KINGDOM ANIMALIA Phylum Chordata Subphylum Vertebrata Class Amphibia

1. KINGDOM ANIMALIAPhylum ChordataSubphylum VertebrataClass 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