Lab 8 Handout

5mammalianheterodontdentition

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Unformatted text preview: ggs
of
amphibians
lack
extra‐embryonic
membranes
and
 shells,
are
usually
encased
in
jelly
coats,
and
are
susceptible
to
desiccation.
Most
forms
have
 an
aquatic
larval
stage
that
possesses
gills
and
undergoes
metamorphosis
into
the
adult.
 Amphibians
are
called
poikilothermic
or
heterothermic
(i.e.
their
body
temperature
varies
 with
the
external
environment)
and
ectothermic
(i.e.
the
source
of
their
body
heat
is
 external).

 
 1.
Examine
the
skeleton
of
the
bony
fish.
Notice
the
location
and
attachment
of
the
pectoral
 girdle
(the
bony
support
of
the
first
pair
of
fins).
How
is
this
different
from
what
you
see
in
 amphibians?
What
skeletal
feature
do
amphibians
have
(and
all
other
vertebrate
lineages)
 that
are
not
seen
in
fishes?
 
 Amniotes
 The
amniotes
are
defined
by
the
presence
of
extra‐embryonic
membranes
that
are
not
 found
in
the
fishes
or
amphibians.
This
evolutionary
 innovation
is
one
of
the
key
traits
that
resulted
in
 truly
terrestrial
vertebrates
because
reproduction
no
 longer
required
water.
We
will
see
a
similar
key
 innovation
in
the
plants.
 The
Amniotic
Egg

 Reptiles
evolved
a
different
type
of
egg
than
that
 found
in
amphibians.
The
amniotic
egg
(sometimes
 called
the
“land
egg”)
freed
reptiles
from
the
 necessity
of
laying
eggs
in
water
(see
figure
4).
The
 
Fig.
3
The
tetrapod
phylogeny
 amniotic
egg
contains
four
extra‐embryonic
(outside



 the
embryo)
membranes.
One
of
these
membranes,
the
amnion,
suspends
and
protects
the
 embryo
in
a
fluid,
eliminating
the
need
for
external
water.
Other
membranes
are
 responsible
for
removal
and
storage
of
waste,
nutrient
storage,
and
gas
exchange.
Although
 we
are
all
familiar
with
the
structure
of
an
amniotic
egg,
there
have
been
extensive
 modifications
during
vertebrate
evolution.
 
 Reptiles

 This
group
includes
turtles,
tuatara,
 snakes,
lizards,
crocodiles,
alligators,
and
 the
extinct
dinosaurs.
These
tetrapods
 show
many
adaptations
to
living
on
land
 that
distinguish
them
from
the
more
 aquatic
amphibians.
Keratin
in
the
scales
 of
these
animals
helps
to
prevent
water
 loss,
allowing
many
types
of
reptiles
to
 Fig.
4
The
amniotic
egg
 live
in
much
drier
habitats
than
earlier
tetrapods.
 Waterproof
skin,
in
conjunction
with
air‐breathing
 young,
helped
free
reptiles
from
reliance
on
wate...
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