Amphibians : The First Terrestrial Vertebrates

Infraphylum: Vertebrata Class Amphibia  Amphibia- means “ double life ”  Live their lives in the water and on land  Tetrapods :  4 muscular limbs & feet  Have toes & fingers (digits)

History of Amphibians  Oldest fossils discovered in Greenland in 1932  400 myo fossil- Ichthyostegalia  Differences from fish:  Loss of some cranial bones  Loss of opercular bones  Reduction of notochord  More rigid vertebral column  4 muscular limbs  Loss of fins/rays  Presence of vertebrae that fuse the vertebral column and the pelvis

Presence of Amphibians  All continents except Antarctica  Absent from many oceanic islands  6,000 modern species

Amphibian Characteristics  Adults are carnivores  Circulatory system:  2 chambered heart (atrium & ventricle)  Gas exchange: breathe through skin and/or with lungs  Ectothermic- body temperature depends on external heat sources  Nictitating membrane- transparent lower moveable eyelid  Vocalization- species specific  Males call to females for mating

Class: Amphibia Order: Caudata  Salamanders  Mostly found in the N. Hemisphere  All have….  Tail throughout life  Both pairs of legs  Terrestrial salamanders  Live in the moist, forest- floor litter  Aquatic larvae  Sometimes live in caves

Class: Amphibia Order: Caudata  Reproduction:  Most fertilize internally  Males deposit sperm on a substrate and females pick up the sperm with their cloaca  Young salamanders look like miniature adults (called newts )  Have gills & tail fin  May be paedomorphic - undergo metamorphosis while retaining larval characteristics

Class: Amphibia Order: Gymnophiona  Caecilians  160 species  Confined in tropical regions  Worm like burrowers  Feed on worms & other invertebrates in the soil  “Segments” are folds in the skin

Infraphylum: Vertebrata Order: Anura  Frogs & Toads  Live in moist environments or dry deserts  Adults…  Lack tails  Caudal vertebrae fuse into a rodlike structure (urostyle)  Long, muscular hind limbs  End in webbed feet

Infraphylum: Vertebrata Order: Anura  Fertilize externally  Eggs & larvae are aquatic  Larvae (tadpoles)  Well-developed tail  Lack limbs until near adulthood  Herbivores  Undergo metamorphosis to turn into an adult

Frogs VS. Toads Frogs Smooth skin Aquatic habitats Toads Dry & warty skin More terrestrial