Paterinida, Rowell, 1965

Kouchinsky, Artem, Alexander, Ruaridh, Bengtson, Stefan, Bowyer, Fred, Clausen, Sébastien, Holmer, Lars E., Kolesnikov, Kirill A., Korovnikov, Igor V., Pavlov, Vladimir, Skovsted, Christian B., Ushatinskaya, Galina, Wood, Rachel & Zhuravlev, Andrey Y., 2022, Early-middle Cambrian stratigraphy and faunas from northern Siberia, Acta Palaeontologica Polonica 67 (2), pp. 341-464 : 370-373

Paterinida gen. and sp. indet.

Fig. 19 .

Material.—Five fragmentary calcium phosphatic ventral valves, including figured SMNH Br151269–151272, from samples 11/2B and 11/16.05, basal Erkeket Formation, Khorbusuonka River, Siberia, Russia. Dokidocyathus regularis Zone, Tommotian stage (correlated with the upper part of Cambrian Stage 2).

Description.—Ventral valve semicircular in outline, up to 1.4 mm wide and 1.2 mm long, strongly convex with prominent apex overhanging the posterior margin. Ventral interarea with a broad subtriangular delthyrium. The outer surface ornamented with concentric wavy folds superimposed with radially oriented plication and radial striation. Brephic ventral valve smooth almost circular, 700–800 μm in diameter, with straight posterior and rounded anterior margins, carries radial furrows terminating at the margins and probably representing setal canals.

Phylum, class, order, and family uncertain

Stem group Brachiopoda indet.

Fig. 20 .

Material.—Two shell fragments consisting of calcium phosphate, SMNH X11001–11002, sample 20/1B. Erkeket Formation, Khorbusuonka River, Siberia, Russia. Lower Botoman Stage (correlated with the lower part of Cambrian Stage 4).

Description.—Both fragments have the same prismatic columnal microstructure consisting of tightly packed continuous prismatic columns, ca. 10 μm in cross-section, oriented perpendicularly to the shell surface. Prisms tightly packed, with density ca. 100 prisms per 0.01 mm 2, up to 200 µm in length, do not branch or anastomose, tetragonal (mostly rectangular) or rarely triangular in cross-section. In the plan view, adjacent prisms tend to be aligned and form parallel and concentric sets on the shell surface. Imbricated growth increments have serrated margins, where protruded parts house openings of the tangential canals, 40–50 μm in diameter, running sub-parallel to the surface of growth lamellae in radial direction with respect to the shell margin. Narrower orthogonal canals, 10–15 µm in diameter, are sub-perpendicular to lamination. Their openings are scattered on the shell exterior and some of them are located within openings of the tangential canals.

Remarks.—The fossil is represented by presumably marginal anterior ( Fig. 20A ) and subapical posterior ( Fig. 20B ) shell fragments. The shell fragments are ca. 2 mm each and their morphology suggests ca. 10 mm diameter of the shell. The prismatic microstructure of the wall is homologous to the layer with compact lamination in the wall of Oymurania gravestocki Ushatinskaya in Kouchinsky et al., 2015 ( Kouchinsky et al. 2015b; Kouchinsky and Bengtson 2017). Shell prisms in Oymurania are however mainly hexagonal and irregularly spaced in the plan view. In having prismatic microstructure of the wall and two sub-perpendicular sets of canals, the new form is most similar to Oymurania , but the overall shell morphology is yet unknown. Unlike other stem-group brachiopods, such as Oymurania Ushatinskaya in Kouchinsky et al., 2015 and Setatella Skovsted, Streng, Knight, and Holmer, 2010 , and linguliform brachiopods ( Williams and Holmer 1992; Cusack et al. 1999; Williams and Cusack 1999) as well as more basal representatives of stem group brachiopods, such as tannuolinids Tannuolina Fonin and Smirnova, 1967 , and Micrina Laurie, 1986 , the acrotretoid columnar microstructure was not observed in this study. However, a comparable prismatic shell structures lacking acrotretoid columns have been documented from tommotiids such as Eccentrotheca Landing, Nowlan, and Fletcher, 1980 , and also in paterinid brachiopods such as Salanygolina Ushatinskaya, 1987 (Balthasar et al. 2009; Holmer et al. 2009). Tangential and orthogonal canals are known from shells of tannuolinids and mickwitziids. The tangential canals represent setigerous tubes similar to the epipunctae ( Jin et al. 2007), whereas the Micrina – Setatella type orthogonal canals are interpreted as punctae with mantle outgrowths (caeca) reaching the periostracum ( Pérez-Huerta et al. 2009). The new form is interpreted herein to be a stem group brachiopod with phosphatic shell and demonstrates a novel combination of features known from tannuolinids and mickwitziids as well as linguliform brachiopods. Canal openings scattered on the outer shell surface have single apertures. In Oymurania , however, the tangential canals are not found within the inner shell layer of tightly packed prismatic columns (Kouchinsky and Bengtson 2017).

Subdivision of prisms into stacked tablets is not observed in the new form described herein.

Phylum and class uncertain

Order Tommotiida Missarzhevsky, 1970

Family Tannuolinidae Fonin and Smirnova, 1967

Genus Tannuolina Fonin and Smirnova, 1967

Type species: Tannuolina mullifora Fonin and Smirnova 1967 ; Atdabanian stage; Altay Sayan Foldbelt, Russia .

Tannuolina cf. pavlovi Kouchinsky, Bengtson, and Murdock, 2010

Fig. 21 .

Material.—Two fragmentary mitral sclerites, SMNH X11003, 11004 and a fragment SMNH X11005, from sample 19/3.25. Erkeket Formation, Khorbusuonka River, Siberia, Russia. Lower Botoman stage (correlated with the lower part of Cambrian Stage 4).

Description.—The apical fragments covered with co-marginal undulating folds with circular pores, up to 50 μm in diameter scattered on the accrescent side. The openings increase in diameter from the apical part towards the aperture. The apical part is flattened, with pores, ca. 5 μm in diameter along its periphery. The decrescent side is not preserved. The accrescent side passes into a flattened lateral side. Pores numerous on the accrescent side, but scarce and small, ca. 5 μm on the lateral side. The inner surface of sclerites smooth.

Remarks.—The fossils are similar to apical parts of mitral sclerites of Tannuolina pavlovi Kouchinsky, Bengtson, and Murdock, 2010 , from the lower Tommotian stage of Siberian Platform, but further comparison is hampered by incomplete preservation.

Figures

Fig.19. Paterinida gen. and sp. indet., ventral valves, from the lower Cambrian Erkeket Formation, Khorbusuonka River, Siberia, Russia; samples 11/2B (A, C, D) and 11/16.05 (B).A.SMNH Br151269.Apical part and subapical proximal margin of the shell.A1,oblique posterior view;A2,posterior view.B. SMNH Br151270.Apical fragment with subapical margin.C. SMNH Br151271.Juvenile specimen showing brephic shell.C1, lateral view; C2, plan view.D. SMNH Br151362. Fragment with distal part of the shell. D1, posterior view; D2, external surface of the fragment; D3, lateral view. Scale bar 500 µm.

Fig. 20. Stem-group Brachiopoda indet. from the lower Cambrian Erkeket Formation, Khorbusuonka River, Siberia, Russia; sample 20/1B. Fragments of shell, SMNH X11001 (A) and SMNH X11002 (B).A1, B2, general view;A3, A4, close-ups showing prismatic walls and openings of presumably setigerous canals; B1, enlargement showing prismatic wall. Scale bar: 500 µm (A1, A2, B2), 125 µm (A4, B1), and 50 µm (A3).

Fig. 21. Tommotiid Tannuolina cf. pavlovi from the lower Cambrian Erkeket Formation, Khorbusuonka River, Siberia, Russia; sample 19/3.25. A, B. Mitral sclerites, SMNH X11003 and 11004, respectively. A1, view on the accrescent side; A2, apical view. C. Fragment of sclerite with large pores, SMNH X11005. Scale bar 250 µm.