evolution of birds (aves)
from vertebrates, amniotes, then diapsids
diapsids split into archosaurs and lepidosaurs
archosaurs split into crocodiles and dinosaurs
dinosaurs split into non-avian dinosaurs and birds
ancestral bird characteristics
- center of gravity shifted to wings
- pygostyle: shortened tail with fused distal vertebrae
- coracoid - strutlike bones in the shoulder girdle
- reduced claw size
- larger sternum
- dietary specializations
how many species of birds are there
~11,200
diurnal
have excellent vision
are most birds diurnal
yes
feathers: structural features
- develop from follicles in skin
- composed mainly of beta-keratin
adaptations of birds for flight
- body size: streamlining and weight reduction
- feathers: structural features
- skeleton
- muscles
body size: streamlining and weight reduction
- streamlining of feathers and feet
- weight reduction adaptations include:
- lack urinary bladders, 1 ovary and males lack a phallus and gonads regress after breeding season
- skeletal features
down feathers
plumulaceous feathers
bristles (feathers)
specialized feathers
like eyelashes or whiskers to shield the face from dirt and debris, protect the eyes during foraging, and help nocturnal birds navigate
contour feathers
body and flight feathers
what are the 5 feather types
- contour
- semiplume
- down
- bristles
- filoplumes
semiplume feathers
intermediate feathers
filoplumes
hair-like sensory feathers
tiny, hair-like feathers found on almost all bird species, characterized by a long, slender shaft (rachis) with a small tuft of barbs at the tip.
act as sensory receptors connected to nerve endings, allowing birds to monitor feather position, detect vibrations, and adjust plumage for flight or insulation.
physical feature adaptations of bird skeletons
- centre of gravity is beneath wings
- large keeled sternum
- reduction in number and fusion of bones
- elongated pelvic girdle: ischium and ilium are thin sheets and attached with a synsacrum
- tail is shortened to ~5 caudal vertebrae that ends in the pygostyle (supports tail feathers)
bird skeletal weight vs mammal skeletal weight
birds have no difference in skeletal weight, the body weight ratio between birds and mammals is the same
they were believed to have lighter skeletons, which is not true
distribution varies: leg bones are heavier and skull is lighter in birds
bird muscle adaptations
major flight muscles:
- pectoralis major for downstroke
- supracoracoideus for powered upstroke
leg muscle mass varies with lifestyle
bird reproduction/sex determination
exclusively oviparoud
genetic sex determination
