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Tetrapods

vertebrate animals having four feet, legs or leglike appendages

Class Amphibia

2nd largest phylum in Animal Kingdom. Includes frogs, toads, newts, salamanders and caecilians

Amphibian Characteristics

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

Land Vertebrates

Have fish ancestry. Evidence in Embryonic gill pouches, Paddle-like limb buds, and Dermal scales in some amphibians and most reptiles

Order Caudata

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.

Order Anura

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.

True Frogs

Aquatic, Large hind legs, Very large tympanic membranes

Toads

More terrestrial, Drier, wartier skin, Smaller hind legs, Very large parotid (poison) glands

Tree Frogs

Small, Arboreal, Suction pads on fingers and toes

Order Gymnophiona

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.

Amphibian Crisis

Amphibians are more threatened and are declining more rapidly than either birds or mammals. 32% of species threatened, 43% of species in decline.

Cause of Amphian Crisis

habitat destruction, pollution, climatic changes, UVB radiation, introduced predators, overexploitation and the Chytrid fungus

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