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.