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 ...
124 ADVANCES IN PALAEOICHTHYOLOGY Fig. 1. Nostolepis alifera sp. nov. SEM micrographs of scales (A-G), crown views, anterior upwards, and thin section photos (H-L). A, LIGG 25-A-2570; B, LIGG 25-A-2568; C, LIGG 25-A-2632; D, LIGG 25-A-2571; E, LIGG 25-A-2549; F, holotype, LIGG 25-A-2550; G, LIGG 25-A-2553; H-J, vertical transverse section of a scale like that in Fig. 1G. Thin section 3758. H, general view; I, details of the right, and J, of the left crown and bordering base parts; K-L, vertical transverse section through the anterior part of a holotype-like scale. Thin section 3759. K, general view; L, the left part at higher magnification. Lūžņi-4 borehole, depth 197.0 (A-B, H-J), 197.2 (C), 207.0 (D, K-L) and 189.8 (E-G) m. m. Přidoli, Jūra Regional Stage, Garzde Beds of the Targale Formation. Abbreviations: avc, ascending vascular canal, b, bone, bmd, bone-like mesodentine, cvc, circular vascular canal, gl, growth lamella, oc, osteocyte cavity, rvc, radial vascular canal. Scale bars: 0.1 mm.
J. Valiukevičius. Silurian acanthodians from Lūžņi-4 125 Fig. 2. Nostolepis alifera sp. nov. Histological structure of a scale like that in Fig. 1B. Vertical longitudinal section. Thin section 3760. A, general view; B, detail of the scale primordium; C, detail of the posterior part of neck with the neck/base junction; D, detail of the central part of crown. Lūžņi-4 borehole, depth 207.0 m. Přidoli, Jūra Regional Stage, Garzde Beds of the Targale Formation. Abbreviations: avc, ascending vascular canal, b, bone, gl, growth lamella, oc, osteocyte cavity, rvc, radial vascular canal, sg, Stranggewebe, sl, Stranglacuna. Scale bars: 0.1 mm. Description. Morphology. Most (flank) scales have posteriorly elongated rhomboidal to elipsoidal crowns from 0.28 to 0.85 mm long. Rare specialized varieties have triangular crowns. The crown plate slopes down slightly anteriorly. A clear elevated triangular medial area and lower lateral areas are distinguished on the crowns. The medial area carries five to eight sub-parallel anterior ridges with rounded crests that fade out at about half of crown length (Fig. 1 C, E-F). Some scales have unevenly long medial ridges of which some point to or converge with the longest central ridges at the posteriormost crown part (Fig. 1 B, G). Short anterior bifurcation of ridges occurs rarely. The medial crown area sometimes has a wide deep central groove (Fig. 1 G). The lateral crown areas contain one to two ridges extending the whole crown length (Fig. 1 D, G) or short, more numerous oblique ridgelets which converge with the longest medial ridges posteriorly (Fig. 1 A-B). The scale bases are rhomboidal (except for specialized varieties, see Fig. 1 D), slightly (Fig. 1 K) to moderately convex, and separated from the necks by a clear rim. The necks are short anteriorly because of the downsloping crown, and frequently contain large pores (up to five basally on each side, see Fig. 1 C).
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124<br />
ADVANCES IN PALAEOICHTHYOLOGY<br />
Fig. 1. Nostolepis alifera sp. nov. SEM micrographs of scales (A-G), crown views, anterior<br />
upwards, <strong>and</strong> thin section photos (H-L). A, LIGG 25-A-2570; B, LIGG 25-A-2568; C, LIGG<br />
25-A-2632; D, LIGG 25-A-2571; E, LIGG 25-A-2549; F, holotype, LIGG 25-A-2550; G, LIGG<br />
25-A-2553; H-J, vertical transverse section of a scale like that in Fig. 1G. Thin section 3758. H,<br />
general view; I, details of the right, <strong>and</strong> J, of the left crown <strong>and</strong> bordering base parts; K-L,<br />
vertical transverse section through the anterior part of a holotype-like scale. Thin section 3759.<br />
K, general view; L, the left part at higher magnification. Lūžņi-4 borehole, depth 197.0 (A-B,<br />
H-J), 197.2 (C), 207.0 (D, K-L) <strong>and</strong> 189.8 (E-G) m. m. Přidoli, Jūra Regional Stage, Garzde<br />
Beds of the Targale Formation. Abbreviations: avc, ascending vascular canal, b, bone, bmd,<br />
bone-like mesodentine, cvc, circular vascular canal, gl, growth lamella, oc, osteocyte cavity,<br />
rvc, radial vascular canal. Scale bars: 0.1 mm.
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