Q. What are the problems that vertebrates needed to solve to adapt to the terrestrial environment since they came from the aquatic habitat? How evolution does solve those problems?
The main problems vertebrates coming from water needed to solve to adapt to the terrestrial environment were the following: the problem of elimination of wastes in a medium where water is less available, the problem of protection against nocent solar radiation, the problem to avoid dehydration, the problem of gamete locomotion in the environment for fecundation, the problem of gas exchange, earlier done by direct contact of water with gills, the problem of body support, since it was water that played this role in fishes.
Solutions for the dehydration problem: thicker and impermeable skin, permeable and moist skin or to lose less water like in amphibians. Solution for the excretion problem: excretion of urea also excreted by uric acid or chondrichthyes, substances that need less water to be dissolved. Solutions for the problem of protection against radiation: skin pigments that filter harmful radiation, feathers, carapaces or hair. Solution for the gamete movement problem: internal fecundation except for most amphibians that have external fecundation. Solution for the gas exchange problem: appearing of lungs and airways. Solution for the body support problem: further development of bony and muscular structures, like claws and limbs.