Origin of Tetrapod Body Plan: water-land transition

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  • Origin of Tetrapod Body Plan: water-land transition
    • Tetrapod Emergence:
      • 1. Lungfish-tetrapod separation
        • 2. Stem-tetrapod diversification
          • 3. Crown-tetrapod emergence
      • Lobe fins
        • Muscular part connecting fin to either shoulder or pelvic girdle
        • Fins are borne on fleshy, lobe-like, scale-covered stalk
        • Appear early in the history of the group
        • Fin/limb skeleton is joined to the girdle via a single bone
      • Endoskeleton
        • Humerus, radial and ulna
        • Paired fins and limbs show one main axis
          • Monoaxial appendages!
        • Fin and limb skeletons show extensive distal endochondral ossification
      • Cosmoid scales
        • 1. Basal, dense lamellar layer of isopedine
        • 2. Middle layer of spongy, vascularised bone
        • Top, complex layer of dentine (cosmine)
        • Outer coating of vitrodentine
        • Broadly similar to the ganoid scales
      • Primitively, broad snouts and small orbits
      • Configuration of Skull bones
        • Conserved pattern of bones is super imposed over the primitive osteichthyan pattern
        • parietal and postparietal bones in dermal skull roof meet in a dermal joint
        • the external manifestation of a endocranial hinge
        • Neurocranium: dorsally hinged and mobile intracranial joint
          • Neurocranium ossifies as two units completely separated by a ventral cranial fissure
      • Large shoulder girdle elements
        • Enlarged clavicles and expanded dorsal part of the girdle
    • Rhizodontida
      • Deepest part of family tree
    • Panderichthyida
      • Fish-tetrapod intermediate
    • Tiktaalik roseae
      • Close relative, another fish-tetrapod intermediate


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