Biol 1309
The Tetrapods - the Road to
Humans !
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The Move to Land...
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first group of vertebrates to move to land -->
amphibians
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Skin
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Breathing
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Locomotion
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http://evolution.berkeley.edu/
evolibrary/article/evograms_04
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Acanthostegia – a missing link?
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About Amphibians

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Divided into groups: two extinct and three
groups of modern amphibians.
The three living:
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
newts and salamanders ("tailed ones")
caecilians ("legless ones")
frogs and toads ("tailless ones")
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The Changes
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Jointed limbs
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Ankles & wrists
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Limb girdles
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Heavier vetebra
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But all is not well...
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Skin
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Eggs
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Reproduction
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Eggs & sperm + external
So we need is better egg and skin?
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The answer?

Water proof skin
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Terrestrial egg
Ta! Da!- the Amniote!
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The Amniote Egg – Remember?
Four extraembryonic membranes:
(1) Amnion – (produces amniotic fluid to cushion the
developing embryo)
(2) Chorion – (allows gas exchange)
(3) Allantois- (stores embryo metabolic wastes)
4) Yolk sac – (supplies embryo with nutrients (yolk)
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The egg gives rise to:
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Reptiles
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Birds

Mammals
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The Reptiles
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Water proof skin w/ scales
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Eggs that can be out of the water
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“Cold-blooded”
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Include:
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Tuatua
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Turtles & Tortoises
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Crocodiles & Alligators
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Lizards
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Snakes
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What about Dinosaurs?

Lots of controversy

Hip style- Bird or lizard?
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archosaurs (ruling reptiles): traditional
dinosaurs, pterosaurs, all crocodiles and birds.
Controversy about ideothermy.
(cold vs warm blooded-ness)
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Lizards (reptiles)

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Most have 4 legs (limb girdles etc.)
Visible ear openings, eyelids + nicitating 3rd
eyelid
Cannot separate lower jaw bones (snakes
can!)

Hemipenes

Tail loss...
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Snakes
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Legless but have residuals

Unhinge jaw

Hemipenes

Still “cold-blooded”
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Birds are Reptiles? Really!

Closely related to crocodiles

Feathers not so important now...

Archaeopteryx:


first non-controversial bird fossil: (145 million years
old)
Had: feathers, teeth, a long tail, decent flier.
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So what about these feathers?
•Likely for insulation
•Flight was a bonus…
•Lots of uses:
•Courtship
•Display etc.
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The Birds
•Numerous types (2nd
largest number of species)
•Warm blooded
•Specialized skeletons
•Specialized organs (next
slide)
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Bird Developments
• “Warm-blooded”
• Light beak (not heavy jaw)
• Gizzard (w/ pebbles)
• Short digestive tract (no storage)
• Air circulation inside skeleton
• Keel (flight muscles)
• External eggs require incubation
• Pelvis = innominate bone
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Interesting Skeletons
Hollow bones!
Keel!
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Birds come in 2 main kinds:
•Ratites:
•Flightless – emu, ostrich,
cassowaries, elephant bird
•Carinates – everybody
else, with a keel!
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Ratites- Flightless Birds
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Onward to THE MAMMALS!
Split off 300 million years ago
Fossils to 170 million
Likely very small initially
19 groups today
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Mammalian Characteristics
• “Warm-blooded”
• Hair
• Mammary glands (specialized
sweat glands)
• Muscular diaphragm
• Specialized teeth
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What Kinds of Mammals are there?
3 Types (based on reproduction):
Monotremes:
egg laying
Poorly developed nipples
Platypus, spiney anteaters (echidna)
Marsupials (pouches)
Premature birth
Kangaroo, opossums
Placentals
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The Monotremes
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Marsupial Examples
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The Marsupials
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The Placentals!
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The Placentals
•Birth canal passage:
–Hip and pelvis changes
•Organ displacement
•Length of care
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Steps to a new embryo!
Fertilization
Zygote
Morula
Blastula
Gastrula
embryo
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Some Development – 1st is Morula
Definition: Spherical
embryonic
mass of blastomeres formed
before the blastula, solid ball
of cells, resulting from
cleavage of the fertilized
ovum.
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Some Development – next is
Blastula
Definition: Early developmental stage of
vertebrate embryos formed by cleavage of
the fertilized egg, in which the embryo
consists of a single layer of cells
surrounding a cavity (the blastocoel)
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The Placenta
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The Human
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