Transcript Amphibians
General Characteristics •First vertebrates on land •4000 species •Strong skeleton to support body weight •Nostrils for breathing through nose •3 chambered heart •Air breathing lungs •Carnivorous diet •Eardrum •Eyelids •Important accommodations needed for land because of… •Oxygen content •Density •Temperature regulation •Habitat diversity Donovan Period •400 million years ago •Mild temperatures and cycles of drought then heavy rainfall, then drought •Unstable environment when many pools evaporated, only those able to acquire atmospheric oxygen survived •Gills would collapse, dry, and lose function •Lobe-finned fish and lungfish were at an advantage •A kind of lung (extension of pharynex) •Bones in fins are like that in arms and legs or early amphibians •Came to land to escape predators or get food bony or cartiliginous structures in lobed fin undergoing modificaiton limb bones of early amphibians Fig. 27.11, p. 462 3 Orders of Amphibians 1. Urodela •Tailed ones •Salamanders, newts, mudpuppies •400 species •Some are entirely aquatic and some live on land •Most walk by bending side to side •Usually internal fertilization – female picks up sperm packet, spermatophore, and inserts it into her cloaca •Born with gills, but these are usually lost in all but aquatic forms •Some do not have lungs or gills and use only skin and mouth for gas exchange In-text, p. 463 2. Anura •Tail-less ones •Frogs and toads •3500 species •More specialized for living on land •Use strong legs to hop •Flick tongue to catch insects •Defense from predators •Camouflage •Secrete mucus – bad tasting or poisonous •Many with poison have a bright color to warn predators 3. Apoda •Leg-less ones •Caecilians •Nearly blind •Look like earthworms •160 species •Burrow through soil •Live in South America, Africa and Southeast Asia •Internal fertilization •Viviparous – live birth Frog Tadpole Aquatic with gills Adults Gills and tail disappear Lateral line Lateral line Finned tail Develops legs •Some frogs do not go through the tadpole phase •Some are strictly aquatic and some are strictly land •Salamanders and caecilians resemble adults when born •Even land dwelling amphibians need a moist habitat •Need to stay moist •Some breath through skin and mouth because they have no lungs •Eggs do not have a shell and dehydrate in air •Male causes female to release eggs and spills sperm while she does this •Some incubate eggs on back, mouth or in stomach •Some are ovoviviparons and viviparons •Ovoviviparons – eggs hatch in uterus •Viviparons – young develop in uterus •Frogs are usually quiet, but may call during mating season •Many want to protect territory or attract females