Fengzuella zhejiangensis He and Yu, 1992

Kouchinsky, Artem, Bengtson, Stefan, Clausen, Sébastien & Vendrasco, Michael J., 2015, An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia, Acta Palaeontologica Polonica 60 (2), pp. 421-512 : 479

Fengzuella zhejiangensis He and Yu, 1992

Fig. 54 .

Material.—Single laterally flattened bilaterally symmetrical sclerite, SMNH X 4776, from sample 7/45 ( Fig. 54A ) and two curved bilaterally symmetrical sclerites, SMNH X 4777 and 4778, from samples 7/55.8, and 7/64 (respectively). Emyaksin Formation, Bol’shaya Kuonamka; correlated with the Delgadella anabara and Judomia zones, Atdabanian Stage. An additional specimen, SMNH X 4779, derives from sample 2001-11b, collected along the Sinyaya River, tributary of the Lena River in the middle reaches ( Rozanov and Missarzhevsky 1966), Atdabanian Stage, but the exact stratigraphic position of the sample is not known.

Description.—Calcium phosphatic sclerites of planispiral and curved types. The planispiral sclerite is ca. 0.3 mm in diameter and consists of 1¼ whorls. The curved sclerites are 0.5–0.8 mm long. Along each side of the sclerites, the wall has two longitudinal depressions separated from each other by a ridge. The central cavity extends from the aperture to the apex, and has an oval or rhomboidal, star-shaped cross-section with convex sides. The wall is multi-layered and consists of basally secreted and adapically overlapping thin growth lamellae ( Fig. 54A 4 , B 2 , D 4 ).

Remarks.— Steiner et al. (2003) noted that curved sclerites predominate (85%) and the planispiral type is rare. It has been also suggested that the scleritome consisted of densely packed growing sclerites with their proximal parts attached to a soft tissue. Presumably, the sclerites had originally a sclerotised organic (non-mineralised?) composition. The outer parts of the growth lamellae were deposited externally, probably within an invaginated tissue.

Stratigraphic and geographic range.—Problematic sclerites of Fengzuella zhejiangensis He and Yu, 1992 were originally described from South and North China, from beds that possibly correlate with the Anabarites trisulcatus – Protohertzina anabarica Assemblage Zone of the lower Meishucunian Stage ( Steiner et al. 2003). That correlation is not certain, however, and the beds might alternatively be correlated with the Qiongzhusian Stage of China and Atdabanian Stage of Siberia ( Steiner et al. 2003, 2007). A single planispiral sclerite similar to Fengzuella is reported, as a coiled and flat discoidal problematicum, from lower middle Cambrian strata of the Kuonamka Formation, Khorbusuonka River, Olenyok Uplift, Siberian Platform ( Müller et al. 1995: 114, fig. 5E, F). Planispiral and transitional sclerites of, probably, a new species of Fengzuella are also available from the upper Series 2 of Laurentia (North Greenland; AK and John S. Peel, unpublished observation).

Figures

Fig. 54. Problematicum Fengzuella zhejiangensis He and Yu, 1992 from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River,Anabar Uplift and middle Lena River, Siberia. A. Planispiral sclerite, SMNH X 4776, sample 7/45; A1, lateral view on the sclerite; A2 and A3, oblique views; A4, close-up of overlapping growth increments. B. Curved sclerite, SMNH X 4778, sample 7/64; B1, lateral view of the fragment; B2, close-up of B3; B3, view on the cross-section of sclerite, in the upper part of B1. C. Curved sclerite, SMNH X 4777, sample 7/55.8; C1, lateral view on the sclerite; C2, transversal view. D. Curved sclerite, SMNH X 4779, sample 2001-11b; lateral (D1), oblique transversal (D2), and oblique apical (D3) views; D4, close-up of the apical end of sclerite. Scale bar: 200 μm, except D1–D3, 300 μm; A4, B2, D4, 60 μm.

Fig. 4. Helcionellid mollusc Bemella? sp. internal moulds from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River,Anabar Uplift, Siberia; sample 7/36.7. A. SMNH Mo 167650; lateral (A1), apertural (A2), and sub-apical (A3) views. B. SMNH Mo 167651; lateral (B1) and upper (B2) views. C. SMNH Mo 167652; apertural (C1), lateral (C2), and sub-apical (C3) views. D. SMNH Mo 167653; D1, close-up of apertural margin in D3; upper (D2) and lateral (D3) views. Scale bar 1200 μm, except D1, 300 μm.

Fig. 2. Derivation of fossiliferous samples (arrows with numbers) and chemostratigraphic correlation of sections 1 and 3 (Malaya Kuonamka River) with sections 6 and 7 (Bol’shaya Kuonamka River). Correlation with carbon isotope features II–VII from stratotypes of south-eastern Siberian Platform (Brasier et al. 1994) according to Kouchinsky et al. (2001). Note that the zero level in all sections corresponds to the water level above which the sections were exposed in 1996. Description of fauna from the lower part of the Emyaksin Formation in complementary outcrops at the Bol’shaya Kuonamka River (below that zero level) will be published elsewhere. Fauna from the overlying Kuonamka Formation is published by Gubanov et al. (2004) and Kouchinsky et al. (2011).