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Impact of Brachial Index on Wing Flexure in Flying Vertebrates

This study investigates the influence of brachial index (BI) on wing flexure among various flying vertebrates, including pterosaurs, bats, birds, and humans. It reveals that a higher BI correlates with a more significant shortening of wingspan during wing upstroke under uniform conditions of humerus angle and wrist span. The research also compares skeletal adaptations across species, highlighting key evolutionary traits in flight mechanics and control. The analysis provides insight into the divergent evolutionary paths of flight in vertebrates, reflecting the role of structural adaptations.

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Impact of Brachial Index on Wing Flexure in Flying Vertebrates

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  1. BI = 0.75 BI = 1.0 BI = 1.25 Effect of brachial index on wing flexure, with uniform humerus angle (left) and with uniform wrist span (right)With the same humeral protraction, higher BI shortens the wingspan more: stiffer wings and lower BI are derived Flexing with uniform humerus angle

  2. Different skeletal mechanisms of shortening the wing during the upstroke in flying vertebrates

  3. pterodactyloid pterosaur “rhamphorhynchid” pterosaur bat Archaeopteryx bird human Comparison of wing skeletons in flying vertebrates(after Steinbacher 1960)

  4. Distribution of brachial index for Gruiformes (left) and Charadriiformes (right)(from Dyke & Rayner 2001)

  5. (A) (B) (C) Pterosaurs: flight control with the wing, with long-axis humeral rotation. Note the large delto-pectoral crests (A) Rhamphorhynchus (faked!) (B) Pterodactylus kochi (C, D) Quetzalcoatlus humeri (Wellnhofer 1991) (D)

  6. Confuciusornis sanctus (Tübingen specimen) Photo G. J. Dyke

  7. Consensus phylogeny of the origin of birds and the evolution of flight adaptations

  8. Consensus phylogeny of the origin of birds and the evolution of flight adaptations

  9. Changchengornis(Ji et al. 1999)

  10. The stiffened tail of Deinonychus(from Ostrom 1969)

  11. Avian phylogeny Left: morphological tree for major Mesozoic groups (from Cracraft 1986)Right: molecular tree of extant groups (from van Tuinen et al. (2000)

  12. Theropod caudal vertebrae Gatesy & Dial (1996)

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