 .

11–13. TSGF16857 , paratype, ventral valve attached to stem and closer views of interior and exterior. 90 m above base. Coll. J. Hansen, 20.07.2008, sample JH-45 .

14. TSGF16863 , paratype, dorsal valve interior. 94 m above base. Coll. J. Hansen, 21.07.2008, sample JH-52. 15 . TSGF16862 , paratype, dorsal valve interior. 94 m above base. Coll. J. Hansen, 21.07.2008, sample JH-52 .

Acanthambonia sp.

Valhallfonna Formation, Profilbekken Member.

16. TSGF16865, exterior margin of valve. 67 m above base. Coll. J. Hansen, 24.07.2008, sample JH-95.

Holotype. Pl. 21, Figs. 6–7; TSGF16861 , dorsal valve; 94 m above base of Olenidsletta Member, Valhallfonna Formation, sample JH-52; Profilstranda, Basissletta, Ny Friesland, Spitsbergen.

Material. 63 dorsal and 8 ventral valves from samples JH-45 and JH-52. The paratypes are TSGF16853 , TSGF16856 , TSGF16857 , TSGF16859 , TSGF16860 , TSGF16862 and TSGF16863 .

Diagnosis. Eoconulus with nearly equidimensional, asymmetrical, subangular outline; generally widest near the front; valve margin not thickened and muscle-scar impressions absent; gently concave posterior and gently convex anterior slopes of dorsal valve; dorsal apex generally posterior to mid-valve length.

Description. Shell asymmetrical and subangular in outline, generally widest near front and with straight posterior margin. Posterior margin 39–60% as wide as valve. Larval shell 0.13–0.18 mm long, with moderately dense, equidimensional micro-pitting. Pits shallow, circular, about 6 µm in diameter. Postlarval shell with coarse growth lines and often scattered, elongate, low tubercles. Rugae low or rugellae variably developed. L/W ratio 0.87–1.10. Largest specimen 0.9 mm long and 0.9 mm wide.

Dorsal valve low to moderately subconical with holoperipheral growth. Apex rounded, located at 16–50% of valve length. Larval shell subcircular, moderately to strongly convex, with posterior margin located at 13–18% of valve length. Posterior slope slightly concave. Lateral slopes straight or slightly convex. Anterior slope gently convex. Pseudointerarea absent. Interior without muscle impressions.

Ventral valve low to moderately subconical but without apex. Pseudointerarea absent. Two specimens attached to thin phosphatic stems of an unidentified fossil.

Remarks. Among the species placed within Eoconulus , E. antelopensis Krause & Rowell, 1975 from the Dapingian of Nevada differs by generally having a wider posterior than anterior margin, clearly visible muscle scars, and concave anterior and lateral slopes of the dorsal valve. E. clivosus Popov, 1975 from the Darriwilian of Kazakhstan is distinguished by having well-developed muscle scars and finer ornamentation consisting entirely of growth lines. E. commutabilis Mergl, 2002 from the Dapingian of Bohemia differs by having the dorsal apex anterior to the midvalve, a more transverse outline, and the maximum width located posteriorly. E. cryptomyus Goryansky, 1969 from the Darriwilian of Estonia and Russia is distinguished by being distinctly transverse in outline and by having a subcentral dorsal apex. E. cuboides Zhang, 1995 from the Darriwilian of South China differs by having an L/W ratio of about 0.84, clearly visible muscle scars, and the maximum width located near the posterior margin. E. dyminensis Bednarczyk & Biernat, 1978 from the Dapingian of Poland is distinguished by having a limbus-like structure along the valve margin, a transverse outline, and the maximum shell width located more posteriorly. E. gemmatus Mergl, 1995 from the Floian of Bohemia differs by being subcircular and slightly convex. E. primus Popov & Holmer, 1994 from the Floian of the South Urals is distinguished by being distinctly transverse and by having a rather low conical dorsal valve and deeply impressed muscle scars. E. rectangulatus Cooper differs by being distinctly transverse, by having the maximum width located in the posterior half, and by having a subcentral dorsal apex. E. robustus Holmer, 1989 from the Darriwilian of Sweden is distinguished by having a markedly more transverse outline, a subcentral dorsal apex and better developed muscle scars. E. semiregularis Biernat, 1973 from Poland differs in having a subcircular outline, finer ornamentation and a more subcentral dorsal apex. E. transversus Wright, 1963 from the Ashgillian of Ireland is distinguished by being twice as large and about two-thirds as long as wide and by having the maximum width located posteriorly. Eoconulus sp. described by Holmer & Biernat (2002) from the Tremadocian of Poland differs by having deeply impressed dorsal muscle scars and a suboval outline.

Occurrence. 90 and 94 m above base of Olenidsletta Member, Valhallfonna Formation, Basissletta in northeastern Ny Friesland, Spitsbergen.

Figures

FIGURE 2 Stratigraphical ranges and diversity of brachiopod species at Basissletta, Spitsbergen, and relative sea levels and percentages of linguliform brachiopods in the total brachiopod fauna. White shading in the last graph indicates stratigraphical intervals without brachiopods. Thicknesses of units are according to Fortey & Bruton (1973). Lithological log and sea level curve are from Hansen & Holmer (2010).