ZOOLOGY –
EARLY TETRAPODS AND MODERN
AMPHIBIANS
THINGS YOU
NEED TO KNOW FROM THIS CHAPTER…
i. What is cutaneous respiration?
i. breeding
season?
ii. winter?
iii. Why can some
frogs survive being frozen?
1. Why does
this kill other animals?
i. What do
mucous glands produce?
ii. What do
serous glands produce?
iii. What do chromatophores do?
i. What is buccal respiration?
ii. How
efficient are frog lungs?
iii. How do frogs
get rid of most of their carbon dioxide?
iv. How do they
get most of their oxygen supply?
i. Describe
their heart.
i. Telencephalon
ii. Mesencephalon
iii. Rhombencephalon
i. Describe
their eyelids.
ii. Can they see
in color or only black and white?
I.
Classification
Phylum Chordata
Class Amphibia
Order Caudata – __________________________________
Order Gymnophiona –
______________________________
Order Anura – ____________________________________
II. Movement Onto Land
A. Land represents a relatively dangerous
habitat for animals.
Adaptations must be made to the
following challenges…
1. The danger of
______________________________________ –
animals are made up
mostly of water and are constantly at risk of
dehydration and death.
2. Oxygen
is ________________ more abundant in air and
diffuses
much more rapidly through air than water.
a. Animals would have to come up with a new
solution to
respiration
to replace gills (which need to be constantly wet).
3. Air is ____________________ less dense and
provides less
buoyancy
than water.
a. Limbs and the skeleton must therefore support
more
weight.
b. Terrestrial habitats selected for…
1)
stronger backbones
2)
muscles to support the body in air
3)
muscles to elevate the head
4)
stronger shoulder and hip girdles
5) a
more protective rib cage
6) ear
structure
7)
longer snout.
c. Adaptations for life on land further included
a skulls,
teeth,
pectoral girdles and jointed limbs.
4. Air fluctuates in temperature more rapidly
than does water;
animals
must adjust to these extremes.
a. Animals must maintain a fairly narrow range
of body
temperature
in order for the enzymes to carry out
___________________________. This led to two solutions
in
tetrapods…
b. ________________________________
– variable body
temperature
derived from heat acquired fro the environment.
1) This is found in ___________________________
and
__________________________________.
c. ____________________________________
– a body
temperature
determined by heat derived from the animal’s
own
oxidative metabolism.
1) This if found in ___________________________
and
___________________________________.
5. Animals in water are exposed to much less UV
radiation.
a. UV radiation causes DNA damage and ultimately
can
lead
to mutations and cancer.
b. Terrestrial animals had to adapt their skin
to this greater
intensity
of UV radiation.
6. Reproduction was about to become a lot more
challenging.
a. Animals in the water can simply squirt their
gametes into
the
water.
b. The sperm can then swim to the egg and
fertilize it.
c. The water can serve as the incubator for the
young.
d. Terrestrial reproduction would involve some
means to
ensure
fertilization and a way to keep the embryos wet
during
development.
B. _______________________,
_______________________ and
________________________________
all made the transition to
terrestrial
life earlier.
1. Recall that arthropods made the transition
thanks to their
_______________________________
which was waterproof, UV
resistant,
and was hard enough to provide protection from the pull
of
gravity.
C. Amphibians are the animals that are most like
the first vertebrates to
make
this transition.
D. Why would they leave the water?
1. The water was already crowded with life.
a. They faced __________________________ for
resources
from similar animals.
b. They faced heavy __________________________
pressures
in the water.
2. However, the land was inhabited only by
plants, snails, and
arthropods.
3. Further, the variety of terrestrial habitats
allows dramatically
greater
opportunities for adaptation.
E. What might have been the driving force for
this transition?
1. Tetrapods evolved
from ________________________________
during
the ____________________________________________,
400
million years ago.
a. This period was a time of mild temperatures,
floods and
droughts.
2. The Devonian freshwater environment was
unstable.
a. As pools evaporated, water fouled and
_____________
levels
declined, only fish with some kind of lung could
survive.
3.
Alfred Romer proposed a seasonal drought hypothesis where
amphibian ancestors developed legs
from selection for migrating
across land to new ponds.
a. The bony elements of the fins of lobe-finned
fishes
resemble the limbs of
amphibians.
4.
A more active lifestyle on land caused these ancestral
amphibians made the following
adjustments…
a. More capillaries and arterial blood from the
last aortic
arch were directed to
the air-filled cavity.
1) This cavity resulted from an
__________________
of the
______________________________ tract.
2) This pouch became filled with air.
3) It would eventually become _________________.
b. Oxygenated blood returned directly to the
heart by a
pulmonary vein to form a
___________________________
_______________________________________________.
F. So, why are amphibians considered to be ______________________?
1.
In contrast to the varied climate of the Devonian, the
________________________
Period was uniformly warm and wet.
2. Tetrapods radiated
into the swampy moss and fern landscape.
a. They ate insects, insect larvae and aquatic
invertebrates.
3. During the Carboniferous, amphibians
developed additional
adaptations
for living in water.
a. Bodies became flatter for moving in water.
b. Early salamanders developed weaker legs and
the tail
became
better developed.
c. Anurans developed webbing on hindlimbs for better
swimming.
4. Today, amphibians are largely confined to wet
habitats. They
rely upon water for…
a. Exchange of oxygen and carbon dioxide.
1) Some salamanders have gills.
2) Some amphibians diffuse gases across their
skin.
a) This requires that their skin remain moist.
3) Some amphibians diffuse gases across moist
mucous
membranes in their mouth.
b. Temperature regulation – water loses and
gains heat
much
more slowly than air.
c. Reproduction
1) Most amphibians deposit eggs and sperm
directly
in
water.
2) The eggs have no shell and would dehydrate on
land. (The eggs are aquatic.)
3) The
larvae (e.g. tadpoles) depend on gills for
respiration.
III. Modern Amphibians
A. Amphibian Characteristics
1.
Over _______________ living species are known in the three
amphibian
orders.
2. The
olfactory epithelium and the ear are redesigned to improve
sensitivity
to airborne sound.
3.
They remain tied to water; eggs are aquatic, and the larvae
depend
on gills for respiration.
4. The
thin skin loses water rapidly; this restricts even terrestrial
forms
to moist habitats.
5. Being ectothermic, their
body temperature depends on the
environment
and restricts their range.
6. Eggs
easily dessicate and must be shed into water or kept
moist.
a.
A few amphibians brood their young.
B.
Salamanders: Order ________________________________ (Urodela)
1. About 360 species of living
salamanders are found mostly in
northern temperate regions.
2. Most are small, under 15
centimeters long, but the Japanese
giant salamander is 1.5 meters long.
3. Usually their limbs are at right
angles to the body; forelimbs and
hindlimbs
are about equal in length.
a. Burrowing species and some aquatic forms may
have lost
their limbs.
4.
Salamanders are _____________________________ as both
larvae and adults, eating worms,
small arthropods and molluscs.
5.
They are ectotherms with a low metabolic rate.
6.
Respiration - Salamanders have a wide array of respiratory
mechanisms.
a. They have extensive vascular nets in their
skin that
exchange both oxygen and
carbon dioxide.
1) Many species in the terrestrial family
Plethodontidae lack lungs and use only
______________________________
respiration.
b. Respiratory gases may also be exchanged
across the
vascularized
lining of the mouth cavity.
b. At various stages, they may also have
external gills,
lungs, both gills and
lungs, or neither.
c. Salamanders with an aquatic stage hatch with
gills and
lose them at
metamorphosis.
1) Where present, lungs are present from birth
and
become
functional following metamorphosis.
2) Aquatic amphibumas
lose their gills and respire by
lungs,
holding nostrils above the water surface.
d. Several diverse
lineages fail to undergo metamorphosis
and retain gills and a
fin-like tail.
1) _____________________________________ -
the
preservation of pre-adult features into adulthood.
C. Caecilians: Order
___________________________ (Apoda) "Caecilian
worms"
1.
About 160 living species of elongate, _____________________,
burrowing
caecilians are known.
2.
They live in tropical forests in South America,
3.
They eat primarily _______________ and small underground
invertebrates.
D.
Frogs and Toads: Order ____________________________ (Salientia)
1.
Over 3450 species of frogs and toads compose the order Anura.
2.
This group is known from the Jurassic period, 150 million years
ago.
3.
Tied to an aquatic mode of reproduction and a water-permeable
skin,
they must be near water.
4.
Ectothermy keeps anurans from inhabiting polar and
subarctic
habitats.
5.
All pass through a tailed larval stage to become tailless, jumping
adults.
6.
Eggs hatch into ______________________ with a long, finned
tail,
no legs, internal and external gills and specialized mouthparts
for
(usually) herbivorous feeding.
7.
There are 21 families of frogs and toads.
a.
Family ________________________ contains the
common
larger frogs in
b. Family ________________________ includes the
tree
frogs.
c.
Family _________________________ contains toads with
thicker
skins and prominent warts.
8.
Anurans are declining worldwide and becoming patchy in
distribution;
the cause is not known.
9.
Life Cycle
a.
Most larger frogs are ___________________ until
breeding
season.
b.
During the breeding season, males are especially noisy
when
trying to attract a female.
c. During winter in temperate climates, they
____________________ in soft
mud in the bottom of pools.
d. Frost-tolerant frogs prepare for freezing by
accumulating
_______________________
and _____________________
in body fluids; this
protects them from the otherwise
damaging effects of
ice-crystal formation.
e. Many are easy prey; they defend themselves by
aggression, concealment,
and poison glands.
10.
Integument and Coloration
a. Frog skin is thin,
moist and attached loosely to the body at
a few points.
b. The inner layer of
epidermis has two types of
integumentary
glands…
1) _________________ glands produce a
protective,
waterproofing secretion.
2) large ______________________ glands produce
a
whitish, watery poison.
c. Specialized pigment
cells, ________________________,
produce skin color in frogs.
d. Many frogs can adjust
their color to blend with their
background and thus
camouflage themselves.
11.
Skeletal and Muscular Systems
a. A well-developed
________________________ of bone
and cartilage provides
protection and muscle anchorage.
b. Anurans show dramatic changes in the
musculoskeletal
system for jumping and
swimming.
c. The vertebral column lost much of its
flexibility in order to
transmit force from
limbs to the body.
d.
The front of the frog skull, containing the brain, eyes, and
nose is lightweight and
flattened; the back of the skull, which
contained the gill
apparatus in fishes, is reduced.
e. The foot generally has five rays and the hand
is four-
rayed; both have several
joints in the digits.
1) This system is derived from the pattern in
rhipidistian lobe-finned fish.
12.
Respiration and Vocalization
a. Amphibians use three
respiratory surfaces for gas
exchange in air.
1) The
skin provides cutaneous breathing.
2) The
mouth provides ____________________
breathing.
3)
Lungs are usually present in adults.
b.
Frogs and toads depend on lung breathing more than
salamanders.
c. Unlike reptiles, birds, and mammals, frogs
& toads don’t
suck air
into their lungs.
1)
Air is forced into the lungs by the mouth muscles.
d.
Carbon dioxide is mostly lost across the ___________
while
oxygen is absorbed across the ______________.
e. The
absorptive surface in a frog lung is 20 cm2 per cc of
air
compared to 300 cm2 for humans.
13. Circulation
a. The circulatory system is
______________________,
with a pumping
_______________________.
b. Separating the oxygenated blood from the
deoxygenated
blood circuit is not
completed.
c. Frog Heart
1) The frog heart has a single undivided
_________________________
and two separate
_________________________.
2) Blood from the body enters through the sinus
venosus and right atrium.
3)
Blood from the lung enters the left atrium.
4)
Both atria contract at the same time, driving blood
into
the ventricle.
5)
When the ventricle contracts, blood moves to the
lungs
or body.
6)
Although there is no septum, deoxygenated blood
goes
primarily to the lungs and oxygenated blood
goes
mostly to the body due to separation by a
spiral
valve in the conus arteriosus.
14.
Feeding and Digestion
a. Most adult amphibians are carnivorous,
feeding on
insects, spiders, worms,
slugs, etc.
b.
They catch prey with a tongue that is attached at the front
of the
mouth.
c. The
free end of the tongue is glandular; a sticky secretion
adheres
to prey.
d. Any
teeth that are present function to hold prey; they do
not
bite or chew.
e.
Larval stages or tadpoles are usually
__________________________;
their digestive tract is
relatively
long.
15. Nervous System and Special Senses
a.
The brain has three fundamental parts.
1)
The forebrain or ___________________________
interprets
the sense of smell.
2) The
midbrain or ___________________________
perceives
vision.
3) The
hindbrain or ___________________________
perceives
hearing and balance.
b. The
brain is gradually assuming more information
processing
ability independent of the spine.
c. However,
a headless frog still has highly coordinated
behavior
based on spinal cord alone.
d. The ear becomes specialized for detecting
airborne
sounds.
1) A
large tympanic membrane or eardrum passes
vibrations
to the inner ear via the columella.
2) The
inner ear has a utricle with three semicircular
canals
and a saccule with a lagena.
3) A lagena is covered with a tectorial
membrane that
is
similar to the mammalian cochlea.
e. Except for blind caecilians,
_________________ is the
dominant sense in many
amphibians.
f. Lachrymal glands and eyelids evolved to keep
the eye
moist, free of dust, and
protected.
1) The upper eyelid is fixed.
2) the lower is folded into a transparent
nictitating
membrane.
g. The amphibian retina contains both rods and
cones; the
cones
provide frogs with color vision.
16.
Reproduction and Development
a.
Frogs and toads are ectothermic; therefore they
breed,
feed,
and grow during the warm seasons.
b. In
the spring, males call to attract females.
c. When
the eggs are mature, females enter the water and
the
males clasp them in ___________________________.
d. As
the female lays eggs, the male discharges sperm over
them.
e. The
jelly layers absorb water and swell; the eggs are
usually
laid in large masses.
f.
Development begins immediately; a tadpole may hatch in
6-9
days.
g.
Three pairs of external gills soon develop into internal gills
covered
with a flap of skin.
h.
Metamorphosis
1) Hindlegs
are first to appear; the forelegs are
temporarily hidden in folds of the
operculum.
2) The tail is resorbed.
3) The intestine becomes shorter.
4) The mouth transforms to the adult
condition.
5) Lungs develop and the gills are resorbed.