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64 ADVANCES IN PALAEOICHTHYOLOGY Diagnosis: Scale ridges short, not reaching the posterior border, where they override older ridges. Alternating ridgelets cover the entire ridge and even the crest; anterior overlapped field pustulate. Tubercles of the plate have nodules at the base of the ridgelets. Description: The holotype (Fig. 3 A) represents a deep scale from the left anterior flank of the fish. It is 3.0 mm deep and 0.7 mm wide. The ridges arising posteriad have convex surfaces and do not form a crest. The anterior overlapped field is wide and pustulate, the free field is covered with two generations of ridges. There are 16 ridges. The longer anterior (younger) ridges overlie posteriorly shorter (older) ridges; both cover only part of the free field. The ridges are covered by ridgelets that alternately reach the crest (Fig. 3 B). The dorsal margin of the scale forms a broad overlapped area (“peg”). The overlay of ridges is more intimate in other scales (Fig. 3 C), where the two or three generations are not so clearly separated as in the holotype. The inner surface of the scale carries an elongate elevation. Only a few ridges are present on the scale (0.9 mm deep and 0.6 mm wide); the ridges are more elongate than in the holotype, and the ridgelets are more distinct. The scale has a pillow-like elevation on the inner surface. The spine assigned to the species, clearly shows the overlay of flat ridges (Fig. 3 C) that are covered anteriorly with pronounced ridgelets. Fine pores of vascular canals open around the ridges in the basal plate. A bony plate with star-like tubercles (Fig. 3 D, E) is assigned to L. canadensis on the basis of comparison with L. superbus and of the co-occurrence with the scales of L. canadensis at the same locality. Only one, the longest margin of the plate, is preserved intact, it is arched downwards; the other margins are broken, so that the position of the plate cannot be established. Its maximum measurements are: width 8.0 mm and length 4.0 mm. The plate is covered with closely packed stellate tubercles of different sizes; they are tiny on the arched margin. The middle area of the plate is covered by tubercles of 2 to 3 generations, older ones are partly covered by younger ones. Each stellate tubercle carries fine ridgelets converging towards its smooth apex. On the bony basal plate, the ridgelets terminate in small nodules; small nodules are also placed irregularly between the tubercles. The same is the case in L. superbus (Gross 1969: figs 8 A, D, 9 G). The concentric lines around the tubercles (on the ridgelets just above the basal plate) are a peculiar feature and reminiscent of growth lines (Fig. 3 E). Three deep open grooves of the sensory line system occur on the plate, two of them form an angle of about 45° on one side, and one short section is preserved on the opposite side (Fig. 3 D). The bony base appears rather compact with small canal openings as seen on the margins of the broken plate. Comparison: Lophosteus canadensis n. sp. and Lophosteus superbus have scales of nearly the same size. The ridges on the free field of the scales are slightly closer to each other in Lophosteus canadensis n. sp. than in L. superbus. The ridges are smaller in L. connexus, and joined at the base on some elements. Alternating ridgelets reaching the top of the ridges are characteristic of L. canadensis. This feature distinguishes the species from all other species of the genus. A crest is not developed like in L. incrementus. Moreover, the bony pustules on the anterior overlapped area and between the ridges are lower and smaller in L. superbus and L. canadensis than in L. incrementus. On the bony plates, nodules on the ridges of the stellate tubercles are present in four species of Lophosteus (Märss 1986: pl. 35, figs 1-14, for the nodules see fig. 13 a);
H.-P. Schultze, T. Marss. Revisiting Lophosteus 65 Fig. 3. Lophosteus canadensis n. sp.; Pridoli, Upper Silurian; Cornwallis Island, Arctic Canada. A, scale of left anterior flank, holotype UALVP 447 66; B, tubercle of A; C, spine, UALVP 447 90; D, bony plate, UALVP 447 65; E, detail from D. SEM pictures, scale bars equal 100 µm except D (1 mm). they are also found in some placoderms and acanthodians. The tips of the stellate tubercles are smoothly convex in L. superbus and L. canadensis, whereas they are sharply pointed in the Australian taxon.
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LATVIJAS UNIVERSITĀTES RAKSTI 679.
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LATVIJAS UNIVERSITĀTES RAKSTI 679.
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Contents Ervīns Lukševičs and Ģ
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ACTA UNIVERSITATIS LATVIENSIS, 2004
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Ervīns Lukševičs, Ģirts Stinkul
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Ervīns Lukševičs, Ģirts Stinkul
Page 13 and 14: Ervīns Lukševičs, Ģirts Stinkul
Page 15 and 16: Olga Afanassieva. Microrelief on th
Page 23 and 24: D.K. Elliott, E. Mark-Kurik, E.B. D
Page 47 and 48: C.G.Miller, T. Marss, H. Blom. New
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Page 59 and 60: H.-P. Schultze, T. Marss. Revisitin
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Page 81 and 82: O.A. Lebedev. A new tetrapod from R
Page 101 and 102: E. Lukševičs, I. Zupiņš. Sedime
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E. Lukševičs, I. Zupiņš. Sedime
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J. Valiukevičius. Silurian acantho
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V. Pernegre, V. Dupret. Biostratigr
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Ž. Žigaite. New telodont from Tuv
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