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Discussion of A Devonian tetrapod-like fish and the evolution of the tetrapod body plan by Edward Daeschler – Academy of Natural Sciences, Philadelphia Neil Shubin – University of Chicago and the Field Museum Farish Jenkins – Harvard University and Museum of Comparative Zoology Nature

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    1. Discussion of • A Devonian tetrapod-like fish and the evolution of the tetrapod body plan • by • Edward Daeschler– Academy of Natural Sciences, Philadelphia • Neil Shubin– University of Chicago and the Field Museum • Farish Jenkins – Harvard University and Museum of Comparative Zoology • Nature • 440:757-763 • BIO101, Oct. 26, 2011

    2. Serious questions remain in the evolution of animals. How did terrestrial animals with four-legs (tetrapods) evolve from marine animals with fins?

    3. Big evolutionary transition! Major changes in morphology (legs vs. fins) and respiration Many more smaller changes (ears, head shape, etc.)

    4. Lobe-Limbed Fish Sarcopterygians – Living members include coelacanths, lungfish and tetrapods! Rod-shaped bones with muscles in the pectoral fins not simple rays supporting a very thin fin

    5. Big evolutionary transition! ?

    6. Should be able to find transitional species Transitional species should be approximately 365-375 MYA Middle to late Devonian age tiktaalik.uchicago.edu

    7. Where are mid-to-late Devonian rocksexposed on the surface? In addition: sparsely populated freshwater in Devonian Three sites in North America, only one was largely unexplored

    8. Welcome to Northern Canada!

    9. Welcome to Northern Canada!

    10. Fossil Site Part of the Fram Formation Laid down in late Devonian Alternating sandstone and siltstone layers. Probably a meandering stream.

    11. Fossil Site

    12. Fossil Site

    13. Fossils 28 partial fossils of this species found. Each gets a name NUFV 108 through NUFV 135 (Nunavut Fossil Vertebrate Collection) Three were fairly complete, with skulls and pectoral girdles and articulated NUFV 108 is the holotype All specimens are currently in the Canadian Museum of Nature in Ontario

    14. Tiktaalik as a Transitional Species – Ancestral Characteristics Body was covered in scales Dorsal view

    15. Tiktaalik as a Transitional Species – Ancestral Characteristics True fins

    16. Tiktaalik as a Transitional Species – Ancestral Characteristics Gills Ceratobranchial Element

    17. Tiktaalik as a Transitional Species – Ancestral Characteristics Probably had lungs too (like coelacanths and lungfish) Large Gular Plates

    18. Tiktaalik as a Transitional Species – Derived Characteristics Flat skull Eyes are more on top of the head, not on the sides

    19. Tiktaalik as a Transitional Species – Derived Characteristics Flattened Ribs

    20. Tiktaalik as a Transitional Species – Derived Characteristics Functional, flexible neck. Pectoral girdle (collar and shoulder bones) are tetrapod-like. Loss of opercular, subopercular and extrascapular bones.

    21. Tiktaalik as a Transitional Species – Derived Characteristics Wrist bones

    22. Tiktaalik as a Transitional Species – Derived Characteristics Wrist bones

    23. Tiktaalik as a Transitional Species – Derived Characteristics Wrist bones

    24. Tiktaalik Ecology Life in shallow water has it’s advantages

    25. Tiktaalik Phylogeny Evaluated 114 morphological characteristics for Tiktaalik and others

    26. Tiktaalik Phylogeny Evaluated 114 morphological characteristics for Tiktaalik and others