Fomitchella 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 acinaciformis Missarzhevsky, 1977

Figs. 66F, G , 67 .

Material.—About 50 phosphatic sclerites, including figured SMNH X5959, 5960, 5962–5968, from samples 5a /17.5 and 5a/18.5 (section 96-5a, Fig. 2 ), Emyaksin Formation, eastern Anabar Uplift, Siberian Platform, Russia. Correlated with the lower part of Cambrian Stage 2.

Description.—Phosphatic, elongated, conical, hollow sclerites, gently curved and slightly compressed in a single plane. Apex somewhat more elongate, almost straight. Basal margin ovoid, lateral sides may have gentle longitudinal depression. Outer surface with radial striation or smooth. Inner surface smooth.

Remarks.—See Fomitchella infundibuliformis for comparison. The holotype of F. acinaciformis came from sample M314/5-10, a mixed sample collected by Vladimir V. Missarzhevsky from the lower Medvezhya Formation at a horizon located 5‒10 m above the base of section M314 Rozanov et al. 1969: 44, fig. 9). The type material of F. infundibuliformis (see above) was collected ca. 4 m above the base of section M314.

Two sclerites illustrated as Maldeotaia bandalica Singh and Shukla, 1981 , from the Watsonella crosbyi Zone of Avalonian southeast Newfoundland (Landing et al. 1989: fig. 7.5, 7.6) are morphologically comparable to Fomitchella acinaciformis and are brought to the latter species. This lowest occurrence in the Fortunian‒Cambrian Stage 2 transition interval is comparable to the species’ lowest known appearance in Siberia.

Stratigraphic and geographic range.—Terminal Fortunian‒ Cambrian Stage 2 of the Siberian Platform and, probably, western Mongolia (see Missarzhevsky 1977) and Avalonia Landing et al. 1989, discussed above).

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. 67. Problematic calcium phosphatic sclerites Fomitchella acinaciformis Missarzhevsky, 1977, from early Cambrian Emyaksin Formation, eastern flank of the Anabar Uplift, Siberia, Russia; sample 5a/18.5, section 96-5a. A SMNH X5962. B. SMNH X5964. C. SMNH X5966. D. SMNH X5967. E. SMNH X5963. F. SMNH X5965. G. SMNH X5968. A1, A3, C, D2, G, lateral; A2, D1, oblique apertural; B, F, oblique apical views; A4, E2, outer surface with fibres at apertural margin. Scale bar 100 μm (A4, E2), 250 μm (A3), 500 μm (A1, A2, B–D, E1, 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.