Devonian red beds indicate severe drought. Fish left the ponds that dried up in search of water. Thompson proposed ecological conditions. Appearance of wetlands at margins of lakes or estuaries. Abundant food for fish that could live in very shallow water.
Limbs are adaptation for locomotion in shallow water.
Gradually amphibians took advantage of terrestrial resources. Pough indicates early amphibians were adapted for aquatic environments. He suggests terrestriality is associated with dispersal of juveniles who would feed on terrestrial invertebrates and have fewer problems with gravity because of small size. Eureptilia Captorhinidae, etc. Diapsida stem taxa 21.