Gapparodus bisulcatus ( Müller, 1959 )

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 : 477

Gapparodus bisulcatus ( Müller, 1959)

Fig. 53A–D .

Material.—Four illustrated sclerites, SMNH X 4764–4767, and 12 additional specimens from sample 1/9; carbonate concretions of the basal Kuonamka Formation, Malaya Kuonamka River; Bergeroniellus expansus Zone , upper Botoman Stage.

Description.—Slender, gently curved, simple bilaterally slightly asymmetrical, and laterally flattened calcium phosphatic sclerites. The longitudinally convex side of the sclerite has a strongly convex surface, whereas the opposite, longitudinally concave side is transversely gently convex or flattened. The two sides have almost the same width. Two longitudinal lateral furrows extend from the basal opening towards the tip. The internal cavity extends to the tip of sclerite. The wall has a lamellar fibrous structure ( Fig. 53D 2 ). Stratigraphic and geographic range.—The occurrence of Gapparodus bisulcatus reported herein from the lower part of Cambrian Stage 4 is the earliest known from the Siberian Platform, where it also occurs in Stage 5 (Kuonamka Formation, Malaya Kuonamka and Bol’shaya Kuonamka rivers; Müller et al. 1995; Kouchinsky et al. 2011). The species ranges from Series 2 through the Furongian Series in South and North China ( Dong and Bergström 2001; Babcock et al. 2007; Steiner et al. 2007). It is also known from the middle–upper Cambrian of Baltica ( Bengtson 1976; Müller and Hinz 1991), upper Series 2–Series 3 of Laurentia ( Clark and Miller 1969; Clark and Robison 1969; Landing 1974; John S. Peel, personal communication 2010), Cambrian of Western Gondwana ( Turkey, Özgül and Gedik 1973), upper Cambrian of Eastern Gondwana ( South Korea, Lee 1975), and middle–upper Cambrian of Kazakhstan ( Abaimova and Ergaliev 1975).

Figures

Fig. 53. Protoconodonts from lower Cambrian basal Kuonamka Formation, Malaya Kuonamka River and Emyaksin Formation, Bol’shaya Kuonamka River, Anabar Uplift, Siberia. A–D. Gapparodus bisulcatus (Müller, 1959), sample 1/9. A. SMNH X 4764; A 1, view on the longitudinally concave side and basal opening of sclerite; A 2, lateral view. B. SMNH X 4765; B 1, lateral view; B 2, view on the longitudinally concave side. C. SMNH X 4766; C 1, lateral view; C , oblique view on the longitudinally concave side and basal opening of sclerite; C , view on the longitudinally concave side. D. SMNH X 4767; D 1, lateral view; D 2, close-up of basal part of D 1. E. Amphigeisina danica (V. Poulsen, 1966), SMNH X 4763; sample 1/9; E 1, view on the basal →

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).