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A Devonian tetrapod-like fish and the evolution of the tetrapod body plan.

A Devonian tetrapod-like fish and the evolution of the tetrapod body plan. Joel Alejandro Jarvis Dela Cruz. Introduction. The origin of major tetrapod features has remained obscure for lack of fossils that document the sequence of evolutionary changes.

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A Devonian tetrapod-like fish and the evolution of the tetrapod body plan.

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  1. A Devonian tetrapod-like fish and the evolution of the tetrapod body plan. Joel Alejandro Jarvis Dela Cruz

  2. Introduction The origin of major tetrapod features has remained obscure for lack of fossils that document the sequence of evolutionary changes • Intermediate between a fish with fins and tetrapods with limbs • Provides unique insights into how and in what order important characters arose. Tiktaalik

  3. Geological Framework Fram Formation • Distinguished by alternating resistant sandstones and recessive siltstones • Remote sections of Nunavut territory in the Canadian Arctic • Early and middle Frasnian stage of the Late Devonian • Found three(3) articulated and numerous isolated specimens of Epistostegalians

  4. Geological Framework • Fauna from the site includes the following: • Asterolepis sp. • Lungfish • Holoptychiidporolepiforms • Osteolepidid • Tristichopteridsarcopterygians • New elpistostegaliansarcopterygian

  5. Systematic Paleontology Distinctive features of Elpistostegalia that unite Elpistostege and Panderichthys are not ambiguous • Flattened skull • Dorsally placed eyes • Elongate snout with paired frontal bones • Enlarged prefrontal bone • Marginal nares • Enlarged spiracle • Dorsoventrally flattened body • Loss of anterior dorsal fin

  6. Diagnosis • Elpistostegaliansarcopterygian differentiated from Panderichthys: • Loss of intertemporal, opercular, subopercular and extrascapular bones • Possession of a snout longer than the postorbital skull roof • Relatively wider spiracular notch • Imbricate ribs • Tiktaalik further differentiated from Elpistostege: • Having narrowly overlapping dorsal scales that are slightly taller than wide • Tikataalik differentiated from Acanthostega: • Presence of lepidotrichia in pelvic and pectoral fins • Elongate hyomandibula • Pectoral fin radials that branch • Dermal supracleithral elements • Precoronoid fossa in the lower jaws • A palate with entopterygoids that do not meet at the midline • Tiktaalik differentiated from both Panderichthys and Elpistostege: • Postfrontal-supratemporal contact • Postfrontal that does not extend anterior to the orbits • Incorporation of the supratemporal into the medial margin of the spiracular notch

  7. Descriptions • Expanded buccal cavity, branchial elements • Large spiracular tract and reduced hyomandibula • Loss of operculum

  8. Descriptions • Expanded shoulder girdle and reduced lepidotrichia • Rigid spinal and axial support

  9. Phylogenetic Relationships • Primitive features • Derived features • Elpistostegalian Fish

  10. Biogeography

  11. Paleobiology • Lives in shallow water and subaerial habitat • Buccal Mechanism for Respiration • Improved range of head movement • Movement across a substrate

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