Aldanella crassa Missarzhevsky, 1969

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 : 347

Aldanella crassa Missarzhevsky in Rozanov et al., 1969

Fig. 18 .

Material.—About 150 phosphatic internal moulds, including figured SMNH Mo182246–182252, from samples 1/50 (section 1, Fig. 4 ), K2/12, K2/13, and 3/6.5 (section 3, Fig. 3), Medvezhya Formation, western Anabar Uplift, Siberian Platform, Russia. Correlated with the uppermost Fortunian Stage.

Description.—Very rapidly expanding, dextrally coiled shell, up to 3.0 mm in diameter, consists of up to 1.5 whorls. Adapical and umbilical surfaces of the whorl gently convex, spire flat or slightly protrudes above the last whorl. Lateral surface of the whorl broadly rounded. Apertural cross-section an asymmetrical broad oval (width/height ratio 1.6–1.9) that is more strongly convex on the umbilical than the adapical side. Sculpture of the shell interior (as replicated on internal moulds; Fig. 18A 1, D) consists of irregular, low transverse folds. Protoconch not clearly delimited, with a

→ Fig. 17. Mollusc Pseudoyangtzespira selindeica Bokova, 1990 (F topotype), internal moulds, from early Cambrian Kugda-Yuryakh Formation , Kotuj River , western Anabar Uplift ; samples K1a/67 (A), section 2; 1/6 (B–E), section 1; S1 (F), Selinde section, southeastern Siberian Platform, Russia. A–F. SMNH Mo182240–182245, respectively. A 1, E 1, F 1, adapical; A 2, B 2, C, D, E 2, F 2, apertural; B 1, umbilical views. Scale bar 500 μm (A, C–F) and 1 mm (B) .

diameter of 140–170 μm. Apex of internal moulds bluntly rounded and sometimes with rounded polygonal imprints 20–40 μm in diameter ( Fig. 18B 2 ).

Remarks.—Similar to Aldanella attleborensis , the species is, however, generally larger with a higher expansion rate and has a larger protoconch. Aldanella crassa in our material from sections 1 and 3 derives from older beds than A. attleborensis (see SOM 1 for species ranges). This is in agreement with Missarzhevsky (1982, 1989) and Parkhaev and Karlova (2011), who mentioned that A. crassa occurs in slightly older beds. The type material for this species was described by Missarzhevsky (in Rozanov et al. 1969) from sample M410/73 from the Ary-Mas-Yuryakh section (section 1 herein; Fig. 4 ).

Figures

Fig. 18. Mollusc Aldanella crassa Missarzhevsky in Rozanov et al., 1969, internal moulds, from early Cambrian Medvezhya Formation, Kotuj River, western Anabar Uplift, Siberia, Russia; samples 1/50 (A, B, D–F), section 1; samples K2/13 (C) and 3/6.5 (G), section 3. A–G. SMNH Mo182246– 182252, respectively. A1, B1, C2, D, E1, F, G1, adapical side; E2, oblique adapical view; A3, oblique umbilical side; A2, B3, C1, G2, apertural views; B2, close-up of apex with polygonal relief. Scale bar 200 μm (B2), 500 μm (A, B1, B3), and 1 mm (C–G).

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.