Obscurania auriculata

Kouchinsky, Artem, Bengtson, Stefan, Landing, Ed, Steiner, Michael, Vendrasco, Michael & Ziegler, Karen, 2017, Terreneuvian stratigraphy and faunas from the Anabar Uplift, Siberia, Acta Palaeontologica Polonica 62 (2), pp. 311-440 : 369-371

Obscurania auriculata (Vasil’eva, 1990)

Fig. 38A–E .

Material.—13 internal moulds, including figured SMNH Mo182359–182363, from samples 1/29.5 and 1/29.2 (section 1, Fig. 4 ), 3/12.2, K2/25, K2/26 (section 3, Fig. 3), Medvezhya Formation, western Anabar Uplift, Siberian Platform, Russia. Correlated with the uppermost Fortunian and lower part of Cambrian Stage 2.

→ Fig. 35. Mollusc Purella cristata Missarzhevsky, 1974 , internal moulds with partly phosphatized shells (B, C), from early Cambrian Medvezhya Formation, western Anabar Uplift, Siberia, Russia; sample 1/50, section 1. A–F. SMNH Mo182343‒182348, respectively. A 1, B 3, C 1, D 2, E 3, F 1, upper; A 2, B 2, C 3, D 1, E 2, F 2, lateral; B 1, C 2, E 1, F 3, subapical views; F 4, enlargement of F 2 showing tuberculate texture. Scale bar 125 μm (F 4), 250 μm (C 3), 500 μm (A, B, C 1, C 2, D, E, F 1 ‒F 3).

Description.—Low cap-shaped shell with broadly oval, slightly flared aperture. Apex rounded, bent, somewhat overhangs arched subapical margin of the aperture and projects slightly beyond it. Internal mould covered by small scattered tubercules (ca. 10 μm wide and 20 μm long) inclined towards the apex.

Remarks.—Parkhaev (2006) and Parkhaev and Demidenko (2010) noted a polygonal texture at the apex. Kouchinsky (2000a) and Parkhaev (2006) interpreted the tubercules as casts of pores in the shell. Obscurania tormoi Devaere, Clausen, and Steiner in Devaere et al., 2013, was distinguished from O. auriculata by a wider and more pronounced subapical sinus, a nearly circular aperture, a more inclined apex, and a flattened subapical field ( Devaere et al. 2013). Other forms with a lower shell with tuberculate ornament on the surface of internal moulds, more elongated aperture, a beak-shaped apex that overhangs the apertural margin, and flattened subapical field were referred to Olenellina alutacea Vasil’eva, 1990 ( Figs. 38H and probably Fig. 40D). The type and single species of Olenellina Vasil’eva, 1990, was described from the upper Kessyusa Formation of the Olenyok Uplift, Siberia, which is correlated herein with Cambrian Stage 2. Obscurania auriculata is reported to be different in having a higher shell, flared aperture, and tubular tubercules distributed en echelon over the surface of internal moulds. In contrast, irregular small tubercles distributed circumferentially on the apex occur in Olenellina (see Vasil’eva 1998: 78, 79). The species is likely also synonymous with material described from Cambrian Stage 2 strata of South China (Xing et al. 1984; Steiner et al. 2004a) as “ Tuberoconus ” paucipapillae Yue in Xing et al., 1984.

Stratigraphic and geographic range. — Uppermost Fortunian and Cambrian Stage 2 of Siberia, east Gondwana (South China), and, probably, West Gondwana (Armorican France).

Figures

Fig. 38. Problematic molluscs from early Cambrian Medvezhya Formation, western Anabar Uplift, Siberia, Russia; samples 1/29.5 (C, D, F), section 1; K2/25 (A), K2/26 (B), and 3/12.2 (E, G, H), section 3. A–E. Obscurania auriculata (Vasil’eva, 1990), internal moulds, SMNH Mo182359 (A), SMNH Mo182360 (B), SMNH Mo182361a (C), SMNH Mo182363 (D), SMNH Mo182362 (E). F, G. Algomella sp., internal moulds, SMNH Mo182361b (F, lateral view arrowed in C2), SMNH Mo182365 (G). H. Olenellina alutacea Vasil’eva, 1990, internal mould, SMNH Mo182366. A1, B1, C1, D2, E1, G1, H1, lateral; A2, B3, D3, E2, G2, H2, upper; A3, B2, C2, D1, E3, F, H3, subapical views. Scale bar 500 μm (A, B, E, F, G), 1 mm (C, D, H).

Fig. 4. The δ13Ccurve for Kotuj River section 1and sampled horizons with fossiliferous samples (arrows with numbers). Shift in stratigraphic column carb at Nemakit-Daldyn–Medvezhya formations contact indicates position of sequence boundary. Stratigraphic ranges and first appearances of fossils (see SOM 1): 2, Oelandiella korobkovi; 3, Securiconus cf. simus; 4, Bemella jacutica?; 8, Anabarella plana; 9, Watsonella crosbyi; 10, Pseudoyangtzespira selindeica; 11, Aldanella crassa; 13, Aldanella attleborensis; 15, Philoxenella spiralis; 16, Barskovia hemisymmetrica; 18, Khairkhania cf. evoluta; 19, Ceratoconus striatus; 21, Salanyella cf. costulata; 23, Purella cristata; 25, Yunnanopleura sp.; 26, Obscurania auriculata; 29, Protoconus cf. crestatus; 32, Siphogonuchites triangularis; 34, Lopochites sp.; 37, first appearance of Halkieria sp.; 39, first appearance of Chancelloria sp.; 40, Tianzhushanella sp.; 42, Khetatheca cotuiensis; 46, Turcutheca sp.; 48, Orthothecid operculum type A; 52, Fomitchella infundibuliformis; 57, Hyolithellus sp.; 62, Selindeochrea missarzhevskyi; 63, Selindeochrea ternaria; 64, Anabarites trisulcatus; 67, Anabarites kelleri; 68, Anabarites biplicatus; 71, Anabarites hexasulcatus; 74, Tiksitheca licis; 75, Cambrotubulus decurvatus; 76, Platysolenites antiquissimus; 77, Blastulospongia sp.