Class Amphibia MOVEMENT ONTO LAND

1. Class Amphibia MOVEMENT ONTO LAND

3. Class Amphibia MOVEMENT ONTO LAND • In order for animals to live on land they: • need to support their own weight (i.e., deal with gravity) • Water more dense and also property of buoyancy • because of this skeletal and muscular systems of terrestrial organisms have to be better developed.

4. Class Amphibia MOVEMENT ONTO LAND • In order for animals to live on land they: • Resist drying • a constant problem in daily life • rate of evaporation in most terrestrial systems very great • resistance to drying is especially important during reproductive stages (i.e., egg) since they can not do anything actively to prevent water loss

5. Class Amphibia MOVEMENT ONTO LAND • In order for animals to live on land they: • deal with rapid temperature changes • daily and seasonal changes in water environment less than in the air • be able to extract oxygen from air • oxygen 20 times more abundant in air than water

6. Amphibian Early Evolution • Amphibian ancestors: Devonian (400 million years ago) • Sarcopterygii (lobe-finned fishes) • had rudimentary appendages • had lungs - could be used used to breathe air • during Carboniferous (350 million years ago)- was good environment for amphibian development • characterized by wet warm environments • lots of swampy areas • during this time amphibians had their greatest rate of evolution

7. Fish-like appendage More like modern amphibians

8. Amphibian Evolution • Amphibians have met challenge of land only half way • still very tied to water skin has to be kept wet at all times • many use skin to aid in respiration • all amphibians are tied to water to reproduce • almost all lay eggs in water and larval stages are aquatic

9. Amphibianscharacteristics - adults • Upper jaw fused to skull

10. Amphibianscharacteristics - adults • with a three chambered (ventricle and two atria)

11. Amphibianscharacteristics - adults • respiration more efficient • respiration through gills (in some), lungs, skin

12. Amphibianscharacteristics - adults • Skin: • no scales; skin smooth, moist with many glands • epidermis with keratin, below is dermis • skin color due to chromatophores located in dermis;

14. Amphibianscharacteristics - adults • Nervous System • 10 pairs of cranial nerves

15. AmphibiaSensory Structures

16. AmphibiaReproduction • are dioecious; • copulation is called amplexus, • fertilization mostly external in frogs and toads and internal in salamanders; • mostly oviparous, some ovoviviparous some viviparous; with development of larva (tadpole

20. Amphibia AdultCharacteristics • limbs - four (tetrapod); some are legless • nostrils open into anterior part of mouth cavity • many (i.e., frogs) have developed vocal chords to produce sounds for mating

21. AmphibiaLarval Characteristics • fish-like • finned tail • lateral line system as in fishes • 3 pairs of gills • 3 pairs of aortic arches • no lungs in early stages

22. Amphibia Larval Characteristics • two chambered heart • no limbs in early development • some show neotony • reach sexual maturity, • while retaining gills and other larval characteristics; • most commonly seen in salamanders • some are permanent "larvae"- called obligatory neotony (ex mud puppy- Necturus)

23. AmphibiaSurvey of Classes • Gymnophonia- (=Apoda); caecilians • very primitive • up to 200 vertebrae • limbs and girdles absent • pantropical; 160 spec

24. AmphibiaSurvey of Classes • Caudata (=Urodella); salamanders • tailed • larvae resemble adults • some aquatic, some fully terrestrial • two pairs of equal limbs • 10-60 vertebrae • no vocal chords • holarctic; 350 species

25. AmphibiaSurvey of Classes • Anura (=Salientia); frogs and toads • larvae and adults very different • adults tailless • hind limbs modified for jumping • 6-10 vertebrae • larvae aquatic; adults more terrestrial, especially toads • no gills as adults • have nictating membrane - prevent dessication of eye • have vocal cords • cosmopolitan; 3400 species