Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

72 ADVANCES IN PALAEOICHTHYOLOGY
All actinopterygians are characterised by the presence of ganoine, all sarcopterygians
by the presence of a broad based peg, cosmine and true enamel. The course of the
lateral line canals in bone is the common character of all osteichthyans. The sister
group relationship of Lophosteus and Climatius is the result of the presence of
symmetrical and paired fin spines, and of tooth whorl. The presence of a spiny process
on the shoulder girdle appears to be a basal character, lost within actinopterygians
more derived than Andreolepis and within sarcopterygians in forms more derived than
Psarolepis. This agrees with the analysis of Zhu et al. (1999), who placed special
importance on the occurrence of spines and spiny processes in early osteichthyans.
Tesserae appear as a unique character of Climatius, because Lophosteus is coded with
tesserae or plates. All osteichthyans have a closed skull roof (plates), a feature not
known from Lophosteus. Still there are plates larger than what is normally considered
as tesserae.
Fig. 7. Interrelationship of Lophosteus. Node 1: 8 1 , 9 2-1 , 11 1 ; node 2: 17 1 ; node 3: 5 1 ; node 4: 2 1 ,
6 1 , 14 1 [bold = unique character change; for explanations see Appendix 2 and text].
Characters of the ornament-like stellate tubercles (also found in Sigaspis) and ridges
(also present in some actinopterygians and sarcopterygians) occur in parallel to
Lophosteus in other gnathostomes. Nodules, another form of ornamentation, is known
in arthrodires (Gross 1973), acanthodians (Gross 1971b) and Lophosteus (Gross 1969).
That such a similar ornament can appear again and again, is very well established.