REPTILES & AMPHIBIANS. The Rise of Amphibians (Devonian Period) A. Amphibians have a body plan and mode reproduction somewhere between “fishes” and “reptiles.” They are vertebrates with a bony endoskeleton and a four-legged aquatic ancestor. REPTILES & AMPHIBIANS.
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A. Amphibians have a body plan and mode reproduction somewhere between
“fishes” and “reptiles.”
They are vertebrates with a bony
endoskeleton and a four-legged aquatic
The 4 classes of terrestrial (tetrapods) vertebrates:
Kingdom: AnimaliaPhylum: ChordataSubphylum: VertebrataClass: Amphibia
1. Life on land presented new challenges to the emerging amphibians.
The idea here is that asteroids that hit
earth caused the mass extinction of
marine life and affected much of the
available O2 at the sea’s surface. Since
the tetrapods had lungs they could take
advantage of gulping air while spending
some of their time on land.
Scientists say no significant genetic
change would be required to make the
transaction from lobed fins to limbs.
They contend that even a single
mutation in one of the so-called,
“master genes” could lead to a big
change in morphology.
a. Water availability was not reliable.
b. Air temperatures were variable, and air itself was not the strong supporting medium that water was, but it was a richer source of oxygen. Lungs had to be modified in ways that enhanced O2 uptake. Circulatory systems became more efficient in rapidly
moving oxygen to cells.
Both of these modifications increase
the capacity for aerobic respiration,
thus generating more ATP for use in
c. New habitats, including vast arrays of
plants, insects, necessitated keener
sensory (vision, hearing, balance) input.
As a result, different regions of the brain
d. Fortunately, climate shifts in the
Carboniferous provided an abundance
of insects as food for the amphibians.
2. Existing amphibians share several
a. All have bony endoskeletons and
usually four legs.
b. Most shed their eggs into water,
which is also home to a free-
swimming larval stage.
c. Depending on their habitat,
amphibians can respire by use of
gills, lungs, skin, and pharyngeal
d. The skin is usually thin and some-
times supplied with glands that
produce toxins. We’ll see this
The word ‘amphibian’ comes from the Greek meaning, “both” (amphi), and bios, meaning, “life”.
It describes cold-blooded animals with backbones that spend their lives both in fresh water and on land.
When we say, ‘cold-blooded’ we mean that the amphibians do not hold or regulate their own body temperature.
Their internal body temperature depends on the external environment. They must absorb the warmth of the sun or become sluggish at very cold temperature to maintain bodily heat.
The Class Amphibia contains three orders:
FROG TOAD SALAMANDER
Most amphibians share 5 key characteristics:
1. Legs – adapted to living on land (frogs, toads, salamanders, newts all have 4 legs)
2. Lungs – larval amphibians have gills, most
adult amphibians breathe with a pair of lungs (salamanders are an exception)
3. Double-loop circulation – two large veins called Pulmonary veins return oxygen-rich blood from the lungs to the heart. Oxygen-rich blood is then pumped to the tissues.
4. Partially divided heart – the atrium of the heart is divided into left and right sides, but the ventricle is not. A mixture of oxygen- rich and oxygen-poor blood is delivered to the tissues.
5. Cutaneous respiration - besides breathing with their lungs, amphibians take up oxygen through their skin.
Double-loop circulation in amphibians:
1. These animals are distinctive with
their long hindlimbs capable of res-
ponding to powerful muscles, which
allow them to leap into the air.
2. Their success on land is due in part
to: the excellent prey-grasping
capability of the tongue attached to the
front of the mouth.
3. Frog skin has mucous glands, poison
glands & antibiotics that provide
protection against pathogens in an
4. Scientists have noticed frog populations
on the decline due to increases in
parasitic attacks, predation, UV
radiation, habitat losses & chemical
Frog versus Toad
Frogs versus Toads
1. Live in temperate zones & in tropical
areas of Central and South America
numbering about 380 species
2. When they walk, the body bends from
side to side, much like a fish moving
3. Adults may retain larval features including
gills and tail.
4. Some larvae may become sexually mature
but not reach a true adult stage
5. Both forms, larval & adult, are carnivorous.
1. As amphibians evolved they lost their limbs & vision, but not their prey-capturing jaws.
2. These unusual creatures live burrowed
in the forest floor where they hunt for
3. Most of the 160 species burrow through the soil,
using touch & smell to pursue insects & earthworms. The few aquatic types use electrical cues.
- Their transition to land involved:
development of legs
more efficient lungs
more efficient heart
Because of this transition from water to land:
Kingdom: AnimaliaPhylum: ChordataSubphylum: VertebrataClass: Sauropsida
Reptiles are found on every continent except for Antarctica, although their main distribution comprises the tropics and subtropics. Though all cellular metabolism produces some heat, modern species of reptiles do not generate enough to maintain a constant body temperature and are thus referred to as "cold-blooded" (ectothermic).
Sea Turtle for an exception: a reptile that elevates its body temperature well above that of its surroundings. Normally they rely on gathering and losing heat from the environment to regulate their internal temperature, e.g, by moving between sun and shade, or by preferential circulation — moving warmed blood into the body core, while pushing cool blood to the periphery
Reptiles evolved from tailed amphibian ancestors. There are nearly 8000 species that are divided into four orders; snakes and lizards, crocodiles and alligators, tortoises and turtles, and tuataras.
dry, scaly skin
tough shell on eggs
eggs are laid on land
During the late Carboniferous, amphibians
gave rise to the amniotes (birds, reptiles, mammals).
A. Four features were critical to amniotes’
escape from water dependency:
1. They produce amniote eggs with internal
covering membranes and a shell, which allow
the eggs to survive in dry habitats.
The word comes from the Greek word for sausage, which the allantois resembles. This sac-like structure is primarily involved in respiration and excretion, and is webbed with blood vessels. It is primarily found in the blastocyst stage of early embryological development, and its purpose is to collect liquid waste from the embryo.
2. First vertebrates to form eggs with
internal membranes that conserve
H2O and cushion an embryo, and
metabolically support it.
3. Amniotes have a toughened, dry or
scaly skin that is resistant to drying.
4. They have a copulatory organ that
permits internal fertilization.
5. Their kidneys are good at conserving
Again, these amniotes (mammals, turtles, lizards, snakes, crocodiles & birds) are the only tetrapods that can reproduce successfully away from aquatic habitats, while having the embryos develop to advanced stage before hatching or being born in a dry habitat.
1. Modification of limb bones, teeth, and
jaw bones allowed greater exploitation
of the insect life emerging in the Late
2. Development of the cerebral cortex permitted
greater integration of sensory input and motor
3. A four-chambered heart fully separated
into two halves and more efficient lungs
allowed greater activity. Crocodilians
were the first to exhibit this feature.
Though the reptiles’ brain is small
compared to it’s body mass, behavior
governed by it is advanced to that seen
4. Descendants of the surviving dinosaurs
became the lineage of reptiles.
5. Transdermal gas exchange seen in
amphibians is abandoned by
reptiles because of their well develop-
Fish Amphibian Reptile, Bird
Humans, birds, and mammals have a 4-chambered heart that completely separates oxygen-rich and oxygen-depleted blood. Fish have a 2-chambered heart in which a single-loop circulatory pattern takes blood from the heart to the gills and then to the body. Amphibians have a 3-chambered heart with two atria and one ventricle.
A loop from the heart goes to the pulmonary capillary beds, where gas exchange occurs. Blood then returns to the heart. Blood exiting the ventricle is diverted, some to the pulmonary circuit, some to systemic circuit. The disadvantage of the three-chambered heart is the mixing of oxygenated and deoxygenated blood. Reptiles, all birds and mammals, have a 4-chambered heart, with complete separation of both systemic and pulmonary circuits.
Reptiles are a diverse group. They are considered an animal because they have basic amniote traits but not those of mammals or birds.
1. The distinctive shell offers protection while
conserving water and body heat.
2. The shell is connected to the skeleton. Their teeth are tough, horny plates designed for gripping & chewing
3. Turtles lay their eggs on land, where
predation is high.
1. Most lizards are small-bodied insect
eaters; their most usual habitats are deserts
and tropical forests.
2. Lizards are also prey for many other animals,
but are quick in movement and have the
unique ability to sever their own tails if it is
grabbed by a predator.
Kingdom: AnimaliaPhylum: ChordataClass: SauropsidaOrder: SquamataSuborder: Lacertilia
1. Snakes are limbless but retain vestiges
of hind limbs; they are excellent
2. Snakes have the ability to swallow prey
larger than they are due to flexible skull
and jaw bones.
3. All snakes are carnivores. Some suffocate their
prey, and some kill their prey with venom.
95% of all living reptiles are composed of Lizards and Snakes.
1. Although they resemble lizards, they
are evolutionarily more ancient. They
resemble amphibians with the brain
and the way they walk.
2. They do not engage in sex until they
are twenty years old!.
3. Only two species remain today;
they live on islands off the shore of
4. Like lizards, tuatarus have a 3rd eye
under the skin with a retina, a lens,
and nerves to the brain. They also
may live to be 60 years old.
Kingdom: AnimaliaPhylum: ChordataClass: SauropsidaOrder: SphenodontiaFamily: SphenodontidaeGenus: Sphenodon
1. Crocodiles and alligators all live in or
2. They are the largest living reptiles.
3. The body plan includes a long snout;
body temperature is regulated behavior-
4. The ventricle of the heart is divided
into right and left chambers – more
like the heart of birds than that of
4. Like other reptiles and birds, crocodilians adjust body temperature with behavioral and physiological mechanisms.
5. They are like birds in displaying complex social behaviors, such as parents guarding nests
and assisting hatchlings into water. This trait
and others suggest that crocodilians and birds
share a common ancestor.
Pages: 444-457 Chap. 26
Pages: 758-759 Chap. 43
Appendix I : Kingdom Animalia