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62 ADVANCES IN PALAEOICHTHYOLOGY
The main visible difference between spines with a triangular cross-section as
depicted by Rohon (1893) and Otto (1991) is in the arrangement of ridge-like tubercles,
which are arranged either in rows or irregularly, and in the difference in depth.
The spine described by Gross (1969: text-fig. 5 E) is of the same type as that from the
Ruhnu bore hole. They are flattened, sculptured on both flattened sides and distally
around the whole spine. Proximally they have a cavity that extends one third of their
length. This spine has some similarities with the cornual plate of placoderms.
Other spine-like elements described by Gross and also those in the Tallinn collection,
were attached to tesserae-like elements in the skin. These have a concave visceral side
and are not fin-spines.
The spine assigned to the sarcopterygian Psarolepis (Zhu and Schultze 1997) has
a very narrow overlapped area. These spines are not inserted deeply in the skin in
contrast to spines of sharks and most acanthodians. Zhu et al. (1999) emphasized the
occurrence of spines in basal osteichthyans (including Lophosteus), acanthodians and
sharks. Advanced sharks and the Early Devonian chondrichthyan Leonodus (Soler-
Gijón and Hampe 2003) possess only symmetrical spines, whereas spines in front of
paired fins are known in Early Devonian sharks (Sahney and Wilson 2001: putative
chondrichthyan; Miller et al. 2003: Doliodus).
A convex plate (GIT 382-25, Fig. 1 B, C) represents a new element. Its maximum preserved
length is 6.6 mm. The plate is convex externally and concave internally; the lateral margins
are broken. It has a short anterior overlapped area. Oval, smooth, abraded tubercles are
distributed in indistinct rows posterior to that area (Fig. 1 C); smaller tubercles are placed
between larger ones. Fine ridgelets occur radially at the margin of each tubercle. The
deeper part of an elongate narrow keel on the concave inner side is partly broken off (Fig.
1 B). Lineations that may represent growth lines are visible in front of the keel. The plate
is symmetrical, belongs to the dorsal midline, and may be comparable to a fulcrum.
An interesting head plate (GIT 232-16 = Pi 6186, Fig. 2) of L. superbus was described
and figured by Märss (1986: 58, pl. 35, fig. 1 a, b). The arched plate shows an open lateral
line canal which bifurcates anteriad around the anterior invagination. The course of the
lateral line nerve is picked out on the inner side by pores that transmitted branching
nerves to the neuromasts in the lateral line canal. The course of the pores and thus the
course of the lateral line nerve on the inner side from a posterior to an anterior invagination
does not show the bifurcation of the canal on the outer side of the plate. Such plates
with an open lateral line canal have already been described and figured by Gross (1969:
figs 5 H, 6 D, 7 A, B).
Lophosteus cf. superbus
2000 Lophosteus sp. cf. L. superbus — Burrow and Turner: 170, 172; fig. 3.3.
Material: part of one scale UQY 8667 (Burrow & Turner 2000: fig. 3.3).
Locality: Bullock Creek, northern Queensland, Australia.
Horizon: Ancoradella ploeckensis Conodont Zone, Jack Formation, lower Ludlow,
Upper Silurian.
Description: Burrow and Turner (2000) gave no description. The scale is reminiscent
of those of L. superbus and have a pustulate anterior field and elevated oblique ridges