Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
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Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ... Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

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19.11.2013 Views

130 ADVANCES IN PALAEOICHTHYOLOGY Nostolepis cf. amplifica Fig. 4 A-M 2003 b Nostolepis amplifica; Valiukevicius, figs 2 A-H, 3 A-I. Range. The lower part of the Šilale Beds of the Minija Formation, Pridoli, Upper Silurian. Material. 72 flank scales. Remarks. N. amplifica was originally defined on large trunk scales having a high robust median crown area ornamented with two to six short parallel ridges fading out at a quarter of crown length, and narrow lateral crown steps delimited by clear oblique neck ridges. Most of the Lužni scales are within the morphologic range of N. amplifica, differing only in having more pronounced, wider bases protruding beyond the anterolateral edges of crowns, and scales generally being smaller (crowns 0.35-0.6 mm long and 0.3-0.85 mm wide). Two reasons preclude definite assignment of the scales to N. amplifica. First, the long stratigraphic gap that separates the isolated occurrence (338.6 m) of N. cf. amplifica from the range of definite N. amplifica (202.4-172.2 m); and second, histologic differences. The Stranggewebe in crowns of N. amplifica is covered by a mantle of highly cellular simple mesodentine and is distinguished by short and narrow Stranglacunae; osteocytes are present in the primordial lamella only; large principal vascular canals develop in each growth lamella (Valiukevicius 2003 b, fig. 3 A-I). These characters are almost opposite in the Lužni scales. The enveloping Stranggewebe mantle of the networked mesodentine is absent here or is very thin (Fig. 4 J-K), Stranglacunae are particularly long and osteocytes are present, though rare, in all growth lamellae (Fig. 4 H, M). The system of main vascular canals is less developed in N. cf. amplifica, and only narrow ascending and radial canals were observed. Nostolepis elegans (Brotzen) 1934 Fig. 5 A-M 1934 Diplacanthoides elegans; Brotzen, pl. 1, fig. 11 a-c. Diplacanthoides insignis; Brotzen, pl. 2, fig. 1 a-b. ? Diplacanthoides crassus; Brotzen, pl. 1, fig. 16 a-b. 1937 ? Diplacanthoides unguiparatus; Lehman, pl. 2, fig. 30. ? Diplacanthoides trilobatus; Lehman, pl. 2, figs 31; pl. 4, figs 64. Diplacanthoides elegans; Lehman, pl. 3, fig. 57. non 1980 Nostolepis arctica; Vieth, pl. 5, figs 1-9. 1998 Nostolepis striata; Valiukevicius, pl. 1, fig. 2 a-b. 1999 a Nostolepis arctica; Vergoossen, figs 2-4. 1999 b Nostolepis striata, ‘elegans’ form group; Vergoossen, pl. 2, figs 15-17. 2002 a Nostolepis striata; Vergoossen, fig. 59. 2002 b Nostolepis striata; Vergoossen, fig. 36. 2002 c Nostolepis striata, ‘elegans’ form group; Vergoossen, figs 93-99. Holotype. Brotzen 1934 a: pl. 1, fig. 11 a-c; a flank scale. Type horizon. The Lower Devonian erratics of the Baltic basin. Range. From Upper Silurian, Ludlow Series to Lower Devonian, Lochkovian.

J. Valiukevičius. Silurian acanthodians from Lūžņi-4 131 Fig. 4. Nostolepis cf. amplifica. SEM micrographs of scales (A-F), crown views, anterior upwards, and thin section photos (G-M). A, LIGG 25-A-2601; B, LIGG 25-A-2606; C, LIGG 25-A-2603; D, holotype, LIGG 25-A-2604; E, LIGG 25-A-2602; F, LIGG 25-A-2607; G-H, vertical transverse section of a holotype-like scale. Thin section 3775. G, general view; H, detail of the left crown part and the base portion at higher magnification; I-K, longitudinal section of a holotype-like scale. Thin section 3777. I, general view; J, detail of the anterior crown part and scale primordium at higher magnification; K, magnified detail of the posterior crown part; L-M, vertical longitudinal section of a scale like that in Fig. 4 C. Thin section 3778. L, general view; M, detail of scale primordium. Lūžņi-4 borehole, depth 338.6 m. Přidoli, Minija Regional Stage, Šilalė Beds of the Minija Formation. Abbreviations: avc, ascending vascular canal, gl, growth lamella, oc, osteocyte cavity, rvc, radial vascular canal, sg, Stranggewebe, sl, Stranglacuna. Scale bars: 0.1 mm.

J. Valiukevičius. Silurian acanthodians from Lūžņi-4<br />

131<br />

Fig. 4. Nostolepis cf. amplifica. SEM micrographs of scales (A-F), crown views, anterior<br />

upwards, <strong>and</strong> thin section photos (G-M). A, LIGG 25-A-2601; B, LIGG 25-A-2606; C, LIGG<br />

25-A-2603; D, holotype, LIGG 25-A-2604; E, LIGG 25-A-2602; F, LIGG 25-A-2607; G-H,<br />

vertical transverse section of a holotype-like scale. Thin section 3775. G, general view; H, detail<br />

of the left crown part <strong>and</strong> the base portion at higher magnification; I-K, longitudinal section of<br />

a holotype-like scale. Thin section 3777. I, general view; J, detail of the anterior crown part <strong>and</strong><br />

scale primordium at higher magnification; K, magnified detail of the posterior crown part; L-M,<br />

vertical longitudinal section of a scale like that in Fig. 4 C. Thin section 3778. L, general view;<br />

M, detail of scale primordium. Lūžņi-4 borehole, depth 338.6 m. Přidoli, Minija Regional Stage,<br />

Šilalė Beds of the Minija Formation. Abbreviations: avc, ascending vascular canal, gl, growth<br />

lamella, oc, osteocyte cavity, rvc, radial vascular canal, sg, Stranggewebe, sl, Stranglac<strong>un</strong>a.<br />

Scale bars: 0.1 mm.

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