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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 fossilIchthyostegalia 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 membranetransparent 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, forestfloor 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 paedomorphicundergo 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” in the skin are folds 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
