Ceratoconus striatus Chen and Zhang, 1980

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 : 355

Ceratoconus striatus Chen and Zhang, 1980

Figs. 26, 27.

Material.—About 150 phosphatic internal moulds, including figured SMNH Mo182297–182302, from samples 1/39.3, 1/46 (section 1, Fig. 4 ), 3/12, 3/12.2, and K2/25 (section 3, Fig. 3), Medvezhya Formation, western flanks of the Anabar Uplift and 20 phosphatic internal moulds, including figured SMNH Mo182303–182306, from samples B-438 and 769, lower Emyaksin Formation, Kengede River, southern flank of the Anabar Uplift, Siberian Platform, Russia. Correlated with the upper Fortunian Stage.

Description.—Long, narrow, conical, ceratoconic shell curved up to 1/4 whorl in one plane with broad oval aperture. Apex conical with a blunt rounded tip. Protoconch not clearly separated. Inner shell surface (as replicated on internal moulds) is smooth or with low‒moderately high transverse folds. Aperture with subapical sinus ( Fig. 27A 2 ). Remarks.—These internal moulds are identical to those of Ceratoconus rusticus (Val’kov, 1987) and C. arcuatus Missarzhevsky, 1989 . Forms with larger and bulbous protoconch (see Ceratoconus aff. striatus below, Fig. 28 ) co-occur with those having more pointed apices (Figs. 26, 27). Both such forms were attributed to Ceratoconus striatus Chen and Zhang, 1980 , by Parkhaev in Rozanov et al. (2010: pl. 29: 7, 8). As recognized herein, C. striatus has more elongated internal moulds with more subdued transverse folds than specimens of C. striatus from South China. Ceratoconus aff. striatus more likely represents a separate species and can be distinguished by a wider and more rounded initial part (protoconch?) and a greater angle of shell expansion.

Stratigraphic and geographic range.— Upper Fortunian and Cambrian Stage 2 of Siberian Platform, South China, and western Mongolia.

Figures

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. 27. Mollusc Ceratoconus striatus Chen and Zhang, 1980, internal moulds, from early Cambrian Emyaksin Formation, Kengede River section, southern Anabar Uplift, Siberia, Russia; samples B-438 (A) and 769 (B–D). A–D. SMNH Mo182303–182306, respectively. A2, subapical; A1, B, D, lateral; C, supra-apical views. Scale bar 500 μm.

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.

Fig. 28. Mollusc Ceratoconus aff. striatus Chen and Zhang, 1980, internal moulds, from early Cambrian Medvezhya Formation, Kotuj River, western Anabar Uplift, Siberia, Russia; samples 3/12.2 (A–C, E), 3/12 (D), and K2/25 (F–H) from section 3. A–H. SMNH Mo182307–182313 (A–G respectively), SMNH Mo160413 (H) (compare H with Kouchinsky 2000a: fig. 7A–G). A1–D1, supra-apical; A2–D2, E–H, lateral; D3, subapical views; A3, apertural area with polygons enlarged. Scale bar 200 μm (A3), 500 μm (A1, A2, B–H).