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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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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.


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REPTILES & AMPHIBIANS

The 4 classes of terrestrial (tetrapods) vertebrates:

  • Amphibians

  • Reptiles

  • Birds

  • Mammals


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  • Scientific classification

    Kingdom: AnimaliaPhylum: ChordataSubphylum: VertebrataClass: Amphibia


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  • Subclasses and Orders of Amphibians

  • Order Temnospondyli- extinctSubclass Lepospondyli- extinctSubclass Lissamphibia Orders

    AnuraCaudataGymnophiona


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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.


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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.


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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.


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Both of these modifications increase

the capacity for aerobic respiration,

thus generating more ATP for use in

increased activity.

c. New habitats, including vast arrays of

plants, insects, necessitated keener

sensory (vision, hearing, balance) input.

As a result, different regions of the brain

further developed.


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d. Fortunately, climate shifts in the

Carboniferous provided an abundance

of insects as food for the amphibians.


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  • Amphibians developed with the characteristics of pharyngeal slits/gills, a dorsal nerve cord, a notochord, and a post-anal tail at different stages of their life. Though early tetrapods (which appeared 390 million years ago in the Devonian period) are often referred to as "amphibians", the first true amphibians appeared during the early Carboniferous period.


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  • Superorder Salientia

  • Triadobatrachus (Triassic)

  • Order Anura (frogs and toads) Jurassic to recent - 5,296 recent species

  • Order Caudata or Urodela (salamanders): Jurassic to recent - 555 recent species

  • Order Apoda (caecilians): Jurassic to recent - 171 recent species


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2. Existing amphibians share several

common characteristics:

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.


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c. Depending on their habitat,

amphibians can respire by use of

gills, lungs, skin, and pharyngeal

lining.

d. The skin is usually thin and some-

times supplied with glands that

produce toxins. We’ll see this

shortly.


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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.


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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.


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The Class Amphibia contains three orders:

  • Anura (frogs and toads)

  • Urodela (salamanders and newts)

  • Apoda (caecilians)


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FROG TOAD SALAMANDER


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NEWTS CAECILIANS


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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)


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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.


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5. Cutaneous respiration - besides breathing with their lungs, amphibians take up oxygen through their skin.


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Double-loop circulation in amphibians:


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  • Life Cycle ‘Metamorphosis” of a Frog (pg. 758-759)


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  • Frogs and Toads (4,000 species)

    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.


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3. Frog skin has mucous glands, poison

glands & antibiotics that provide

protection against pathogens in an

aquatic habitat.

4. Scientists have noticed frog populations

on the decline due to increases in

parasitic attacks, predation, UV

radiation, habitat losses & chemical

pollution.


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Frog versus Toad

  • Frog has two bulging eyes

  • strong, long, webbed hind feet that are adapted for leaping and swimming

  • smooth or slimy skin (generally, frogs tend to like moister environments)

  • Frogs tend to lay eggs in clusters.


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Frogs versus Toads

  • Toads have stubby bodies with short hind legs (for walking instead of hopping)

  • warty and dry skin (usually preferring dryer climates)

  • paratoid (or poison) glands behind the eyes

  • The chest cartilage of toads is different.

  • Toads tend to lay eggs in long chains.


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  • Salamanders

    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

    through water.


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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.


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  • Caecilians

    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

    invertebrate prey.

    3. Most of the 160 species burrow through the soil,

    using touch & smell to pursue insects & earthworms. The few aquatic types use electrical cues.


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  • Summary of amphibians:

    • They are vertebrates

    • they have bony endoskeleton

    • They have four legs

    • Their body plan and mode of reproduction is somewhere between “fishes” and “reptiles”


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- Their transition to land involved:

development of legs

more efficient lungs

more efficient heart


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Because of this transition from water to land:

  • Amphibians had to contend with a drier habitat. This required a modified way to enhance oxygen uptake through their lungs

  • This drier habitat required that they go back to a water environment for laying of eggs


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  • Legs, sufficient to support their body weight, allowed them to move from land to water when necessary.

  • Their circulatory systems became more efficient to provide oxygen to all cells which, over time, increased the capacity for aerobic respiration and subsequently greater production of ATP – allowing for more activities.


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  • Scientific Classification of Reptiles

    Kingdom: AnimaliaPhylum: ChordataSubphylum: VertebrataClass: Sauropsida


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  • REPTILES

  • Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane. Today they are represented by four surviving orders:

  • Crocodilia (crocodiles, caimans and alligators): 23 species

  • Rhynchocephalia (tuataras from New Zealand): 2 species

  • Squamata (lizards, snakes and amphisbaenids ("worm-lizards")): approximately 7,600 species

  • Testudines (turtles): approximately 300 species


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REPTILES & AMPHIBIANS

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).


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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


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REPTILES & AMPHIBIANS

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.

  • A reptile has the following features;

    cold blooded

    dry, scaly skin

    tough shell on eggs

    eggs are laid on land


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  • The Rise of Amniotes - Reptiles

    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.


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  • Amniote egg contains a membraneous sac that surrounds and protects the embryo.


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  • Allantois

    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.


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  • The structure first evolved in reptiles and birds as a reservoir for nitrogenous waste, but also as a means for oxygenation of the embryo. Oxygen is absorbed by the allantois through the egg shell . The allantois functions similarly in monotremes, which are egg-laying mammals.


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  • In most marsupials, the allantois is avascular, having no blood vessels, but still serves the purpose of storing nitrogenous waste. Also, most marsupial allantoises do not fuse with the chorion.

  • In placental mammals, the allantois is the precursor of the mature umbilical cord


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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.


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4. They have a copulatory organ that

permits internal fertilization.

5. Their kidneys are good at conserving

water.

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.


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  • “Reptiles” demonstrate certain advantageous features compared to amphibians.

    1. Modification of limb bones, teeth, and

    jaw bones allowed greater exploitation

    of the insect life emerging in the Late

    Carboniferous.

    2. Development of the cerebral cortex permitted

    greater integration of sensory input and motor

    response.


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REPTILES & AMPHIBIANS

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

in Amphibians.

4. Descendants of the surviving dinosaurs

became the lineage of reptiles.


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5. Transdermal gas exchange seen in

amphibians is abandoned by

reptiles because of their well develop-

ed lungs.


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  • Circulatory systems

    Fish Amphibian Reptile, Bird

    Mammal


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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.


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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.


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  • A Sampling of Existing Reptiles – (Latin, to creep)

    Reptiles are a diverse group. They are considered an animal because they have basic amniote traits but not those of mammals or birds.

    A. Turtles

    1. The distinctive shell offers protection while

    conserving water and body heat.


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2. The shell is connected to the skeleton. Their teeth are tough, horny plates designed for gripping & chewing

food.

3. Turtles lay their eggs on land, where

predation is high.


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  • Anatomy of a Box Turtle


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  • Turtle shell structure


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  • Turtle eggs and newborn


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  • Lizards

    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.



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  • Scientific classification

    Kingdom: AnimaliaPhylum: ChordataClass: SauropsidaOrder: SquamataSuborder: Lacertilia


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  • Snakes

    1. Snakes are limbless but retain vestiges

    of hind limbs; they are excellent

    predators.

    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.


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95% of all living reptiles are composed of Lizards and Snakes.


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  • Tuataras

    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!.


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3. Only two species remain today;

they live on islands off the shore of

New Zealand.

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.


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  • Scientific Classification of Tuataras

    Kingdom: AnimaliaPhylum: ChordataClass: SauropsidaOrder: SphenodontiaFamily: SphenodontidaeGenus: Sphenodon


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  • Crocodilians

    1. Crocodiles and alligators all live in or

    near water.

    2. They are the largest living reptiles.

    3. The body plan includes a long snout;

    body temperature is regulated behavior-

    ally (ectothermic).


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4. The ventricle of the heart is divided

into right and left chambers – more

like the heart of birds than that of

other reptiles.


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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.


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  • ReptilianOrders

  • Procolophonida (extinct)

  • Araeoscelidia (extinct)

  • Avicephala (extinct)

  • Younginiformes (extinct)

  • Ichthyopterygia (extinct)

  • Placodontia (extinct)

  • Nothosauria (extinct)


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  • Orders (cont.)

  • Plesiosauria (extinct)

  • Prolacertiformes (extinct)

  • Pterosauria (extinct)

  • Saurischia (extinct)

  • Ornithischia (extinct)


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  • Reptilian Orders (cont.)

  • Testudines

  • Squamata

  • Sphenodontia

  • Crocodilia


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  • Kingdom: AnimaliaPhylum: ChordataSubphylum: VertebrataClass: AmphibiaSubclasses and Orders

  • Order Temnospondyli- extinctSubclass Lepospondyli- extinctSubclass Lissamphibia Orders: AnuraCaudataApoda


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  • Reading Assignment:

  • Pages: 338-342 Chap. 20

    Pages: 444-457 Chap. 26

    Pages: 758-759 Chap. 43

    Appendix I : Kingdom Animalia

    - tetrapods

    - amniotes


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