Protoconus cf. crestatus Yu, 1979

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 : 371

Protoconus cf. crestatus Yu, 1979

Fig. 41 .

Material.—Three internal moulds, SMNH Mo182379– 182381, from samples 1/50 and 1/6 (section 1, Fig. 4 ), Medvezhya and Kugda-Yuryakh formations, western Anabar Uplift, Siberian Platform, Russia. Correlated with upper Fortunian and lower part of Cambrian Stage 2.

Description.—Bilaterally symmetrical, cap-shaped shell with broad oval aperture. Apex rounded, not clearly separated from the rest of the shell. Inner surface of the shell (replicated by the internal mould) with two parallel longitudinal thickenings that flank a wide median buttress that defines the entire dorsal side of the internal mould ( Fig. 41A 1, B 3, C 1).

Remarks.—Subapical side short with the subapical shelf that is diagnostic for the genus Protoconus ( Devaere et al. 2013; Fig. 41A 3). The furrows and median buttress are covered with a low nodular texture with positive relief on the mould ( Fig. 41C 1, C 4). The nodules are ca. 5 μm in diameter. Yang et al. (2014) reported moulds and partial conchs of P. crestatus from the late Fortunian (Assemblage Zone 2) of South China. The latter species is similar and probably synonymous with Purella tianzhushanensis Yu, 1979 . The latter was also described by Hamdi (1995: pl. 12: 1, 2) from the Latouchella – Obtusoconus Assemblage Zone (Upper Shale Member, Soltanieh Formation, Albortz Mountains, Iran).

→ Fig. 36. Molluscs Yunnanopleura accurata ( Bokova, 1985) , internal moulds with partly phosphatized shells (B, H), from early Cambrian Nemakit-Daldyn (A, E, H) and Emyaksin (B–D, F, G) formations, Anabar Uplift, Siberia, Russia; samples K1a/47 (A) and 2/A (E), section 2; 3/0 (H), section 3; 4/27.5 (C, G), section 96-4, and 5/0 (B, D, F), section 96-5. A–H. SMNH Mo182349 (A), SMNH Mo160405 (B; see also Kouchinsky 2000a: fig. 4I), SMNH Mo182350–182355 (C–H, respectively). A 1, B 1, C 2, D, E 1, F 1, G 2, H 1, upper; A 2, B 3, E 2, F 3, H 3, subapical; A 3, B 2, C 1, F 2, G 1, H 2, lateral views. Scale bar 500 μm (A, B, C 2, D–G, H 3), 1 mm (C 1, H 1, H 2).

Figures

Fig. 41. Problematic mollusc Protoconus cf. crestatus Yu, 1979, calcium phosphatic internal moulds, from early Cambrian Medvezhya and Kugda-Yuryakh formations of western Anabar Uplift, Siberia, Russia; samples 1/50 (A) and 1/6 (B, C) from section 1. A–C. SMNH Mo182379 (A), SMNH Mo182380 (B), SMNH Mo182381 (C). A1, B3, C1, upper; A2, B1, C3, subapical; A3, B2, C2, lateral; A4, supra-apical views; C4, close-up of lateral surface in C3. Scale bar 125 μm (C4), 500 μm (A, B, C1–C3).

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.