Groups of Mammals
Classification of Mammals
• Mammals range in size from a tiny shrew (1.5
grams) to a blue whale (150 tons)
• Mammals inhabit more environment than any
other vertebrates
• Modern mammals are classified into three
groups
– Monotremes
– Marsupials
– Placental Mammals
Monotremes
• Monotremes are a small group of organisms
found only in Australia and New Guinea
• Monotremes share more traits with reptiles
than with other mammals.
• Monotremes are the only living mammals
that lay eggs
Monotremes are similar to reptiles
because…
• Monotremes have legs that sprawl to the side
instead of being under the body
• Monotremes are the only mammals to have a
cloaca
– A common passage way for the digestive,
reproductive and urinary systems
• Adult monotremes DO NOT have teeth
Monotremes are like other mammals
because…
• Monotremes have hair
• Monotremes produce milk to feed their young
– However, female monotremes DO NOT have
nipples
– Young drink milk that oozes from glands that are
located on their mother’s belly
Marsupials
• Marsupials include: Wombats, Koalas, and
opossums
• Females of most marsupials have a pouch,
and their young spend most of their time
developing inside the pouch while they nurse
and grow
Marsupials
• Marsupials are the most diverse mammals in
Australia
– Marsupials are also found in South America and
North America
Marsupials
• The habitats and lifestyles of marsupials in
Australia, New Zealand, and nearby islands are
similar to those of placental mammals
• Examples:
– Kangaroos and Wallabies often live in large groups
like deer (a placental mammal)
– Tree kangaroos are similar to monkeys because
both can climb
– Gliders and possums are similar in habits to
squirrels
Placental Mammals
• Cats, dogs, cows, horses, and humans are
placental mammals
• Placental mammals make up nearly 95% of all
mammal species
• The young of placental mammals develop
inside the female’s uterus
– Here they are nourished by nutrients from her
blood
Placental Mammals
• Placental Mammals have a longer period of
internal development than marsupials
• Placental Mammals are more developed at
birth than the young of marsupials
• There are many types of placental mammals,
which vary greatly in size, shape, diet and
habits
Domestic Mammals
• Domestic Mammals are animals that have
been kept and bred by people for special
purposes
• Domestic Mammals may provide work, food,
clothing, or companionship
• Most Domestic Mammals are placental
mammals whose association with humans
dates back up to 15,000 years
Domestic Mammals
• Domestic Mammals include: dogs, cats,
cattle, horses, donkeys, mules, rabbits, sheep,
goats, pigs, camels, llamas, and alpacas
How Domestic Mammals are Made
• Various breeds of domestic mammals have been
developed through selective breeding
– Example: Some breeds of goat produce more milk than
others
• Some domestic mammals are hybrids of two
species
– Example: Mules are formed from a female horse and
male donkey