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.

8. KEY CONCEPT 26.2 Reptiles were the first amniotes.

9. Reptiles are a diverse group of amniotes.
Reptiles share several characteristics.
ectotherms
covered with dry scales
reproduce by laying or retaining amniotic eggs
three-chambered heart
cloaca

10. Reptiles have two reproductive strategies.
Oviparous reptiles deposit eggs into an external nest.
Viviparous reptiles retain eggs and give birth to live offspring.

11. Reptiles have been evolving for millions of years.
Over time, amniotes evolved into three different groups.
synapsids
anapsids
diapsids

12. The diversity of ancient reptiles led to the evolution of modern reptiles, birds, and mammals.

13. There are four modern groups of reptiles.
Turtles, tortoises, and terrapins are the remaining anapsids.
bony shell encases body
200 species

14. Sphenodonts are closely related to lizards.
diapsids
primitive characteristics
two species

15. shed skin at regular intervals flexible skull Jacobson’s organ
Snakes and lizards are very closely related and share a number of features.
diapsids
shed skin at regular intervals
flexible skull
Jacobson’s organ
brain
tongue
Jacobson’s
organ

16. Crocodilians are more closely related to birds than other diapsids.
semi-aquatic predators
23 species

17. KEY CONCEPT 26.3 Birds have many adaptations for flight.

18. Birds evolved from theropod dinosaurs.
Birds and many theropods share anatomical features.
hollow bones
fused collarbones that form V-shaped wishbone
rearranged muscles in the hips and legs
“hands” that have lost their fourth and fifth fingers
feathers

19. The oldest undisputed fossilized bird is Archaeopteryx.

20. A bird’s body is specialized for flight.
Birds have several unique features that allow them to fly.
wings to produce flight
strong flight muscles to move the wings
active metabolism that provides energy to the muscles
hollow bone structure to minimize weight
gonads active during only part of year
small
intestine
large
lung
gizzard
kidney
cloaca
crop
sternum (keel)
heart
liver
pectoral muscle

21. Wings are structures that enable birds to fly.
airfoil shape
covered with feathers

22. Air sacs help a bird meet its oxygen demand during flight.

23. Birds have spread to many ecological niches.
The shape of a bird’s wing reflects the way it flies.
short and broad
long and narrow

24. The shape of a bird’s wing reflects the way it flies. wide and broad
small
intestine
large
lung
gizzard
kidney
cloaca
crop
sternum (keel)
heart
liver
pectoral muscle
stout and tapered

25. Differences in the shape of a bird’s beak reflects how it eats.
spearlike
hooked
chisel-shaped
blue-footed booby
Bald eagle
green woodpecker

26. Birds show great diversity in their foot shape. webbed heavy claws
different toe location
blue-footed booby
bald eagle
green woodpecker

27. KEY CONCEPT 26.4 Evolutionary adaptations allowed mammals to succeed dinosaurs as a dominant terrestrial vertebrate.

28. All mammals share several common characteristics.
Mammals are active, large-brained, endotherms with complex social, feeding, and reproductive behaviors.

29. All mammals share four anatomical characteristics.
hair to retain heat
mammary glands to produce milk

30. All mammals share four anatomical characteristics.
a middle ear with three bones to hear higher-pitched sounds
chewing jaw to break up food quicker

31. A set of adaptations in the mammalian jaw makes chewing possible.
secondary palate closes off air passages
muscles move jaw side-to-side

32. Modern mammals are divided into three main groups.
Monotremes lay eggs.
duck-billed platypus
echidna

33. Marsupials give birth to live young that grow to maturity inside a pouch.
opossum
kangaroo
wombat
koala

34. Eutherians give birth to live young that have completed fetal development.
most familiar mammals
humans
Eutherians filled many niches after the extinction of the dinosaurs.