Fomitchella aff. acinaciformis Missarzhevsky, 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 : 408

Fomitchella aff. acinaciformis Missarzhevsky, 1977

Fig. 66A–E .

Material.—About 50 phosphatic sclerites, including figured SMNH X5954–5958, from samples 5a/9, 5a/10.5, and 5a/17.5 (section 96-5a, Fig. 2 ), from the lower Emyaksin Formation, eastern Anabar Uplift, Siberian Platform, Russia. Correlated with the lower part of Cambrian Stage 2.

Description.—Relatively tall conical phosphatic sclerites with somewhat flared apertural margin, rounded in apical view. The middle part of the sclerite is oval in cross-section and tapers into a gently recurved narrow tip with rounded cross-section. Outer surface with fine transverse concentric striation and with radial striation at the apertural margin.

Remarks.—This form differs from Fomitchella acinaciformis in having a wider, almost circular aperture and less lateral compression of the upper part of the sclerite.

Figures

Fig. 66. Problematic calcium phosphatic sclerites Fomitchella aff. acinaciformis Missarzhevsky, 1977 (A–E), Fomitchella acinaciformis Missarzhevsky, 1977 (F, G), and Fomitchella sp. (H), from early Cambrian Emyaksin Formation, eastern flank of the Anabar Uplift, Siberia, Russia; samples 5a/10.5 (A, B, E), 5a /17.5 (C, F–H), 5a/9 (D), section 96-5a. A–H. SMNH X5954–5961, respectively. A1, oblique apical; A3, C2, D2, H3, apical; A2, B, C3, D1, E1, F, G2, G3, H1, H2, lateral; E2, apertural; G1, oblique apertural views; C1, close-up of apertural margin with fibres (note two inserted sclerites). Scale bar 50 μm (C1), 250 μm (A1, B, C2, C3, E, H), 500 μm (A2, A3, D, F, G).

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.