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2nd largest phylum in Animal Kingdom. Includes frogs, toads, newts, salamanders and caecilians
Jointed appendages, poikilothermic, Skin naked, often with poison glands, Eggs lack amniotic membranes, Feed primarily on invertebrates, Eyelids keep eyes moist, ears, larynx for vocalization, Small lungs usually present in adults; gas exchange also occurs across moist skin. 3-chambered heart - 2 atria and a ventricle (1 more chamber than in fish heart), Most have metamorphic life cycle - larval stages in water, adults on land, Reproduction usually occurs in water.
Origin of Tetrapods
An extinct group of Sarcopterygians probably gave rise to the first amphibians, First semi-terrestrial vertebrates appear in the Devonian (370 MYA), Transition probably occurred in the water.
In order to live on land...
Sturdy skeleton, esp. vertebral column, Lungs, Internal fertilization, Protection against dehydration, Hearing apparatus, Limbs are needed.
Tetrapods on land
Many present-day fish can breathe air and crawl out on land, this includes the Mudskipper, Walking catfish, and Snakehead fish
Have fish ancestry. Evidence in Embryonic gill pouches, Paddle-like limb buds, and Dermal scales in some amphibians and most reptiles
Moderm Amphibians, includes salamanders and newts. Have long tail, lack middle ear, and have two pairs of limbs. 350 species (approx.), Vert. column divided into 4 regions, Internal fertilization by means of spermatophore, Larvae usually aquatic, have external gills, Great size range.
Aka Salientia. Includes frogs and toads. Tailess, elongated hind legs for jumping and swimming, five to nine presacral vertebrate with transverse process (except the first), postsacral vertebrae fused into rodlike urostyle, well developed larynx, External fertilization by amplexus, Eggs usually laid in water, Larvae (tadpoles) have internal gills.
Caecilians; elongate, limbless; segmented by annular grooves, specialized for borrowing, tail short and pointed, rudimentary left lung. Only living amphibians with dermal scales, Most species give birth to live young.
Amphibians are more threatened and are declining more rapidly than either birds or mammals. 32% of species threatened, 43% of species in decline.
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