unit 8.3 class amphibia

1

Unit 8.3

Class Amphibia

2

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.

3

Transition from Sea to Land

4

•Coelacanth

5

Eusthenopteron

6

Panderichthys

7

Tiktaalik

8

9

10

Amphibians

11

12

13

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.

15

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

16

Evolution of CirculationFish Amphibian

17

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

18

19

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

20

Newt – Salamander With Rough Skin

21

Paedomorphosis

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

22

23

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!!

24

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.

26

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.

29

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.

30

Poison Dart Frogs

31

32

33

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!

35

The End