Mammals - OnMyCalendar

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