flight Flashcards
(36 cards)
hypotheses for why flight evloved?
• Textbook lists several hypotheses:
○ Escape from terrestrial predator
○ A leaping insectivore
○ A pouncing proavis
○ A balancing raptor
• More traditional hypotheses:
○ Arboreal ("tree down")
○ Cursorial ("ground up")describe arboreal theory
• Arboreal (tree down) • Flight evolved in an arboreal climber • Evidence from Archaeopteryx ○ Upright body posture ○ Grasping claws on forewings ○ Claw curvature like living climbers/perchers ○ Long tail for balance on trees • Critique ○ Was it coordinated enough for land?
describe cursoiral theory
• Cursorial (ground up)
• Forearms used as planning surfaces
○ Origin of flight in bipedal runners
• Flapping provided propulsion
○ Critique- flapping would reduce traction
• John Ostrum (1986)
○ Proposed running forms used wings to capture prey
• Archeopteryx not well designed for strong flight
○ Heavy skeleton (solid bones)
○ Small sternum lacking keel
○ Unfused carpometacarpus
flight diagram
origin of flight late triassic? (proto)
• Origin of flight- late triassic birds?
Protoavis- although it
predates Archaeopteryx by 75 million years, it is considerably more advanced than Archaeopteryx…Protoavis is more closely related to
modern birds than is Archaeopteryx.
— Sankar Chatterjee
•
describe birds. derived from?
• “birds are glorified reptiles” - huxley
• Derived from theropod dinosaurs
○ Dromeosaurian theropods
bird synapomorphies with theropods
• Synapomorphies: birds and generalized theropods
1. Hollow, pneumatic bones 2. Elongate, mobile S-shaped neck 3. Foot with three toes pointed forward and one extending backward 4. Digitigrade posture 5. Ankle joint forms between tarsal bones, not between tarsals and tibia + fibula 6. Feather precursors or true feathers
cladogram for bird origin
- Cladistically, birds are part of coelursaurian monophyletic clade
- Transition from nonavian dinosaurs to birds happened in a stepwise fashion
- Hence, transitional forms present mosaic of plesio and apomorphic states
describe Sinosaurpteryx
filamentous protofeather in basal theropod
describe Sinornithosaurus. feathers?
• Early cretaceous dromosaur
• Liaoning fossil beds, china
• Body covered with a layer of integumentary filaments
○ Hollow; 1-5 cm long
○ Very little resemblance to avian feathers
Probably not for insulation, but for camouflage, display, and species recognition
describe the other two feathered dinos
• Protarchaeopteryx & Caudipteryx • Late jurassic to early cretaceous • Liaoning, china • Vaned feathers ○ Flat surfaces on both sides of a central shaft
feather phylogeny
describe feather structure - functions of calamus and rachis? tracts? areas without feathers?
• Develop from follicles (pits)
• Form tracts called pterylae
• Body regions without feathers called apteria
• Calamus
○ Base of the feather (“quill”)
○ Hollow to provide blood supply
• Rachis
○ Hollow section - blood vessels and nerves can run through
○ supports the barbs (side branches)
○ Barbs are collectively called vane - more SA, serves as a blanket, windbreaker, display color, etc - resist mechanical pressure by interlocking barbs = serves as a sheath
feather structure: barbules?
• Barbules
○ Finer filaments branching perpendicularly from the barbs:
○ Proximal barbules:
§Extend from lower (proximal) surface of barbs
○ Distal barbules:
Extend from upper (distal) surface of the barbs
○ Have hooklets that wrap around proximal barbules of preceding barb = maintains the structure of the vane
pic of feather structure
types of feathers?
1. Contour • Body feathers • Flight feathers 2. Semiplume 3. Down • Various types 4. Bristles 5. Filoplumes
selective pressures imposed by flight?
- Uniform body shape
• Flight requires aerodynamic shape to reduce resistance (narrow front tip to reduce friction)- Limited body size
• Power output (two times body mass need 2.25 times the power for take-off)
- Limited body size
what is power a function of? what is wingloading?
• Power is a function of:
○ Muscular force per beat
○ Wingbeat frequency
§ Wingbeat frequency is indirectly related to body size
• Therefore, to fly, larger birds must increase muscle mass as they get larger (must reduce weight elsewhere)
• Wingloading: mass of bird divided by the wing area - indication of the power
• The lighter the wing loading, the less power needed to sustain flight
when did feathers appear? why?
• Appeared long before true flight
• Perhaps arose multiple times; some not true feathers (protofeathers)
• Thermoregulation?
Possibly used for social display, camouflage, species recognition, covering nests (heat)
non avian feathered?
microraptor gui - feathers lack barbules
anchiornis huxleyi has feathers that lack barbules and preserve pigments
Archaeopteryx reptilian traits
- Thecodont teeth
- Long bony tail (no pygostyle)
- Claws on forelimbs
- Abdominal ribs
- Sternum poorly developed
- Bone not hollow - lack pneumatic ducts
- Amphicoelous vertebrae
- Small synsacrum
Archaeopteryx derived avian traits?
• Feathers (??) (contour flight) • Furcula (wishbone) (17 on diagram) • Tibiotarsus (3) ○ Some ankle bones (tarsals) fused to tibia • Tarsometatarus (2) Other tarsals fuse with the metatarsals
Archaeopteryx feathers
• Well developed • Asymmetrical vanes • Arrangement of flight feathers ○ Like modern birds ○ Primaries on phalanges and seconderies on radius/ulna • Arrangement of tail feathers ○ Different than modern birds • Body covering of feathers ○ Similar to modern birds • Feathers on legs
Archaeopteryx feathers
• Well developed • Asymmetrical vanes • Arrangement of flight feathers ○ Like modern birds ○ Primaries on phalanges and seconderies on radius/ulna • Arrangement of tail feathers ○ Different than modern birds • Body covering of feathers ○ Similar to modern birds • Feathers on legs
