Markuelia secunda

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 : 423

Markuelia secunda Val’kov in Val’kov and Karlova, 1984

Fig. 60 .

Material.—Single specimen, SMNH X11293, from sample 11/16.05, basal Erkeket Formation, Khorbusuonka River, Siberia, Russia. Dokidocyathus regularis Zone, Tommotian stage (correlated with the upper part of Cambrian Stage 2).

Remarks.—The fossil represents a phosphatised enrolled embryo (as described by Bengtson and Yue, 1997), whose worm-like segmented body is tightly coiled into a sphere, ca. 0.5 mm in diameter. Although tail spines are not revealed, as in the previously described material, presence of short, conical spines on trunk annuli suggests affinity with Markuelia secunda Val’kov in Val’kov and Karlova, 1984 (see Dong et al. 2010). Annuli are ca. 30 µm thick at the middle. The spines are 30–40 µm long. Different species of Markuelia reportedly occurs in the Cambrian Stage 2 of Siberia, Miaolingian Series of China and Australia, Furongian Series of China, and Lower Ordovician of Laurentia (Dong et al. 2010).

Globula of unknown affinity, 0.2–0.3 mm in diameter is found in the Kuonamka Formation, lower Mayan Stage beds (sample 19/5B, correlated with the lowermost Drumian Stage). It is phosphatised and deformed into a tri-lobate shape ( Fig. 69J ). The fossil is identical to the globulae reported from the Tommotian and Atdabanian Stages of the Anabar Uplift ( Kouchinsky et al. 2015a: fig. 73B).

Stratigraphic and geographic range.— Markuelia secunda is known from the upper part of Cambrian Stage 2, Siberian Platform, Russia.

Phylum Tardipolypoda Chen and Zhou, 1997

Class Xenusia Dzik and Krumbiegel, 1989

Order Scleronychophora Hou and Bergström, 1995

Family Eoconchariidae Hao and Shu, 1987

Genus Microdictyon Bengtson, Matthews, and Missarzhevsky, 1986

Type species: Microdictyon effusum Bengtson, Matthews, and Missarzhevsky, 1986 ; Rhombocorniculum cancellatum Zone , upper part of Cambrian Stage 3; Geres Member of the Shabakty Group, Ushbas River, Lesser Karatau, Kazakhstan.

Microdictyon robisoni Bengtson, Matthews, and Missarzhevsky, 1986

Fig. 61A .

Material.—Single sclerite, SMNH X11294, from sample 22/67, Sekten Formation, Lena River, Siberia, Russia. Kounamkites Zone, Amgan stage (correlated with the Wuliuan Stage).

Description.—Dome-shaped fragmentary sclerite with a maximum dimension of ca. 1 mm in the plan view and ca. 0.3 mm in height. Distinct, almost circular holes ranging from ca. 20 μm in diameter at the margin to 80 μm at the middle of sclerite, surrounded by 5–7 nodes. The nodes are expressed as cones with flattened tops shifted towards the centre of the sclerite. There is a narrow closed channel in each cone open at the base. Openings of the holes through the sclerite are each surrounded by a basal ring.

Stratigraphic and geographic range.—Wuliuan Stage in Siberia ( Russia) ( Kouchinsky et al. 2011) and Laurentia (Bengtson et al. 1986; Peel et al. 2016).

Figures

Fig. 60. Scalidophoran Markuelia secunda Val’kov in Val’kov and Karlova, 1984 from the Cambrian Erkeket Formation, Khorbusuonka River, Siberia, Russia; sample 11/16.05. Phosphatized enrolled embryo in different views (A1–A3), SMNH X11293. Scale bar 250 µm.

Fig. 69. Problematic fossils from the lower Cambrian Erkeket Formation, Khorbusuonka River, Siberia, Russia; samples 11/16.1 (K), 19/11.75 (A, I), 19/12.75 (B), 19/16 (D, F, G, H), 19/18 (C, E), and 19/5B (J). A. Tubular diagenetically phosphatised cyanobacterial trichomes, SMNH X11337. B–H. Problematic silicified tubes, SMNH X11338–11344, respectively. H2, enlargement showing presumably initial part of the tube. I. Problematic phosphatized tubes longitudinally merged, SMNH X11345. I1, close-up of I2, showing apertures of the tubes. J. Globula, SMNH X11346. K. Disk-like fossil, SMNH X11347. K1, plain view; K2, lateral view. Scale bar: 500 µm (B–G, H1), 250 µm (I2, J, K), 125 µm (I1), 50 µm (A, H2).

Fig. 61. Lobopodian (A) and bradoriid (B–D) calcium phosphatic fragments, from the lower Cambrian Erkeket Formation, Khorbusuonka River (B, C) and Tyuser (D), and Sekten (A) formations, lower reaches of the Lena River, Siberia, Russia; samples 19/3.25 (C), 19/31.75 (B), 21/57.75 (D), and 22/67 (A). A. Microdictyon robisoni Bengtson, Matthews, and Missarzhevsky, 1986, sclerite, SMNH X11294. B. Mongolitubulus spinosus (Hinz, 1987), spine, SMNH Ar75002. C. Mongolitubulus reticulatus Kouchinsky, Bengtson, Clausen, Gubanov, Malinky, and Peel, 2011, spine, SMNH Ar75003. D. Cambria sibirica Neckaja and Ivanova, 1956, carapace, SMNH Ar75001; D1, anterior view; D2, D3, dorsal view. Scale bar: 250 µm A–C) and 1.25 mm (D).