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H.-P. Schultze, T. Marss. Revisiting Lophosteus
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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.