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Paleozoic Tetrapod Origins/Radiation: Introduction/Overview

Paleozoic Tetrapod Origins/Radiation: Introduction/Overview. The Movement to Land. origins (mid-late Devonian) sarcopterygian ancestry land invasion of plants & invertebrates. Rhipidistian Crossopterygian Ancestry. radiations: late Paleozoic/early Mesozoic

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Paleozoic Tetrapod Origins/Radiation: Introduction/Overview

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  1. Paleozoic Tetrapod Origins/Radiation: Introduction/Overview

  2. The Movement to Land • origins (mid-late Devonian) • sarcopterygian ancestry • land invasion of plants & invertebrates

  3. Rhipidistian Crossopterygian Ancestry • radiations: late Paleozoic/early Mesozoic • ancestors to modern amphibians (Temnospondyls) • data: skulls, labyrinthodont teeth, limbs/girdles

  4. advantages/selective forces influencing the move to land • increasingly xeric environment • predation pressure • absence of competition on land • untapped food resource on land (insects) • low O2 levels in warm stagnant pools; lungs preadaptive • dispersal opportunities

  5. physical properties of air & water • density & viscosity • gravity • temperature extremes • oxygen & dissolved gases

  6. key problems associated with terrestrial existence • Respiration • Desiccation • structural support & locomotion 4. sensation 5. feeding

  7. gravity & support/locomotion; solutions • modifications of vertebral column • zygapophyses- interlock/link adjacent vertebrae to prevent sagging/twisting • notochord replaced by centrum • pectoral & pelvic girdles strengthened

  8. major structural changes • limbs/girdles- better support & muscle attachments • skull/jaws- new feeding modes • vertebrae- better support • lungs

  9. Labrynthodont Tooth

  10. modifications to the pelvic girdle • pectoral girdles free from head; allowing head movement • pelvic girdle fused to vertebrae allowing thrust • enlarged muscle attachment

  11. Pelvic Girdles

  12. zygapophyses

  13. respiration • gills do not function efficiently in air; gill filaments adhere reducing surface area & evaporation • lungs are internal respiratory structures that protect from desiccation • cutaneous respiration

  14. sensory • lateral line system relies on density of water • changes required for sound detection; sound transfer from air--->fluid

  15. reproduction • fishes generally have external fertilization & development • external fertilization & development is rare among terrestrial organisms; gametes can't withstand desiccation • solutions: amniotic/cleidoic egg; air/water barrier

  16. Ichthyostega

  17. Acanthostega

  18. Skull Anatomy

  19. Amniotic Egg

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