353 million years ago: earliest amphibians and reptiles.
Amphibians, which are among the earliest tetrapods, descended from fish such as Eusthenopteron. They are the first species to develop legs from fish fins. For the purpose of reproduction, amphibians need to be in the water where females lay eggs for males to fertilize. They may spend some time out of the water. However, they cannot live in dry places since part of their life cycle occurs in the water. The oldest known amphibian fossil is Tiktaalik, found off the coast of northern Canada, on Ellesmere Island, dated 375 million years ago.
Reptiles evolved from amphibians and do not depend on water for survival. Their skin is thick which prevents dehydration, and males fertilize their eggs inside the female. They need not be near the water since they have a shell protection. These adaptations let them move away from the coast and populate dry places. The oldest known reptile fossil is Casineria kiddi, dated 340 million years ago.
New fish species were discovered recently and found to have hand-shaped fins which they use to walk on the sea floor. This discovery offers a clue on how these adaptations could have evolved.