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Animal Evolution – The Vertebrates

Animal Evolution – The Vertebrates. Chapter 23. Chordates. Most are coelomate, bilateral animals All share four features: Notochord supports body Nervous system develops from dorsal nerve cord Embryos have pharynx with slits Embryos have tail that extends past anus. Lancelet Body Plan.

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Animal Evolution – The Vertebrates

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  1. Animal Evolution – The Vertebrates Chapter 23

  2. Chordates • Most are coelomate, bilateral animals • All share four features: • Notochord supports body • Nervous system develops from dorsal nerve cord • Embryos have pharynx with slits • Embryos have tail that extends past anus


  4. Invertebrate Chordates • Many of the animals that preceded vertebrates were like the simplest chordates – the urochordates • Sea squirts • Other tunicates

  5. Larval Form of a Sea Squirt notochord nerve cord gut

  6. atrial opening (water out) oral opening (water in) Adult Tunicate pharynx with gill slits

  7. Cephalochordates • Lancelets • Fish-shaped filter feeders that lie buried in sediments • Chordate characteristics of adult: • Notochord lies under dorsal nerve cord • Pharynx has gill slits • Tail extends past anus

  8. Hagfish Body Plan tentacles gill slits (twelve pairs) mucus glands

  9. Trends in the Evolution of Vertebrates • Shift from notochord to vertebral column • Nerve cord expanded into brain • Evolution of jaws • Paired fins evolved, gave rise to limbs • Gills evolved, gave rise to lungs

  10. Craniates • Cranium is a chamber of cartilage or bone that encloses all or part of a brain • First craniates evolved by 530 million years ago

  11. Evolution of Jaws • First fishes lacked jaws • Jaws are modifications of the anterior gill supports

  12. Evolution of Fishes cartilaginous fishes ray-finned fishes lobe-finned fishes tunicates lancelets hagfishes lampreys amphibians “reptiles” birds mammals lungfishes amniotes tetrapods jawed vertebrates lungs or swim bladder vertebrates craniates ancestral chordates

  13. Jawed Fishes • Most diverse and numerous group of vertebrates • Two classes: • Cartilaginous fishes • Bony fishes

  14. Cartilaginous Fishes • Most are marine predators • Cartilaginous skeleton • Main groups: • Skates and rays • Sharks • Chimaeras (ratfishes)

  15. Bony Fishes • Includes 96 percent of living fish species • Three subclasses: • Ray-finned fishes • Lobe-finned fishes • Lung fishes

  16. Evolution of Amphibians • Lobe-finned fishes arose during the early Devonian • Used their fins to travel over land from pool to pool

  17. Evolution of Amphibians

  18. Early Amphibians • Lungs became more effective • Chambers of the heart became partially separated, making circulation more efficient

  19. Modern Amphibians • All require water at some stage in the life cycle; most lay eggs in water • Lungs are less efficient than those of other vertebrates • Skin serves as respiratory organ

  20. Living Amphibian Groups • Frogs and toads • Salamanders • Caecilians

  21. Evolution of Reptiles • Reptiles arose from amphibians in the Carboniferous • Adaptations to life on land • Tough, scaly skin • Internal fertilization • Amniote eggs • Water-conserving kidneys

  22. Reptilian Radiation • Adaptive radiation produced numerous lineages • Extinct groups include: • Therapsids (ancestors of mammals) • Marine plesiosaurs & ichthyosaurs • Dinosaurs and pterosaurs

  23. Living Reptiles Four orders made it to the present day: Crocodilians Turtles Tuataras Snakes and lizards

  24. Crocodile Body Plan stomach brain lung kidney heart liver intestine cloaca

  25. Turtles and Tortoises • Armorlike shell • Horny plates instead of teeth • Lay eggs on land

  26. Tuataras • Only two living species • Live on islands off the coast of New Zealand • Look like lizards, but resemble amphibians in some aspects of their brain and in their way of walking

  27. Lizards and Snakes • Largest order (95 percent of living reptiles) • Most lizards are insectivores with small peglike teeth • All snakes are carnivores with highly movable jaws venom gland hollow fang

  28. Birds • Only birds have feathers • Arose from reptilian ancestors • Feathers are highly modified reptilian scales

  29. Amniote Eggs • Like reptiles, birds produce amniote eggs • Inside the egg, the embryo is enclosed in a membrane called the amnion • Amnion protects the embryo from drying out

  30. Amniote Egg

  31. Adapted for Flight • Four-chambered heart • Highly efficient respiratory system • Lightweight bones with air spaces • Powerful muscles attach to the keel

  32. Mammals • Hair • Mammary glands • Distinctive teeth • Highly developed brain • Extended care for the young

  33. Mammalian Origins • 200 million years ago, during the Triassic, synapsids gave rise to therapsids • Therapsids were the reptilian ancestors of mammals • The first mammals had evolved by the Jurassic

  34. Three Mammalian Lineages • Monotremes • Egg-laying mammals • Marsupials • Pouched mammals • Eutherians • Placental mammals

  35. Living Monotremes • Three species • Duck-billed platypus • Two kinds of spiny anteater • All lay eggs

  36. Living Marsupials • Most of the 260 species are native to Australia and nearby islands • Only the opossums are found in North America • Young are born in an undeveloped state and complete development in a permanent pouch on mother

  37. Living Placental Mammals • Most diverse mammalian group • Young develop in mother’s uterus • Placenta composed of maternal and fetal tissues; nourishes fetus, delivers oxygen, and removes wastes • Placental mammals develop more quickly than marsupials

  38. Earliest Primates • Primates evolved more than 60 million years ago during the Paleocene • First primates resemble tree shrews • Long snouts • Poor daytime vision

  39. Hominoids • Apes, humans, and extinct species of their lineages • In biochemistry and body form, humans are closer to apes than to monkeys • Hominids • Subgroup that includes humans and extinct humanlike species

  40. From Primates to Humans “Uniquely” human traits evolved through modification of traits that evolved earlier, in ancestral forms

  41. Trends in Lineage Leading to Humans • Less reliance on smell, more on vision • Skeletal changes to allow bipedalism • Modifications of hand to allow refined hand movements • Bow-shaped jaw and smaller teeth • Longer lifespan and longer period of dependency

  42. Adaptations to anArboreal Lifestyle • During the Eocene, certain primates became adapted to life in trees • Better daytime vision • Shorter snout • Larger brain • Forward-directed eyes • Capacity for grasping motions

  43. Australopiths • Earliest known is A. anamensis • A. afarensis and A. africanus arose next • All three were slightly built (gracile) • Species that arose later, A. boisei and A. robustus, had heavier builds • Exact family tree is not known

  44. Humans Arise • First member of the genus Homo is H. habilis • Lived in woodlands during late Miocene

  45. Homo erectus • Evolved in Africa • Migrated into Europe and Asia about 1.5 million - 2 million years ago • Had a larger brain than H. habilis • Was a creative toolmaker • Built fires and used furs for clothing

  46. Homo sapiens • Modern man evolved by 160,000 years ago • Had smaller teeth and jaws than H. erectus • Facial bones were smaller, skull was larger

  47. Colonization by H. sapiens

  48. Homo Neanderthalensis • Early humans that lived in Europe and Near East • Massively built, with large brains • Disappeared when H. sapiens appeared • DNA evidence suggests that they did not contribute to modern European populations

  49. Where Did H. sapiens Arise? • Two hypotheses: • Multiregional model • African emergence model • Both attempt to address both biochemical and fossil evidence

  50. Multiregional Model • Argues that H. erectus migrated to many locations by about 1 million years ago • Geographically separated populations gave rise to phenotypically different races of H. sapiens in different locations • Gene flow prevented races from becoming species

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