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Tetrapods: Origins & Radiation PART III

VERTEBRATE ZOOLOGY (VZ Lecture11 – Fall 2012 Althoff - reference PJH Chapter 9). Tetrapods: Origins & Radiation PART III. Tetrapod Origins. Earliest-known tetrapods are from the Late Devonian …~360 MYA

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Tetrapods: Origins & Radiation PART III

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  1. VERTEBRATE ZOOLOGY (VZ Lecture11 – Fall 2012 Althoff - reference PJH Chapter 9) Tetrapods: Origins & RadiationPART III

  2. Tetrapod Origins • Earliest-known tetrapods are from the Late Devonian …~360 MYA • Genus Acanthostega is now considered the earliest tetrapod…replacing Ichthyostega…found skull and skeletal remains in Greenland area and other subsequent finds in Latvia, Scotland, Australia, Asia, and North America • Most recent analysis suggest these early tetrapods were more fish-like than originally believed • Two major lineages that emerge after that were the batrachomorphs and reptilomorphs

  3. By start of Cenozoic…. • ~60 MYA • Only remaining nonamiotic tetrapods were the lineages still present today: frogs salamanders caecilians • Since late Paleozoic, amniotes have dominated SIGHTLESS HEAD SMOOTH SKIN Caecilia nigncans

  4. Batrachomorphs • Early Carboniferous 354-290 MYA • Included temnospondyls…the largest and longest lasting group of primitive, extinct _____________ tetrapods (Fig. 9-1, p198) • Thus, another example of a “successful” group at one time…but not around today Reptilomorphs • Early Carboniferous 354-290 MYA • Both ____________ and _____________ • Small, agile animals. Jaw design that suggested they fed on terrestrial invertebrates

  5. Which one of these tetrapods has more “aquatic” form? 1 Acanthostega 2 5 4 3 2a 4a 5a Icthyostega 1a? 3a Fig. 9-7 p207 PJH

  6. More Aquatic vs. More Terrestrial Form Acanthostega Icthyostega • Forelimb • Zygapophyses • Ribs • Sacral connection • Tail fin

  7. Amniotic egg: progressive development Characteristic of: turtles, lepidosaurs (lizards & relatives), crocodilians, birds, & monotremes Fig. 9-12 p213 PJH

  8. Placental Mammals: Beyond Amniotic Egg • Mammals still considered “amniotes” • Egg-laying mammals (monotremes…duck-billed platypus) have amniotic egg • Marsupials…transition to true placentals • For placental mammals, the placenta now is ___________ to certain membranes (chorionic and allantoic) in the amniotic” egg…and yolk is absent because nourishment (and removal of metabolic waste) is accomplished by the placenta). More about this when we examine mammalian reproduction in detail

  9. Synapsid (mammals) Anapsid (primitive amniotes & turtles) Lateral view Adductor muscle Adductor muscle Cross-sectional view Fig. 9-15 p217PJH

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