Pseudoyangtzespira selindeica Bokova, 1990

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 : 345

Pseudoyangtzespira selindeica Bokova, 1990

Fig. 17.

Material.— 25 phosphatic internal moulds from sample 1/6 (section 1, Fig. 4 ) and a single internal mould from K1a/67 (section 2, Fig. 1), including figured SMNH Mo182240– 182244, from lowermost Kugda-Yuryakh Formation (SOM 1) and P. selindeica topotype, SMNH Mo 182245, from the uppermost Ust’-Yudoma Formation , Selinde section, southeastern Siberian Platform , Russia. Correlated with lower part of Cambrian Stage 2 .

Description.—Slightly dextrally coiled up to one whorl, rapidly expanding shell. Spire does not project or slightly projects beyond the upper margin of the aperture (Fig. 17A 2, C, D, E 2, F 2). Aperture extended irregularly oval or ovoid in outline, with length/width ratio ca. 3. Apical part indistinctly separated from rest of conch. Inner surface of the shell (reflected by internal moulds) smooth (Fig. 17A–E) or with low and regular comarginal folds (Fig. 17F).

Remarks.— Pseudoyangtzespira selindeica Bokova, 1990 was first described from the uppermost Ust’-Yudoma Formation of the Selinde section of the southeastern Siberian Platform (Fig. 17F). The specimens from the Anabar Uplift are represented by smooth internal moulds generally similar to A. crassa Missarzhevsky in Rozanov et al., 1969 (compare Fig. 17A–E with Fig. 18 ), although they derive from younger beds than those containing undoubted topotype A. crassa . P. selineica has a faster expanding, less coiled, more regularly transversely folded shell wall with a more extended apertural outline.

Stratigraphic and geographic range.—Fortunian–Cambrian Stage 2 transitional beds of Siberia.

Figures

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.

Fig. 18. Mollusc Aldanella crassa Missarzhevsky in Rozanov et al., 1969, internal moulds, from early Cambrian Medvezhya Formation, Kotuj River, western Anabar Uplift, Siberia, Russia; samples 1/50 (A, B, D–F), section 1; samples K2/13 (C) and 3/6.5 (G), section 3. A–G. SMNH Mo182246– 182252, respectively. A1, B1, C2, D, E1, F, G1, adapical side; E2, oblique adapical view; A3, oblique umbilical side; A2, B3, C1, G2, apertural views; B2, close-up of apex with polygonal relief. Scale bar 200 μm (B2), 500 μm (A, B1, B3), and 1 mm (C–G).