flight Flashcards
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
origin of feathers and initial role?
• Ancestrally from epidermal scales
○ Embryonically a mix of dermis and epidermis
○ Like reptile scales also contain beta-keratin
• Ectotermic thermoregulation
○ Initial role of feathers probably in temperature regulation
○ Social?
• Aerodynamic design
○ Well developed in archaepteryx
weight reducing adaptations - pneumonic bones? body size?
- Pneumatic bones
○ Spaces with cross struts - strong even though its hollow
○ Varies with body size and lifestyle
• Skeleton vs body mass (how much of the mass the skeleton is):
• Rat: 5.6% body mass
• Pigeon: 4.4% body mass
• Frigate bird: wing span of 2.3 m; skeleton 4 ounces (115 gms), less than its feather weight
weight reducing - fusion of skeletal elements !!!!
• Synsacrum
○ Fused:
§ Last thoracic; all lumber; 2 sacral; anterior few caudal
§ Also fusion with pelvic girdle to some extent
• Tail
○ Short; approx. 5 caudal vertebrae; forms pygostyle - much more reduced than ancestors who needed more balancing
• Ribs
○ Long, thin, jointed - allow for movement for breathing
§ Uncinate process
• Skull
○ Extensive fusion; teeth lost (use gizzard)
weight reducing - strength !!!!
• Increased strength and skeletal rigidity
• Synsacrum
○ Broad, flat - support in the pelvic region
• Ribs
○ Thin, flat
○ Uncinate process - gives strength
• Thoracic vertebrate
○ Joined via strong ligaments
• Tail
○ Short; approx. 5 caudal vertebrae; pygostyle
• Strong pectoral girdle
○ Scapula, coracoid, sternum
○ Clavicles fused to form furcula (wishbone) - increased strength
•
which flight muscles are enlarged? ratio?
• Large flight muscles • Pectoralis ○ Pulls wing downward ○ Sternum to humerus • Supracoracoideus ○ Pulls wings upward ○ Sternum to coracoid • Ratio of pectoralis to supracoracoideus ○ Smaller species: 20:1 ○ Larger species: 3:1
muscle in species with short and rapid flight?
• Species with short, rapid flights (grouse, ptarmigans)
○ Use twitch fibres (anaerobic)
○ Have few mitochondria and little myoglobin (“white meat”)
Fatigue easily - rapid glycogen depletion; rapid lactic acid buildup
muscle n species with long sustained flights
• Species with long sustained flights (ducks, songbirds)
○ Lots of oxidative fibres (aerobic)
○ Abundant mitochondria and myoglobin (“red meat”)
○ Very resistant to fatigue
describe blood flow and respiration for flight. go back and look at diagram !!!
• Circulation and gas exchange
• Large heat; high blood flow - 4 chambers (2 for inspiration 2 for expiration)
• Respiration unique with air sacs and 2 cycle air flow (2 inspirations and 2 expirations that does away with residual air)
• Parabronchial lung (modified faveolar lung)
• 9-12 air sacs depending on species
○ Air in parabronchi and blood capillaries flow at right angles to each other
○ More efficient than concurrent flow
Oxygen and glycogen = fuel , oxygen combusts it
use The secondary bronchi and parabronchi
most
aves taxonomy
describe palaeognathe aves - dont fly
• Ratites - flightless
○ Rheas, ostriches, Emus, Kiwis (4 orders)
• Share a palaeognathus palate
○ Long prevomers - extended to articulate with palatines ans pterygoids
○ Large basipterygoid process
palaeognthae phylogeny controversy
• Controversy on phylogeny
○ Evolved from a single ancestor
§ Southern hemisphere distribution resulted from breakdown of Gondwanaland
§ DNA analysis supported this view
○ Evolved convergently from a number of different groups
§ Similar selective pressure from a common life-style (all 4 orders have a strong tie to the ancestor)
§ Palate - primitive - not indicate relationship: might also be via neoteny from neognathus form
•
bird synapomorphies with coelursaurs
Additional synapomorphies with coelurosaurs (a more derived theropod)
7. Furcula (wishbone) by fusion of clavicles
8. Fused bony sternum
9. Birdlike sleeping posture with head tucked under forearm (wing)
• Recent studies: collagen from a 68 my old T.rex similar to peptides from a bird
• Dromeosaurs and bird like features
○ Flexing of wrists sideways
○ Shoulder joint allowing more range of movement of arms
