The main problems vertebrates coming from water needed to solve to adapt to the terrestrial environment were the following: the problem to avoid dehydration; the problem of elimination of wastes in a medium where water is less available; the problem of protection against nocent solar radiation; 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, to lose less water, or moist and permeable skin, like in amphibians. Solution for the excretion problem: excretion of urea (also excreted by chondrichthyes) or uric acid, substances that need less water to be dissolved. Solutions for the problem of protection against radiation: skin pigments that filter harmful radiation, feathers, hair or carapaces. Solution for the gamete movement problem: internal fecundation (except for most amphibians, that have external fecundation). Solution for the gas exchange problem: appearing of airways and lungs. Solution for the body support problem: further development of muscular and bony structures, like limbs and claws.