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AMPHIBIANS. Amphibians Amphibians are tetrapods (four foot)! The name is derived from the presence of four muscular limbs and feet with digits!. Amphibians occur on all continents except Antarctica! Modern amphibians belong to three orders!. Order Caudata – salamanders
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Amphibians • Amphibians are tetrapods (four foot)! The name is derived from the presence of four muscular limbs and feet with digits!
Amphibians occur on all continents except Antarctica! • Modern amphibians belong to three orders!
Order Caudata – salamanders • Order Anura - frogs and toads • Order Gymnophiona – caecilians
Order Caudata • They posses a tail throughout life!
Most terrestrial salamanders live in moist forest floor litter and have aquatic larva! A number live in caves!
Members of the family Salamandridae are commonly called newts! They spend their lives in water and often have a caudal fin! Range in size from a few centimeters to 1.5 meters (Andias japonicus)!
The largest in North America is the hellbender (Cryptobranchus alleganiensis) which grows to about 65 cm!
Most salamanders have internal fertilization! Males produce a spermatophore which they deposit onto a leaf! The female picks it up and places it in a special pouch called a spermatheca and fertilization happens!
Larva are similar to adults only smaller! Many salamanders undergo incomplete metamorphosis and are paedomorphic! (They become sexually mature while still showing larval characteristics!)
Order Gymnophiona – caecilians • Wormlike burrowers that feed on invertebrates in the soil! They appear segmented because of folds in the skin that cover the separations between muscle bundles!
Fertilization is internal in caecilians! • Order Anura • Includes about 3,500 species of frogs and toads!
Adults lack tails and caudal vertebra fuse into a rodlike structure called a urostyle! • Hindlimbs are long and muscular and end in webbed feet!
Fertilization is almost always external and eggs usually are aquatic! • Larval stages called tadpoles have well developed tails!
Unlike adults, the larva are herbivores and posses a beaklike structure used in feeding!
The term toads usually refers to anurans with relatively dry and warty skin that are more terrestrial than other members of the order! • True toads belong to the family Bufonidea!
External Structure And Locomotion! • Their skin is designed to protect against infective microorganisms, ultraviolet light, desication, and injury!
It also functions in gas exchange, temperature regulation, and the absorption and storage of water! • Amphibians have no scales, feathers, or hair!
The skin is highly glandular and its secretions aid in protection! They help keep the skin moist! • They produce toxic chemicals that discourage potential predators!
The skin is mostly smooth but some have warts, usually as the result of keratin deposits!
Chromatophores are specialized cells in the skin that are responsible for skin color and color changes!
Compared to fish, the amphibian skull is flattened, smaller, and have fewer bony elements! • Changes in the jaws and jaw muscles allow terrestrial vertebrates to crush prey held in the mouth!
The backbone of amphibians is modified to provide support and flexibility on land! • Unlike fish, amphibians have a neck!
The first vertebra is the cervical vertebra which moves against the back of the skull and allows the head to nod vertically! • The last trunk vertebra is the sacral vertebra!
It anchors the pelvic girdle to the vertebral column to provide increases support! • A ventral plate of bone called the sternum supports the forelimbs and internal organs. It is reduced or absent in frogs and toads!
The pelvic girdle of amphibians consists of three bones (the ilium, ischium, and pubis) that attach pelvic appendages to the vertebral column!
Long hindlimbs and powerful muscles form an efficient lever system for jumping in anurans!
Nutrition and the Digestive System! • An adult bullfrog will prey on small mammals, birds and other anurans! • Most larva are herbivorous and feed on algae and other plant matter!
Most salamanders use only their jaws to capture prey but anurans use their tongue and jaws to capture prey. Amphibians are the first animals we have studied to have a tongue!
Gas Exchange • Terrestrial animals spend much less energy moving air across gas exchange surfaces than do aquatic organisms because air contains 20 times more oxygen than water!
Amphibian skin is moist and richly supplied with capillary beds! These two factors permit the skin to function as a respiratory organ! Gas exchange across the skin is called cutaneous respiration!
This can occur on land or in water! • In salamanders 30 – 90% of respiration can occur across the skin! • Gas exchange can also occur across the surface of the mouth and pharynx!
This is called buccopharyngeal respiration and account for about 7% of respiration! • The amount of gas exchange in these two methods cannot be increased when metabolic rate increases!
Temperature Regulation • Amphibians are ectothermic (cold blooded)! They depend on external heat sources to maintain body temperature! • Animals in water loose heat very quickly!
When amphibians are in water they take on the temperature of the water they are in! On land they can regulate their temperature more easily!
Temperature regulation is mainly behavioral! • Many are nocturnal! • Some warm themselves by basking in the sun, especially after eating because it speeds up digestion!
Nervous And Sensory Functions • similar to other vertebrates! • The brain is divided into three regions; forebrain, midbrain, hindbrain!
Forebrain – contains the olfactory centers and the regions that regulate color changes! • Midbrain – assimilates sensory information and initiate motor responses!
