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Evolution of Flight in Bats: Locomotion Mechanics and Aerodynamics

Explore how powered flight evolved in bats through the generation of lift at low speeds and adaptations for efficient flight. Learn about wing loading, aerodynamic principles, and specific mechanisms for stopping the up-stroke. Discover the unique skeletal features that aid in bat flight.

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Evolution of Flight in Bats: Locomotion Mechanics and Aerodynamics

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  1. Lecture 9 – Locomotion: Flight Powered flight has evolved several times: Pterosaurs Insects Birds

  2. Powered Flight : Bats Supported by digits 2-5 Skin - patagium

  3. Generation of Lift Turbulent Flow Laminar flow – parallel movement of air streams Velocity across top is higher than bottom. Bernoulli’s Theorem Laminar Flow P is air pressure. Cis a constant. dis the density of air, and V is velocity. Lift = P(Lower) – P(Upper)

  4. Bats tend to be slow fliers. Myotislucifugus(little brown bat)- 20 MPH Eptesicusfuscus(big brown bat)- 40 MPH Tadaridabrasiliensis(Brazilian free-tailed bat) – up to 60 MPH

  5. Generation of lift at low flight speeds. 1. Increase camber, or curvature of the wing. 2. Increase angle of attack (even a symmetric airfoil can generate lift this way)

  6. Generation of lift at low flight speeds. 3. Wing size and shape. Wing loading: Body weight /surface area. Body Weight Surface Area Wing Load House wren 11.0 g 48.4 cm2 0.24 g/ cm2 Glossophaga 10.6 g 99.3 cm2 0.11 g/ cm2 Myotis4.2 g 67.6 cm2 0.06 g/ cm2 b. Aspect ratio - length / width Tadarida– high aspect ratio Artibeus – low aspect ratio

  7. Stopping the up-stroke: Shoulder-locking mechanism Greater tuberosity of humerus Mollossids Eumopsperotiswestern bonneted bat Vespertilionids also.

  8. Moderately well-developed shoulder locking. Modest greater tuberosity *Situation similar in phyllostomids

  9. Poorly developed shoulder locking mechanism: entirely muscular. Sac-winged bats – Emballonuridae.

  10. Other Adaptations for Flight Keeled manubrium of sternum. Some (Natalidae) have rigid axial skeleton. 1. Compressed thoracic vertebrae - not fused, but very tightly interconnecting 2. Fused sacral vertebrae and fused lumbar vertebrae

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