Chapter 18

1. Chapter 18 0 Amphibians

2. Bones supporting gills Tetrapod limb skeleton Figure 18.18A • 18.18 Amphibians were the first tetrapods—vertebrates with two pairs of limbs • Amphibians • Were the first tetrapods with limbs allowing movement on land

3. What Is an Amphibian? • What Is an Amphibian? • An amphibian is a vertebrate that, with some exceptions: • lives in water as a larva and on land as an adult • breathes with lungs as an adult • has moist skin that contains mucous glands • lacks scales and claws

4. Most amphibian embryos and larvae • Still must develop in water

5. Evolution of Amphibians • Evolution of Amphibians • The first amphibians appeared in the late Devonian Period, about 360 million years ago. • The transition from water to land required that the terrestrial vertebrates had to: • breathe air, • protect themselves and their eggs from drying out, and • support themselves against the pull of gravity.

6. Evolution of Amphibians • Early amphibians evolved several adaptations that helped them live at least part of their lives out of water. • Bones in the limbs and limb girdles of amphibians became stronger, permitting more efficient movement.

7. Evolution of Amphibians • Lungs and breathing tubes enabled amphibians to breathe air. • The sternum formed a bony shield to support and protect internal organs, especially the lungs.

8. Evolution of Amphibians • Amphibian Adaptations Lungs Pelvic Girdle Leg Bones: The legs of a land vertebrate must be strong enough to hold its weight. Skin: The skin and the lining of the mouth cavity of many adult amphibians are thin and richly supplied with blood vessels. Watery mucus is secreted by glands in the skin.

9. Evolution of Amphibians • In many adult amphibians, the internal surfaces of the lungs are richly supplied with blood vessels and folds that increase surface area. Lungs

10. Form and Function in Amphibians • Form and Function in Amphibians • The class Amphibia is relatively small and diverse.

11. Form and Function in Amphibians • Feeding • Tadpoles are typically filter feeders or herbivores that graze on algae. • Their intestines help break down hard-to-digest plant material and are usually filled with food. • The feeding apparatus and digestive tract of adults are meat-eating structures.

12. Form and Function in Amphibians • Adult amphibians are almost entirely carnivorous. • Many salamanders and frogs have long, sticky tongues specialized to capture insects.

13. Form and Function in Amphibians • In a frog’s digestive system, food slides down the esophagus into the stomach. Esophagus Mouth Stomach

14. Form and Function in Amphibians • The breakdown of food begins in the stomach and continues in the small intestine. Stomach Small intestine

15. Form and Function in Amphibians • The liver, pancreas, and gallbladder secrete substances that aid in digestion. Gallbladder Liver Pancreas

16. Form and Function in Amphibians • At the end of the large intestine is a muscular cavity called the cloaca, through which digestive wastes, urine, and eggs or sperm leave the body. Large intestine (colon) Cloaca

17. Form and Function in Amphibians • Respiration • In most larval amphibians, gas exchange occurs through the skin and the gills. • Adult amphibians typically respire using lungs, but some gas exchange occurs through the skin and the lining of the mouth.

18. Form and Function in Amphibians • Circulation • In frogs and other adult amphibians, the circulatory system forms a double loop. • The first loop carries oxygen-poor blood from the heart to the lungs and skin, and takes oxygen-rich blood from the lungs and skin back to the heart.

19. Form and Function in Amphibians • The second loop transports oxygen-rich blood from the heart to the rest of the body, and carries oxygen-poor blood from the body back to the heart.

20. Form and Function in Amphibians • Amphibian Circulation and Excretion Heart Lung Kidney Ureter Urinary bladder Cloaca

21. Form and Function in Amphibians • The amphibian heart has three separate chambers: • left atrium • right atrium • ventricle

22. Form and Function in Amphibians To body, lungs and skin To body, lungs and skin • Amphibian Heart From Lungs From Body Left atrium Right atrium Ventricle

23. Form and Function in Amphibians • Excretion • Amphibians have kidneys that filter wastes from the blood. • Urine travels through tubes called ureters into the cloaca. • Urine is then passed directly to the outside, or temporarily stored in a small urinary bladder just above the cloaca.

24. Form and Function in Amphibians • Reproduction • In most species of amphibians, the female lays eggs in water, then the male fertilizes them externally. • In a few species, including most salamanders, eggs are fertilized internally. • After fertilization, frog eggs are encased in a sticky, transparent jelly.

25. Form and Function in Amphibians • The jelly attaches the egg mass to underwater plants and makes the eggs difficult for predators to grasp. • The yolks of the eggs nourish the embryos. • Most amphibians abandon their eggs after they lay them. • A few amphibians take care of both eggs and young.

26. Form and Function in Amphibians • Frog Metamorphosis Adult Frog Fertilized eggs Young Frog Tadpoles

27. Form and Function in Amphibians • Adults are typically ready to breed in about one to two years. • Frog eggs are laid in water and undergo external fertilization.

28. Form and Function in Amphibians • The fertilized eggs hatch into tadpoles a few days to several weeks later. Fertilized eggs

29. Form and Function in Amphibians • Tadpoles gradually grow limbs, lose their tails and gills, and become meat-eaters as they develop into terrestrial adults. Young frog Tadpole

30. Form and Function in Amphibians • Movement  • Amphibian larvae move by wiggling their bodies and using a flattened tail for propulsion. • Adult salamanders walk or run. • Frogs and toads, have well-developed hind limbs that enable them to jump long distances.

31. Form and Function in Amphibians • Response  • Amphibians have well-developed nervous and sensory systems. • An amphibian's eyes are protected from damage and kept moist by a transparent nictitating membrane. • This membrane is located inside the regular eyelid and can be closed over the eye.

32. Form and Function in Amphibians • Amphibians hear through tympanic membranes, or eardrums, located on each side of the head. • Many amphibian larvae and adults have lateral line systems that detect water movement.

33. Form and Function in Amphibians • Frog’s Sense Organs

34. Figure 18.18B–D Groups of Amphibians The three groups of amphibians alive today are: • salamanders • frogs and toads • caecilians

35. Groups of Amphibians • Salamanders • Salamanders and newts have long bodies and tails. • Most have four legs. • Both adults and larvae are carnivores. • Adults usually live in moist woods, where they tunnel under rocks and rotting logs.

36. Groups of Amphibians • Frogs and Toads • Frogs and toads have the ability to jump. • Frogs tend to have long legs and make lengthy jumps. • Toads have relatively short legs and are limited to short hops.

37. Groups of Amphibians • Frogs are generally more closely tied to water than toads. • Toads often live in moist woods and even in deserts.

38. Groups of Amphibians • Caecilians • Caecilians are legless animals that live in water or burrow in moist soil or sediment. • Caecilians feed on small invertebrates such as termites. • Many have fishlike scales embedded in their skin.