Leptostega hyperborea Parkhaev, 2005

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 : 431-433

Leptostega hyperborea Parkhaev, 2005

Fig. 12 .

Material.—Four incomplete calcium phosphatic internal moulds, including three figured specimens SMNH Mo 167667–167669 from sample 7/70. Uppermost Emyaksin

Formation, Bol’shaya Kuonamka River; Calodiscus -Erbiella Zone, lower Botoman Stage.

Description.—Laterally compressed shell nearly orthoconic shell, with sub-central or slightly inclined apex ( Fig. 12A 1 ). The length/width ratio at the apertural region is ca. 2.7. The inner shell surface (as reflected by internal moulds) carries strong and broad concentric folds, prominent on the narrow sides of the moulds. The aperture narrows slightly towards the sub-apical side.

Remarks.—The moulds were collected from the type beds of Leptostega hyperborea Parkhaev, 2005 (see Remarks for Mackinnonia anabarica ). L. hyperborea is reported from the Botoman and, probably, Amgan Stages (herein and Kouchinsky et al. 2011, respectively), thus, occurs within Stage 4—lower Drumian Stage of Siberia. Leptostega Geyer, 1986 was first described from the basal middle Cambrian of Spain ( Geyer 1986; see Kouchinsky et al. 2011: 133 for comparison of L. irregularis Geyer, 1986 with L. hyperborea ), Acadoparadoxides mureroensis Zone , lower Leonian Stage. The lower part of the zone can be correlated with the upper Toyonian Stage of Siberia ( Geyer 1998, 2005; Geyer and Landing 2004) and the Series 2/Series 3 transition.

Stratigraphic and geographic range.—Lower Botoman Stage and, probably, Amgan Stage, Siberian Platform.

Figures

Fig. 12. Helcionellid mollusc Leptostega hyperborea Parkhaev, 2005 internal moulds from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River, Anabar Uplift, Siberia; sample 7/70. A. SMNH Mo 167667; lateral (A1), oblique supra-apical (A2), and apertural (A3) views. B. SMNH Mo 167668; lateral (B1) and upper (B2) views. C. SMNH Mo 167669; lateral view. Scale bar 600 μm, except C, 1200 μm.

Fig. 1. Map showing location of sections 1, 3, Malaya Kuonamka River; 6, 7, Bol’shaya Kuonamka River.