During the Carboniferous Period, amphibians were the first vertebrates to live on land, and they thrived in swamps and wetlands surrounded by forests.
However, their "skin" and "eggs" were not made to withstand the dryness on land. Their eggs were the same as those of fish; they were laid in water, and the progeny born from the eggs grew to maturity inwater. They moved onto land when they matured, and their skin excreted a slimy liquid to protect their bodies from drying out.