The following changes occured in the organisms that helped them
survive in the terrestrial environment:
- Respiratory system: The biggest change that occured when life
moved from aquatic to the terrestrial environment is the change in
the gas exchange organ. The swimbladder modified
into the primitive lung helping the organism to take oxygen from
the air. In fishes swimbladder helps in buoyancy. Due to evolution
the swimbladder formed the lungs. Lungfish are found only in
Africa, South America and Australia.The lung is connected to the
pharynx. When their pools dry up they survive by burrowing into the
mud and sealing themselves within a mucous-lined burrow.
- Heart Chambers: Fishes have a two-chambered heart but that was
not enough so the amphibians evolved a three-chambered heart except
for crocodiles who have a four-chambered heart. This involves
partial mixing of blood, and it ispumped at a higher pressure.
- Weight bearing: Due to buoyancy marine creatures don't have a
problem in supporting their own weight, but terrestrial animals
spend a lot of energy in movement.Formation of limbs took place to
overcome this problem
- Protection from heat: The temperature on the land changed
drastically and quite fast. Terrestrial organism evolved mechanisms
to protect themselves from these fluctuations. They even changed
their metabolic activities.
- Use of water and evolution of kidneys: To keep a certain amount
of water in the body kidneys evolved in such a way that they were
able to filter the waste products and save as much water as
possible. Moisture in the skin was there to prevent its drying up.
Urea was stored in the bladder and excreted out.
- Other changes like placement of eyes on the head and head, neck
mobility helped the organisms in locomotion, sense of direction,
protection from predators etc.