Vertebrates are characterized by having a backbone, skull, and internal skeleton. They include fish, amphibians, reptiles, birds, and mammals. Fish live exclusively in water and have fins and scales. Amphibians can live on land and in water, are ectothermic, and have moist skin. Reptiles are amniotes that lay shelled eggs and most have scales and four legs. Birds are endothermic, lay shelled eggs, have feathers, beaks, and wings. Mammals are endothermic and feed their young with milk produced by mammary glands.

2. Distinctive Characteristics of Vertebrates
- All animals that belong to vertebrates also belong to the phylum Chordata
(flexible rod between the nerve cord and the digestive tract)
- Have a skull and several other skeletal bones which form an endoskeleton.
- Higher nervous system (central nervous system and peripheral nervous
system)
- Skin covers their body. They can have scales, feathers, hairs, or nails, as
external skeletons.

3. 1. Fishes
Fishes are aquatic animals. They can be found nearly
all aquatic environments. They are cold blooded. They warm
themselves by absorbing heat from their environment.
Animals that absorb heat from outside are called
ectotherms. Ecto means “outside”, while therm means “body
temperature”.
Common Types of Vertebrates

4. Fish have fins which make them distinct from the other vertebrates.
Fins – help fishes in keeping balance and propelling and steering
through the water.
Types and functions of fins:
caudal fin or tail fin (main fin) – It helps fishes to
move forward in water
dorsal and anal fins (top and bottom) – Used by
fishes for balance
paired pectoral (found each side) – Help fishes to
steer and hover in water

5. Scales – serves as protection against any injury or
infection.
Gills – These are special organs used by fishes in order
to breathe underwater.
Lateral line system – It helps in the detection of
underwater vibrations and in determining their source
through the small sensory hairs contained in the lateral
system.

6. Swim bladder or air bladder – It helps the fishes in moving up or down in the water.

7. 2. Amphibians
Amphibians derive heat from the outside. This is the reason why they are
called cold-blooded. Their body temperature is dependent on the temperature of
their outside surroundings. In warm environments, they are active. However, in cold
environments, they become exhausted.
Amphibians are carnivorous in general. They eat fishes, small reptiles,
crustaceans, and other amphibians when they are in water. On the other hand, they
eat worms and insects when they are on land.

9. 3. Reptiles
Like fishes and amphibians, reptiles are also cold-blooded or ectotherms. The
bodies of reptiles have scales. These scales develop as surface cells filled with keratin.
Having a backbone or spinal cord column is common among most reptiles except for
snakes.
Reptiles are born as amniotes eggs. These eggs can live outside the water.
Having four legs is also common to most reptiles. Claws can be found on their toes.
There are reptiles which have no legs such as snakes and some lizards.
Eyes serve as the most important sense organ to reptiles. This excludes the
snakes since they are blind. Reptiles can detect objects around through their vision.
They do not have external ears. They only have an eardrum near their eyes and close
to the surface of their skin.

11. 4. Birds
Birds are warm-blooded (endotherm) vertebrates. This means that they
generate much heat from their own metabolism. Their temperature does not
change with the temperature of their own surroundings.
Birds lay eggs. The young develops inside the egg and hatches when its body parts
are complete. Birds take care of their young.
Birds can see and hear well, but they cannot smell and taste as well. They
also have flexible necks, so they can turn their heads halfway around and see what
is behind them.

12. Bird’s feathers are made up of keratin, other proteins, and light-reflecting
pigments which insulate their body.
Classification of birds feathers:
contour feathers – rigid and form the shape of the birds (found on body tail and
wings)
down feathers – soft and fluffy feathers (found under the contour feathers)
flight feathers – long, stiff feathers (tip and trailing edge of wings and tail)
Male birds show off the feathers to attract mate. An example is the Palawan
peacock pheasant. It uses its beautiful tail ornamental feathers to attract the peahen.

13. contour feathers down feathers
flight feathers

14. Birds have beaks that they use for getting food,
protecting themselves from enemies, cleaning and repairing
their feathers. Beaks are made of the same material that make
up birds feathers called keratin.

15. Birds have feet in different shapes and
sizes. The feet serve a very important function in
the bird’s body. These appendages support the
body of the birds when they stand, walk, and run
on different surfaces as well as the shape and sizes
of the claws and the arrangement, length, and
degree of webbing depends upon every bird’s
specific use of the feet and particular habitat.

16. 5. Mammals
Mammals are warm-blooded animals. Even if the temperature outside is low,
their body temperature remains high. All mammals have furs or hairs. These body
structures prevent the loss of body heat in mammals. Hairs are also made of keratin.
Characteristics of mammals:
1. A mammal has a mammary glands that produce milk. Dogs, cats, carabaos,
cows and horses are some of the mammals that feed their young on milk.
2. The egg cell is fertilized inside the body of the female.

17. Placentals Group (biggest group of mammals)
Embryo develops inside the mother’s womb and receives food and oxygen
through placenta. Dogs, cats, cows, and horses are some of the examples that belong
to this group.
Marsupial Group (second group of mammals)
The young are born before their development is complete. The tiny babies
complete their development inside the pouch (marsupium) that is attached to the
mother’s nipples. Koalas and kangaroos are marsupials.
Monotremes Group (smallest group)
The mothers lays the eggs that have the developing embryos inside. An
example is the duck-billed platypus. The duck-billed platypus lays two eggs in a nest
made of leaves. It sits or incubates the eggs with its body warmth until they hatch.
Then, it feeds the young by letting them lick the milk on her furs.

18. Placentals Group

19. Marsupial Group

20. Monotremes Group