Gerronostroma sp.
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publication ID |
https://doi.org/ 10.4202/app.2007.009 |
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persistent identifier |
https://treatment.plazi.org/id/03A887AE-FFAE-FFA0-FCD0-FEDD5DB6AC04 |
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treatment provided by |
Felipe |
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scientific name |
Gerronostroma sp. |
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Fig. 6A–C View Fig .
Material.— 7 specimens from localities 1 and 3, broken, abraded, commonly with stylolitized margins.
Description.—Skeleton laminar or low domical. Laminar specimens up to 50 mm thick, their basal lengths exceeding 100 mm. Heights of domical skeletons up to 70 mm. Laminae well defined, usually planar, with numerous foramina. Laminae sporadically inflecting slightly into pillars, forming zigzag pattern ( Fig. 6A View Fig 1 View Fig ). In other areas laminae thick and planar, tripartite, with lighter axial zones ( Fig. 6B View Fig ). Foramina well−developed, but nearly absent from some parts of the skeletons. Laminae spacings between 200 and 500 µm. Laminae up to 250 µm thick, in some parts of skeleton thinner (30–100 µm), making the interlaminar spaces up to 400 µm wide. Pillars stout or crumpled, long, passing through 1–4 interlaminar spaces, perpendicular to laminae or oblique. Most of them 75 to 200 µm thick. Within specimens of phase 2 pillars thinner (30–100 µm), and longer, intersecting at least two interlaminar spaces.
The inner structure of specimens revealing a great range of variation, thus two phases have been distinguished, replacing each other successively, very rarely laterally. Phase 1 forming the dense parts of skeletons, whereas phase 2 appearing in areas consisting of thin skeletal elements.
Phase 1 ( Fig. 6A–C View Fig ) present in bottom and centrals of skeletons, rarely as terminating phase. Laminae thick (up to 250 µm), planar, in some parts of skeletons inflecting into thick pillars or revealing tripartite structure ( Fig. 6B View Fig ). Galleries subrectangular or, more commonly, oval. Foramina present, only in some parts of skeletons numerous. Dissepiments common, flat or slightly convex. Pillars 75–200 µm thick, 0.7–2.5 mm long, superposed, intersecting 1–4 interlaminar spaces, perpendicular to laminae or, less commonly, oblique. In areas neighbouring mamelons pillars longer, of height up to 2.5 mm. Pillars thickened in their upper parts, directly below the overlying laminae, rarely dichotomically branching, mostly in areas adjacent to mamelons. Mamelons numerous, low, with relief up to 2 mm, consisting of thick and long pillars, forming an axial canal, up to 1.5 mm long, intersecting skeletons at distances not exceeding 5 mm.
P h a s e 2 ( Fig. 6A–C View Fig ) in central and upper parts of skeletons, commonly as a terminating phase. Laminae planar, thin, not exceeding 100 µm, in some areas penetrated by numerous foramina. Galleries rectangular or subrectangular. Pillars thicker than in phase 1, exceeding 100 µm in diameter, simple, postlike, perpendicular or oblique to laminae, oval or irregularly rounded in tangential sections. Pillars long, intersecting at least two interlaminar spaces, thickened in parts lying directly below laminae. Dissepiments rare, of low convexity. Mamelons numerous.
Statistics.—Kruskal−Wallis test and multiple comparison test after Kruskal−Wallis test performed on skeletons assigned to Gerronostroma revealed significant differences between the specimens of Gerronostroma cracoviensis ( Gürich, 1904) and Gerronostroma sp. ( Table 2). Two sample Kolmogorov−Smirnov tests on Gerronostroma cracoviensis and Gerronostroma sp. , were also applied. They revealed differences between these two species (at the 0.05 level of significance), when considering thickness of pillars and laminae, pillar spacing and length.
Discussion.— Gerronostroma sp. closely resembles specimens of Clathrostroma cf. jukkense described by Stearn (1988) from the Famennian of Alberta, Canada. Both species are characterised by two phases replacing each other successively or—only in Stearn's (1988) specimens—contemporaneously. Differences between these two species are visible in tangential sections. Specimens from Famennian of Canada reveal less densely packed skeletal elements, and the pillars are more conspicuous.
Stratigraphic and geographic range.—Southern Poland, Dębnik Anticline, both slopes of the Racławka Valley between Dubie and Paczółtowice villages. Góra Żarska Member of the Dubie Formation. Quasiendothyra communis – Quasiendothyra regularis Zone ( Palmatolepis marginifera –middle Palmatolepis expansa conodont zones), Famennian.
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