32.2 Section Objectives – page 848 Distinguish among the three groups of living mammals. Compare reproduction in egg-laying, pouched, and placental mammals. 32.2 Section Objectives – page 848

Section 32.2 Summary – pages 848 - 851 Mammal Classification Scientists place mammals into one of three subclasses based on their method of reproduction. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Placental mammals: A great success Placental mammals give birth to young that have developed inside the mother’s uterus until their body systems are fully functional and they can live independently of their mother’s body. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Placental mammals: A great success The uterus is a hollow, muscular organ in which offspring develop. Nourishment of the young inside the uterus occurs through an organ called the placenta which develops during pregnancy. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Placental mammals: A great success The time during which placental mammals develop inside the uterus is called gestation. Development inside the mother’s body ensures that the offspring are protected from predators and the environment during the early stages of development. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Pouched mammals: The marsupials A marsupial is a mammal in which the young have a short period of development within the mother’s body, followed by a period of development inside a pouch made of skin and hair on the outside of the mother’s body. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Pouched mammals: The marsupials Most marsupials are found in Australia and surrounding islands. Scientists have found fossil marsupials on the continents that once made up Gondwana. These fossils support the idea that marsupials originated in South America, moved across Antarctica, and populated Australia before Gondwana broke up. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Monotremes: The egg layers The duck-billed platypus is a monotreme, a mammal that reproduces by laying eggs. Spiny anteaters, also called echidnas, belong to this subclass as well. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Monotremes: The egg layers Monotremes are found only in Australia, Tasmania, and New Guinea. Only three species of monotremes are alive today. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Monotremes: The egg layers The platypus, a mostly aquatic animal, has a broad, flat tail, much like that of a beaver. Its rubbery snout resembles the bill of a duck. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Monotremes: The egg layers The platypus has webbed front feet for swimming through water, but it also has sharp claws on its front and hind feet for digging and burrowing into the soil. Much of its body is covered with thick, brown fur. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Monotremes: The egg layers The spiny anteater has course, brown hair, and its back and sides are covered with sharp spines that it can erect for defensive purposes when threatened by enemies. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Origins of Mammals The first placental mammals appeared in the fossils record about 125 million years ago. Scientists trace the origins of placental mammals from a group of mouse-sized animals to a group of reptilian ancestors called therapsids. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Origins of Mammals Therapsids had features of both reptiles and mammals. They existed between 270 and 180 million years ago. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Origins of Mammals The mass extinction of the dinosaurs at the end of the Mesozoic Era, along with the breaking apart of Pangaea and changes in climate, opened up new niches for early mammals to fill. The Cenozoic Era is sometimes called the golden age of mammals because of the dramatic increase in their numbers and diversity. Section 32.2 Summary – pages 848 - 851

Section 32.2 Summary – pages 848 - 851 Origins of Mammals Artiodactyls 220 species Cetaceans 79 species Carnivores 270 species Primates 230 species Rodents 2000 species Chiropterans 925 species Perissodactyls 270 species Insectivores 375 species Placental mammals 4400 species Proboscids 2 species Therapsids mammal-like reptiles Marsupials 280 species Reptiles Amphibians Fishes Monotremes 3 species Invertebrates Species numbers are approximate and subject to change pending discoveries or extinctions. Section 32.2 Summary – pages 848 - 851

3 Subclasses within the class Mammalia: Prototheria or Monotremes (3 species) Metatheria or Marsupials (275 species) Eutheria or placental mammals (3982 species)

Monotremes Most primitive mammals Only 3 species: duck-billed platypus and two spiny anteaters, or echidnas Oviparous; eggs with a leathery shell; mothers nourish their young with milk after young hatch Lack nipples Live only in Australia & New Guinea The name monotreme means one-holed (i.e.cloaca)

Echidna & Duck-billed Platypus

Marsupials Viviparous Immature young are incubated in the pouch Tasmanian wolf

Flying Squirrel

Tasmanian Devil

Marsupial Mouse

Koala (Aboriginal for no drink …They sleep for 19 hrs/day)

Wombat

Kangaroo

Wallaby

Marsupial Pouch

Opossum

The only time you see an opossum…