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60 ADVANCES IN PALAEOICHTHYOLOGY Fig. 1. Lophosteus superbus; upper Pridoli, Upper Silurian. A, spine GIT 382-118, borehole Ruhnu-500, 152.2 m depth, Estonia; B, C, middorsal plate GIT 283-25, Ohesaare cliff, Saaremaa, Estonia. b, inner side; c, detail of external side with preserved tubercles. Dusted with NH 4 Cl. Scale bars equal 1 mm. One nearly complete spine (GIT 382-118, Fig. 1A) has been discovered in bore hole Ruhnu-500, Estonia, at 152.2 m depth. Its maximum length is 40 mm. It is flat. The anterior crest carries large elongate ridge-like tubercles on the lower half and much smaller tubercles (a third to a half in length) in the dorsal half of the anterior crest; there is an abrupt change in size. The elongate tubercles on the lateral sides are much smaller (one fourth the large tubercles) and are arranged in parallel rows. The base of the spine is remarkably long, reaching about half the length of the spine, so that one has to assume that the spine was attached at a low level to the body. Fragmentary material of such completely flat spines are found in acetic residues; these flat spines have a similar sculpture on both sides (see also Gross 1969: fig. 5 E). We assume that specimens of L. superbus carry several spines and spine-like elements of very variable size, shape and sculpture, based on the occurrence of differently shaped spines with the same ornamentation. Altogether eight different types of spines and spinelike elements have been found (see also Rohon 1893: pl. 1, figs 38-39a; Gross 1969: figs 4 A, D, 5 B, D, E; Gross 1971a: fig 3 A, C; Otto 1991: fig. 1). Rohon (1893: pl. 1, figs 38-39 a) figured two spines of Lophosteus superbus, both are 7.1 mm deep and
H.-P. Schultze, T. Marss. Revisiting Lophosteus 61 around 3 mm (3.3 and 2.8 mm) wide. Both have a triangular cross-section and a thicker proximal end. Smaller ridge-like tubercles form distinct longitudinal rows, whereas a row of larger ridge-like tubercles intersects the rows of finer ridge-like tubercles (Rohon 1893: pl. 1, fig. 38). It is not quite clear which is the leading edge of the spine (it should be the edge with coarser sculpture). The figure of the other spine(Rohon 1893: pl. 1, fig. 39 a) presents perhaps the posterior side of the spine. Gross (1969) distinguished symmetrical and asymmetrical spines that precede median unpaired and paired fins respectively. They posses narrow, smooth overlapped areas at the base of the spines. Gross (1947, 1971b) also described acanthodian spines without such an overlapped area. Gross (1969: 25; text-figs 4 A-E, G-H, 5 A-E) figured symmetrical spines from the midline of the trunk; the anterior edge and both sides of the two spines described are sculptured, whereas on the posterior side of the third it is absent. A few spines also have sculpture on their distal posterior side. The largest spines although broken are 3.6 mm long and 1.5 mm wide, and their largest ridge-like tubercles are 0.9 mm long. The third spine has a length of 3.1 mm, a width of 1.15 mm, and 0.8 mm long ridge-like tubercles. Still, most spines are less than 2 mm long. The ridge-like tubercles are parallel to the longest edge of the spine, and the rows of ridge-like tubercles run parallel to each other. All ridge-like tubercles can be of uniform size, or they become smaller on the sides. The unsculptured side of the spines is more or less concave proximally, and flat or convex distally. In several spines the proximal end is narrower than the distal. Gross (1969: 25) did not find a narrow and smooth anterior margin in symmetrical spines. He (1969: text-figs 3 D, 4 I) also described some symmetrical spine-like elements. They are relatively wide with tightly packed tubercles, have a low depth and a convex lower side. Asymmetrical spine-like elements are more common, and possibly represent the anterior margin of paired fins (Gross 1969: 25; text-figs 3 E, G, 4 F). Their proximal end has a smooth edge. The sculpture is less regular on such spines, the tubercles continue slightly onto the visceral side. Their wider side can be twice as broad as the narrower side. Gross (1971: text-fig. 3 C) figured a fragment of a spine-like element which carries a very large ridge-like tubercle anteriorly, and ridge-like tubercles on the sides that are more than four times shorter. The fragment is 4.8 mm deep and 2.2 mm wide. Another asymmetrical spine-like element (Gross 1971: text-fig. 3 A, B) has ridge-like tubercles of different size, but all are relatively short. The estimated maximum length of this element is 7.5 mm, the width 3.6 mm. Big pores, which can open in pairs between the tubercles, are extraordinary for spines, and might belong to the lateral line system according to Gross (ibid.: 135). The pores better support an interpretation of the structure as a plate rather than as a spine. Otto (1991: 348) described a mediodorsal fin spine, that is a ca. 4 mm deep, bilaterally symmetrical, pyramidal element with a broken basal part and a triangular cross-section. The posterior side lacks sculpture, which, however, is present on the two anterior sides. The largest ridge-like tubercles are arranged in a row along the anterior edge, whereas the tubercles on the lateral sides are of different size and not arranged in distinct rows. The spine has a cavity in its base. Otto (1991) expressed the opinion that this spine is a true mediodorsal fin spine, whereas the spine-like elements described by Gross (see above) are not fin spines.
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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
Page 9 and 10: 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
Page 57 and 58: ACTA UNIVERSITATIS LATVIENSIS, 2004
Page 59: H.-P. Schultze, T. Marss. Revisitin
Page 63 and 64: H.-P. Schultze, T. Marss. Revisitin
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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