FURTHER PHYLOGENETIC CONSIDERATIONS IN FISHES
Two important series of evolutionary events occurred during the evolution of the Osteichthves:
1. Evolution of teleosts
One of these was an evolutionary explosion of teleosts. It began about 150 million Years ago. It produced a vast diversity of living teleosts of today.
2. Evolution of terrestrial vertebrates
The second series of events is the evolution of terrestrialism. There are two views about the evolution of terrestrial vertebrates:
(a) Lung fishes as ancestors of land vertebrates:
The functional lungs are present in modern lungfishes. It suggests that the lungfish lineage is the ancestor of modern terrestrial vertebrates. But most cladistics and anatomical evidence indicates that the lungfish lineage gave rise to no other vertebrate taxa.
(b) Osteolepiforms as ancestors of land vertebrates:
Osteolepiforms are now taken as ancestors of terrestrial vertebrates. They are also belonged Sarcopterygii. These fishes live in shallow -water habitats. It saved these fishes from the predator. Young osteolepiforms inhabited very shallow water. The concentration of oxygen was reduced in the warm and shallow water environments. It favored the evolution of sarcopterygians lungs. There was abundant food, in the form of arthropods and other invertebrates at edge of water. It favored shallow- water and terrestrial feeding. Some modification in appendages and eye lenses took place. It allowed these fish to move between land / water interfaces. These see with eye in air. The brief movement of vrtebrates on land allowed them to exploit land food resources. These resources were used by terrestrial arthropods for the previous 50 million. Millions of years passed before the development of terrestrial vertebrates.