Siphogonuchites triangularis Qian, 1977

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 : 373-375

Siphogonuchites triangularis Qian, 1977

Figs. 44C , 45A, B .

Material.—Over 25 phosphatized fragments of sclerites and phosphatic internal moulds, including figured SMNH X5793, 5801, 5802, from samples 1/50 (section 1, Fig. 4 ), 3/0, 3/0.1, and 3/12.2 (section 3, Fig. 3), Medvezhya Formation and pyritised sclerites/internal moulds from samples K1a/36A and K1a/41A (section 2, Fig. 1), upper Nemakit-Daldyn Formation, western Anabar Uplift, Siberia, Russia. Correlated with the upper Fortunian Stage.

Description.—Elongated asymmetrical sclerites, curved irregularly with curvature either almost in one plane (sometimes S-shaped) but often helically twisted up to 90°. Cross-section irregularly triangular, trapezoidal, or polygonal. Upper/convex sclerite surface transversely arched, with one to three pronounced longitudinal ridges separated by shallow longitudinal furrows. Longitudinal and transverse rugae with a regular pattern of low bumps where rugae intersect. Lower/concave surface smooth and flattened transversely. Sharp lateral ridges at intersection of upper and lower surfaces.

Remarks.—Initially described from the Watsonella crosbyi Assemblage Zone (Zone 3 of the Meishucunian), the type species Siphogonuchites triangularis Qian, 1977 , is known to range from Meishucunian Assemblage Zone 1 in South China, where it co-occurs with maikhanellids (e.g., Maikhanella multa ) and other siphogonuchitids, such as Dabashanites mirus Chen, 1979 , and Lopochites spp. (Qian and Bengtson 1989; Steiner et al. 2004a, 2007; Yang et al. 2014; see below). Qian and Bengtson (1989) discussed variability and provided a comprehensive synonymy of the species and genus (see also Devaere et al. 2013). Siphogonuchites triangularis was first reported in Siberia from the basal Pestrotsvet Formation at Selinde (Khomentovsky and Karlova 1993, not illustrated therein) and, questionably, as Siphogonuchites aff. S. triangulariformis [sic!, should be triangularis ] from 60 m below the top of the Ust’-Yudoma Formation at the Mount Konus section (Khomentovsky et al. 1990: 34, pl. 8: 6) on the southeastern Siberian Platform. This occurrence was assigned to the Purella antiqua Zone (Khomentovsky and Karlova 1993).

Stratigraphic and geographic range.— Terreneuvian Series of Siberia (Khomentovsky et al. 1990), western Mongolia (Voronin et al. 1982; Esakova and Zhegallo 1996), South China (Steiner et al. 2007; Yang et al. 2014), and Cambrian Stage 2 of France ( Devaere et al. 2013).

Figures

Fig. 44. Siphogonuchitid sclerites from early Cambrian Nemakit-Daldyn Formation of western Anabar Uplift, Siberia, Russia; samples K1a/43 (A), 1282 (B), K1a/36A (C), 2/A (D, E, G), and K1a/47 (F, H–J) from section 2. A, D–G. Siphogonuchites subremualis (Bokova, 1985), calcium phosphatic internal moulds, SMNH X5791 (A), SMNH X5794–5797 (D–G, respectively). A1, oblique lateral view of basal part of articulated sclerite group; A2, lateral view of sclerites; D1, view of lower surface of sclerite; D2, lateral view; E1, view of upper surface at distal end; E2, transversal view; G1, G2, views of lower side of basal part of sclerite. B. Dabashanites mirus Chen, 1979, group of articulated phosphatized sclerites, SMNH X5792; B1, B2, oblique lateral views. C. Siphogonuchites triangularis Qian, 1977; pyritised internal mould in lateral view, SMNH X5793. H–J. Tianzhushania longa Qian, Chen, and Chen, 1979; calcium phosphatic internal moulds, SMNH X5798–5800, respectively; H, J, lateral; I, transverse views. Scale bar 250 μm (A), 500 μm (B, D1, E–J), 1 mm (C, D2).

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.