Birds Flashcards
Archaeopteryx
- Discovered in 1861; 150 mya
- Still very “reptile-like” in its skeleton: long bony tail, clawed fingers
- But… Flying feathers!
-> asymmetrical - First bird? First flying dinosaur?
- Perfect intermediate/transitional form
- The link between birds & Theropod dinosaurs
Early Feathered “Dinosaurs”
- E.g., Sinosauropteryx
- Compsognathid Dinosaur
- Fine filamentous feathers (no flight) - E.g., Caudipteryx
- Short forelimbs
- Symmetrical vaned feathers (no flight)
Bird-like “Dinosaur” (or “Dinosaur”-like Bird?)
Feathers of similar design
- Downy, vanes, asymmetrical, pennaceous..
- Long, mobile, S-shaped neck
- A furcula or fused clavicle (wishbone!)
- Specialised lunate wrist bones that permit folding wing down
- Saurischian-like pelvis (but directed posteriorly like birds)
But still with…
- Grasping forelimb (fused in birds)
- No large keel on sternum
- Long tail (pygostyle in birds)
- Teeth (birds are toothless)
Birds: Feathers Before Flight
Feathers originally evolved for thermoregulation
- Downy feathers in small theropods
DID NOT evolve from membrane-winged Pterosaurs!
Feathers or flight first?
- Birds: feathers 1st
- Pterosaurs & bats: flight 1st, no feathers
Origin of Bird Flight
- Arboreal Hypothesis (Trees -> Down)
- Ancestors were tree climbers, jumping from branch to branch
- Gliding: less energy and minimal wing flapping - Cursorial Hypothesis (Ground -> Up)
- Flapping flight from ground-dwelling bipedal runners
- Used wings like a plane
- Wing-assisted incline running
Why Fly?
- Air = unexploited habitat
- Food: flying insects
- Avoid predators
- Rapid travel & migration
Adaptations for Flight
- Feathers & wings
- support, propulsion, streamlining - Skeleton
- must provide a light but rigid airframe - Muscles
- huge muscles to meet demands of flight, aerodynamic stability - Digestion
- Must meet high-energy demands of flight - Respiratory System
- must meet high oxygen demands and cool the body
- nine interconnected air sacs (oxygen storage) - Nervous system
- must have superb sensory systems for high-velocity flight
Feathers = High Power, Little Weight
Keratinized, on the epidermis
- still supplied with living tissue
Hollow quill (calamus)
- emerges from skin follicle and forms into a shaft/rachis
- Rachis bears numerous barbs
- Up to several hundred barbs are arranged to form a flat, webbed surface, the vane
- Each barb resembles a miniature feather with many barbules (hold/zip it together)
Flight Mechanics
Birds have to:
- Generate enough force to exceed mass
- Provide forward propulsion while in air to keep moving
WINGS
- Streamlined with a concave lower surface (cambered)
- Feathers on leading edge tightly packed
- Air moves smoothly & faster over the wing creating lift with minimal drag
LIFT
- Some lift comes from positive pressure against the underside of the wing
- Most lift comes from negative pressure above the wing
Preventing Stalling
- Stalling (or completely dropping out of the sky!!) is prevented by a *wing slot along the leading edge
*Slots direct rapidly moving air across the leading surface
- The alula (winglet): group of small feathers on the “thumb”, provides a midwing slot
- Wing-tip slots: gaps between the primary feathers
Flapping Flight
- Horizontal thrusting force - primaries (on hand bones)
- vertical lifting force - secondaries (on ulna)
- greatest power from the downstroke
- A powered upstroke is essential for hovering and fast, steep takeoffs
Bird Skeleton
- The main contributor to being lightweight!
- Inherited from basal theropod dinosaurs
Light, delicate bones laced with air cavities (pneumatized)
- Human skeleton is 12% of body mass
- Bird skeleton ONLY 5% of body mass
Fused Bones & Bones Adapted for Flight
Vertebral column is very rigid
- Vertebrae fused except for cervical vertebrae
Ribs are mostly fused with vertebrae, pectoral girdle, and sternum
Additional bony structures fused with pelvic girdle
- supports legs and provides rigidity for flight
Furcula and lunate wrist
- elastic furcula (wishbone) stores energy as it flexes during wing beats
- Lunate wrist permitted swivel motion for flight
Keel on sternum (for huge pectoralis muscles)
The Skull and Jaws
Skull is fused into one piece
- Braincase and orbits are large to hold a larger brain and eyes
Modern birds have a horny keratinous break molded around bony jaws
Need Muscles to Fly, Too!
- Pectoralis muscles
- Depress the wing in flight and are attached to the keel - Supracoacoideus muscle
- raises the wing, is also attached to the keel
