1. Milk Production
All females have mammary glands which make milk for their young, and only these
organisms suckle their young from mammary glands. Most of these babies suckle milk
from their motherʼs teats. Some do not have teats so their babies suckle on hairs near the
mammary glands. The young often stay with their mothers for an extended period of time,
though they usually do not be feed on milk for the whole time. They mature more slowly
than most other animals and need more looking after by their mothers to become healthy
adults.
Hair or Fur
All have some component of hair or fur, something no other animal has. It may be coarse,
stray hairs like on the chin of a whale or a thick, fur coat like on a bison. The coat of most
of these organisms have guard hairs or longer hairs that protect the soft underhair. Guard
hairs may develop into quills like you would see on a porcupine. Hair or fur is used to keep
them warm and to help keep their body temperature constant, which is called being warm -
blooded or endothermic. The underhairs provide most of this warmth.
Some characteristics such as live birth and being warm-blooded, are shared by most
mammals but may also be seen in other animals.
Warm-Blooded (Endothermic)
All are warm blooded, or endothermic, which means they can regulate their body
temperature separately from the environment. For example, the musk ox can keep a body
temperature well above the frigid temperatures of the arctic. These organisms must eat a
lot more than ectothermic animals to make this body heat and they use their hair or fur to
keep the heat from being lost to the environment.
Live Birth
Most give birth to live young as opposed to laying eggs. The young develop inside the
mother and are nourished by a placenta.
Cold Blooded
These organisms are cold blooded so need to bask in the sunshine and use their
environment to maintain their body temperature.
Feathers
These organisms are covered with feathers, varying from very small to quite large
Lay eggs
These organisms generally do not give birth to live young and instead lay eggs which need
to hatch.
Live on the water and on the land
These organisms are unusual because they can live both on water and on the land at
various stages of their life cycle

2. Breathe through Gills
These organisms do not have lungs and instead get their oxygen through gills
Beaks
These organisms have beaks
Smooth skin
These organisms have smooth often slightly moist/slimy skin
Rough Skin
These organisms have rough bumpy dry skin and occasionally scales