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Amphibians
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Lecture notes on Amphibians
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19_AMPHIBIANS AMPHIBIANSSUBPHYLUM VERTEBRATA General Characteristics
- limbs can support weight on
land
- feet with digits - allows them
to transmit muscle-
generated forces to the
ground
- paedomorphosis
- life stages - water and land
- gills converted to lungs
- pair of external eardrums
- digestion adapted to carnivorous diet
- found in damp habitats
- moist skin for gas exchange
- external fertilization
Distinct Characteristics
FISHES AMPHIBIANS
not entirely aquatic, but
most of the larval stages
Mode of life entirely aquatic
live in water and move
to land
scale covered
Skin texture no scales, but moist skin
skin
takes place through
mainly through
Method of lungs mainly; skin, oral
gills, except
breathing cavity, and gills are also
lungfishes
functional
Body
ectothermic
metabolism
Eggs lay eggs that must be kept moist
Reproduction external fertilization
, Mode of Life
ADAPTATION TO LIFE ON LAND
LOCOMOTION
- a fish is buoyed up by the water and its body
weight may be effectively zero
- on land, however, the body is usually held up by
limbs, and the skeleton and all of the internal
organs have to become structurally modified in
order to cope with the new downwards pull of
gravity
- vertebrae and the muscles around the
backbone have to become modified to prevent
the body from sagging between the limbs
- instead of a smooth gliding motion, the limbs FEEDING
have to operate in a jerky fashion producing - earliest tetrapods had to modify the ways in
steps to propel the body forwards which they fed and breathed
- profound modifications had to occur in the - jaw movements of tetrapods are also much
lobed fin before it became a moderately simpler than those of most fishes
effective land limb - first tetrapods presumably fed on small fishes
and the increasing numbers of terrestrial
invertebrates
RESPIRATIONS
- air-breathing needs lungs, or some equivalent
supported vascular surface, instead of gills
- buccal pumping, where air is sucked into the
mouth and throat, and then rammed into the
lungs by raising the floor of the mouth; seen
especially in frog
- early tetrapods breathed partly, or mainly, by
buccal pumping — this is suggested by their
broad mouths and short, straight ribs
SENSORY SYSTEMS AND WATER BALANCE
- eyesight was even more
important on land than in
shallow ponds (tetrapods have
larger eyes than their
precursors)
- early tetrapods had a poor
sense of hearing in air, as did
their ancestors
- main bone associated with
hearing in modern amphibians
and reptiles, the stapes, is
present in early tetrapods
-
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