vertebrate flight

Question 1

lift

Answer 1

air flowing around the wing creates low pressure on the upper surface
- this ‘sucks’ the wing upwards, generating lift

Question 2

drag

Answer 2

force exerted on an object moving through a fluid; always orientated in the direction of relative fluid flow. drag is minimised by streamlining

Question 3

thrust

Answer 3

force induced in the direction of flight, opposing the drag force. thrust is produced by flapping, hence the need for large flight muscles

Question 4

evolution of flight

Answer 4

•flight has evolves only 4 times:
- insects, pterosaurs, birds and bats
• convergent evolution
- evolution of the same functional trait in
unrelated lineages
- wings of insects, pterosaurs, birds and bats are
analogous structures
•macroevolution
- once powered flight is attained, flying lineages
radiate quickly

Question 5

ground up scenario ( flight evolution )

Answer 5

given a bipedal cursorial ( running ) ancestor of a flying linneage, flight must have procceded from the ground to the air

Question 6

trees down scenario ( flight evolution )

Answer 6

given an arboreal ancestor of a flying linneage, flight must have procceded from the tree into the air

Question 7

why did flight evolve?

Answer 7

• escape predators
• catch flying prey
• movement from place to place
• access to new niches
• hind legs used as weapons

Question 8

pterosauria

Answer 8

• derived from bipedal, terrestrial archosaur - ‘ground up’ scenario
• late triassic to end of cretaceous ( 200 - 65 MYA )
• wing supported by elongated 4th digit
• keeled sturnum
• pteroid bone
• endothermic?

Question 9

pteranodon longiceps

Answer 9

• 6m wingspan, but only 12kg
• comparitevly small body
• wing bone thick but hollow
• flew by soaring
• large brains and optic nerves
• large crested head
• beak used for scooping up fish
• modern analogue - pelican

Question 10

aves ( birds )

Answer 10

• derived from bipedal, terrestrial coelurosaurs - ‘ground up’ scenario
• similarities with pterosaurs: hollow bones, keeled sternum, stout humerus
• differences: bird wing supported by radius and modified wrist bones
• feathers

Question 11

avian skeleton

Answer 11

• keeled sturnum
• unicate processes on ribs
• bones of pelvis fused
• limbs moved by muscles near centre of body
• beak and gizzard
• tail vertebrate reduced

Question 12

avian feather

Answer 12

• modified scales
• flight feathers : stiff, light and interlinked by
  barbules to form an efficient aerofoil
• streamlining
• renewable

Question 13

chiroptera (bats)

Answer 13

• bat fossils are uncommon
  •oldest are from the eocene (55 MYA)
• bats are related to the Dermoptera (flying lemurs)
  and have close affinity with primates - ‘trees down’
• membranous wung supported by the arm and digits 2-5
• keeled sternum; fused clavicles, scapula and sturnum
• new bone, the calcar supports the uropatagium from the heel
• wings have a high chamber (generate lift) and low wing loading (mass/area) giving a low stall speed and high manoeuvrability
• limbs moved by muscles near centre of body
• most species only 5-10g

Question 14

disadvantages of flight

Answer 14

• energetically very costly
• constrains body size and morphology
• flight lost in struthiformes (ostrich/emu) and penguins

Question 15

convergent evolution

Answer 15

• pterosaurs, birds and bats are only distantly related but have independently evolved flight
• convergence:
  • aerofoil
  • light body weight
  •keeled sternum
  •reduction and fusion of bones

Question 16

homology

Answer 16

• the wings of bats are homologous to your arms
• the pentadactyl limb structure is inherited from the common ancestor of tetrapods, but it has evolved different functional morphologies