Ch. 34

1. Ch. 34 The Origin and Evolution of Vertebrates

2. Chordates • Bilaterally symmetrical • Deuterostomes

3. Derived Characters of Chordates • Notochord • Dorsal, hollow nerve cord • Pharyngeal slits/clefts • Muscular postanal tail

4. Notochord • A longitudinal, flexible rod located between the gut and nerve cord • Present in all chordate embryos • Composed of large, fluid filled cells encased in a stiff, fibrous tissue • Extends throughout most of the length of the animal as a simple skeleton • Jointed skeleton develops around notochord • Remains seen in intervertebral disks

5. Dorsal Nerve Cord • Hollow, dorsal to the notochord • Brain and spinal cord develops from this primitive nerve cord

6. Pharyngeal Slits or Clefts • Opening of pharynx to the outside through several pairs of slits • Permits water to enter the mouth to exit without passing through the entire digestive system • May serve as suspension feeding devices in invertebrates • Modified for gas exchange in aquatic vertebrates • Become part of the ear (eustachian tube) in terrestrial vertebrates

7. Muscular Postanal Tail • Extends beyond anus • Contains skeletal elements and muscles • Propulsive force in aquatic species

8. Subphylum Cephalochordata • Most basal (earliest ) group • Lancelets • Adult • possess all 4 chordate characteristics • Marine filter feeders • use pharyngeal slits • Feeble swimmers with fishlike motions • Live in sand

9. Subphylum Urochordata • Tunicates (sea squirts) • Cloaked in a celluloselike tunic • Sessile • Some are colonial • Filter feeders • incurrent siphon  slits in pharynx  excurrent siphon • Larva • free swimming • possess all 4 chordate characteristics • Adults • lack a notochord, a nerve cord, and tail • only possess pharyngeal slits

10. Derived Characters of Craniates Craniates • Chordates with a head • Brain at anterior end of dorsal hollow nerve cord, eyes, sensory organs, skull • Allowed for complex movement and feeding patterns Neural Crest • Collection of cells that appears near the dorsal margins of the closing neural tube in an embryo • Teeth, bones of skull, dermis of face, types of neurons, sensory capsules

11. Derived Characters of Craniates • Gill slits that allow water to be pumped through the slits for sucking in food and gas exchange • Higher metabolic rate • Extensive muscular system • Heart with at least 2 chambers • Red blood cells with hemoglobin • Kidneys to clean waste from blood

12. Agnathans • Two Classes • Myxini • Petromysontida • Jawless vertebrates • oval, slitlike mouth • Lacked paired fins • Bottom-dwellers • Some were active and had paired fins

13. Myxini (Hagfish) • Basal group • Skull of cartilage • Retain notochord • Small brain, eyes, ears, and a nasal opening • Scavengers • Slime glands

14. Derived Characters of Vertebrates • More extensive skull • Vertebrae of bone • Dorsal, ventral, and anal fins in aquatic species • Pronounced cephalization • Brain and sense organs at anterior end • Attached to the nerve cord

15. Derived Characters of Vertebrates Vertebrate Skeleton Axial skeleton • cranium, vertebrae, ribs, sternum, hyoid • main support for larger body size and fast movements Appendicular skeleton • girdles and two pairs of appendages (fins, legs, or arms)

16. Derived Characters of Vertebrates • Closed Circulatory System • Ventral chambered heart • 2-4 chambers • Arteries • carry blood away from the heart • blood is oxygenated in lungs/gills • Capillaries • site of gas exchange and diffusion of other substances • Veins • carry blood back to the heart

17. Derived Characters of Vertebrates • Greater metabolic demands • Generation of ATP consumes oxygen • adaptations exist such as lots of mitochondria in muscle tissues • More active  larger amounts of organic molecules needed • adaptations for feeding, digestion, and nutrient absorption • Closed circulatory system

18. Vertebrate Diversity • Class Agnatha • Now split into Myxini and Petromyzontida • Class Chondrichthyes • Class Osteichthyes • Now split into Actinopterygii, Sarcopterygii (Actinistia and Dipnoi) • Class Amphibia • Class Reptilia • Class Aves • Class Mammalia

19. Vertebrate Diversity

20. Classes Grouped by… • Column • Jaws • Lungs • Legs • Amniotic egg • Milk • Feathers

21. Vertebrate Diversity

22. Lampreys (Petromyzontida) • Most basal lineage of vertebrates • Marine and freshwater • Most are parasites • Cartilage skeleton • Notochord is the axial skeleton

23. Derived Characters of Gnathostomes • Vertebrates with jaws • Enlarged forebrain • Lateral line system in aquatic vertebrates

24. Class Chondrichthyes • Sharks, Rays, and their relatives • Cartilage fishes • Skeleton strengthened by calcified granules • Tail for propulsion • Dorsal fins are stabilizers • Pectoral and pelvic fins – lift • Most are carnivorous some are suspension feeders • Sharp, colorless vision

25. Class Chondrichthyes • Teeth evolved from modified scales (placoid) • Lateral line system • External fertilization • oviparous, ovoviviparous • Internal fertilization via claspers • few are viviparous • Cloaca is present

26. Osteichthyans • Ray-finned and lobe-finned fishes • Bony skeleton • Scales • Mucus glands in the skin • Lateral line system • Operculum covering gills • Swim bladder for buoyancy • External fertilization • oviparous

27. Osteichthyans • Class Actinopterygii • ray finned • Major source of protein for humans

28. Osteichthyans • Sarcopterygii • lobe finned • Rod shaped bones surround by a thick layer of muscle in their pelvic and pectoral fins Actinistia • Coelancanths Dipnoi • lung fishes • ancestor of amphibians and all other tetrapods

29. Derived Characters of Tetrapods • Four feet • Limbs with digits • Head separated from body by a neck • Pelvic girdle bones fused to backbone

30. Amphibians • “both ways of Life”

31. Class Amphibia Order Urodela (“tailed ones”) • salamanders, newts Order Anura (“tail-less ones”) • frogs, toads Order Apoda (“legless ones”) • caecilians

32. Class Amphibia • Metamorphosis • Tied to water for reproduction • Dioecious • sexually, external fertilization • Amplexus • 3 chambered heart • Cutaneous and pulmonary respiration

33. Derived Characters of Amniotes Amniotic egg • Adaptation for a terrestrial habitat • Prevents desiccation Monophyletic group-the amniotes • Reptiles, birds • mammals (although most have dispensed with the shell)

34. Amniotic Egg

35. Class Reptilia Order Chelonia • turtles Order Squamata • lizards and snakes Order Crocodilia • alligators and crocodiles

36. Class Reptilia • Keratin scales • Gas exchange via lungs • Most are dioecious • internal fertilization • oviparous (most); some are ovoviviparous • Ectothermic • 3 chambered heart with a partially divided ventricle

37. Class Aves • Birds • Archeopteryx • Anatomy modified to enhance flight • Bones have a honeycombed structure • No urinary bladder • One ovary • no teeth (reduces weight) • gizzard

38. Class Aves • Endothermic • 4 chambered heart • Dioecious • internal fertilization • incubation • Feathers made of keratin • Sternal keel

39. Class Aves Ratites • flightless b/c no keel • ostrich, rhea, emu, kiwi, cassowary Carinates • sternal keel present • fly • exception - penguins

40. Derived Characters of Mammals • Hair made of keratin • Endothermic • Fat layer under skin • High metabolic rate • Mammary glands • Large brains, capable learners • Four chambered heart • Differentiated teeth • Efficient lungs • Alveoli, diaphragm • Dioecious • internal fertilization • most are viviparous

41. Monotremes Oviparous Australia and New Guinea Platypuses, echidnas (spiny anteater) Milk comes from fur b/c they lack nipples

42. Marsupials Marsupiam (maternal pouch) Opossum, koala, kangaroos

43. Eutherians Placental Mammals Viviparous Placenta Longer gestation

44. Convergent Evolution

45. Derived Characters of Primates • Hands and feet adapted for grasping • Opposable thumb • Large brain • Short jaws • Forward facing, close together eyes • Well developed parental care

46. Derived Characters of Humans • Large Brain • Bipedal locomotion • Language, symbolic thought, artistic expression, manufacture and use of tools