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Biology
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32-2 Diversity of Mammals
Photo Credit: ©Zefa (RM)/M. Botzek/Masterfile
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Diversity of Mammals
The three groups of living mammals are:
monotremes
marsupials
placentals
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4. Monotremes and Marsupials
Monotremes lay eggs.
Monotremes share two notable characteristics with reptiles:
The digestive, reproductive, and urinary systems all open into a cloaca.
Females lay soft-shelled eggs that incubate outside the body.
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5. Monotremes and Marsupials
Only three species of monotremes exist today: the duckbill platypus and two species of spiny anteaters, or echidnas.
These animals are found in Australia and New Guinea.
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6. Monotremes and Marsupials
Marsupials bear live young, but at a very early stage of development.
Young marsupials complete their development in an external pouch.
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Placental Mammals
Placental Mammals
Placental mammals are named for an internal structure called the placenta, which forms when the embryo's tissues join with tissues from within the mother's body.
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32-2
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32-2
Most mammals are
monotremes.
marsupials.
placental mammals.
placental marsupials.
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32-2
Monotremes are the only group of mammals that
lay eggs
have hair.
feed their young with milk.
are endotherms.
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32-2
Ant-eating mammals on different continents look similar to each other because they are all
a result of divergent evolution.
adapted to similar ecological opportunities.
recently evolved from a common ancestor.
evolved from an ant-eating reptile.
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32-2
What is the function of the placenta?
production of milk
exchange of materials between fetus and mother
digestion of food
protection of a young mammal after birth
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