Tiksitheca licis Missarzhevsky

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 : 423-425

Tiksitheca licis Missarzhevsky in Rozanov et al., 1969

Fig. 79A–C, K–M .

Material.—Thousands of internal moulds and partially phosphatized tubes, including figured SMNH X6034–6038, from the Manykay, Nemakit-Daldyn, Medvezhya, and lower Emyaksin formations, Anabar Uplift, Siberian Platform, Russia. Correlated with the upper Fortunian and lower part of Cambrian Stage 2.

Description.—Curved to almost straight calcareous tubes with rounded triangular, radially symmetrical cross-section, slowly expanding from the apical part. The wall may include relatively prominent, transverse flanges and intervening growth lines (Kouchinsky and Bengtson 2002). Inner surface of the tube with transverse growth lines (as reflected on internal moulds).

Remarks.—The presence of flanges in a wall with anabaritidtype microstructure is also known from Anabarites tristichus (Kouchinsky and Bengtson 2002) , and is compatible with the interpretation of Tiksitheca licis as an anabaritid (see remarks by Missarzhevsky in Rozanov et al. 1969: 114). The type material of T. licis from sample M423/13 (Fig. 3), which is a horizon in section 3 of this report, was collected by Vladimir V. Missarzhevsky from the Medvezhya Formation.

Partly phospatized slightly irregularly curved tubes preserved with diagenetic phosphatic inner and outer crusts are found in sample 3/10 from the Medvezhya Formation ( Fig. 80A–E, G ). Numerous distinct straight or slightly undulating growth increments are replicated on their outer surfaces. The tubes have rounded triangular outer cross-sections, and their internal moulds would normally be identified as Tiksitheca licis . The latter occur in the same beds of the Medvezhya Formation (SOM 1). In addition to T. licis , rare problematical, longitudinally twisted tubes with rounded triangular cross-section, known as Kugdatheca voluta Missarzhevsky in Rozanov et al., 1969, were extracted from several samples ( Fig. 79N, O , SOM 1).

Stratigraphic and geographic range.— The type species Tiksitheca licis is known from the upper Fortunian Stage and commonly occurs throughout the strata correlated herein with lower part of Cambrian Stage 2 in Siberia and reportedly ranges into the upper part of Cambrian Stage 2 (Kouchinsky et al. 2009 and references therein). The species is often listed with T. korobovi and T. voluta (see Kouchinsky et al. 2009). Tiksitheca licis and Tiksitheca spp. are also reported from the upper Fortunian–lower part of Cambrian Stage 3 of South China (Li et al. 2007). Tiksitheca licis occur in the Terreneuvian strata of western Mongolia, Iran, India, and Kazakhstan (see Kouchinsky et al. 2009 and references therein).

Genus Cambrotubulus Missarzhevsky in Rozanov et al., 1969

Type species: Cambrotubulus decurvatus Missarzhevsky in Rozanov et al., 1969; lower Cambrian ( upper Fortunian –lower part of Cambrian Stage 2); mouth of the Ary-Mas-Yuryakh Creek , Kotuj River, Siberia, Russia .

Figures

Fig. 79. Anabaritids from early Cambrian Medvezhya (A, B, D–G, I, J, L, M, P) and Emyaksin (C, H, K, N, O) formations of Anabar Uplift, Siberia, Russia; samples 3/12.2 (A, B, D, F, G), K2/21 (L), K2/26 (E, M), section 3; 5a/1.2 (C, H, K, N, O), section 96-5a; 1/22 (I, J), 1/29.5 (P), section 1. A–C, K, L. Tiksitheca licis Missarzhevsky in Rozanov et al., 1969, internal moulds, SMNH X6034, 6035 (A, B, respectively), SMNH X6037 (C), SMNH X6036 K), SMNH X6038 (L). A, B2, C, K, L, lateral views; B1, transverse view of apertural end. M. T. licis, SMNH X3410 (see also Kouchinsky and Bengtson 2002: fig. 6 and Kouchinsky et al. 2009: fig. 39E), lateral view of tube replaced by celestite and barite. D–J, P. Cambrotubulus decurvatus Missarzhevsky in Rozanov et al., 1969, internal moulds, SMNH X6039–6045 (D–J, respectively), SMNH X6048 (P). D–H, I1, J, P, lateral views; I2, transverse view of apertural end. N. Kugdatheca voluta Missarzhevsky in Rozanov et al., 1969, SMNH X6046. N1, lateral view of internal mould; N2, oblique transverse view of apical end. O. K. voluta?, lateral view of internal mould, SMNH X6047. Scale bar 500 μm (M, O), and 1 mm (A–L, N, P).

Fig. 80. Problematic tubes from early Cambrian Medvezhya Formation, western Anabar Uplift, Siberia, Russia; samples 3/10 (A–E, G) and K2/26 (F), section 3. A–E, G. Tiksitheca licis? Missarzhevsky in Rozanov et al., 1969, SMNH X6049–6053 (A–E, respectively), SMNH X6054 (G). Calcium phosphatic internal moulds and outer coatings of conchs. F. Problematic tube or sclerite, lateral view of internal mould, SMNH X6055. Scale bar 250 μm (G), 500 μm (A–E), 1 mm (F).