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Unit 8.3

Class Amphibia

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Tetrapods• Animals with 4 limbs.

– Amphibians– Reptiles– Birds– Mammals

• Evolved from lobe finned fish in the Devonian period (middle of the Paleozoic).

• The first tetrapods were amphibians.

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Transition from Sea to Land

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•Coelacanth

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Eusthenopteron

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Panderichthys

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Tiktaalik

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Amphibians

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Adaptations to live on land• Gills are usually lost by

adulthood• Lungs function• Breathe through skin – Called

cutaneous respiration• Secrete mucus

– Prevent dehydration– Aids in respiration – Allows a

medium through which oxygen can pass through skin to blood vessels.

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More Adaptations to live on land

• Skeleton – Fins evolve into limbs– Bony vertebral column

supports body underneath it

• Air is not as buoyant as water

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Evolution of CirculationFish Amphibian

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Class Amphibia• Land and water

– Reproduce in water• Skin with mucoid secretions

– Respiration• No scales, feathers or hair• Heart with 3 chambers

– 2 atria– 1 ventricle

• One cervical vertebra – can turn neck only slightly

• Exothermic – need a 4 chambered heart to be endothermic

Exothermic

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Order Caudata• Salamanders comprise order.• A long tail is the defining

characteristic of this order.• Salamanders have 4 legs.

Usually, the front legs have 4 digits and the hind legs have 5 digits.

• May be fully aquatic, amphibious, or fully terrestrial as adults

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Newt – Salamander With Rough Skin

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Paedomorphosis

Paedomorphosis is the retention of juvenile characteristics in the adult form.

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Family Plethodontidae

• No lungs!!• Breathes through skin

exclusively as an adult.• The larger of the two

families of salamanders.• Lack aquatic larvae and

hatch as miniature adults from eggs laid on land – must be very moist land!!

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Family Salamandridae

• Members have lungs.• True salamanders and

newts.• Usually have rough skin

(not as reliant on cutaneous respiration).

• Usually brightly colored with contrasting bands.

• Aquatic larval stage with external gills

Giant Salamander

• The largest amphibians on the earth today.

• Can reach sizes up to 1.8 meters (6 ft) in length.

• Folds in their skin increase their surface area allowing for more oxygen absorption to occur.

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Order Anura• Anura means “tail-less”.• Frogs and toads.• No tail in adult, but present in

larval stage.• Long hind limbs, shortened

body, and webbed feet characterize Anurans.

• Considered to be the best jumpers of all vertebrates (up to 50 times their body length).

Toads vs. Frogs

• Most toads arose due to convergent adaptations to drier climates, not separate lineages.

• Skin is thicker to conserve water.

• Lungs are better developed due to reduced cutaneous respiration.

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Mating• Frogs often return to their

pond of origin to breed.• Males call out to females with

a sound unique to each species.

• Mate by amplexus. The male mounts the female, stimulates her to release eggs by squeezing her pelvis, and then externally fertilizes the eggs.

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Poison Dart Frogs

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Order Apoda• Caecilians are the only type of

Apodan.• Defining feature is their lack of

legs – resemble worms or snakes.

• Skin glands produce mucous to assist in cutaneous respiration.

• Live underground in tropical regions.

• Least studied and understood amphibian.

Order Apoda• Caecilians have reduced

eyes due to their subterranean lifestyle, but are not completely blind.

• Many species undergo internal fertilization and have viviparous births.

• Internal copulation may last 2 to 3 hours!

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The End