1. CHAPTER 32: AMPHIBIANS

2. Amphibian  Greek  Amphi means “double” or “on both sides”  Bios means “life”  Reflects their ability to live in the aquatic world and the terrestrial world

3. Fossil Evidence  Evolved from lobe-finned fish about 370 million years ago  Most paleontologists think that amphibians evolved directly from rhipidistian fish - similarities in the skeletal features

5. Ichthyostega  Earliest known amphibian fossil  Now extinct  Fossil found in 370-million year old rock in Greenland  Strong build - four legs supported by hip and shoulder bones - each leg had a foot with five toes  Bony scales  Long fin extending the length of the tail - tail used to propel the animal through the water  Grew up to one meter

7. THE RISE AND FALL OF AMPHIBIANS

8. Carboniferous Period  Age of amphibians begins - common  14 families existed early carboniferous - nearly all aquatic or semiaquatic  Late carboniferous 34 families

9. Permian Period  Amphibians reached their greatest diversity  40 families  Many began to leave the marshes for dry uplands - many terrestrial amphibians had bony plates and armor - grew to be very large - skin prevented water loss  Mid-permian, 60% of all amphibian species were completely terrestrial - marked the peak of amphibian success

10. End of Permian Period  Therapsid - terrestrial reptile - successful in replacing all terrestrial amphibians  Over half of the remaining amphibians were aquatic

11. Triassic period  Only 15 families of amphibians - including the first frogs  Aquatic  Some grew to sizes up to four meters long

12. Jurassic Period  Only 2 families survived - anurans (frogs and toads) - urodeles (salamanders and newts)  Age of amphibians over

13. THE SUCCESS OF AMPHIBIANS

14. Mesozoic Period  Anurans and urodeles - only amphibians to survive the age of reptiles  All amphibians descended from anurans and urodeles

15. Tertiary Period  Invasion of wet habitats  Today over 4,200 species of amphibians  37 families  Not as diverse in form or habitat as Permian amphibians

16. CHARACTERISTICS OF MODERN AMPHIBIANS

17. Legs  Frogs and salamanders have four legs  Caecilians lost their legs during the evolutionary course of adapting to a burrowing existence

18. Lungs  Most larval amphibians have gills  As adults gills disappear and breathing is accomplished with a pair of lungs - except lungless salamanders  Lungs have much less surface area than reptilian, bird, or mammalian lungs and are poorly developed  Breathe by lowering the floor of the mouth to suck in air and then raising it back up to force the air down into the lungs

19. Cutaneous Respiration  Supplement the use of their lungs by respiring directly through the skin  The skin is moist and provides an extensive surface area  Limits the maximum body size - only efficient when there is a high ratio of skin surface area to body volume

20. Pulmonary Veins  Return oxygenated blood to the heart for repumping  Allows the oxygenated blood to be pumped to the tissues at a much higher pressure than it has when it leaves the lungs  High pressure allows the blood to travel quickly

21. Partially Divided Heart  Partitioned internally to form chambers  Incomplete division - atrium divided into left and right - ventricle not divided

23. FROGS AND TOADS <>

24. Anura  Order of frogs and toads  A means “without”  Oura means “tail”  3,680 species in 22 families  Live in environments ranging from deserts to mountains and ponds to puddles  Most adults are carnivores - eat insects

25. Reproduction  Return to water  Eggs laid directly in the water - lack water tight external membrane and would dry out if not in water  Eggs are fertilized externally  Young hatch into fishlike larval forms called tadpoles

26. Tadpoles  Live in water  Most are herbivores  Feed on algae  After growth body changes into adult frog

27. Metamorphosis  Tadpoles tail, gills and lateral line system disappear  Legs grow from the body  A saclike bladder in the throat divides to become lungs  Pulmonary vein develops, and the heart develops its internal walls

29. SALAMANDERS

30. Urodela  Order of salamanders  Oura means “tail”  Delos means “visible”  Elongated bodies, long tails, and smooth, moist skin  369 species in 9 families  Range in size from 10cm to.3m - exception is the Asiatic salamander at 1.5m  Unable to stay away from water for long periods of time

32. Reproduction  Lay eggs in water or moist places  External fertilization  Few species have a type of internal fertilization - the female picks up sperm packets deposited by males

33. Metamorphosis  Not dramatic  Young are carnivores  Resemble small versions of adults  Except the young have gills

34. CAECILIANS

35. Apoda  Order of caecilians  A means “without”  Poda means “foot”  168 species, 6 families  Legless, wormlike  Grow about.3m  Some can be up to 1.2m

36. Reproduction  Male deposits sperm directly into female  Female may bear live young  Female may also lay eggs that develop externally - depends on the species

37. LEOPARD FROG

38. External Structures

39. Skin  Mucous glands within the skin - supplies a lubricant to keep the skin moist  Needed for respiration  No skin glands that secrete poison or foul-tasting substances  Coloration for protection

40. Tympanic Membrane  Eardrum  Sound causes it to vibrate  Tiny bone transmits the vibrations to the middle ear  In the middle ear are ciliated sensory cells that detect sound and help maintain balance  Can hear in both water and air

42. Internal Structures

43. Reproduction  Produce large numbers of sperm and egg cells  Males establish breeding territories and call to females using vocal sacs  Male climbs on the females back  When the female releases a cluster of eggs, the male discharges sperm over them  External fertilization

44. Brain  More developed than fish (except for the cerebellum)  Cerebrum is able to process a wider assortment of sensory information

45. Cloaca  Part of the excretory system  Cavity where undigested food, urine, and egg or sperm cells pass through  All material exits the body through the cloacal opening

46. Skeleton  Nine vertebrae and no ribs  From the sacral vertebrae extends the urostyle back to the pelvic girdle  The hind leg bones insert directly into sockets in the pelvic girdle  Two bones of the pelvic girdle and the sacral vertebrae act as a shock absorber

48. Tongue  Flicks out, curls around prey, flicks back into mouth  Upper jaw lined with small, sharp teeth, to prevent the prey from escaping  Two large teeth project inward from the roof of the mouth to impale struggling prey  Food swallowed whole