The main problems coming
from water to solve to to
the terrestrial were the
following: problem to avoid
; the problem of
of wastes in medium where water
less available; the of protection
against solar radiation; the
of gamete locomotion the
environment for ; the
problem of exchange, earlier done
direct contact of with gills; the
of body support, it was
water played this role fish.

Solutions for dehydration problem:
thicker impermeable skin, to
less water, or and permeable
skin, in amphibians. Solution the
excretion problem: of urea
(also by chondrichthyes) or
acid, substances that less
water to dissolved. Solutions for
problem of protection radiation:
skin pigments filter harmful
radiation, , hair or carapaces.
for the gamete
problem: internal fecundation (
for most amphibians, have external
fecundation). for the gas
problem: appearing of
and lungs. Solution the body
support : further development
of and bony structures,
limbs and claws.