Transcript KINGDOM ANIMALIA - Blue Valley School District

KINGDOM ANIMALIA
Phylum Chordata
Subphylum Vertebrata
Class Amphibia
Vertebrate Classes
History
Chordate group to evolve after fish were
true tetrapods = Amphibians
Ichthyostega presents rudimentary
amphibian features (different from fish)
– Girdles = skeletal bones connecting the central
skeleton to the bones of the appendages
– Other skeletal strengthening: rib cage and
cranium
Ichthyostega still retained a caudal fin and
scales
History
Ancient and modern
amphibians have
features that enhance
their survival on land
but also limit this
existence.
Most amphibian
evolution took place
when Earth was warm,
humid, and swampy
(350 mya).
Insects were
abundant.
No pressure to
develop into a truly
terrestrial animal.
Common Features
Well-muscled appendages, supported
by an central and peripheral skeleton
Further development of lungs
Skin highly vascularized, other site of
gas exchange, and maintains water
balance
Circulatory system now includes a 3chamber heart
– Increased pressure to peripheral arteries
– Atrium separated by septum, but still
one ventricle
– More efficient but still mixing of
oxygenated/deoxygenated blood
All of these features serve to increase
the mobility of amphibians
Common Features
Other features illustrate
the amphibian’s primitive
nature:
– ectothermic-sluggish when
cold, hibernation or death
– respiration through skin
requires it to be thin and
moist
– lose lots of water through
skin and must keep it
continually moist to prevent
lethal desiccation
– must reproduce in the water
since eggs would dry up on
land
– aquatic larval stage more
closely related to fish than
terrestrial animals
Common features
Novelty = pedicellate
bicuspid teeth
– crown and base = dentine
– middle = fibrous connective
tissue
– bicuspid = 2 cusps/points
3 Main Groups
Caecilians (165 species)
Salamanders (502
species)
Anurans (frogs/toads,
4000 species)
Caecilians
Tropical, limbless amphibians
Resemble giant earthworms and burrow in the
ground
– unlike other tetrapods, skin is bound to body wall
musculature which bestows great burrowing
efficiency
– powerful body with well-developed endoskeleton
– skull used as battering ram as it burrows
Carnivorous: eat
earthworms if terrestrial,
fish/inverts if aquatic
Caecilians
Tiny eyes if present
(most are vestigial,
covered by skin)
Chemosensory
tentacles on head in
front of eyes used to
locate food
Internal fertilization;
some species bear
live young while
others lay eggs
Salamanders
Most closely resemble
amphibian tetrapod
ancestor
Long tails, 2 pairs of
limbs of approximately
the same size
Primarily live in
Northern Hemisphere
(abundant in cool,
moist forests, only 1
type tropical)
Salamanders
Generally
(semi)terrestrial
as adults
Most pass
through larval
stage
– few days to a
few years
– some species
never
metamorphose
(axolotl)
Anurans
“without tail”
Most successful, diverse,
evolutionarily divergent of
the living amphibians
Jumping locomotion
allowed exploitation of
new terrestrial niches
Live in almost any climate
(except high latitudes in
Arctic, Antarctic, some
oceanic islands, some
extremely dry deserts)
Anurans
Adaptations for
jumping
locomotion
– Hind limbs much
longer than
forelimbs
– Short trunk
– Tail lost
– Flattened head
– Large eyes
Anurans
Many deposit eggs in water; get freeswimming tadpoles
Others lay terrestrial eggs
Some carry their eggs with
them