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Unit 8.3 Class Amphibia. 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. Transition from Sea to Land. Coelacanth. Eusthenopteron. Panderichthys. - PowerPoint PPT Presentation
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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