Placental Mammals Objectives

• Explain how placental mammals develop.

• Give an example of each type of placental mammal.

I. Placental Mammals

• Mammals are divided into groups based on how they develop.

A. A placental mammal is a mammal whose embryos grow in an organ called a uterus. An organ called the placenta attaches the embryo to the uterus.

B. The length of time between fertilization and birth is called the gestation period.

II. Anteaters, Armadillos, and Sloths A. A few mammals have

unique backbones that have special connections between the vertebrae. This group includes anteaters, armadillos, and sloths.

B. Most mammals in this group eat insects they catch with their long, sticky tounges.

http://www.quantum-conservation.org/EEP/anteater.gif

http://t1.gstatic.com/images?q=tbn:ANd9GcRGwDmlK_YYVOcvW1p41SaOzcMZlxpz8dOqSHm8tZiHZBJsHL61zDjBMOo5

III. Insectivores

A. Insectivores make up another group of mammals that eat insects. This group includes moles, shrews, and hedgehogs.

B. Most members of this group are small, have long, pointed noses, small brains, and simple teeth.

http://t1.gstatic.com/images?q=tbn:ANd9GcRAEpJ4G2CnQVxF-Fjr93syeHRh5VpPW9pCnns3P0mRDz1rD79hGRRiBGGXcw

http://animal.discovery.com/tv/a-list/creature-countdowns/hissy-fits/images/hissy-shrew.jpg

IV. Rodents

A. More than one-third of mammal species are rodents. Rodents live on every continent except Antarctica.

B. Squirrels, mice, rats, guinea pigs, porcupines, and chinchillas are all rodents.

C. Rodents have one set of incisors in their upper jaw. Rodents gnaw and chew so much that their teeth wear down. But that doesn’t stop their chewing––their incisors grow continuously!

http://t3.gstatic.com/images?q=tbn:ANd9GcTJNyS_yEUb2-x0bpKj6am1vOk1mgkxjGKEDvy8EWh-1BghmbrhsiXk5KuQEg

V. Rabbits, Hares, and Pikas A. Rodents are similar to a group

of mammals that includes rabbits, hares, and pikas. Like rodents, they have sharp gnawing teeth.

B. Unlike rodents, this group has two sets of sharp incisors in their upper jaw. Their tails are also shorter than rodent’s tails.

http://wnpf.org/Upload/Images/pika2.jpg

Difference between rabbits and hares

VI. Flying Mammals

A. Bats are the only mammals that fly. Bats are active at night. They sleep in protected areas during the day. Most bats eat insects or other small animals. But some bats eat fruit or plant nectar.

B. Most bats use echoes to find their food and their way. Using echoes to find things is called echolocation. http://animals.nationalgeogr

aphic.com/animals/mammals/common-vampire-bat/

Graphing Gestation Periods

Animal Human Hamster Dog Cat Pig Horse Blue Whale

Elephant

Gestation Period (days)

270 16 61 63 114 336 360 660

VII. Carnivores A. Mammals that have large canine

teeth and special molar teeth for slicing meat are called carnivores.

B. Many mammals in this group eat only meat, but other members of this group are omnivores or herbivores that eat plants.

C. Bears, cats, dogs, otters, raccoons and pinnipeds––the group of fish-eating ocean mammals that includes seals, sea lions, and walruses––are all carnivores.

http://www.firstpeople.us/pictures/bear/1600x1200/Feeling_Grizzly-1600x1200.jpg

VIII. Trunk-Nosed Mammals

A. Elephants are the only mammals that have a trunk. The trunk is a combination of an upper lip and a nose.

B. An elephant uses its trunk in the same ways we use our hands, lips, and nose. Elephants use their trunks to put food in their mouths and to spray water on their backs to cool off.

http://t1.gstatic.com/images?q=tbn:ANd9GcRbLc-YJ7Bl4WyscDgLdxe7errpfc42yl3tqFnmla1fdVKHGQqATjRbk8Q1ig

IX. Hoofed Mammals A. Horses, pigs, deer, and

rhinoceroses are some of the many mammals that have thick hoofs.

B. A hoof is a thick, hard pad that covers a mammal’s toe. The hoof is similar to a toenail or a claw, but it covers the entire toe.

C. Hoofed mammals are divided into two orders ––odd-toed and even-toed––based on how many toes are on each foot.

http://t2.gstatic.com/images?q=tbn:ANd9GcQgOMnNUaHophfvQLTG8WvocSkS7DZ4cqZYpzO6qCmxcxpiCTbiiSM-bRbI

X. Cetaceans

A. Cetaceans are a group of mammals made up of whales, dolphins, and porpoises. All cetaceans live in the water.

B. While they may look like fish, cetaceans have lungs and nurse their young.

C. Like bats, cetaceans use echolocation to find fish and other animals.

http://www.dolphinworld.org/stories/porpoise.jpeg

XI. Manatees and Dugongs A. The smallest group of mammals that

live in the water are manatees and dugongs. This group includes three species of manatees and the dugong.

B. Manatees and dugongs use their front flippers and a tail to swim slowly through the water. They live along coasts and rivers where they eat seaweed and water plants.

C. Like cetaceans, manatees and dugongs surface to breathe air.

http://t2.gstatic.com/images?q=tbn:ANd9GcSkM4i4fAw66zQBerpqu1HqRzbAbIpvOo8GW0HNDWiZVrHK09UBf5LjHrBUWA

XII. Primates

A. Scientists classify prosimians, monkeys, apes, and humans as primates.

B. These animals have five fingers on each hand and five toes on each foot. Primates have opposable thumbs, which allow them to hold objects.

C. Primates have a larger brain than most other mammals the same size have. They are considered highly intelligent animals.

Carnivore Conservation Debate

• Some carnivores are endangered due to habitat loss, hunting, and poaching.

• One reason people kill these carnivores is because they eat their livestock.

• Sometimes people kill them for their fur or body parts.

• Should wolves be protected? • What steps should be taken to support your

viewpoint? • Write a paragraph stating your opinion.