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Evolution of Tetrapods: From Stem Tetrapods to Mammals

Explore the evolution of tetrapods from the Carboniferous to the Cenozoic era, including the transition from stem tetrapods to mammals, reptiles, birds, and their unique reproductive strategies. Discover the development of features like the amniotic egg, mammalian traits, and flight adaptations in birds.

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Evolution of Tetrapods: From Stem Tetrapods to Mammals

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  1. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes - Tetrapods 350 mya Devonian 417 mya

  2. Radiation of the “stem tetrapods” !!! Carboniferous Old friends a fish

  3. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes - Tetrapods Caecilians Salamanders Frogs

  4. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes The amniotic egg was a big advance - amnion protects the embryo - yolk sac provides nourishment - allantoic sac holds waste produced by embryo Resist desiccation Provision embryo allows for colonization of dry habitats

  5. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes SYNAPSID Amniote ancestor Hylonomus Casineria ANAPSID (turtles?) DIAPSID

  6. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes The Permian Formation of Pangaea dries the landscape; amniotes dominate like the gymnosperms. shelled egg and the seed

  7. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes Dimetrodon – a Pelycosaur Pelycosaurs The Permian The synapsids radiate and dominate Dicynodonts Gorgonopsids Therapsids Cynodonts Mammals A cynodont

  8. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes Mammals - excellent transitional sequences from cynodont ‘reptiles’ - first fossils with all mammalian features (jaw, ear, dentition, fur) date to ~200 mya - Morganucodontids

  9. Radiations of Mammals They diversify during the Mesozoic, but the modern groups radiate and dominate in the Cenozoic

  10. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes Mammals - Monotremes: lay eggs, “sweat” milk

  11. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes Mammals - Monotremes: egg laying, “sweat” milk - Marsupials: live birth to embryo – attaches to nipple to complete development. Mother does not need to abandon the nest/young to feed. Pygmy possum – Australia (opossums in Western Hemisphere)

  12. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes Mammals - Monotremes: egg laying, “sweat” milk - Marsupials: live birth to embryo – attaches to nipple to complete development. Mother does not need to abandon the nest/young to feed. - Placentals: Longer internal development allows for precocial behavior (independence on birth); placental allows for direct, energy-efficient transfer of nutrients between blood systems of mother and offspring. FOOD DIGESTION Each energy transformation is less than 100% efficient Nutrients in bloodstream of mother Milk production in mammary glands FOOD for OFFSPRING Placenta Nutrients in bloodstream of offspring DIGESTION

  13. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes Mammals - Monotremes: egg laying, “sweat” milk - Marsupials: live birth to embryo – attaches to nipple to complete development. Mother does not need to abandon the nest/young to feed. - Placentals: Longer internal development allows for precocial behavior (independence on birth); placental allows for more direct and energy-efficient nutrient transfer precocial altricial

  14. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes In the Mesozoic, the synapsids are replaced by the great diapsid radiations of Ichthyosaurs, Pterosaurs, and Dinosaurs Archosaurs: Dinosaurs, Pterosaurs, Crocodilians, Birds Lepidosaurs:Lizards, Snakes, Sphenodonts) Diapsida Ichthyosaurs Younginiformes

  15. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes - Archosaurs Crocodilians Pterosaurs Ornithiscians Dinosaurs Sauropods Theropods Carnosaurs Saurischians Birds

  16. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes Birds: (derived traits) No teeth Feathers and endothermy flight feathers keeled breastbone Clavicles united into wishbone Pneumatic skeleton (houses air sacs from respiratory system) Unidirectional respiration

  17. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes In the Mesozoic, the synapsids are replaced by the great diapsid radiations of Ichthyosaurs, Pterosaurs, and Dinosaurs Archosaurs: Dinosaurs, Pterosaurs, Crocodilians, Birds Lepidosaurs:Lizards, Snakes, Sphenodonts) Diapsida Ichthyosaurs Younginiformes

  18. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes - Lepidosaurs Keuhniosaurs Squamates Scales, moveable quadrate (double hinged jaw), hinged skull Rhynchocephalians (Tuatara)

  19. 5. Major Phyla Deuterostomes: l. Chordata Vertebrata Gnathostomes Tetrapods - Amniotes - Lepidosaurs - Squamates

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