1. KEY CONCEPT Reptiles, birds, and mammals are amniotes.

2. Amniote embryos develop in a fluid-filled sac.
The amniotic sac contains everything an embryo needs to grow.
some develop inside mother’s body
some develop inside a tough, semipermeable shell

3. The amniotic egg allowed vertebrates to reproduce on land.
Allantois Holds waste materials as the embryo grows
Embryo
Amnion Protects and surrounds the embryo
Chorion
Allows gas exchange
with outside environment
Yolk sac Contains the nutrient
supply for the growing
embryo

4. Anatomy and circulation differ among amniotes.
The first animals walked in a sprawl.
Other amniotes, including dinosaurs, evolved a more upright stance.

5. All amniotes have two circuits of blood vessels.
pulmonary circuit moves blood from the heart to the lungs
systemic circuit moves blood from the heart to the rest of the body

6. Amniotes have a three- or four-chambered heart.
reptiles hearts have three chambers
birds and mammals hearts have four chambers
THREE-CHAMBERED HEART
FOUR-CHAMBERED HEART

7. Amniotes can be ectothermic or endothermic.
Amniotes manage body heat in different ways.
Ectotherms have body temperatures determined by the surrounding environment.
Endotherms use metabolic heat to keep tissues warm.
Endotherms can live in a wider range of climates than ectotherms.