Biology
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32-2 Diversity of Mammals
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32-2 Diversity of Mammals
Diversity of Mammals
The class Mammalia contains about 4500 species.
Tooth structure and the number and kind of bones in
the head are used to classify mammals.
The most important way to categorize living
mammals is by the way they reproduce and develop.
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32-2 Diversity of Mammals
Diversity of Mammals
The three groups of living mammals are:
•
monotremes
•
marsupials
•
placentals
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32-2 Diversity of Mammals
Monotremes and Marsupials
How do the three groups of living mammals
differ from one another?
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32-2 Diversity of Mammals
Monotremes and Marsupials
Monotremes
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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32-2 Diversity of Mammals
Monotremes and Marsupials
Young monotremes are nourished by their mother's
milk, which they lick from pores on her abdomen.
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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32-2 Diversity of Mammals
Monotremes and Marsupials
Marsupials
Marsupials bear live young, but at a very
early stage of development.
Young marsupials complete their
development in an external pouch.
When marsupials reproduce, the fertilized
egg develops into an embryo inside the
mother's reproductive tract.
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32-2 Diversity of Mammals
Monotremes and Marsupials
Once born, the embryo crawls across its mother's fur
and attaches to a nipple.
Nipples are located in a pouch called the marsupium
on the outside of the mother's body.
The embryo spends several months attached to the
nipple.
The young marsupial will drink milk until it grows
enough to survive on its own.
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32-2 Diversity of Mammals
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 Diversity of Mammals
Placental Mammals
In placental mammals, nutrients, oxygen,
carbon dioxide, and wastes are
exchanged efficiently between embryo
and mother through the placenta.
The placenta allows the embryo to develop
for a longer time inside the mother.
Most placental mammals care for and nurse
their young after birth.
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32-2 Diversity of Mammals
Placental Mammals
There are twelve orders of placental mammals.
•
Insectivores (insect eaters with long, narrow
snouts and sharp claws)
•
Sirenians (large, slow moving mammals that
live in aquatic environments)
•
Cetaceans (aquatic mammals that must
come to the surface to breathe)
•
Rodents (have a single pair of long, curved
incisor teeth)
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32-2 Diversity of Mammals
Placental Mammals
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Perissodactyls (hoofed mammals with an odd
number of toes on each foot)
•
Artiodactyls (hoofed mammals with an even
number of toes on each foot)
•
Lagomorphs (herbivores with two pairs of
incisors and hind legs adapted for jumping)
•
Carnivores (have sharp claws and teeth that
they use to catch, kill, and eat prey)
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32-2 Diversity of Mammals
Placental Mammals
•
Chiropterans (winged mammals)
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Xenarthrans (simple teeth without enamel, or
no teeth)
•
Primates (highly developed cerebrum and
complex behaviors)
•
Proboscideans (mammals with trunks)
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32-2 Diversity of Mammals
Biogeography of Mammals
How did convergent evolution cause
mammals on different continents to be
similar in form and function?
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32-2 Diversity of Mammals
Biogeography of Mammals
Biogeography of Mammals
Earth’s geography has shaped today’s mammals.
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32-2 Diversity of Mammals
Biogeography of Mammals
During the Paleozoic Era, the continents were one
large landmass, and mammals could migrate freely
across it.
As continents drifted apart during the Mesozoic and
Cenozoic, ancestors of mammal groups were
isolated from one another.
Each landmass took with it a unique array of mammal
groups.
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32-2 Diversity of Mammals
Biogeography of Mammals
Similar ecological opportunities on the
different continents have produced some
striking examples of convergent evolution
in mammals.
Landmasses merged in the late Cenozoic,
and mammals dispersed into new habitats.
Living mammals reflect the diversity that
resulted.
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32-2 Diversity of Mammals
Biogeography of Mammals
Convergent Evolution in Mammals
Chinese Pangolin
Nine-Banded
Armadillo
Common Echidna
Giant Anteater
Aardvark
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32-2
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32-2
Most mammals are
a. monotremes.
b. marsupials.
c. placental mammals.
d. placental marsupials.
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32-2
Monotremes are the only group of mammals that
a. lay eggs
b. have hair.
c. feed their young with milk.
d. are endotherms.
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32-2
Rabbits belong to an order of mammals called
the
a. cetaceans.
b. lagomorphs.
c. proboscideans.
d. chiroptera.
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32-2
Ant-eating mammals on different continents look
similar to each other because they are all
a. a result of divergent evolution.
b. adapted to similar ecological opportunities.
c. recently evolved from a common ancestor.
d. evolved from an ant-eating reptile.
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32-2
What is the function of the placenta?
a. production of milk
b. exchange of materials between fetus and
mother
c. digestion of food
d. protection of a young mammal after birth
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