Anabarites compositus 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 : 420-421

Anabarites compositus Missarzhevsky in Rozanov et al., 1969

Fig. 77 .

Material.—Over one hundred internal moulds with rare fragments of phosphatized walls, including figured SMNH X3677–3679, 3681–3684, 6029, 6030, from sample 5a/34.5 (see Kouchinsky et al. 2009; Fig. 77A–I ), and probably also several glauconitised internal moulds, including figured SMNH X6031, 6032, from sample 5a/18.5, Emyaksin Formation, eastern Anabar Uplift, Siberian Platform, Russia. Correlated with lower part of Cambrian Stage 2.

Description.—Almost straight tubes with rounded hexagonal inner cross-section ( Fig. 77G, J ) and transverse, flanged growth lines. Internal protrusions of the conch wall are obliquely inclined towards the aperture ( Fig. 77H 1) and replicated as three rows of notches in the middle of each depression on the internal mould ( Fig. 77F 2 , I, K). A semi-circular pocket in the inner surface of the tube wall is associated with each protrusion ( Fig. 76E, H 1, D 2). These structures produce chevron-like elements on the internal moulds.

Remarks.—The internal indentations on Anabarites compositus tubes are spine-like and rounded in cross-section (Kouchinsky et al. 2009: fig. 30A, B). They differ from the blade-like, longitudinally elongate indentations along the axis of the tube moulds in A. tristichus (compare Fig. 77K with Fig. 76A ). The pocket-like structures in the wall of A. compositus are reminiscent of the circumferential internal folds in the walls of Aculeochrea rugosa Val’kov and Sysoev, 1970 ( Fig. 78 ) and A. ornata Val’kov and Sysoev, 1970 (see Kouchinsky et al. 2009: fig. 49). For this reason, Missarzhevsky (1989: 193) assigned A. compositus to Aculeochrea Val’kov and Sysoev, 1970.

Spine-like protrusions covered by “lamellae” are apparently present in Aculeochrea trilamellosa Vasil’eva, 1998, and Aculeochrea mesezhnikovi Vasil’eva, 1998 (Vasil’eva 1998: pl. 16: 1–5, pl. 17: 1, 2, 5). The “lamellae” presumably represent similar structures on the internal moulds as the chevrons in A. compositus . Aculeochrea mesezhnikovi is reportedly different from A. compositus in having “lamellae” situated in depressed parts of the mould (grooves), whereas the more prominent and wider lobes are devoid of such “laminae” (Vasil’eva 1998). Aculeochrea trilamellosa similarly has three longitudinal rows of “lamellae” and a circular cross-section of the internal mould. The illustrations by Vasil’eva (1998) do not, however, allow a more detailed comparison with Anabarites compositus . A fossil from the upper lower Cambrian of England misidentified ( Hinz 1987: pl. 14: 37, 38) as A. compositus actually resembles Selindeochrea tricarinata (Missarzhevsky; see also Brasier 1989: 135), but most likely represents the orthothecid hyolith Gracilitheca .

Stratigraphic and geographic range.— Lower part of Cambrian Stage 2, Siberian Platform.

Figures

Fig. 77. Anabaritid Anabarites compositus Missarzhevsky in Rozanov et al., 1969, from early Cambrian Emyaksin Formation, Anabar Uplift, Siberia, Russia; samples 5a/34.5 (A–I) and 5a/18.5 (J, K), section 96-5a. A–K. SMNH X3677 (A; see also Kouchinsky et al. 2009: fig. 29A–C), SMNH X3679 ( B; see also Kouchinsky et al. 2009: fig. 29F, G), SMNH X3678 (C; see also Kouchinsky et al. 2009: fig. 29D–E), X6029 (D), SMNH X3682 (E; see also Kouchinsky et al. 2009: fig. 30A–E), SMNH X3684 (F; see also Kouchinsky et al. 2009: fig. 31), SMNH X3683 (G; see also Kouchinsky et al. 2009: fig. 30F–H), SMNH X6030 (H), X3681 (I; see also Kouchinsky et al. 2009: fig. 29J), SMNH X6031 (J), and SMNH X6032 (K). A1, B–D, F2, H2, I, K, lateral views of internal moulds and calcium phosphatic inner and outer coats on the tube walls; A2, A3, enlargement of “chevrons” on surface of internal mould; E, fragment of inner coating with protrusions directed towards apertural end of tube; F1, enlargement of F2 showing external surface of inner coating with “ chevrons” and partly preserved phosphatized apertural flanges; G, transverse view of partly phosphatized tube; H1, enlargement of H2 showing “chevrons” and internal protrusions of the wall preserved by inner phosphatic coating of conch; J, transverse view of internal mould. Scale bar 100 μm (A2, A3, F1), 250 μm (H1), and 500 μm (A1, B–D, F2, G, H2, I–K).

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.

Fig. 76. Anabaritids from early Cambrian Medvezhya (A–D) and Emyaksin (F, E) formations, Anabar Uplift, Siberia, Russia; samples K2/25 (A, B), K2/26 (C), section 3; 5/0 (F), section 96-5; 5a/34.5 (E), section 96-5a; and 1/29.2 (D), section 1. A–C, F. Anabarites tristichus Missarzhevsky in Rozanov et al., 1969, SMNH X3671 (A; see also Kouchinsky et al. 2009: fig. 26C), SMNH X3672 (B; see also Kouchinsky et al. 2009: fig. 26D), SMNH X3409 (C; see also Kouchinsky and Bengtson 2002: figs. 2, 3 and Kouchinsky et al. 2009: fig. 26A, B), SMNH X6027 (F). A, B, F, lateral views of calcium phosphatic internal moulds; C1, lateral view of celestite-barite replaced tube with calcium phosphatic internal mould; C2, internal protrusion of the wall enlarged; C3, transverse view. D. Anabarites hexasulcatus (Missarzhevsky, 1974), SMNH X6028; D1, lateral; D2, transverse views. E. Anabarites hariolus (Val’kov, 1987), SMNH X3697 (see also Kouchinsky et al. 2009: fig. 36K–M). E1, transverse view of apertural end; E2, E3, lateral views; E4, transverse view of apical end. Scale bar 25 μm (C2), 500 μm (A, B, C1, C3, D–F).

Fig. 78.Anabaritid Aculeochrea rugosa (Val’kov and Sysoev, 1970), internal moulds, from early Cambrian Manykay Formation, eastern Anabar Uplift, Siberia, Russia; sample 4/4, section 96-4. A. SMNH X6033. B. SMNH X3773 (see also Kouchinsky et al. 2009: fig. 50G). C. SMNH X3768 (see also Kouchinsky et al. 2009: fig. 50A–B). A, B2, C, lateral; B1, transverse views. Scale bar 500 μm.