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GLGY 305 Lectures 6-9
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GLGY 305 Lectures 6-9
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GLGY 305 Lectures 6-91. Cephalochordata Early ancestors of vertebrates did not
have
a vertebral column. They had a
flexible noto- chord.
The evolution of the notochord was
the first step towards the evolution of
all vertebrates including humans!
One of the earliest ancestors of all
verte- brates is Pikaia.
2. Early Tetrapods: Tiktaalik Tiktaalik is an extinct lobe-finned fish
that
represents the next stage in
vertebrate evo- lution: it has weight-
bearing elbows, simple wrist bones,
and rays that resemble fingers.
Because of this, Tiktaalik is
sometimes called a fishapod: a fish
with feet.
Tiktaalik had gills and lungs
Tiktaalik lived in shallow waters and,
al- though Tiktaalik didn't venture
onto land, it was pre- adapted to
make this transition
3. Tetrapoda vertebrates with four true limbs. Early
tetrapods like Ichthyostega were
among the first animals to live on
land.
Although they lived on land, they were
bound to water in order to reproduce
Modern tetrapods have lost their gills,
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, GLGY 305 Lectures 6-9
but retain their lungs. Primitive
tetrapods like am- phibians (e.g. frogs,
newts, toads and sala- manders) still
require water in order to repro- duce
4. Tetrapoda diagnosed by
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, GLGY 305 Lectures 6-9
Diagnosed by limbs with:
•A shoulder girdle
•Humerus
•Radius and ulna
•Phalanges
Homologous
structures
5. Amniota Amniotic eggs can be laid on land
without
drying out.
Key step in evolution of completely
terrestrial lifestyle, and commonly
associated with the advent of reptiles
Humans and other mammals are also am-
niotes
6. Amniota: Diapsids (Diapsida) Diapsida defined as birds, lizards, and a
the
descendants of their most recent
common ancestor
Diagnostic derived features include
upper and lower temporal openings
(fenestra) in skull roof
Thought to provide accommodation for
bulging of contracted jaw muscles, as
well as increased surface area for
attachment of these muscles
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, GLGY 305 Lectures 6-9
7. What are these? Diapsida: Dinosaurs!
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