Oelandiella korobkovi Vostokova, 1962

Kouchinsky, Artem, Bengtson, Stefan, Landing, Ed, Steiner, Michael, Vendrasco, Michael & Ziegler, Karen, 2017, Terreneuvian stratigraphy and faunas from the Anabar Uplift, Siberia, Acta Palaeontologica Polonica 62 (2), pp. 311-440 : 331-332

Oelandiella korobkovi Vostokova, 1962

Figs. 6 , 7A–C, E , 8A, B .

Material.—Several hundred internal moulds, including figured SMNH Mo181931–181939, 181942–181944, from samples 1/50, 1/46, 1/45, 1/39.3, 1/29.2 (section 1, Fig. 4 ), K1a/27A, K1a/28A, K1a/82 (section 2, Fig. 1), K2/21, K2/22, K2/23, K2/24, K2/25, K2/26, 3/12, 3/12.2, 3/12.5 (section 3, Fig. 3), 5/10, 5/10B, 5a/1, and 5a/1.2 (sections 96-5 and 96- 5a, Fig. 2 ), Medvezhya and Emyaksin formations (SOM 1), Anabar Uplift, Siberian Platform, Russia. Correlated with upper Fortunian and lower part of Cambrian Stage 2.

Description.—Bilaterally symmetrical, tightly coiled up to one whorl, rapidly expanding and laterally compressed shell covered with distinct transverse rugae. Aperture elongate oval in outline, with length/width ratio 1.5–2.0, gently curved in sagittal plane. Subapical margin of aperture arched. Apical part of shell curved, indistinctly separated and projects slightly beyond the apertural margin. Supra-apical side (dorsum) long and evenly convex. Inner surface of the shell (as replicated by internal moulds) with distinct straight comarginal folds that cross the dorsum.

Remarks.—A potential synonymy of Oelandiella Vostokova, 1962 to Latouchella Cobbold, 1921 was first suggested by Missarzhevsky (in Rozanov et al. 1969 and Missarzhevsky 1989) and is followed by some authors (e.g., Parkhaev and Demidenko 2010: 1054). By contrast, Devaere et al. (2013) maintained the genus Oelandiella and extended its synonymy. It is also worth mentioning that Cobbold (1935) described a new species from the Montagne Noire under the name Latouchella angusta , which Devaere et al. (2013) placed in potential synonymy with O. korobkovi . Although L. costata and O. korobkovi clearly represent two different species, the distinction between the genera Latouchella and Oelandiella is currently weakly constrained.

Latouchella costata Cobbold, 1921 , was described from internal moulds from Cambrian Stage 3 of Avalonia (i.e., Shropshire, England). It differs from internal moulds of Oelandiella korobkovi Vostokova, 1962 , and O. sibirica Vostokova, 1962 , from Siberia mainly by the fact that the transverse ribs do not cross its dorsum ( Gubanov and Peel 1998, 1999), as well as by a narrower and more extended apex (compare Gubanov and Peel 1998: fig. 1A with Figs. 6A 1, B 1, 7E, and 8A 1 herein). The apices in L. costata from Shropshire and O. korobkovi from Siberia and China may be laterally deflected in slightly asymmetrical morphological variants (Qian and Bengtson 1989; Gubanov and Peel 1998, 1999; Parkhaev and Demidenko 2010). Gubanov and Peel (1999) also discussed variable density and regularity of the transverse ribbing on internal moulds of O. korobkovi .

Yang et al. (2014: fig. 18 C, D) and Devaere et al. (2013: fig. 4) illustrated internal moulds and conchs with coarse transverse rugae identical to those in our material. Herein, we accept that the O. korobkovi is also present in South China and France according to Devaere et al. (2013). Although Oelandiella –like forms first appear in the upper Nemakit-Daldyn Formation of the western Anabar Uplift (Fig. 9), internal moulds with coarse, high-amplitude, wellspaced corrugation ( Figs. 6A–E , 8A, B ) are only available herein from the upper Fortunian and Fortunian–Cambrian Stage 2 transitional beds represented by the Medvezhya and lower Emyaksin formations. These internal moulds were defined as Latouchella memorabilis (Rozanov et al. 1969; see also Parkhaev 2008: fig. 3.14 E, F), where they occur with other forms that have lower and denser transverse folds ( Fig. 7A, B ). By contrast, the conch of O. sibirica Vostokova, 1962 , was originally characterised as having an irregular alternation of differently expressed and tightly spaced transverse rugae (see Gubanov and Peel 1999). We concur with the latter authors and find the differences insufficient to differentiate these species. Indeed, some of the moulds of O. korobkovi have irregularly spaced and differently expressed transverse rugae ( Figs. 6F , 7C ). The ribbing in O. korobkovi from South China and France also appears to express a high degree of variability.

The lower stratigraphic range of O. korobkovi remains questionable, because the oldest material is usually represented by internal moulds of unsatisfactory preservation often referred to as Oelandiella sp. or Bemella sp. Such forms, Oelandiella ? sp. and Bemella ? sp. (Fig. 9) are available in our collection from the upper Nemakit-Daldyn Formation. In our material, the upper range of O. korobkovi overlaps with Watsonella crosbyi and extends into Cambrian Stage 2 (SOM 1). Undoubted O. korobkovi are not identified from Cambrian Stage 3, or trilobite-containing beds; thus, the species probably disappears in the upper part of Cambrian Stage 2 on the Siberian Platform.

Stratigraphic and geographic range.—Upper Fortunian and Cambrian Stage 2; Siberian Platform and Altai-Sayan Folded area, western Mongolia, and Gondwana (South China, France, and Iran).

Figures

Fig. 6. Helcionellid mollusc Oelandiella korobkovi Vostokova, 1962, internal moulds, from early Cambrian Medvezhya Formation, Kotuj River, section 3, western Anabar Uplift, Siberia, Russia; samples K2/25 (A–C), 3/12.2 (D), K2/26 (E), and K2/24 (F). A–F. SMNH Mo181931–181936, respectively. A1, B1, C, D2, E2, F1, lateral views; A2, B3, D1, E3, apertural views; A3, B2, E1, subapical views; F2, upper view. Scale bar 1 mm.

Fig. 7. Helcionellid molluscs, internal moulds, from early Cambrian Medvezhya Formation, Kotuj River, section 1, western Anabar Uplift, Siberia, Russia; samples 1/50 (A, B), 1/46 (C, F), 1/45 (D), and 1/29.5 (E). A–C, E. Oelandiella korobkovi Vostokova, 1962, SMNH Mo181937–181939 (A–C, respectively), SMNH Mo181942 (E). D, F. Securiconus cf. simus Jiang, 1980, SMNH Mo181940 and 181941, respectively. A1–D1, E, F, lateral views; A2, B3–D3, apertural views; A4–C4, D2, subapical views; A3, B2, C2, upper views. Scale bar 1 mm.

Fig. 8. Helcionellid molluscs, internal moulds, from early Cambrian Emyaksin Formation, Bol’shaya Kuonamka River, section 96-5a, eastern Anabar Uplift, Siberia, Russia; sample 5a/1.2. A, B. Oelandiella korobkovi Vostokova, 1962, SMNH Mo181943 and 181944, respectively. C, E. Oelandiella korobkovi? Vostokova, 1962, SMNH Mo181945 and 181947, respectively. D. Securiconus cf. simus Jiang, 1980, SMNH Mo160411 (see also Kouchinsky 2000a: fig. 6A–F). A1, B, C2, D1, E2, lateral views; A2, E1, D2, subapical views; A3, C3, apertural views; E3, D3, upper views; C1, close-up of subapical area with polygons. Scale bar 125 μm (C1) and 1 mm (A, B, C2, C3, D, E).

Fig. 4. The δ13Ccurve for Kotuj River section 1and sampled horizons with fossiliferous samples (arrows with numbers). Shift in stratigraphic column carb at Nemakit-Daldyn–Medvezhya formations contact indicates position of sequence boundary. Stratigraphic ranges and first appearances of fossils (see SOM 1): 2, Oelandiella korobkovi; 3, Securiconus cf. simus; 4, Bemella jacutica?; 8, Anabarella plana; 9, Watsonella crosbyi; 10, Pseudoyangtzespira selindeica; 11, Aldanella crassa; 13, Aldanella attleborensis; 15, Philoxenella spiralis; 16, Barskovia hemisymmetrica; 18, Khairkhania cf. evoluta; 19, Ceratoconus striatus; 21, Salanyella cf. costulata; 23, Purella cristata; 25, Yunnanopleura sp.; 26, Obscurania auriculata; 29, Protoconus cf. crestatus; 32, Siphogonuchites triangularis; 34, Lopochites sp.; 37, first appearance of Halkieria sp.; 39, first appearance of Chancelloria sp.; 40, Tianzhushanella sp.; 42, Khetatheca cotuiensis; 46, Turcutheca sp.; 48, Orthothecid operculum type A; 52, Fomitchella infundibuliformis; 57, Hyolithellus sp.; 62, Selindeochrea missarzhevskyi; 63, Selindeochrea ternaria; 64, Anabarites trisulcatus; 67, Anabarites kelleri; 68, Anabarites biplicatus; 71, Anabarites hexasulcatus; 74, Tiksitheca licis; 75, Cambrotubulus decurvatus; 76, Platysolenites antiquissimus; 77, Blastulospongia sp.

Fig. 2. Composite δ13Ccurve for the Bol’shaya Kuonamka River sections 96-4, 5, and 5a and sampled horizons with fossiliferous samples (arrows with carb numbers). Arrow 4/4 indicates “marker bed with angustiochreids” (Val’kov 1975; Kouchinsky et al. 1999). For section 96-6 see Kouchinsky et al. (2001, 2015a). Shift in stratigraphic column at Manykay–Emyaksin formations contact indicates position of sequence boundary. Stratigraphic ranges and first appearances of fossils (see SOM 1): 1, first appearance of helcionellid molluscs; 2, Oelandiella korobkovi; 3, Securiconus cf. simus; 6, Obtusoconus vostokovae; 7, Obtusoconus cf. mirabilis; 8, Anabarella plana; 13, Aldanella attleborensis; 14, Aldanella cf. sibirica; 22, Purella antiqua; 24, Yunnanopleura accurata; 34, Lopochites sp.; 35, Tianzhushania longa; 37, first appearance of Halkieria sp.; 38, Chancelloria symmetrica; 42, Khetatheca cotuiensis; 44, Conotheca cf. mammilata; 46, Turcutheca sp.; 47, Cupitheca sp.; 50, Orthothecid operculum type C; 51, Protohertzina anabarica; 52, Fomitchella infundibuliformis; 53, Fomitchella aff. infundibuliformis; 54, Fomitchella acinaciformis; 55, Fomitchella aff. acinaciformis; 56, Hyolithellus vladimirovae; 57, Hyolithellus sp.; 60, Selindeochrea cf. tecta; 61, Selindeochrea tripartita; 62, Selindeochrea missarzhevskyi; 63, Selindeochrea ternaria; 64, Anabarites trisulcatus; 65, Anabarites latus; 66, Anabarites natellus; 67, Anabarites kelleri; 68, Anabarites biplicatus; 69, Anabarites tristichus; 70, Anabarites compositus; 71, Anabarites hexasulcatus; 72, Anabarites hariolus; 73, Aculeochrea rugosa; 74, Tiksitheca licis; 75, Cambrotubulus decurvatus; 76, Platysolenites antiquissimus.