1. KINGDOM ANIMALIA Phylum Chordata Subphylum Vertebrata Class Amphibia

2. Vertebrate Classes

3. History
Chordate group to evolve after fish were true tetrapods = Amphibians
Ichthyostega presents rudimentary amphibian features (different from fish)
Girdles = skeletal bones connecting the central skeleton to the bones of the appendages
Other skeletal strengthening: rib cage and cranium
Ichthyostega still retained a caudal fin and scales

4. History
Ancient and modern amphibians have features that enhance their survival on land but also limit this existence.
Most amphibian evolution took place when Earth was warm, humid, and swampy (350 mya).
Insects were abundant.
No pressure to develop into a truly terrestrial animal.

5. Common Features
Well-muscled appendages, supported by an central and peripheral skeleton
Further development of lungs
Skin highly vascularized, other site of gas exchange, and maintains water balance
Circulatory system now includes a 3-chamber heart
Increased pressure to peripheral arteries
Atrium separated by septum, but still one ventricle
More efficient but still mixing of oxygenated/deoxygenated blood
All of these features serve to increase the mobility of amphibians

6. Common Features
Other features illustrate the amphibian’s primitive nature:
ectothermic-sluggish when cold, hibernation or death
respiration through skin requires it to be thin and moist
lose lots of water through skin and must keep it continually moist to prevent lethal desiccation
must reproduce in the water since eggs would dry up on land
aquatic larval stage more closely related to fish than terrestrial animals

7. Common features Novelty = pedicellate bicuspid teeth
crown and base = dentine
middle = fibrous connective tissue
bicuspid = 2 cusps/points

8. 3 Main Groups Caecilians (165 species) Salamanders (502 species)
Anurans (frogs/toads, 4000 species)

9. Caecilians Tropical, limbless amphibians
Resemble giant earthworms and burrow in the ground
unlike other tetrapods, skin is bound to body wall musculature which bestows great burrowing efficiency
powerful body with well-developed endoskeleton
skull used as battering ram as it burrows
Carnivorous: eat earthworms if terrestrial, fish/inverts if aquatic

10. Caecilians Tiny eyes if present (most are vestigial, covered by skin)
Chemosensory tentacles on head in front of eyes used to locate food
Internal fertilization; some species bear live young while others lay eggs

11. Salamanders Most closely resemble amphibian tetrapod ancestor
Long tails, 2 pairs of limbs of approximately the same size
Primarily live in Northern Hemisphere (abundant in cool, moist forests, only 1 type tropical)

12. Salamanders Generally (semi)terrestrial as adults
Most pass through larval stage
few days to a few years
some species never metamorphose (axolotl)

13. Anurans “without tail”
Most successful, diverse, evolutionarily divergent of the living amphibians
Jumping locomotion allowed exploitation of new terrestrial niches
Live in almost any climate (except high latitudes in Arctic, Antarctic, some oceanic islands, some extremely dry deserts)

14. Anurans Adaptations for jumping locomotion
Hind limbs much longer than forelimbs
Short trunk
Tail lost
Flattened head
Large eyes

15. Anurans Many deposit eggs in water; get free-swimming tadpoles
Others lay terrestrial eggs
Some carry their eggs with
them