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