Mammals can be classified by: tooth structure bones in the head methods of reproduction and developing Three groups of living mammals: Monotremes Marsupials Placentals

Lay eggs Digestive, reproductive, and urinary systems open into a cloaca, like a reptile Monotreme means “single opening” Eggs are incubated outside of the body Young monotremes are nourished by their mother’s milk, licked from pores on the surface of her abdomen Only three living species: duckbill platypus, and two species of spiny anteaters, or echinadas Found in Australia and New Guinea Perry the Platypus is a monotreme!

Bear live young at a very early stage of development Usually completes development in an external pouch, or a marsupium, on the mother’s body Marsupials are named after this structure Lives in pouch several months, drinking the mother’s milk and growing Opossum Koala Kangaroo

Named after their internal structure, the placenta, which is formed when the embryo’s tissues join with tissues from within the mother’s body Usually after birth, the mom cares for their young Nutrients, oxygen, carbon dioxide, and wastes are exchanged between embryo and mom through the placenta, allowing the embryo to develop much longer than a marsupial (pg in your textbook shows the order of placental mammals.) Elephant Shrew Whale

Mouse/ Rat ……………… Rabbit ………………………………………… Dog ……………………………………………… Horse ………………………………………………… Elephant ……………………………………………. Whale ………………………………………….... Cow…………………………………………… Giraffe………………………………………. Human ………………………………………………… Between Days Days About 62 Days 11 Months 22 Months Months About 9 Months About 15 Months 9 Months

When the continents separated into different parts of the world, the animals there adapted to their environment. Similar ecological opportunities on the different continents have produced some examples of convergent evolution in mammals. (pg 832)