 Although the earliest <unk> were primarily <unk> , they had the ability to feed on land . Later , <unk> and <unk> , some well adapted to terrestrial life , also fed on land . Some <unk> became better adapted toward life in water , and shifted their diets toward aquatic organisms . The first primarily aquatic <unk> were <unk> in the <unk> . <unk> and <unk> became independently aquatic and also returned to this type of feeding . 
