Protohertzina anabarica Missarzhevsky, 1973
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publication ID |
https://doi.org/ 10.4202/app.00289.2016 |
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persistent identifier |
https://treatment.plazi.org/id/03AD87A8-FFCE-6D7E-FFF3-FAB5644F879F |
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treatment provided by |
Felipe |
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scientific name |
Protohertzina anabarica Missarzhevsky, 1973 |
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Protohertzina anabarica Missarzhevsky, 1973
Figs. 56–58 View Fig View Fig .
Material.—Thirty-five phosphatic sclerites from the topotype locality M419 (section 2 herein), at the mouth of the Kotujkan River, including SMNH X5888–5906, from samples M419/12, K1b/8, K1b/13, 2/4, and 2/7 (section 2, Fig. 1), lower Nemakit-Daldyn Formation, Anabarites trisulcatus Zone ; and three specimens, SMNH X5907–5909, from sample 96-4/4 (section 96-4, Fig. 2 View Fig ), middle Manykay Formation, Angustiochrea lata Zone (Val’kov1975),Anabar Uplift, Siberian Platform, Russia. Correlated with the lower part of the Fortunian Stage.
Description.—Simple, bilaterally symmetrical, spine-shaped apatitic sclerites, up to 3 mm long, gently curved in the sagittal plane (fragments without basal part) but up to 90° curvature in base–tip transition (in more complete, longer specimens), cross-section continuously expands from the tip towards the flared basal part. Internal cavity extends into the tip. Convex side of sclerite is rounded, smooth, with single, shallow, basal furrow ( Figs. 56C View Fig 2 View Fig , 57G 1). Opposite, longitudinally concave side of sclerite with well-defined median ridge bordered by two usually distinct lateral ridges. Cross-section, with more or less pronounced ridges, varies from broad to narrow depending on growth stage. Ridges become more prominent gradually towards the broader basal part of sclerite, apex (tip), where the cross-section is somewhat elongated in the sagittal plane. Wall composed of multiple layers of fibres longitudinally oriented on outer surface of sclerites ( Figs. 56E View Fig , 57F 1).
Remarks.—According to Missarzhevsky (1973: 54), the holotype came from sample M41/12 from the Nemakit-Daldynian Stage in the western Anabar Uplift. However, this number is a typographic error, because section M41 is located on the middle Lena River (Churan) and its basal beds belong to the Dokidocyathus regularis Zone of the middle Tommotian Stage (Rozanov et al. 1969). The correct sample number is thus M419/12 (section 2 herein, see Fig. 1, SOM 1). The 1.2 mm-long holotype illustrated by Missarzhevsky (1973: pl. 9: 1, 2) is now lost and probably represented a fragment with a broken-off basal part. Missarzhevsky (1973) mentioned the variable morphology of Protohertzina anabarica in the first description of the species. The morphological variations of P. anabarica sclerites from the topotype material illustrated in this study ( Figs. 56 View Fig and 57; samples M419/12, K1b/8, K1b/13, and 2/7) support these earlier observations and are assigned to that same species.
In the topotype material, more compressed forms co-occur with more rounded ones as described by Missarzhevsky (1973: fig. 3). The flared basal part is often not preserved and thus only slender spinose distal fragments remain. Those with broad basal parts are similar to P. robusta Qian, 1977 , and apparently, Hertzina pensa Khomentovsky, Didenko, and Pyatiletov, 1982 , which was described from the uppermost Nemakit-Daldyn Formation (Koril Member). Protohertzina anabarica internal moulds also occur in the middle Manykay Formation of the eastern Anabar Uplift ( Fig. 58 View Fig ). The slender
Fig. 55. Opercula of orthothecid hyoliths type C (A, B, D, F, J) and type D (G, H), and undetermined (C, E, I), from early Cambrian Medvezhya (B–D, → F, G) and Emyaksin (A, E, H) formations, Anabar Uplift , Siberia , Russia; samples K2/22 (G, H), section 3; 5/10 (F), 5/10B (J), section 96-5; 5a/1.2 (I), a/34.75 (A), section 96-5a; M314/12 (B–D, F), Fomitch River section. A, B, D, F, J. Partly phosphatized of opercula, SMNH Mo 160464 (A; see also Kouchinsky 2000b: fig. 7A), SMNH X5880 View Materials (B), SMNH X5882 View Materials (D), SMNH X5883 View Materials (F), SMNH X5886 View Materials (J). D and F represent calcium phosphatic coatings of inner surface of opercula viewed from external (D) and visceral (F) surfaces; B 1, D 2, lateral; A, B 3, D 3, J, apical views; views of dorsal (B 2, D 1) and ventral (B 4) margins; F 1, view of inner surface of operculum; F 2, oblique view of dorsal margin. C. Partly phosphatized operculum, SMNH Mo160469 (see also Kouchinsky 2000b: fig. 7M). C 1, lateral; C 2, apical views; C 3, view of presumably ventral margin. E, I. Calcium phosphatic internal moulds of opercula, SMNH X5884 View Materials (E), SMNH X5887 View Materials (I). E 2, I 2, apical; E 1, lateral views; I 1, view on the lower (presumably ventral) margin, as in I 2. G, H. Dolomitized internal mould of opercula, SMNH X5885 View Materials (G), SMNH X5881 View Materials (H). G, lateral; H, apical views. Scale bar 500 μm (A–F, I, J), 1 mm (G, H) .
forms with a less robust appearance and narrower rounded basal part ( Figs. 56A–E, H View Fig , 57A–G, K, 58B) are similar to P. unguliformis Missarzhevsky, 1973 , first described in the same publication by Vladimir V. Missarzhevsky from the basal Pestrotsvet Formation in the Yudoma-Maya region, southeastern Siberian Platform, and subsequently reported worldwide (P. unguliformis- type sclerites) often in association with P. anabarica (or P. anabarica -type sclerites). According to the original descriptions by Missarzhevsky 1973: 55), P. anabarica differs from P. unguliformis in having a more isometrical cross-section, a less strongly defined median keel, and distinctly expressed lateral ribs. More or less slender topotype specimens are however treated herein under P. anabarica , given the morphological variability of P. anabarica sclerites noted in their original description, and a significantly younger age of the topotype material of P. unguliformis from the southeastern Siberian Platform which needs further study. The wall of P. anabarica elements is composed of very elongate, needle-like crystallites with a longitudinal orientation (e.g., Fig. 57F 1, I 1, I 2).
Fig. 57. Protoconodonts Protohertzina anabarica Missarzhevsky, 1973 . P. anabarica - type sclerites (H–J) and P. unguliformis - type sclerites (A–G, K), → from early Cambrian Nemakit-Daldyn Formation, western flank of the Anabar Uplift, Siberia, Russia; sample 2/7, section 2. A–K. SMNH X5896–5906, respectively. Note longitudinal fibres exposed on the lateral side (F 1) of sclerite. Scale bar 250 μm (A–D, F 1, G, H, J), 500 μm (E, F 2, I, K).
Stratigraphic and geographic range.— Terreneuvian Series; Siberia, Laurentia ( Conway Morris and Fritz 1980; Nowlan et al. 1985; McIlroy and Szaniawski 2000; Pyle et al. 2006), Kazakh Terrains, western Mongolia, Gondwana (South China, Iran, India; Missarzhevsky 1973; Qian and Bengtson 1989; Brasier and Singh 1987), and Avalonia (Landing et al. 1989). See also Parkhaev and Demidenko (2010) and Kouchinsky et al. (2012: online appendix 1).
| SMNH |
Department of Paleozoology, Swedish Museum of Natural History |
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