Download Amphibians

Presenters
Kencho Galey
Samdrup Rinzin
Tshering Phuntsho
 Amphibians are a group of animals that include modern-
day frogs and toads, caecilians, and newts and
salamanders. These animals' ancestors were the first to
venture out from the water and adapt to life on land.
Amphibian larvea are often aquatic and go through a
complex metamorphosis process as they grow to
adulthood. They have moist skin and do not have scales,
feathers or hair.
 The life cycles of amphibians reflects their evolutionary
history of bridging land and water. Most amphibians lay
their eggs in freshwater. A few species tolerate brackish
water and some species lay their eggs on land.
Extraordinarily, some species even carry their eggs inside
their body. Although life cycles of amphibians vary from
species to species, they all share the following three basic
stages of development: egg, larva, adult.
 Amphibian eggs do not have a hardened shells which means
amphibians are not amniotes like reptiles, birds, and mammals.
Instead, amphibian eggs consist of a gelatinous envelope that
must remain moist to survive. Eggs hatch to release tiny larvae
which later undergo a metamorphosis into the adult form.
 Many amphibians can absorb oxygen directly into their
bloodstream through their skin and are also able to expell carbon
dioxide waste back into the air. The skin of amphibians lacks
scales and hair. It is smooth and sometimes moist, making it
quite permeable to gases and water.
 This permeability is thought to make amphibians particularly
vulnerable to toxins in air and water such as herbicides,
pesticides, and pollutants. Amphibians have been sharp decline
throughout many areas worldwide. This is thought to be an early
warning sign of a troubled environment.
 Amphibians are divided into three groups which include newts
and salamanders, frogs and toads, and caecilians.
 Newts and salamanders are slender-bodied amphibians that have a long tail
and four legs. Newts spend most of their life on land and return to water to
breed. Salamanders, in contrast, spend their entire lives in water.
 Frogs and toads belong to the largest of the three groups of
amphibians. Adult frogs and toads have four legs but do not have tails.
 Caecilians are the least-known group of amphibians. Caecilians have
no limbs and only a very short tail. They have a superficial resemblance
to snakes, worms, or eels but are not closely related to any of these
animals.
General characterstics
The living amphibians have very different body forms but the
members of the various orders share the following
characteristics:
 A bone endoskeleton with varying numbers of vertebrae; ribs
present in some, absent or fused to vertebrae in others. None
possess an exoskeleton and the notochord (a rod of tissue) does
not persist in adults.
 A smooth, thin, porous skin containing both mucus glands and
poison glands.
 Four limbs (tetrapod) which may vary in size with the forelimbs
of some being much smaller than the hindlimbs; some are
legless. Limbs have varying numbers of digits and webbed feet
are often present; no true nails or claws.
 The mouth is usually large with small teeth in upper or both
jaws; two nostrils open into the anterior part of the mouth cavity.
 Respiration is accomplished either separately or in combination
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by lungs, skin, and gills; some larval types possess external gills
and these may persist throughout life.
A three-chambered heart consisting of two atria and one
ventricle.
Body temperature regulation is ectothermic (cold-blooded) in
nature. That is, the body is heated from without rather than
from within (endothermic).
Separate sexes (dioecious) with internal fertilization via
spermatophore (a sperm packet on a stalk) in salamanders and
caecilians, but external fertilization in frogs and toads. Larvae
develop in water or very moist environments and undergo
complete metamorphosis. Amphibians are the only vertebrates to
undergo complete metamorphosis.
Pity the poor amphibian for they know not biologically what
they are. They begin life as a legless animal with gills and tail like
a fish and end up a with four legs and lungs like a reptile. Yet
clearly they are neither fish nor reptile. They are amphibians, the
only vertebrates that lead a double life.
Difference between amphibians and fish
 Fish and amphibians are different because fish must live in water to
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survive. Amphibians, however, are born in water but live on land and in
the water.
A major difference between the two is that amphibians breathe using
gills or spiracles when they are young and develop lungs as they grow:
fish rely on gills for their entire lives.
Amphibians undergo metamorphosis as they grown from young to
adult, but fish do not undergo this radical change.
Read more.
Amphibians have eyelids and ears; fish do not.
Amphibians are capable of vocalisations; as far as we know, fish are not.
Amphibians have moist skin, whilst fish have scales.
Ancester of amphibians
 The first amphibians evolved from lobe-finned fishes approximately 370
million years ago during the Devonian Period. Early amphibians included
creatures such as Diplocaulus, Ophiderpeton, Adelospondylus, Diplocaulus,
and Pelodosotis. The world of those early amphibians was quite different than
it is today.
 The Crossopterygians, a group of primative lobe-finned fish are believed to be
the ancestors of amphibians. Which is similar to lung fish. Amphibians
originated from from a tetrapod. Early tetrapods were like fish but may have
had limbs to move on the bottom of marshes. In later fossils, the limbs were
found further below to lift the animal off the ground. Eventually, amphibians
arose the ability to breath through the air as well as water.
Adaptions in water
 streamlined body shape for swimming - no movement of head is
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beneficial during swimming - easier to swim through water.
thin and moist skin allows for gaseous exchange (cutaneous
respiration) - allows for water exchange (osmosis).
long, powerful,legs with 5 toes ble to jump great distances, and
change direction quickly - webbed toes aid in swimming.
Their eyes is positioned on top of head - it gives the them a wide
angled visual field; allows them to remain in water with only part
of head exposed lower.
eyelid transparent - able to see under water.
large and bulging - aid in swallowing; - detect movement and
velocity of an object
 a flat disk-like tympanic membrane around their ear that
streamlines the body, prevents water from entering ear
canal.
 very large and broad mouth able to catch and eat large prey.
 Their tongue is attached at front of mouth - enables it to be
flicked out quickly long and sticky - prey sticks to it when
caught.