Purella antiqua ( Abaimova, 1976 )

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 : 364

Purella antiqua ( Abaimova, 1976)

Figs. 31, 32, 33A–F, H.

Material.—Over 500 phospatic internal moulds with fragments of phosphatized shells, including figured SMNH Mo160403, 160406, 182323–183337, from samples 4/27.5, 5/0, 5/0.25 (sections 96-4 and 96-5, Fig. 2 ), 2/A, 1282, K1a/43, and K1a/47 (section 2, Fig. 1), from the upper Manykay, Nemakit-Daldyn, and basal Emyaksin formations (SOM 1), Anabar Uplift, Siberian Platform, Russia. Correlated with the Fortunian Stage.

Description.—Shell low, conical, with blunt apex that does not project beyond the apertural margin. Aperture ovoid with length/width ratio 1.3–1.5. Dorsal side with a broad longitudinal fold (Fig. 34C 2). The shell is composed of comarginally elongated scales (Fig. 31). The apical area is externally smooth, without scales, and is composed of densely juxtaposed microtubules with radial orientation Kouchinsky 2000a; Figs. 31A, 32A).

Remarks.— Abaimova (1976) described the morphological variation of Purella antiqua conchs from a single sample collected from the same horizon and locality as samples 1282, 2/A, K1a/43, and K1a/47 (SOM 1). The assemblage of remains includes internal moulds with fragmentary phosphatized shells up to 1.5 mm long, sometimes bearing a median buttress rimmed by two shallow furrows. These molds are smooth at the apex, but concentrically sculptured distally, with a different shape of the aperture. The apices range from those with an almost central position of the apex to those with the apex overhanging the apertural margin (see variable position of the apex in Abaimova 1976: figs. 5, 8, 11, 15). Such a variation was suggested to distinguish Purella antiqua from “other helcionellids” ( Abaimova 1976: 175). One of the specimens illustrated by Abaimova (1976: pl. 20: 15) is similar to Stenothecoides accuratus Bokova, 1985 , described from the same locality and bed, but is identified in this report as Yunnanopleura accurata ( Bokova, 1985) (discussed below).

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

Figures

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.