Class Amphibia

Vertebrates Move to the Land

Necessary Changes for a Terrestrial Lifestyle

   

Class Amphibia

•      400 million years BP (Devonian period)

•      Arose from Sarcopterygians – Icthyostega

 

•      Able to survive on land, but still tied to water

•    reproduction

•    larval stages

 

Characteristics

•      Bony Endoskeleton

•    Variations in:

•   Body form

•   Number and type of vertebrae

•   limbs

 

•      Skin smooth and moist

 

•      Respiration

•    gills

•    skin

•    lungs

 

•      Circulatory System

•    3-chambered heart •    incomplete separation of pulmonary and systemic blood

 

•      Ectothermal (Poikilothermic; “cold-blooded”)

 

•      Excretion

•    paired kidneys

•    Urea

 

•Brain 

Olfactory Lobes Cerebrum (thinking) Optic Lobes Cerebellum (coordination) Spinal Cord

 

•Reproduction  

 

Taxonomy

 

·         Order Gymnophiona

•      Worm-like

•      Vertebral column (95-285 vertebrae) and ribs

•      No limbs

•      Tropical - South America, Africa, SE Asia

•      Lay eggs in moist soil near water

 

•      Order Caudata

•      Similar body plan to paleozoic ancesters

•    limbs at right angles to body, forelimbs and hindlimbs of equal size

•      Some completely aquatic, but most have aquatic larvae and terrestrial adults

 

•      Both larvae and adults carnivorous (eat worms, arthropods, small molluscs)

•      Respiration

•    skin

•    external gills

•    lungs present in terrestrial forms

•   BUT a very successful group (plethodontid salamanders), have lost lungs, "breathe" entirely through skin & are terrestrial

•      Reproduction

•    fertilization is internal, female picks up spermatophore packet deposited by male

 

•      Some salamanders show: Paedomorphosis

•    adults retain juvenile characteristics & some characters of adult are eliminated

 

 

• Order Anura

•      Adults are carnivores, aquatic larvae herbivorous

•      Size range from 1 cm Brazilian sp. to the 30 cm Goliath frog (it eats rats & ducks!!)

•      Habitats - fully aquatic to moist terrestrial

•      Morphology

•    Skin

•   thin, permeable & must generally remain moist (except spp. such as toads)

•   dermal layer may have mucous & poison glands

•   pigmented chromatophore cells also located in dermis

•    Skeleton/Muscles

•   specialized for jumping/swimming

•   caudal (tail) vertebrae fused into a rigid urostyle & helps in transferring muscular force to hind limbs

•   skull somewhat reduced, light

 

•      Respiration

•    skin (most carbon dioxide lost through skin)

•     lungs (perhaps most important in oxygen uptake)

•      Vocalization

•    both males and females have vocal chords in larynx, but males are better developed

•    sound produced by forcing air over vocal chords

•    calls of frogs are spp. specific