Chancelloria symmetrica, Li and Chen, 1992

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 : 384

Chancelloria symmetrica Vasil’eva, 1985

Fig. 47A, B, F .

Material.—Single 7+1 sclerite from sample 5a/18.5; single 8+1 and three 6–7+1 sclerites from 5a/34.5; 7+1, 8+1 and 9+1 sclerites from 5a/34.75 (section 96-5a, Fig. 2 ); single 7+1 sclerites from samples 1/6 (section 1, Fig. 4 ) and K2, as well as several disarticulated sclerites from K2/60 (section 3, Fig. 3), including figured SMNH X5828, 5829, and 5833, from the Kugda-Yuryakh and Emyaksin formations, Anabar Uplift, Siberia, Russia. Correlated with Cambrian Stage 2.

Description.—Articulated sclerites consist of 6–8 lateral rays gently curved away from the plane of the basal facet and the one central ray ( Fig. 47A, F ). The rays are enlarged at their bases. Base of the central ray 1.5‒2.0 times greater in diameter than the lateral ray bases. Basal facet of each ray flattened, covered with a polygonal network ( Fig. 47B ), and has a central foramen. Facets of the rays lie on a shared, flattened basal surface.

Remarks.— Chancelloria symmetrica was described by Vasil’eva (1985) from the Cambrian Stage 2 equivalent beds of the Siberian Platform. Conspecific forms are reported from western Mongolia, Australia, and South China (Parkhaev and Demidenko 2010: 901), although the assignment of sclerites from South China to C. symmetrica by Parkhaev and Demidenko (2010) was questioned by Moore et al. (2014). Chancelloria cf. eros Walcott, 1920 , described from the Emyaksin Formation (Kouchinsky et al. 2015a), is different from C. symmetrica in having relatively longer, slim rays which are much less inflated at their bases. A polygonal microstructure on the basal facet of one articulated sclerite ( Fig. 47B ) is similar to the botryoidal microstructure observed in other chancelloriid sclerites (see Bengtson et al. 1990; Moore et al. 2014).

Figures

Fig. 47. Sclerites of Chancelloria from early Cambrian Emyaksin (A, B) and Kugda-Yuryakh (D, E, F) formations, and a problematic sclerite from Medvezhya Formation (C), Anabar Uplift, Siberia, Russia; samples 5a/34.5 (A, B), section 96-5a; K2/21 (C), K2/60 (D, E), and K2 (F), section 3. A, B, F. Chancelloria symmetrica Vasil’eva, 1985, SMNH X5828, 5829 (A, B, respectively), SMNH X5833 (F). A, F, calcium phosphatic internal moulds; B, basal surface of internal mould with outer phosphatic coating of the wall. C. Calcium phosphatic internal mould of a problematic sclerite, SMNH X5831. C1, lateral view; C2, basal part enlarged. D, E. Chancelloria sp., fragmentary internal moulds of central rays, SMNH X5830 (D), SMNH X5832 (E). Scale bar 125 μm (C2), 250 μm (A, B, C1, E), 1 mm (D, F).

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. 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.