Amniotes

All the basic features of amniotes

1. 26.1 Amniotes
KEY CONCEPT
Reptiles, birds, and mammals are amniotes.

2. 26.1 Amniotes
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. 26.1 Amniotes
•The amniotic egg allowed vertebrates to reproduce on
land.
Embryo
Allantois
Holds waste materials
as the embryo grows
Yolk sac
Contains the nutrient
supply for the growing
embryo
Amnion
Protects and
surrounds the
embryo
Chorion
Allows gas exchange
with outside environment

4. 26.1 Amniotes
Anatomy and circulation differ among amniotes.
•Other amniotes, including dinosaurs, evolved a more
upright stance.
•The first animals walked in a sprawl.

5. 26.1 Amniotes
•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. 26.1 Amniotes
•Amniotes have a three-or four-chambered heart.
–reptiles hearts have three chambers
THREE-CHAMBERED HEART
–birds and mammals hearts have four chambers
FOUR-CHAMBERED HEART

7. 26.1 Amniotes
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.