Moving Up the Evolutionary
Tree……
It is widely accepted that the
Devonian lobe-finned fishes were ancestral to
the amphibians. Lobe-finned fishes and early
amphibians both had :
1) limbs
2) lungs
3) internal nares to respire air
Two hypotheses have been proposed to explain
the evolution of amphibians from lobe-finned
fishes:
1) Lobe-finned fishes capable of moving from
pond-to-pond had an advantage over those that
could not.
2) The supply of food on land, and the absence
of predators, promoted adaptation to land
(plants & insects provided new food source).
The first amphibians diversified during
Carboniferous Period (commonly known as the
Age of Amphibians).
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I. Class Amphibia
 about _______ species
 like fish, are __________; they depend upon
external heat to regulate body temperatures.
Amphibian features not seen in bony fish include:
 Limbs with girdles of _____ that are adapted
for walking on land.
 A _______ that can be used for catching
prey as well as sensory input.
 __________ that help keep the eyes moist.
 Ears adapted for detecting ______ waves
moving through the thin (as compared to
water) medium of the air.
 A larynx adapted for vocalization(males
croak)
 A larger brain than that of fish, and a more
developed cerebral cortex.
 Skin that is thin, smooth, non-scaly, and
contains numerous ______ glands; the skin
plays an active role in osmotic balance and
respiration.
 Development of a _____ that is permanently
used for gas exchange in the adult form,
although some amphibians supplement lung
function by exchange of gases across a
porous (moist) skin.
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 A _____ double-loop circulatory system that
replaces the single-loop circulatory path of
fish.
 Development of a ____-chambered heart
that pumps mixed blood before and after it
has gone to the lungs.
 larval/juvenile stages in
_____, and their adult life
on land
 adults return to water to
mate and lay eggs
 ________ fertilization:
male clasps back of female
as sperm and eggs
deposited into water
 eggs hatch into tadpoles in about ____ days
 Frogs, toads, salamanders, and mud
puppies are in this transitional group
between water and land
The evolution of the amniotic egg expanded
the success of vertebrates on land
 amniotic egg - a reproductive adaptation
that enabled terrestrial vertebrates to
complete their life cycles on land and sever
ties to their aquatic origins
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 protective membranes & porous shell
enclosing the embryo
 Has 4 specialized membranes --- amnion,
yolk sac, allantois, & chorion
o _________ is a thin membrane surrounding
a salty fluid in which the embryo "floats"
o _________ encloses the yolk or protein-rich
food supply for embryo
o _________ stores nitrogenous wastes made
by embryo until egg hatches
o _________ lines the inside of the shell &
regulates oxygen & carbon dioxide exchange
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 Shell leathery & ___________
 _________ animals have dispensed with the
shell; instead, the embryo implants in the
wall of the uterus and obtains nutrients from
the mother. However, the four
extraembryonic membranes are retained as
important structures in the development of
mammalian embryos.
 Reptiles, birds and mammals make up a
monophyletic group, the __________
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J. Class Reptilia
 represented by 7000 species
 first evolved during the
Carboniferous time
 partly displaced amphibians in
many environments
 Arose from ancestral reptile group called
cotylosaurs (small, lizard like reptile)
 Mesozoic Era called Age of Reptiles

 Dinosaurs dominated life on land for 160
million years
 first vertebrates to make a complete
transition to life on land (more food & space)
Terrestrial Adaptations:
 dry, watertight skin covered by scales made
of a protein called keratin to prevent
desiccation (water loss)
 toes with claws to dig & climb
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 geckos have toes modified into suction cups
to aid climbing
 snakes use scales & well developed
muscular & skeletal systems to move
 lungs for respiration
 double circulation of blood through heart to
increase oxygen to cells
 partial separation in ventricle to separate
oxygenated & deoxygenated blood
 ectothermic - body temperature controlled
by environment
 may bask or lie in sun to raise body
temperature or seek shade to lower body
temperature; known as thermoregulation
 water conserved as nitrogen wastes
excreted in dry, paste like form of uric acid
crystals
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