Oymurania gravestocki Ushatinskaya, 2015
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publication ID |
https://doi.org/ 10.4202/app.00037.2013 |
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persistent identifier |
https://treatment.plazi.org/id/039D2740-FF83-F044-E16D-03DBFA08FA36 |
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treatment provided by |
Felipe |
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scientific name |
Oymurania gravestocki Ushatinskaya |
| status |
sp. nov. |
Oymurania gravestocki Ushatinskaya sp. nov.
Figs. 3–13.
Etymology: In honour of the Australian palaeontologist David Gravestock.
Type material: Holotype: PIN 4194 View Materials /101 (Fig. 3A) . Paratypes: PIN 4194 View Materials /102, 103, 104 (Fig. 3B, C, D) .
Type locality: 61°04’18’’N, 126°10’44’’E, Oy-Muran section, middle reaches of the Lena River , left bank, 3.2 km upstream of the Gostinaya River, southeastern part of the Siberian Platform ( Fig. 1 View Fig ) GoogleMaps .
Type horizon: Bed 1, Oy-Muran section, Pestrotsvet Formation, Leptosocyathus polyseptus Zone, Atdabanian Stage , lower Cambrian .
Material.—In addition to the type material, the following specimens were obtained from the Oy-Muran section: 10 shells and shell fragments from samples 3A 01/2, 3А 01/3 and A-87-06-03 ( Fig. 2 View Fig ), including figured PIN 4194/104, 107, from the Leptosocyathus polyseptus Zone ; 11 shell fragments from samples 3А 01/12 and 3А 01/13, Pestrotsvet Formation, Carynacyathus pinus Zone (Bed 6), Atdabanian Stage; and a single cyrtoconic shell fragment, FUB Oym9-09 from the Porocyathus squamosus-Botomocyathus zelenovi Zone (Laticephalus-Erbiella Zone), Bed 9, lower Botoman Stage (Fig. 3E). Two orthoconic shells Oymurania? gravestocki PIN 4194/105, 106 (Fig. 4), from sample 3А 01/13 are questionably attributed herein to the same species as complementary valves of its bimembrate organophosphatic skeleton (see discussion). Additionally, eight shell fragments are available from section Bachik ( Fig. 1 View Fig ), samples 3А 03/62 and 3А 03/73, Perekhod Formation, Nochoroicyathus kokoulini Zone, Atdabanian Stage. Assemblages of orthoconic to cyrtoconic calcium phosphate shells attributed to Oymurania gravestocki are also described herein from samples 7/42.3, 7/45, 7/47.5, 7/47.7, and 7/48.5, Emyaksin Formation, Bol’- shaya Kuonamka River section 7, Delgadella anabara Zone, Atdabanian Stage (ca. 30 shells and apical fragments, including SMNH X5285–X5289; Figs. 5 View Fig , 6) and from Bed 21, Member 3 of the Perekhod Formation, Achchagyi-Kyyry-Taas section, Bergeroniellus micmacciformis-Erbiella Zone, lower Botoman Stage (ca. 100 shells and apical fragments, including SMNH X5290–X5304 and FUB AK21-001–019; Figs. 7–13).
Description.—Almost orthoconic to cyrtoconic, nearly bilaterally symmetrical, rapidly expanding organophosphatic shells with rounded blunt or tapered and up to 90º inclined apex. Width and length of the aperture are nearly equal. Shell height does not exceed the diameter of aperture. Subapical margin of the aperture bends outward (Fig. 3A 1 –A 3, B 1) and forms a prominent platform extended along the subapical margin and consisting of a series of growth increments (Fig. 3E). Subapical side gradually passes into convex lateral sides. Apical part sub-central (Figs. 4A, B, 6, 7A, B) to posteromarginal ( Figs. 8 View Fig –10). Initial part of the shell (Fig. 7) less than 200 μm in diameter, without growth increments and with irregularly folded hemi-spherical surface, indistinctly separated from the mature shell. Outer surface of the mature shell is circumferentially ornamented with co-marginal or undu-
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lating folds of growth increments. The inner shell surface is generally smooth, with growth lines, fine tuberculation and polygonal ornamentation (Figs. 6C 3, 9B, 11A 2, A 3, A 6, B).
Microstructure.—Shell wall (up to 0.25 mm thick) has a laminated structure (Figs. 3A 4, 12C 2, 13B). In the outer portion of the wall, lamination is obliquely arranged towards
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the outer shell surface and consists of spaciously arranged laminae (Fig. 10E–H). The inner portion of the wall is more compact and less distinctly laminated more or less parallel to the inner shell surface (Figs. 10H, 13A). Compact and more spacious types of lamination co-occur in the wall (Figs. 10E–H; 11B: arrows b and c). The laminae (ca. 5 μm thick) are perforated by thin open canals (2–4 μm in diameter), as observed on exfoliated apical (Figs. 4C 1: arrow a; 5A 3, A 4) and distal ( Fig. 13B, F View Fig ) parts of the shell. The canals continue through several successive laminae in perpendicular direction (Figs. 10F, 13B). The canals are often filled ( Fig. 5A View Fig 3) and/or encrusted by apatite and are represented by columns 2–5 μm in diameter) that traverse spaces between laminae Fig. 3A 4, 10F). These spaces are up to 10 μm thick (Figs. 10E, F, 13A), partly or completely filled with apatite. The ends of columns commonly produce tuberculation on the entire outer shell surface (Figs. 3A 2, A 4, 7A, 12A 5, A 6, A 8), 100–300 tubercles per 0.01 mm 2.
The edges of growth increments are indented with depressions containing openings of two types of coarser canals 10–20 μm in diameter). Canals of the first type (radial) run obliquely or parallel to the surface of growth lamellae in radial direction with respect to the shell surface and open at the edges of growth increments (Figs. 10G, 12A 3, B 1, C 2).
Canals of the second type (orthogonal) penetrate through the shell wall nearly perpendicular to the growth lamellae (Figs. 10G arrowed, 12A 5, A 6, A 8 arrowed, B 1) and open on the inner shell surface (Figs. 10E arrowed; 11B: arrow a). Openings of radial and orthogonal canals are both observed on the shell exterior where they are located in groups of two or three within the same depression or indentation in the wall (Fig. 12A 3, A 5, A 6, A 8, B 1). The aperture of the radial canal always occupies a more proximal position in the group, where one or two orthogonal canals open distally. In smaller specimens (Fig. 7) or in the proximal part of larger shells (Fig. 12A 6), one radial and one orthogonal canal open close to each other within the same radially extended depression or pit (2–3 such depressions/pits per 0.01 mm 2 on the outer surface of 1–2 mm sized specimens). Rare small pits of that kind occur on the juvenile shells (Fig. 7C 3 arrowed) and early mature shell (Figs. 4C 1: arrow c, 7). The depressions become more extended radially at later growth stages (Fig. 12A 1 –A 4, A 7). In most distal locations, the canals open in indentations of the edges of growth increments. These indentations have a deltoid shape extended radially and pointed proximally (Fig. 12A 5, A 8, B 1). Each of the deltoids contains a single opening of a radial canal at the narrow end and usually two openings of orthogonal canals in the broader external part.
Fig. 6. Orthoconic (presumably dorsal) valves of stem group-brachiopod Oymurania gravestocki Ushatinskaya gen. et sp. nov. from the lower Cambrian → Emyaksin Formation, Bol’shaya Kuonamka section 7, Siberia. A. SMNH X5287, sample 7/48.5; upper (A 1), oblique lateral (A 2), and supra-apical (A 3) views. B. SMNH X5288, sample 7/48.5; lateral (B 1) and upper (B 2) views. C. SMNH X5289, sample 7/47.7; lateral (C 1, C 4), upper (C 2), apertural (C 3), and subapical (C 5) views. Scale bar 600 μm, except A 2, 1200 μm.
Remarks.— The general morphology of the shell varies from nearly orthoconic with sub-central apex to cyrtoconic with postero-marginal apex. The Achchagyi-Kyyry-Taas assemblage contains almost orthoconic (Fig. 7A, B) as well as slightly cyrtoconic (Fig. 7C, D) but otherwise very similar relatively small forms. Larger specimens from that assemblage are represented by shells with up to 90° curved apices ( Figs. 8 View Fig –10). Shells with blunt wider apices with evidence of erosion (Figs. 10A–D, 12C 1) co-occur with those having tapered and narrower apices ( Figs. 8 View Fig , 9 View Fig ). The same variants of preservation of cyrtoconic and almost orthoconic shells from other localities are observed (Figs. 3–6). The subapically stacked growth lamellae are also susceptible to erosion and poorly preserved in larger specimens. In a single case, however, a broad and probably complete series of subapical lamellae is found attached to an apical fragment of a cyrtoconic shell (Fig. 3E).
Fragmented shells described by Vasil’eva (1998: pls. 48– 50) from the Atdabanian Stage of the Lena-Aldan area of the Siberian platform as problematic Stratosia exhibit a similar acrotretoid columnar microstructure and canals penetrating the wall subparallel to lamination ( Vasil’eva 1998: 117). Without access to the original material it is difficult, however, to conclude on the affinity of Stratosia with Oymurania .
A single ventral valve of Oymurania sp. described by Skovsted et al. 2014 from Cambrian Stage 3 of Morocco as mitral sclerite of Micrina sp. probably represents a new species of Oymurania . It has a less inclined apex and low
→ Fig. 7. Stem group-brachiopod Oymurania gravestocki Ushatinskaya gen. et sp. nov., small specimens from the lower Cambrian Perekhod Formation, Achchagyi-Kyyry-Taas section, Siberia. A, B. Orthoconic (presumably dorsal) valves, FUB AK21-006 (A) and AK21-015 (B). C, D. Cyrtoconic (presumably ventral) valves, FUB AK21-004 (C) and SMNH X5290 (D); arrow in C 3 points to a single opening of canal on the juvenile shell. Lateral (A 1 –D 1), subapical (A 2 –D 2), and upper (A 3 –D 3) views. Scale bar 300 μm.
ridges situated on the inner side of the subapical platform and apparently lacks the triplets of pores in distal parts of the shell ( Skovsted et al. 2014: fig. 10).
Another species of stem-group brachiopods, Tannuolina pavlovi Kouchinsky, Bengtson, and Murdock, 2010 known from the lowermost Tommotian Stage of northeastern margin of the Siberian Platform ( Kouchinsky et al. 2010) was first described under the name Tannuolina sibirica Sipin (nomen nudum) by Sipin (2001) in his yet unpublished Doctoral candidate thesis. Kouchinsky et al. (2010) were unaware of the description of T. sibirica therein, since the thesis was inaccessible to them at the time of publication. The sellate and mitral sclerites of the species were collected from the top 0.2 m of the Sukharikha Formation and the lowermost 1.7 m of the Krasnoporog Formation, from three localities along the Sukharikha River, among which section 1 ( Sipin 2001) corresponds to the type locality of T. pavlovi . These beds were attributed by Sipin (2001) to the Spinulitheca billingsi – Tannuolina sibirica Zone and correlated with the Nochoroicyathus sunnaginicus Zone of the Tommotian Stage.
Stratigraphic and geographic range.— Atdabanian and lower Botoman Stages (~Cambrian Stage 3), Siberian Platform.
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