32-2 Diversity of Mammals

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:

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monotremes

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marsupials

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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. Slide 6 of 25 Copyright Pearson Prentice Hall

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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. Slide 9 of 25 Copyright Pearson Prentice Hall

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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. Slide 11 of 25 Copyright Pearson Prentice Hall

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32-2 Diversity of Mammals

Placental Mammals

There are twelve orders of placental mammals.

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Insectivores (insect eaters with long, narrow snouts and sharp claws)

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Sirenians (large, slow moving mammals that live in aquatic environments)

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Cetaceans (aquatic mammals that must come to the surface to breathe)

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Rodents (have a single pair of long, curved incisor teeth) Slide 12 of 25 Copyright Pearson Prentice Hall

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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)

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Artiodactyls (hoofed mammals with an even number of toes on each foot)

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Lagomorphs (herbivores with two pairs of incisors and hind legs adapted for jumping)

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Carnivores (have sharp claws and teeth that they use to catch, kill, and eat prey) Slide 13 of 25 Copyright Pearson Prentice Hall

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32-2 Diversity of Mammals

Placental Mammals

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Chiropterans (winged mammals)

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Xenarthrans (simple teeth without enamel, or no teeth)

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Primates (highly developed cerebrum and complex behaviors)

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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. Slide 18 of 25 Copyright Pearson Prentice Hall

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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 Slide 19 of 25 Copyright Pearson Prentice Hall

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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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Rabbits belong to an order of mammals called the

a. cetaceans. b. lagomorphs. c. proboscideans. d. chiroptera.

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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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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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