1. Chapter 42 Amphibians

2. 42-1 Origin and Evolution  Amphibian comes from the Greek for “double” and “life”  Evolved from lobe-finned bony fishes  370 million years ago  Became the first vertebrates to live on land

3. Adaptation to Land  Hypothesis?  Drying up pools vs. limited food and space  Left water to escape predation and competition  Numerous species of fish in water  Terrestrial invertebrates became new food supply

4. Early Amphibians  Ichthyostega: earliest known fossil  4 strong limbs  Homologous to pectoral/pelvic fins  Primitive lungs  Overall fish-like body  Organs for detecting scents and sounds in air  Large, sharp teeth

5. Diversification  3 Orders  Anura: frogs and toads  Urodela: salamanders  Apoda: caecilians

6. Modern Amphibians  Key characteristics  Metamorphosis  Change from aquatic larval stage to terrestrial adult form  Moist, thin skin w/ no scales  Feet lack claws and are often webbed  Use gills, lungs, and skin in respiration  Eggs lack shells

7. Order Anura  Anuran means “tailless”  Frogs and toads  Smooth moist skin vs. rough bumpy skin  Many spend at least part of their life in water  Body adapted for jumping  Adults are carnivores  Some have sticky tongue that is extended  Many return to water to reproduce  External fertilization

8. Order Urodela  Salamanders  Elongated body, long tail, moist skin  Range in size (a few cm to 1.5 m)  Habitat:  Most live in N. America & Central America  No species found in Australia  Reproduction  Lay eggs in water = swimming larva  Lay eggs in moist land env. = hatch into mini adult  Internal fertilization  Females pick up sperm packets

9. Order Apoda  Common name Caecilian  Live in tropical areas  Specialized group of legless amphibians  Resemble small snakes  Often blind  Small eyes located under skin or bone  Rarely seen  Detect prey through a chemosensory tentacle located on the side of the head  Internal fertilization

10. 42-2 Characteristics of Amphibians  External Covering  Skin serves 2 functions  Respiration and protection  Moist and permeable to gases and water  Mucous glands supply lubricant  Also can contain glands that secrete foul-tasting or poisonous substances  Make amphibians vulnerable to dehydration

11. Internal anatomy  Terrestrial vertebrates must rely on internal skeleton for support  Vertebrae of spine interlock  Cervical vert. allow neck movement  Strong limbs  Connect to pectoral and pelvic girdles  Specializations for absorbing force  Fused bones: radio-ulna & tibiofibula

13. Heart and Circulatory System  Divided into 2 loops  Pulmonary circulation  Carrys deox. blood from heart to lungs, returns ox. Blood back to heart  Systemic circulation  Carries ox. blood from heart to muscles and organs, brings deox. Blood back to heart  Advantage over single loop (fish)  Faster blood flow

15. Respiration  Larval amphibians (tadpoles) respire through gills and skin  Most adults lose gills during metamorphosis  Respire through lungs= pulmonary respiration  Use positive pressure breathing  Diagram page 826  Respire through skin= cutaneous respiration

17. Digestive system  Elastic esophagus and stomach allows amphibian to swallow large amounts of food  Glands in stomach secrete gastric juices for breakdown  Pyloric sphincter relaxes and food moves to small intestine  Small intestine  Duodenum (upper portion)  Ileum (coiled middle portion)  Mesentery (membrane like plastic wrap that holds small intestine in place)  Digestion is completed and nutrients released into body

18. Digestion system cont’d  Large intestine  Indigestible wastes are collected  Pushed by muscle cavity into  Cloaca  Cavity also collects from kidneys, bladder, eggs, sperm  Waste exit the body through vent

20. Excretory system  Kidneys: primary excretory organ  Filter nitrogenous waste from blood  Wastes + water = Urine  Larvae excrete the wastes as ammonia  Very toxic  Adults excrete wastes as urea  Uses more energy but conserves water

21. Nervous system  Brain about same size as fish  Olfactory lobes are larger (sense of smell)

22. Sense organs  Lose lateral line system in metamorphosis  Smell, sights, hearing more well developed  Eyes covered by transparent, movable membrane called nictitating membrane  Sound receptors located inner ear  Transmitted by the tympanic membrane (eardrum) and the columnella (small bone that connects the two)