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Bio II Rupp. Background  Evolved 370 mya from sarcopterygii  Name means “double” “life”

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Presentation on theme: "Bio II Rupp. Background  Evolved 370 mya from sarcopterygii  Name means “double” “life”"— Presentation transcript:

1 Bio II Rupp

2 Background  Evolved 370 mya from sarcopterygii  Name means “double” “life”

3 Adaptation to Land  Bad hypothesis Movement overland from shrinking pools of water to larger pools Short overland crossing do not allow time for change  Better hypothesis Escape from predation and competition to land where resources were plentiful—insects and plants

4 Characteristics of Early Amphibians  Similar to sarcopterygii Skull Limbs Shape

5 Icthyostega continued  Four strong limbs—homologous to pectoral fins  Lung breather  Teeth for eating fish  Seven toes on hind foot—today’s amphibians have five

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8 Diversification  Evolutionary split in the Devonian and Carboniferous period  One line became modern amphibians

9 Diversification continued  Other line was forerunner to modern reptiles  Approximately 4500 species of amphibian today Anura—3000 species Urodela—400 species Apoda—160 species

10 Modern Characteristics

11 Aquatic Larva to Terrestrial Adult-- Metamorphosis

12 Moist, thin, scaleless skin

13 Claw-free feet, typically webbed

14 Gills, lungs, and skin for respiration

15 No multicellular egg membranes

16 Large mouth with upper and lower teeth

17 Three-chambered heart

18 Ectothermal

19 Paired kidneys

20 Ten pairs of cranial nerves

21 Separate Sexes

22 Order Anura  Name means “without tail”  Frogs and toads  Found worldwide except polar regions  Toads = rough and bumpy skin  Frogs = smooth and moist skin  Spend at least part of their life in water, some are totally aquatic  Built to jump Long, strong hind legs Short, shock absorbing forelimbs  Eat almost anything  Return to water for fertilization and mating  Larval tadpole stage

23 Toad versus Frog

24 Order Urodela  Tailed amphibians  Elongate body, long tail, moist skin, four limbs  Few centimeters to 1.5 meters long  Carnivorous  Typically nocturnal  Found in the Americas, Africa, Asia, and Europe  Many lay eggs in water— metamorphosis  Family Plethodontidae is the largest group— lungless, gas exchange through skin  Terrestrials hatch into mini adults—direct development  Internal fertilization— spermatophore  Some females retain eggs until hatching  Necturus

25 Urodelans

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27 Urodelans continued  Paedomorphosis—retention of pre-adult structures  Non-metamorphic species are termed perennibranchiate

28 Apodans  Name means “without feet”  Typically called caecilians  Resemble snakes  Average 30cm in length some reach 1.5m  Small eyes located under skin or bone— typically blind  Burrowers  Relatively little is known  Teeth for prey capture  Chemosensory tentacles on head  Believed to have internal fertilization  Some females stay with eggs until hatching  Some are viviparous  Found in Asia, Africa, and S. American tropical regions

29 Apodans continued

30 External Covering  Two major functions Respiration Protection  Gas exchange is aided by mucous glands to keep the skin moist

31 External covering continued  May secrete poisons  May desiccate quickly if not near water  Nocturnal to avoid desiccation

32 Internal Anatomy  Strong vertebral column to support weight on land  Strong limbs  Pectoral and pelvic girdles  Cervical vertebrae for neck movement

33 Internal Anatomy—circulatory system  Double circulation—two loops  Pulmonary circulation—carries deoxygenated blood from heart to lungs  Systemic circulation—carries oxygenated blood to body  Faster blood flow than a single loop system like fish

34 Internal Anatomy—circulatory system continued

35  First division in pulmonary and systemic pumping  Deoxygenated blood enters sinus venosus of right atria  Oxygenated blood enters left atria  Blood enters the ventricle— structure minimizes mixing of bloods  Conus arteriosus valve separates blood and sends to lungs or body

36 Respiration  Larval amphibians use skin and gills  Adults use skin and lungs  Cutaneous respiration is important due to small surface area of lungs  Positive pressure breathing The mouth changes the pressure in the airway Nostrils control direction of the airflow

37 Respiration continued

38 Digestive system  Adults are carnivorous  Larvae are typically herbivorous  Organs Pharynx Esophagus Stomach Liver Gall bladder Small intestine Large intestine Cloaca

39 Digestive system continued  Elastic stomach and esophagus allow swallowing of large prey  Stomach secretes gastric juices  Pyloric sphincter allows digested food to move to the small intestine  Upper portion of small intestine is the duodenum  Middle portion of the small intestine is the ileum

40 Digestive system continued  Mesentery holds the small intestine together  Digested food, urinary wastes, and eggs and sperm pass into the cloaca before exiting the vent  Liver produces bile stored in the gall bladder  Pancreas secretes enzymes to help break down food in the small intestine

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43 Excretory system  Kidneys are the primary organ One located on each side of the spine Filter nitrogenous wastes, mix with water, and excrete as urine  Kidneys to urinary ducts to urinary bladder  Bladder can serve as a water reservoir organ in dry times  Larval amphibians excrete ammonia which is toxic  Adults transform ammonia into urea, which is less toxic and conserves water

44 Excretory system continued

45 Nervous system  Brain is divided into lobes Olfactory Cerebrum—behavior and learning Optic lobes Cerebellum—muscular coordination, not well developed Medulla oblongata—involuntary muscle control, heart and breathing  Ten pairs of cranial nerves  Spinal cord and PNS

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48 Sense organs  Larval amphibians have a lateral line system like a fish—it is lost during metamorphosis

49 Sense organs continued  Eyes Covered by nictitating membrane Large optic lobes

50 Sense organs continued  Hearing Tympanic membrane—external eardrum Columella—small bone between typanum and internal ear Inner ear fluid carries vibrations from columella Sounds are converted to electrical impulses by small hair cells Electrical impulses are transmitted to the brain

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53 Reproduction—life cycle  Males have bean-shaped testes near the kidneys  During breeding the sperm cells pass to kidneys, then urinary ducts, then the cloaca  Females have thin-walled ovaries located near the kidneys  Eggs mature, burst through the ovaries, move towards oviducts, become coated in jelly-like material, and exit the cloaca

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55 Reproduction—courtship and fertilization  Mating calls are species unique—caused by forcing air back and forth from lungs to mouth over vocal sacs  Amplexus—males climb onto female and embrace her  When the female releases the eggs the male coats them in sperm—direct external fertilization  Frog calls Frog calls

56 Reproduction-courtship and fertilization

57 Reproduction--metamorphosis  A few days after fertilization tadpoles hatch  Tadpoles survive using an attached yolk sac  Develop three pairs of gills Development of operculum Spiracle on left side  Mouth eventually opens, legs grow, and tail and gills disappear  Thyroxine is the hormone responsible for causing the physical changes

58 Reproduction—metamorphosis continued

59  Some species do not lay eggs in water, but they find a moist place or construct small nests  Some salamanders remain in a larval stage their entire lives (Mexican axolotl— paedomorphosis) (Necturus— perrenibranchiate)  Some amphibians bypass metamorphosis and hatch as miniature adults (metamorphosis in egg) (Longtail salamander)

60 Reproduction—metamorphosis continued

61 Reproduction—parental care  Some species offer protection to their young  Many times the father is the protector  Male Darwin frog, Rhinoderma darwinii, takes young into his vocal sacs—they hatch and go through metamorphosis in his body (found in Chile)

62 Reproduction—parental care continued  Female gastric-brooding frogs (probably extinct) Swallow the eggs Development in stomach Stomach stops producing acids during brooding  Some females sit on their eggs, typically poison dart frogs

63 Reproduction—other parental care strategies

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