Chapter 42 Amphibians 42 1 Origin and Evolution

Chapter 42 Amphibians

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

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

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

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

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

Order 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

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

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

42 -2 Characteristics of Amphibians External Skin Covering serves 2 functions Respiration Moist and protection 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

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

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 Faster over single loop (fish) blood flow

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

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

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

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

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

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)