Siphogonuchites subremualis ( Bokova, 1985 )

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 : 375-377

Siphogonuchites subremualis ( Bokova, 1985)

Fig. 44A, D–G .

Material.—Over 100 phosphatized sclerites and phosphatic internal moulds, including figured SMNH X5791, 5794–5797, from samples 2/A, 1282, K1a/43, and K1a/47 (section 2, Fig. 1), upper Nemakit-Daldyn Formation, western Anabar Uplift, Siberia, Russia. Correlated with the upper Fortunian Stage.

Description.—Flattened sclerites curved in one plane. Cross-section low triangular to trapezoid. Sclerites taper towards the base and form a shaft with irregular cross-section ( Fig. 44A, F, G ). Upper/convex surface of sclerite with two longitudinal ridges separated by a shallow furrow. The ridges gradually merge into a single ridge that continues towards the acute distal end of the sclerite ( Fig. 44E ). The ridges are transversed by faint folds that laterally continue at an angle towards the axis of the sclerite ( Fig. 44F 2 ). The lower/concave surface of the sclerite is smooth with faint longitudinal striation and rugae. Articulated sclerites are of different thicknesses and packed next to each other along their shaft-like basal parts ( Fig. 44A ).

Remarks.—Articulated sclerites are also known from Siphogonuchites triangularis ( Esakova and Zhegallo 1996: pl. 11). The scleritome of S. triangularis was probably composed of broader and slim sclerites that were adjacent to each other ( Esakova and Zhegallo 1996). We agree with Esakova and Zhegallo (1996), who considered Siphogonuchites subremualis a distinctive species. S. subremualis sclerites have two prominent ridges along their almost bilaterally symmetrical blades that are much shorter and taper much faster proximally (to the base) and distally (to the pointed tip) than those of S. triangularis .

Stratigraphic and geographic range.— Upper Fortunian Stage of the Siberian Platform.

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. 2. Composite δ13Ccurve for the Bol’shaya Kuonamka River sections 96-4, 5, and 5a and sampled horizons with fossiliferous samples (arrows with carb numbers). Arrow 4/4 indicates “marker bed with angustiochreids” (Val’kov 1975; Kouchinsky et al. 1999). For section 96-6 see Kouchinsky et al. (2001, 2015a). Shift in stratigraphic column at Manykay–Emyaksin formations contact indicates position of sequence boundary. Stratigraphic ranges and first appearances of fossils (see SOM 1): 1, first appearance of helcionellid molluscs; 2, Oelandiella korobkovi; 3, Securiconus cf. simus; 6, Obtusoconus vostokovae; 7, Obtusoconus cf. mirabilis; 8, Anabarella plana; 13, Aldanella attleborensis; 14, Aldanella cf. sibirica; 22, Purella antiqua; 24, Yunnanopleura accurata; 34, Lopochites sp.; 35, Tianzhushania longa; 37, first appearance of Halkieria sp.; 38, Chancelloria symmetrica; 42, Khetatheca cotuiensis; 44, Conotheca cf. mammilata; 46, Turcutheca sp.; 47, Cupitheca sp.; 50, Orthothecid operculum type C; 51, Protohertzina anabarica; 52, Fomitchella infundibuliformis; 53, Fomitchella aff. infundibuliformis; 54, Fomitchella acinaciformis; 55, Fomitchella aff. acinaciformis; 56, Hyolithellus vladimirovae; 57, Hyolithellus sp.; 60, Selindeochrea cf. tecta; 61, Selindeochrea tripartita; 62, Selindeochrea missarzhevskyi; 63, Selindeochrea ternaria; 64, Anabarites trisulcatus; 65, Anabarites latus; 66, Anabarites natellus; 67, Anabarites kelleri; 68, Anabarites biplicatus; 69, Anabarites tristichus; 70, Anabarites compositus; 71, Anabarites hexasulcatus; 72, Anabarites hariolus; 73, Aculeochrea rugosa; 74, Tiksitheca licis; 75, Cambrotubulus decurvatus; 76, Platysolenites antiquissimus.