Mammals can be classified by:

tooth structurebones in the headmethods 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. 830-831 in your textbook shows the order of placental mammals.)

Elephant

Shrew

Whale

• Mouse/ Rat ………………...............• Rabbit ………………………………………….........• Dog ………………………………………………• Horse …………………………………………………• Elephant …………………………………………….• Whale …………………………………………....• Cow……………………………………………• Giraffe……………………………………….• Human …………………………………………………

Between 18-21 Days28-31 Days

About 62 Days11 Months22 Months

10-14 MonthsAbout 9 Months

About 15 Months9 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)