Halkieria spp.

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 : 382-384

Halkieria spp.

Fig. 46.

Material.—Over 50 fragmentary phosphatized sclerites and internal moulds, including figured SMNH X5812–5827, from samples 1/29.2, 1/22, 1/6 (section 1, Fig. 4 ), K1a/35A, K1a/67 (section 2, Fig. 1), K2/26, K2/60, K2, 3/12.2, 3/22.5 (section 3, Fig. 3), 5a/6, 5a/18.5, 5a/34.5, 5a/34.75 (section 96-5a, Fig. 2 ), upper Nemakit-Daldyn, Medvezhya, Kugda-Yuryakh, and Emyaksin formations, Anabar Uplift, Siberian Platform, Russia; correlated with the upper Fortunian and lower part of Cambrian Stage 2.

Discussion.—The majority of sclerites, represented by 35 internal and external moulds and fragments of the wall, are identified as cultrate sclerites referred to Halkieria sp. type A (Fig. 46A, B, I, M, N). They are 2.5–3 times longer than wide, with a flattened broadly triangular cross-section through the sclerites and an irregularly narrow oval cross-section through the lumen (as replicated by internal moulds). The sclerites are gently S-shaped, with the distal end directed dorsally. A distinct median ridge extends from the basal foramen to the pointed distal tip on the upper (dorsal) side, where it is joined by longitudinal ribs and striae. Whereas the dorsal surface is convex in cross-section, the ventral surface is flattened to slightly concave with thin and frequent transverse terraces oriented subparallel to the edge of the foramen. The oval foramen is 1/4 of the maximal sclerite width. The basal part of many sclerites is deflected 60‒90° to the blade of the sclerite. The inner surface of the wall may also be covered with small pits, as replicated by tubercles on the internal moulds (Fig. 46A 2). The sclerites are similar to those described as the cultrate sclerites of H. sacciformis (Meshkova, 1969) by Parkhaev and Demidenko (2010) and of H. trianguliformis Mambetov in Missarzhevsky and Mambetov, 1981 from Malyi Karatau ( Kazakhstan).

The five cultrate sclerites of Halkieria sp. type B from samples 5a/34.5 and 5a/34.75 (Fig. 46E, F) are fragments of internal moulds (length/width ratio ˃ 3.0). The main

Fig. 46. Sclerites of Halkieria spp. from early Cambrian Nemakit-Daldyn (H, L), Medvezhya (I, G, M–O), Kugda-Yuryakh (A, B, J), and Emyaksin (C–F, → K, P) formations, Anabar Uplift, Siberia, Russia; samples K2/60 (A, B, J) and K2/26 (G), section 3; K1a/35A (H, L), section 2; 1/22 (I, M, O) and 1/ 29.2 N), section 1; and 5a/34.5 (C–F, K, P), section 96-5a. A, B, I, M, N. Halkieria sp. type A, cultrate sclerites, SMNH X5812, 5813 (A, B, respectively), SMNH X5816 (I), SMNH X5822 (M), SMNH X5823 (N). A 1, transversal view of internal mould; A 2, close-up showing tuberculate ornamentation of internal mould; A 3, I 1, M, view of upper (dorsal) side of calcium phosphatic internal moulds; I 2, lateral view; B, upper view of internal mould fragment; N 1, view of lower (ventral) side of phosphatized sclerite; N 2, view of base; N 3, transverse view of opposite broken end. C, D, G, J, O. Halkieria sp. , phosphatized sclerites, SMNH X5814, 5815 (C, D, respectively), SMNH X5819 (G), SMNH X5825 (J), SMNH X5824 (O). E, F. Halkieria sp. type B, calcium phosphatic internal moulds of cultrate sclerites, SMNH X5817, 5818, respectively. E 1, lateral view; E 2, F 1, view of lower (ventral) side; F 2, basal part enlarged. H, L. Halkieria sp. , dolomitised internal moulds, SMNH X5820, 5821, respectively. H 1, L 1, lateral views; H 2, L 2, views of lower (ventral) side. K, P. Halkieria sp. type C, calcium phosphatic internal moulds of presumed palmate sclerites, SMNH X5826, 5827, respectively. K 1, view of apical part; K 2, view of lower (ventral) side; P 1, lateral view; P 2, view of upper (dorsal) side. C 1, apical; C 2, D 1, O 1, lateral; C 3, D 2, G, J, O 2, lower (ventral) side views;. Scale bar 100 μm (A 2), 250 μm (C 2, D 1, G), 500 μm (A 1, A 3, C 1, C 3, D 2, E 1, F 2, J, K, P), 1 mm (H, L, M, N).

part (i.e., blade) is slightly arcuate, has a broadly lenticular cross-section, and intersects the elongate basal part at a right angle. The bases are asymmetrical and rounded triangular or rhomboidal in cross-section. Their foramen is probably elongately elliptical.

Halkieria sp. type C (Fig. 46K, P) is represented by three triangular, flattened, arcuate internal moulds of presumably palmate sclerites with slightly twisted distal parts. The basal part is narrow and elongate, but the detailed structure of this part of the sclerite is unknown. The moulds are covered with fine longitudinal striae.

Several sclerites of Halkieria sp. have a convex upper surface and a flattened lower surface. They are longitudinally bent up to 90° and have a blunt distal end. An oval foramen is situated in the middle of the rhomboidal base. The sclerites are divided by a low median ridge into two almost bilaterally symmetrical sides. A single elongate specimen Fig. 46C 1) has two additional low ridges parallel to the median ridge and a wall composed of transversely elongate laths (Fig. 46C 2). The oldest Halkieria sp. in the collections is from the upper Nemakit-Daldyn Formation (sample K1a/35A). These specimens are represented by two internal moulds composed of blocky dolomite (Fig. 46H, L).

Remarks.— Halkieria sp. is known from the upper Nemakit-Daldyn Formation (Fig. 46H, L) correlated with the upper Fortunian. Halkieria spp. are also reported from the upper Ust’-Yudoma Formation (30 m below its top, middle part of the Purella Zone ) in the Uchur-Maya region (Khomentovsky et al. 1990: pl. 4: 8, pl. 5: 1 – 4, pl. 6: 1, 2; Khomentovsky and Karlova 2005). The latter forms are reminiscent of Halkieria sp. type A sclerites from the Medvezhya Formation illustrated herein (see Fig. 46A, B, I, M, N). In South China, the oldest known halkieriids are from upper Assemblage Zone 2

Annelitellus yangtzensis – Obtusoconus honorabilis Subzone ; Yang et al. 2014). In Avalonia (southeast Newfoundland), Halkieria stonei Landing in Landing et al., 1989 occurs in the regionally oldest assemblages of the lower Watsonella crosbyi Zone (Landing 1992; Landing et al. 1989, 1998).

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. 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.