Chapter 43Mammals

Section 1

Origin and Evolution of Mammals

Characteristics• Endothermy- regulate own body

temperature- metabolism• Hair- all mammals have some hair-

made of keratin• Completely divided heart- four-

chambered heart- no mixing of blood

Characteristics• Milk- females produce milk to feed

offspring- made of fats, proteins, and sugars– Produced by mammary glands- modified sweat

glands located on thorax or abdomen

• Single jawbone- fossils identified by bones

• Specialized teeth- for eating

Ancestors of Mammals• Synapsids- gave rise to mammals

• Single opening in a bone behind eye socket

• Looked like modern lizards

• Specialized teeth

Therapsid• Also gave rise to mammals

• Rich fossil record of transitional forms between therapsids and mammals exists

Early Mammals• Dinosaurs co-existed with

mammals

• Early mammals were about the size of a mouse

• Large eye sockets suggests that early mammals were active at night

Diversification of Mammals• Monotremes- oviparous- lay

eggs• Marsupials- viviparous- give

birth to live young- young develop in pouch

• Placental mammals- viviparous- develop in mother’s uterus- nutrition from placenta

Monotremes

Marsupials

Placental Mammals

REVIEW!!!• What is the function of hair in

mammals?

• Differentiate between monotremes, marsupials, and placental mammals.