(bony fish) is divided into two subclasses: ray-finned (Actinopterygii)
and lobe-finned (Sarcopterygii).
There are only four living genera of lobe-finned fish, but the group
is known from fossils that date back to the very beginning of the
class, 400 million years ago in the Devonian period. The paired fins
of the lobe-finned fish are thought to have given rise to the limbs
of the tetrapods.
living lobe-finned fish include 3 genera of lung-fish, one of each
in Australia, Africa and South America. The remaining genus contains
one species, the coelacanth.
in the western Indian Ocean in 1938, the coelacanth represents a group
of fishes that had been thought to be extinct for about 70 million
comparisons of mitochondrial DNA have shown that lung-fishes are more
closely related to the terrestrial tetrapods than are coelacanths.
Therefore, many of the features that were supposed to link the living
coelacanth with terrestrial tetrapods probably result from convergent
museum has a life-sized cast made from a real coelacanth.