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Interest Grabber
Section 32-1
A Warm Body
Because mammals and birds generate heat within their bodies, they are
endotherms. Other types of chordates control body temperature by
behavior. These animals are ectotherms.
1. Mammals and birds eat much more food than do other types of
chordates. Why do you think this is necessary?
2. What body features do endotherms have that would provide insulation
to conserve heat produced within the body? Would you expect
ectotherms to have such features?
3. What are two examples of endotherms? What is the specific type of
insulation that each one has?
Section Outline
Section 32-1
32–1
Introduction to the Mammals
A. Evolution of Mammals
B. Form and Function in Mammals
1. Body Temperature Control
2. Feeding
3. Respiration
4. Circulation
5. Excretion
6. Response
7. Movement
8. Reproduction
The Structure of a Bear’s Heart
Section 32-1
Left
atrium
Right
atrium
Right
ventricle
Left
ventricle
Complete
division
Figure 32–4 The Jaws and Teeth of
Mammals
Section 32-1
CARNIVORE
Canines are pointed teeth. Carnivores
use them for piercing, gripping, and tearing.
In herbivores, they are reduced or absent.
HERBIVORE
Jaw
joint
Jaw joint
Wolf
Horse
Chisel-like incisors are used for
cutting, gnawing, and grooming.
Molars crush and grind food. The ridged shape of the wolf’s molars and premolars
allows them to interlock during chewing, like the blades of scissors. The broad,
flattened molars and premolars of horses are adapted for grinding tough plants.
Interest Grabber
Section 32-2
Marsupials Versus Placentals
Kangaroos and humans are both mammals because of the characteristics
they share. Still, they display enough different characteristics to result in a
kangaroo being classified as a marsupial and a human being classified as
a placental mammal. Consider what you know about kangaroos and
humans, and then answer the questions that follow.
1. How do the young of kangaroos develop,
and how do the adults care for their young?
2. How do humans and kangaroos differ from one another in caring for their
young?
3. What characteristic do humans and kangaroos have in common in terms
of caring for their young?
Section Outline
Section 32-2
32–2
Diversity of Mammals
A. Monotremes and Marsupials
1. Monotremes
2. Marsupials
B. Placental Mammals
C. Biogeography of Mammals
Compare/Contrast Table
Section 32-2
Orders of Placental Mammals
Order
Characteristics
Examples
Insectivores
Long, narrow snouts, sharp
claws
Shrews, hedgehogs, moles
Sirenians
Water-dwelling, slow-moving
Manatees, dugongs
Cetaceans
Live and breed in ocean, come
to surface to breathe
Whales, dolphins
Chiropterans
Winged, capable of true flight
Bats
Rodents
Single pair of long, curved incisor
teeth in upper and lower jaws
Mice, rats, voles, squirrels,
beavers, porcupines, chinchillas
Compare/Contrast Table continued
Section 32-2
Orders of Placental Mammals
Order
Characteristics
Examples
Perissodactyls Hoofed, with an odd number of
toes on each foot
Horses, tapirs, rhinoceroses,
zebras
Carnivores
Sharp teeth and claws
Tigers, hyenas, dogs, foxes, bears,
raccoons, walruses
Artiodactyls
Hoofed, with an even number of
toes on each foot
Cattle, sheep, goats, pigs, ibex,
giraffes, hippopotami, camels
Proboscideans Trunks
Asian and African elephants,
mastodons and mammoths
Compare/Contrast Table continued
Section 32-2
Orders of Placental Mammals
Order
Characteristics
Examples
Lagomorphs
Two pairs of incisors in upper
jaw, hind legs allow leaping
Snowshoe hares, rabbits
Xenarthrans
No teeth (or very small teeth in
the back of the jaw)
Sloths, anteaters, armadillos
Primates
Highly developed cerebrum and
complex behaviors
Lemurs, tarsiers, apes, gibbons,
macaques, humans
Figure 32–13 Convergent Evolution
of Insect-Eating Mammals
Section 32-2
Chinese
Pangolin
Nine-Banded
Armadillo
Common
Echidna
Giant Anteater
Aardvark
Interest Grabber
Section 32-3
Skeletal Features of Primates
Recall that primates are an order of mammals. One difference that exists
between primates and other mammals is in the structure of the primate
skeleton. Some examples of primates include humans, lemurs, monkeys,
and apes.
1. How are the external features of your hands different from the external
features of the paws of a dog or the hooves of a horse?
2. Primates are bipedal, or capable of walking on two limbs. What is an
advantage of being bipedal?
3. What are some characteristics of your skeleton that enable you to stand
and walk?
Section Outline
Section 32-3
32–3
Primates and Human Origins
A. What Is a Primate?
1. Fingers, Toes, and Shoulders
2. Well-Developed Cerebrum
3. Binocular Vision
B. Evolution of Primates
1. Prosimians
2. Anthropoids
Section Outline continued
Section 32-3
C. What Is a Hominid?
1. Early Hominids
2. Australopithecus
3. Paranthropus
4. Kenyanthropus
5. How Do the Branches Connect?
D. The Road to Modern Humans
1. The Genus Homo
E. Out of Africa—But Who and When?
F. Modern Homo sapiens
Comparison of Skulls of Human
Ancestors
Section 32-3
Large brow
ridge
Large nose
Large canine
teeth
Face protrudes
forward
Australopithecus afarensis
Weak brow
ridge
Homo erectus
Large
brain
case
Round, high
skull
Inflated
cheeks
Large
nose
Even teeth
Strong chin
Neanderthal
Cro-Magnon
Modern Homo sapiens
Figure 32–16 Human and Gorilla
Skeletons
Section 32-3
Comparing Human and Gorilla Skeletons
Modern Human
Modern Gorilla
Modern Human
Modern Gorilla
Skull atop
S-shaped spine
Skull atop
C-shaped spine
Spinal cord exits
at bottom of skull
Spinal cord exits
near back of skull
Arms shorter than
legs; hands do not
touch ground
during walking
Arms longer than
legs; hands touch
ground during
walking
Pelvis is bowlshaped
Pelvis is long
and narrow
Thigh bones angled
inward, directly
below body
Thigh bones angled
away from pelvis

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