chapter24_Sections 4-8

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Albia Dugger • Miami Dade College

Cecie Starr

Christine Evers

Lisa Starr

www.cengage.com/biology/starr

Chapter 24


Animals II: The Chordates

(Sections 24.4
-

24.8)

24.4 Amphibians: The First Tetrapods



Amphibians
, the first tetrapods, branched off from the lobe
-
finned fishes



Most spend some time on land, but return to the water to
reproduce



amphibian



Tetrapod with a three
-
chambered heart and scaleless skin
that typically develops in water, then lives on land as a
carnivore with lungs


The Move Onto Land




Transition to land required many physical changes:


Skeletal changes to develop front and hind limbs


Division of the heart into three chambers to allow blood
flow in two circuits, one to the body and one to lungs


Changes to the inner ear improved detection of airborne
sounds


Eyes became protected from drying out by eyelids


Transition to Tetrapods




Skeleton of a Devonian
lobe
-
finned fish, and
two early amphibians,
Acanthostega
,
and
Ichthyostega


Early Amphibians?

Modern Amphibians





Salamanders and newts
resemble early
tetrapods in body form



Salamander Gait



Early tetrapods
probably used the same
motion as salamanders
to walk in water before
one lineage ventured
onto land

ANIMATION: Salamander locomotion

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Frogs and Toads


Frogs and toads belong
to the most diverse
amphibian lineage



Modern amphibians
such as the
American
toad
are carnivores



The flattened disk
visible behind the eye is
the eardrum

Frogs



Long, muscular
hind limbs allow
the adult frog to
leap



The larval frog
(tadpole) is a
swimmer with a
long tail and no
legs

Declining Amphibian Diversity




Amphibian populations throughout the world are declining or
disappearing


many due to shrinking or deteriorating habitats



Other factors include introduction of new species in
amphibian habitats, long
-
term shifts in climate, increases in
ultraviolet radiation, and spread of pathogens and parasites



Chemical pollution of aquatic habitats also harms amphibians


Frog Deformity





Infection by a fluke
caused abnormal
limb development

Key Concepts





The Transition From Water to Land



Tetrapods, animals that walk

on four legs, evolved from a
lineage of lobe
-
finned fishes


Amphibians were the first tetrapod lineage


They can live on land, but their eggs must develop in water
and their skin is not waterproof

24.5 Evolution of the Amniotes




Amniotes, the first vertebrates able to complete their life cycle
on dry land, have water
-
conserving skin and kidneys, and
amniote eggs




Fertilization usually takes place inside the female’s body



amniote egg


Egg with internal membranes that allow the amniote
embryo to develop away from water



Amniote Egg




A bird’s egg has a hard
shell that encloses the
embryo and amniote
membranes (yolk sac,
amnion, chorion, and
allantois)

Fig 24.14, p. 384

albumin (“egg white”)

allantois

yolk sac

embryo

chorion

amnion

hardened shell

Amniote Egg

ANIMATION: Amniote egg

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Two Lineages



There are two lineages of amniotes:
reptiles

(including birds
and the extinct
dinosaurs
) and mammals



reptile


Amniote subgroup that includes lizards, snakes, turtles,
crocodilians, and birds



dinosaur


Reptile lineage abundant in the Jurassic to Cretaceous;
now extinct with the exception of birds



Proposed Amniote Lineages


Mammals diverged early: Note the reptile clade includes birds

Fig 24.15, p. 384

Crocodilians

Lizards, snakes

Turtles

Mammals

Reptiles

Birds

Proposed Amniote Lineages

Dinosaurs of the Jurassic


Shows the early bird
Archaeopteryx

and an early mammal


Key Concepts




The Amniotes



Amniotes have waterproof skin, and their eggs contain
membranes that enclose the embryo in fluid


These and other traits allowed the amniotes to expand into
dry habitats


Reptiles (including birds) and mammals are the two
modern amniote lineages

ANIMATION: Crocodile Body Plan

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24.6 Nonbird Reptiles




The major groups of nonbird reptiles are lizards, snakes,
turtles, and

crocodilians



All nonbird reptiles
are
ectotherms
, which adjust their
temperature by their behavior



By contrast, birds and mammals are
endotherms
, which
produce heat by metabolic activity


Key Terms




ectotherm



Animal that controls its internal temperature by altering its
behavior; for example a lizard



endotherm


Animal that generates heat by its metabolism; for example
a bird or mammal

Lizards and Snakes



Lizards and snakes are
covered with scales



All snakes are
carnivores with teeth,
but not all have fangs



Most lay eggs, but
some give birth to live
young



Hognose snakes




Turtles



Turtles and tortoises
have a bony shell
attached to their
skeleton,
and a horny
beak rather than teeth



Some feed on plants
and others are
predators





Galápagos tortoise


Crocodilians




Crocodiles, alligators,
and caimans are the
closest living relatives of
birds



All are carnivores and

spend much of their
time in water



Spectacled caiman


ANIMATION: Tortoise Shell and Skeleton

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24.7 Birds: Reptiles With Feathers




Birds

are descendants of feathered dinosaurs



Body plans of most species are highly modified for flight, with
lightweight bones, powerful muscles



Feathers increase wing
-
surface area and increase lift



bird


An animal with feathers


Adapted to Flight



Birds have lightweight
bones and a large
sternum

Fig 24.18b, p. 386

pelvic
girdle

porous,
lightweight
bone

sternum
(breastbone)

pectoral girdle

B

Adapted to Flight

Energy for Flight


Flight requires a lot of energy:
Among modern vertebrates,
only birds and bats fly by flapping a pair of wings




Energy For Flight




Energy for flight is provided by aerobic respiration
and a
highly efficient respiratory system



A unique system of air sacs keeps air flowing continually
through lungs



A relatively large, four
-
chambered heart pumps blood quickly
from the lungs to wing muscles and back

Mating House Sparrows


Lacking a penis, the male must bend his body so his cloaca
covers his mate’s




ANIMATION: Avian Bone and Muscle
Structure

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24.8 Mammals: The Milk Makers




Mammals

diversified after dinosaurs were gone



Like birds, mammals are endotherms; their fur (or hair) helps
them retain internally produced heat



mammal


Animal with hair or fur


Females secrete milk from mammary glands


Mammalian Traits



Only mammals have
four differently shaped
kinds of teeth



Having teeth of multiple
shapes allows
mammals to process a
wide variety of foods


Fig 24.20, p. 387

premolars

incisors

molars

canines

Mammalian Traits

Three Mammalian Lineages



monotremes


Egg
-
laying mammals



marsupials


Mammals in which young are born at an early stage and
complete development in a pouch on the mother’s surface



placental mammals


Mammals in which a mother and her embryo exchange
materials by means of an organ called the placenta

Monotremes



Oldest mammalian
lineage



Lay eggs with a leathery
shell, similar to reptiles



Three species: duck
-
billed platypus and two
kinds of spiny anteater

Marsupials



Most marsupials live in
Australia and nearby
islands



Kangaroos and koalas
are the best known



The opossum is native
to North America

Placental Mammals



Maternal and embryonic
tissues form a placenta



Embryos grow fast, and
offspring are born fully
formed



Placental mammals
outcompete other
mammalian lineages

ANIMATION: Structure of the placenta

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ANIMATION: Mammalian Dentition

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