Lopochites sp.

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 : 378

Lopochites sp.

Fig. 45C–K .

Material.—Over 30 internal moulds with fragments of phosphatized walls, including SMNH X5803–5811, from samples 1/46, 1/45, 1/39.3 (section 1, Fig. 4 ), K2/12, K2/20, K2/21, K2/24, 3/10, 3/12.2 (section 3, Fig. 3), 4/27.5, 5/10, 5/10B, 5a/1.2 (sections 96-4, 96-5, 96-5a), Medvezhya and lower Emyaksin formations, Anabar Uplift, Siberia, Russia; upper Fortunian Stage.

Description.—Elongate, narrow, helically twisted (up to 90º) and gently longitudinally bent sclerites. Cross-section narrow oval at the base and broader, irregular oval distally. Foramen narrow, oval, and slightly bent, separated from the rest of sclerite by a shallow circumferential depression. Surface of sclerite covered with longitudinal striae; fine transverse striae at the base. Wall composed of longitudinally oriented fibres ( Fig. 45D ).

Remarks.— Lopochites spp. occur in the Terreneuvian Series of South China, western Mongolia, and Iran ( Esakova and Zhegallo 1996; Steiner et al. 2004a). Specimens of Lopochites spp. described from South China (Qian and Bengtson 1989) are phosphatized sclerites, in contrast with our material which is comprised of phosphatic internal moulds. Occasionally, preserved walls of the Siberian sclerites suggest that the outer surface was smooth and lacked the prominent longitudinal ridges present in species from South China and western Mongolia. The outer wall is however not completely preserved and may show a smooth inner surface just above the internal moulds ( Fig. 45D ). The sclerites are similar to Lopochites in being helically twisted longitudinally and in having a narrow irregularly oval foramen, a rounded cross-section of the distal part (e.g., Qian and Bengtson 1989: fig. 13E 6, E 7) and similar microstructure of the wall (Qian and Bengtson 1989: fig. 14). Lopochites sp. is generally more similar to L. curtus Grigorieva (in Voronin et al. 1982), whereas L. latazonalis is broader and shorter.

Figures

Fig. 45. Siphogonuchitid sclerites from early Cambrian Medvezhya (A, B, D, E, G, H, J, K) and Emyaksin (C, F, I) formations, Anabar Uplift, Siberia, Russia; samples 1/50 (A), 1/45 (H), 1/39.3 (E), section 1; 3/0 (B) and 3/10 (D, G, J, K), section 3; 4/27.5 (C), section 96-4; and 5/10 (F, I), section 96-5. A, B. Siphogonuchites triangularis Qian, 1977, phosphatized sclerites, SMNH X5801, 5802, respectively. A1, A2, B1, lateral views; A3, B2, transverse views of basal end. C–K. Lopochites sp., calcium phosphatic internal moulds with partly preserved phosphatized walls (D), SMNH X5803–5811, respectively. Lateral views with basal end toward bottom of figure. Scale bar 200 μm (D2), 250 μm (C, D1, F, I), 500 μm (A, B, E, G, H, J, K).

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.