Chapter 42 Amphibians I. Origin and Evolution of Amphibians A. Early Amphibians 370 million years ago B. Shared characteristics with lobe finned fishes (coelacanth) 1. Pectoral Fins/Pelvic fins homologous to forelimbs and hindlimbs 2. Lungs/similarities of skull and vertebral column C. Diversification of Amphibians 1. Reptiles and amphibians diverged 286-360 mya II. Modern Amphibians (4500 species) A. Amphibian definition lives both in water and on land B. Characteristics of amphibians 1. Skin moist, thin, no scales, mucous secreting glands 2. Feet if present then webbed and lack claws 3. Toes soft padded 4. Respiration most use gills (larva); lungs and skin (adult 5. Reproduction external; eggs are usually laid in water, no membranes or shells 6. Metamorphosis means change in morphology; a. Aquatic larva (gill breathers and 2 chambered hear, herbivoresplant eaters) b. Terrestrial adult (lung and skin breathers and 3 chambered heart, carnivores- meat eaters) III. Taxonomy of Amphibians A. Kingdom- Animalia B. Phylum- Chordata C. Sub-phylum- Vertebrata D. Class- Amphibia E. Orders- 1. Apoda- a = without; pod = foot 160 species of Caecilians, blind, tropical 2. Urodela- ur = tail; delos = visible 400 species of salamanders and newts 3. Anura- an = without, ur = tail; largest order 3900 species of frogs and toads IV. Urodela (salamanders or newts = amphibians with tails) A. Size: few cm to 1.5 meters B. Habitat: Northern hemisphere (not Australia) water/land C. Morphology 1. Elongated body, four short limbs, tail, clawless toes, skin soft and moist, lungs or gills 2. Freshwater salamanders keep gills all of their lives- Mudpuppies East U.S>; Axolotl Rocky Mountains D. Reproduction: Water Moist land (live adult form), internal fertilization
Comparison to Lizard: Salamander Lizard Body Shape + + Tail + + Legs + + Body Covering Skin Scales Claws - + E. Protection 1. Glands- secrete poison or bad taste 2. Skin change color (camouflage); warn of poison orange or red F. Examples 1. Largest (~2ft) American hell bender (streams) 2. Mud puppy- America Midwest - red gills 3. Japanese hellbender 4. Red Eft (newt)- at 2months land dweller with lungs 5. Crimson spotted newt- land dweller with aquatic larva V. Anura (Frogs and Toads = amphibians without tails) A. Toads 1. Adaptations for land living (lungs/hind legs) 2. Habitat- loose moist soil or dry areas 3. Protection a. Bury/crouch loose soil or hole b. Skin Color and texture (grey/green and rough) camouflage c. Glands best defense poison 4. Major enemy- snake 5. Diet- gardners friend eats 3x weight in bugs B. Frogs 1. Habitat- near water 2. Protectiona. Coloration (leopard frog) grayish green with dark spots surrounded by yellow/white underbelly white (great for water) b. Leaping (out of harm s way) c. Glands (secrete mucus) 3. Size- 1cm to feet 4. Diet- Carnivore, insects, worm, crayfish Large bull frog eats small birds and mice 5. Examples a. Leopard frogs b. Western African frog largest frog about 30cm long and can jump about 9.9 feet, eats rats and ducks c. Bullfrog- legs can be 10 inches VI. Characteristics of Amphibians A. External structures
1. Skin a. Thin, moist, loose b. Lacks scales c. Rich supply of blood vessels for 0 2 exchange d. Secret mucous to retain moisturize, or bad taste poison for protection 2. Leg and skeletal adaptations (fused bones for strength) a. Short front legs functions (fused radioulna) i. Prop up on land ii. Absorb shock of landing iii. Inner toes thumb in male clasps female and squeezes out eggs to fertilize b. Hind legs functions (fused tibiofibula) i. Swimming ii. Jumping c. Lumbar vertebrae i. Fused into single bone called urostyle for strength 3. Head a. Eyes i. Location vision of top of head ii. Functions- protection; aids in feeding by holding the food on tongue, eyelids protect against water loss on land or in water iii. Nictitating membrane- 3 rd eyelid a. Joins lower lid b. Protects eyes underwater b. Nostrils (called nares) i. Locations- on top of head ii. Function- respiration c. Tympanic membrane (eardrums) i. Location- on body surface just behind the eyes on the side of head ii. Function- hearing iii. Eustachian tube- maintains balance or equilibrium (breathes through mouth to eardrum through tube) iv. Inner ear functions to equalize the pressure as the amphibian descends/ascends in the water d. Mouth i. Large with tongue attachment in the front ii. Teeth none for chewing a. Vomerine teeth- project from the bones at the top of the mouth, function to hold prey to be swallowed
b. Maxillary teeth- cone shaped in the upper jaw, facing back to throat e. Internal nostrils (nares)- breathing from external nares bring air into mouth f. Eustachian tubes- back of throat in the upper palate- maintains equilibrium g. Vocal sacs- two holes in the lower jaw at back of the mouth; used to make sounds especially in mating; large in males h. Gullet opening- opening to the stomach (expands to accommodate large food) i. Glottis- Opening to lungs (slit-like) B. Internal anatomy and organ systems 1. Heart and circulatory system a. Two cycle i. Systemic: carries O 2 and blood from heart to muscles and organs of the body and brings deoxygenated blood back to the heart ii. Pulmonary: carries deoxygenated blood from the heart to the lungs and then O 2 and blood from the lungs to the heart b. Heart i. 3 chambers ii. Left atrium: receives blood from the lungs with O 2 iii. Right atrium: receives blood from the body through a vein called the vena cava which dumps it into the sinus venosus (with 02 and CO2) iv. Ventricle: Contracts and sends blood to the lungs and the body through the conus arteriosus v. Conus arteriosus divides blood into the CAP: C= carotid arch (blood to head) A= aortic arch (blood to muscles and organ) P= pumocutaneous arch (blood to the lungs, skin and mouth) c. Respiratory System i. Larval amphibians respire through their skin and gills ii. Adult amphibians respire through their lungs and skin a. Pulmonary respiration: (positive pressure breathing) lower the floor of the mouth, air rushes into mouth and through the nares; closing the nares and raise the floor of the mough creats a + pressure forching air through the glottis, down the larynx to the bronchii and into the lungs b. Cutaneous respiration: (Skin breathing) Capillary blood vessels allow for gas exchange
d. Digestive system: Digestion and absorption of food i. Gullet- Opening to the stomach (elastic) ii. Stomach cavity- where digestion begins iii. Gastric glands- secrete the digestive juices into the stomach iv. Pylorus- region at the lower end of the stomach between the stomach and small intestine a. Pyloric sphincter (valve) controls the rate at which the stomach contents empty into the small intestine v. Small intestine- food absorption takes place through capillaries going to all parts of the body a. Mesentery- resembles plastic wrap and holds the small intestine in place b. Duodenum- upper end of the small intestine just past the pyloric valve c. Ileum- middle coiled portion of the small intestine vi. Large intestine- colon indigestible waste collects and goes to the cloaca vii. Cloaca- common urogenital opening a. Colon- feces b. Kidney tubes/urinary ducts- urine, sperm, eggs viii. Vent- anal opening allows the contents of the cloaca to be expelled ix. Liver- partially covers stomach a. Produces bile which breaks down fat b. Stores sugar in the form of glycogen x. Gallbladder- stores bile xi. Pancreas- small ribbon like structure near the stomach a. Secretes enzymes that enter the small intestine b. Break down food into small molecules sugars 2. Excretory system a. Skin- removes CO2 waste b. Liver removes blood waste c. Kidneys- remove nitrogen waste i. Lay on either side of the spine ii. Urinary ducts carry nitrogenous wastes to the cloaca d. Urinary bladder- stores urine and helps conserve water 3. Nervous system a. Brain i. Olfactory lobes- smell ii. Cerebrum- interprets sensory information iii. Optic lobes- sight iv. Cerebellum muscular coordination
v. Medulla oblongata- involuntary functions of the heart and lungs vi. Cranial nerves- 10 pair vii. Spinal cord- communicates with body via spinal nerves 4. Reproductive system/reproduction a. Male i. Testes- produce sperm (bean shaped organs, yellow) ii. Vasa efferentia- carry sperm to kidneys (urinary ducts and cloaca) iii. Seminal vesicle- stores sperm b. Female i. Ovaries- produce eggs and release into abdomen ii. Oviducts- carry eggs to the urinary duct (long, coiled, and ciliated) and cloaca iii. Ovisac stores eggs c. Fertilization i. Female lays around 200 eggs ii. Season: spring (april to may) iii. Amplexus- male from forces the eggs out of females cloaca with claspers (thumbs) iv. Direct and external- Male covers eggs with sperm v. Egg (jellylike) coat functions a. Protection b. Binding creates larger mass and is harder for predators to eat c. Constant temperature d. Food for hatchling tadpole VII. Fog Development/survival A. Metamorphosis- change of body into another form through genes Tadpole (larva) Adult Respiration Gills Lungs Heart 2 chamber 3 chamber Habitat Water Land Diet Plants Animals Appendages Fins Legs Tail Yes No B. Regeneration 1. Tadpoles and salamanders CAN regenerate injured/lost parts 2. Adult frogs and toads CANNOT regenerate C. Hibernation/Estivation 1. Ectothermic- cold-blooded and cannot control body temperature 2. Fat Bodies- internal shock absorber and food supply for dormancy
3. Hibernation- winter dormancy (torpor) to escape cold 4. Estivation- summer dormancy to escape heat