Selindeochrea, Valkov, 1982

Kouchinsky, Artem, Alexander, Ruaridh, Bengtson, Stefan, Bowyer, Fred, Clausen, Sébastien, Holmer, Lars E., Kolesnikov, Kirill A., Korovnikov, Igor V., Pavlov, Vladimir, Skovsted, Christian B., Ushatinskaya, Galina, Wood, Rachel & Zhuravlev, Andrey Y., 2022, Early-middle Cambrian stratigraphy and faunas from northern Siberia, Acta Palaeontologica Polonica 67 (2), pp. 341-464 : 434-436

Genus Selindeochrea Val’kov, 1982

Type species: Selindeochrea tecta Val’kov, 1982; lower part of Cambrian Stage 2; upper reaches of the Selinde River, Siberia, Russia .

Selindeochrea ternaria (Missarzhevsky in Rozanov et al. 1969)

Fig. 67C .

Material.—Single calcium phosphatic internal mould, SMNH X11317, from sample 15/23, Chuskuna Formation (upper part of the Kessyusa Group), Khorbusuonka River, Siberia, Russia. Watsonella Zone, Cambrian Stage 2.

Remarks.—Fragment of internal mould radially symmetrical in cross-section, with three prominent narrow lobes separated by V-shaped grooves.

Stratigraphic and geographic range.—Upper Fortunian Stage and lower part of Cambrian Stage 2 of the Siberian Platform ( Russia) and South China.

Phylum, class, order, and family uncertain

Genus Coleoloides Walcott, 1889

Type species: Coleoloides typicalis Walcott, 1889 ; lower Cambrian , Brigus Formation ; Manuel’s Brook , Conception Bay, Newfoundland, Canada .

Coleoloides trigeminatus Missarzhevsky in Rozanov et al., 1969

Fig. 68A–C, K–M .

Material.—Over ten calcium phosphatic and glauconised internal moulds, including figured SMNH X11326 (C), sample 11/2B, lower Erkeket Formation, Khorbusuonka River and SMNH X11329 (M), sample 21/22, Tyuser Formation, lower reaches of the Lena River, Dokidocyathus regularis Zone, Tommotian stage (upper part of Cambrian Stage 2), Siberia, Russia. Additional material from the Tommotian stage, lower Pestrotsvet Formation of southeastern Siberian Platform includes: SMNH X11325 (B) and SMNH X11328

L), from sample M303/2, Tiktirikteekh Brook, middle Lena River, D. regularis Zone (see Rozanov et al. 1969: 31, text-fig. 6), SMNH X11327 (K), sample 479a, section “Dvortsy”, Aldan River, Nochoroicyathus sunnaginicus Zone (collected by Anatolij K. Val’kov), and SMNH X11324 (A), sample 510, section Ulakhan-Sulugur, Aldan River, N. sunnaginicus Zone (collected by Anatolij K. Val’kov). Siberia, Russia.

Description.—Somewhat irregularly curved and helically twisted or straight internal moulds representing fragments of very slowly expanding thin-walled tubes, 0.1–0.2 mm in diameter, with 6–12 longitudinal lobes. The lobes rounded in cross-section and separated by narrower intervening grooves. Initial part circular in cross-section, ca. 0.1 mm in diameter ( Fig. 68K ). At ca. 0.5 mm from probably broken off and incompletely preserved apical end, the cylindrical initial part transforms abruptly into a tube with six lobes, helically twisted anticlockwise. The lobes bifurcate at a later growth stage. Tube fragments greater than 0.2 mm in diameter have up to 12 lobes ( Fig. 68B, L ).

Remarks.— Coleoloides trigeminatus Missarzhevsky in Rozanov et al., 1969, was first described from the Dokidocyathus regularis Zone of the Tommotian stage, Siberian Platform as elongated, somewhat helically twisted and irregularly curved phosphatic internal moulds, ca. 0.1 mm in diameter, typically with six longitudinal ribs. The latter commonly run spirally around the longitudinal axis of the mould. The initial stage of growth has not been previously illustrated. Missarzhevsky (1982, 1989) indicated C. trigeminatus among anabaritids, but the affinity of Coleoloides to a particular group of the earliest tubular fossils remains problematic. Although cross-sections of C. trigeminatus and Anabaritellus hexasulcatus are very similar in shape, they are markedly different in diameter, which is 3–4 times greater in A. hexasulcatus and retains its six-folded cross-section at later stages of growth ( Kouchinsky et al. 2009: fig. 33; Kouchinsky et al. 2017: fig. 76D). Brasier 1984: 234) and Qian and Bengtson (1989: 130–131) synonymised C. trigeminatus with C. typicalis Walcott, 1889 , with the latter showing a considerable variability in number of thin longitudinal ridges on the surface of internal moulds. However, this synonymy is not supported herein.

Stratigraphic and geographic range.—Tommotian stage correlated with the upper part of Cambrian Stage 2), Siberian Platform ( Russia), and, probably, Cambrian Stage 2 of Avalonia and South China (see Kouchinsky et al. 2009).

Coleoloides cf. paucistriatus Poulsen, 1967

Fig. 68E–J .

Material.—Over ten calcium phosphatic and glauconised internal moulds from sample 11/2B, basal Erkeket Formation, Khorbusuonka River, Siberia, Russia; Dokidocyathus regularis Zone, Tommotian Stage (upper part of Cambrian Stage 2). Additional material from the Tommotian Stage, lower Pestrotsvet Formation of southeastern Siberian Platform ( Russia) includes: SMNH X11334 and X11336, from sample M303/2, Tiktirikteekh Brook, middle Lena River, D. regularis Zone (see Rozanov et al. 1969: 31, text-fig. 6), SMNH X11331, from sample 171–174, Bydyangaya Brook, middle reaches of the Lena River, Nochoroicyathus sunnaginicus Zone (see Val’kov 1982: 27, text-fig. 8), and SMNH X11332, X11333, and X11335, from sample 510, section Ulakhan-Sulugur, Aldan River, N. sunnaginicus Zone (collected by Anatolij K. Val’kov).

Description.—Irregularly curved and helically twisted internal moulds with initial part ( Fig. 68E ) circular in cross-section and cylindrical in shape, ca. 0.5 mm long and 50–70 µm in diameter. The tubes expand slightly from the initial part and acquire two ( Fig. 68E 1 ), four and then eight longitudinal lobes running spirally clockwise around the longitudinal axis of the mould. The lobes are crest-shaped in cross-section and separated by flattened faces. New longitudinal ribs gradually intervene in the middle of the faces between the available ribs. A specimen with diameter ca. 100 µm shows 4 ribs ( Fig. 68I ), those ca. 150 µm in diameter have 8 ribs ( Fig. 68F ), and at a ca. 250 µm diameter the number of longitudinal ribs reaches 12 ( Fig. 68H, J ). Ribs evenly spaced and separated from each other by flattened faces, ca. twice the width of the ribs.

Remarks.—Similar to Coleoloides paucistriatus Poulsen, 1967 , in having up to 12 longitudinal ribs and wide flattened faces between them. Different from co-occurring Coleoloides trigeminatus in having ridged lobes and wide flattened faces between them. There are six lobes in C. trigeminatus at the initial part, whereas two spiral lobes in C. cf. paucistriatus . Superficially similar to internal moulds of Anabarites isiticus Missarzhevsky (see Kouchinsky et al. 2009: fig. 35) from the Tommotian stage of south-eastern Siberian Platform, but A. isiticus has ca. 3 times greater diameter, higher expansion rate and consistent tri-radial symmetry. By contrast, cross-section of C. cf. paucistriatus can be four-ray symmetrical. It suggests that the general symmetry of the body in Coleoloides , of either a stable radial or bilateral type, is unlikely reflected by morphology of the tube.

Phylum Foraminifera d’Orbigny, 1826

Class, order, and family uncertain

Genus Platysolenites Pander, 1851

Type species: Platysolenites antiquissimus Eichwald, 1860 ; lower Cambrian (Terreneuvian Series); near Kunda, Estonia .

Figures

Fig. 67. Anabaritids, internal moulds (A–F) and other problematic tubes G–I) from the lower Cambrian Kessyusa Group (B–D, H, I) and Erkeket Formation (A, E–G), Khorbusuonka River, Siberia, Russia; samples 11/16.05 (A), 11/2B (E, F), 15/23 (B–D, H, I), and 20/1B (G). A. Anabarites tristichus Missarzhevsky in Rozanov et al., 1969, SMNH X11315. A1, transversal view of the tube; A2, lateral view. B. Anabarites hexasulcatus (Missarzhevsky, 1974), SMNH X11316. C. Selindeochrea ternaria Missarzhevsky inRozanov etal.,1969),SMNHX11317.D.Cambrotubulus sp., SMNH X11318.E, F. Anabarites korobovi (Missarzhevsky in Rozanov and Missarzhevsky, 1966), SMNH X11319 and 11320, respectively. G. Coleolella billinsi (Sysoev, 1962), SMNH X11321. H, I. Platysolenites antiquissimus Eichwald, 1860, SMNH X11322 and 11323, respectively. Scale bar: 250 µm (A) and 500 µm (B–I).

Fig. 68. Problematicum Coleoloides Walcott, 1889, internal moulds of tubes, from the lower Cambrian Erkeket (C, D), Tyuser (M), and Pestrotsvet (A, B, E–L) formations,Siberia, Russia; samples 11/2B (C) and 11/16.1 (D) from Khorbusuonka River; sample 21/22 (M) from lower reachesof Lena River;sample M303/2 (B, H, J, L) from Tiktirikteekh Brook (Rozanov et al. 1969: 31, text-fig. 6), sample 171–174 (E) from Bydyangaya Brook (Val’kov 1982: 27, textfig. 8) middle reaches of the Lena River, sample 479a (K) from section “Dvortsy”,Aldan River, and sample 510 (A, F, G, I) from section Ulakhan-Sulugur, Aldan River (Fig. 1). A–C, K–M. Coleoloides trigeminatus Missarzhevsky in Rozanov et al., 1969, SMNH X11324–11329, respectively.D. Coleoloides sp., SMNH X11330. E–J. Coleoloides cf. paucistriatus Poulsen,1967, SMNH X11331–11336, respectively.A1, B2, C2, E1, F2, G1, H2, I1, L2, lateral view;A2, B1, C1, F1, H1, L1, transversal view; E2, G2, I2, transversal view in the apical part. Scale bar: 500 µm (M) and 250 µm (A–L).

Fig. 1. Locality maps. A. Map of the Siberian Platform. B. Khorbusuonka River. Localities referred to in the main text: 96-1, 96-2, 96-3, Malaya Kuonamka (MK) and 96-6, 96-7, 96-8, Bol’shaya Kuonamka (BK) rivers, eastern flank of the Anabar Uplift; 3, 11, 15, 19, 20, Khorbusuonka River, Olenyok Uplift; 21, 22, Lena River lower reaches, Ulakhan-Ald’yarkhay Brook; Le, Lena River middle reaches, Tiktirikteekh and Bydyangaya Brooks; Al, Aldan River, between sections “Dvortsy” and Ulakhan- Sulugur. Margin of the Siberian Platform is shown by a dashed line in A.